Information

How does DNA determine all of our hereditary traits?


It's my understanding that DNA codes only for protein synthesis. Does that mean that hereditary traits, like the shape of our nose, are determined only by the proportions in which various proteins are synthesised in various parts of our body ?


Does that mean that hereditary traits, like the shape of our nose, are determined only by the proportions in which various proteins are synthesised in various parts of our body ?

Yes, more or less!

A trait that is called heritable is a trait which variance in the population is in part at least explained by genetic variance. Most of these heritable traits, however, are also affected by environmental variation (and other sources of variance). For more information, please have a look at the post Why is a heritability coefficient not an index of how “genetic” something is?

So when you say

[… ] are determined only by the proportions in which various proteins [… ]

The term "only" is a bit misleading. Other sources of variance exist that will affect the variance for this trait. However, it is a pretty good approximation to say that the heritable information is conveyed via the transmission of DNA and the phenotypic expression of this DNA is mediated via proteins.

We refer to theDNA -> RNA -> protein having some phenotypic impactrelationship by the term central dogma of molecular biology. You might want to read more about it or maybe have a look at an online course such as this one from Khan academy for example. You will want to know the terms translation and transcription.

Now, in reality DNA can affect an individual's phenotype by means other than proteins (or polypeptides to keep it more general) that are synthesized from it. Indeed, many loci (locus=position on a chromosome) affect the expression of other proteins, others are translated into RNA but not transcribed into proteins (e.g. rRNA, tRNA, RNAi,… ) but yet still have an important action on a cell's physiology.


Click here to order our latest book, A Handy Guide to Ancestry and Relationship DNA Tests

Can a couple sire a baby that is significantly darker or lighter than either individual?

-A curious adult from North Carolina

The short answer is, yes! A couple can have a baby with a skin color that isn’t between their own. The long answer, though, is much more interesting.

The long answer has to do with the parts of your DNA that give specific instructions for one small part of you. In other words, your genes.

It turns out that there isn’t just one or even a few genes involved in skin color. There are hundreds of different stretches of DNA all working together that decide your skin color.

Some of these genes can have big effects while others fine-tune a final color. On top of all that, your actions can help change how your body reads your DNA! For example, staying out in the sun turns on genes that darken your skin.

Different Types of Genes Get Shuffled Around

Everyone has two copies of each gene, one from their mom and one from their dad. The copies are mostly the same.

Note the word mostly. If we all had the same DNA we’d all be identical twins!

Turns out that we are all unique because sometimes the copies of each gene are slightly different. Scientists call these slightly different genes “alleles”.

These genes and alleles are kind of like a deck of cards. Each gene is like a different card (ace, two, three… jack, queen, king). And, like cards that come in different suits (spades, clubs, diamonds, hearts), there's more than one version of each card.

Imagine your mom and dad give you one of each card from their own decks. You’ll get two jacks, but they might be of the same suit (two jacks of hearts) or different (one jack of hearts and one jack of spades). In genetics, the word for two of the same is homozygous, the word for one of each is heterozygous.

Now let’s pretend the black cards would lead to dark skin and the red cards would lead to light skin. If you have a dark dad (all clubs and spades) and a light mom (all hearts and diamonds) you will end up with one red card and one black card like this:

This mixed hand would give you medium toned skin.

If your partner has similar parents, then he or she will also end up with a mixed deck. Maybe something like this:

When you have a baby together, you and your partner will each give a random half of your cards to your baby.

Odds are the baby will get black and red cards. But it’s possible that your baby will get all red cards from both of you like this:

In this case, the baby would be much lighter than either of you.

The same logic applies to the black cards. If by chance your baby got mostly clubs and spades from you and your partner, then the baby would end up with much darker skin than either of you:

As you can see, if you have two babies, they might end up with very different decks! And so very different skin colors.

This random dealing actually happens. Some mixed race parents have twins that look very different (click here, here and here for some great pictures of real-life examples).

Some of these families answer your question: parents can have children with skin color that is significantly lighter or darker than their own.

Sometimes One Gene is Stronger than the Others

Sometimes a particular gene can have a much bigger effect than other genes. Scientists call this “different effect size.”

In the previous card example, we pretended that every card had the same value. Having a red queen had the same impact as a red two.

A more accurate game would be if each red number card had a different point value. A red queen would add a higher score than a red two. Some genes matter a lot and some just fine-tune the color.

To make the card game even more accurate, we can add one more rule: if you get two queens of hearts, you get an extra 1,000 points. Let’s see how that rule can impact things.

Imagine a slight variation on the two parents from before. In this case, your hand has one queen of hearts and your spouse’s hand has one queen of hearts like this:

You both have the around the same skin color as before because neither of you get the bonus points for two queens of hearts. But there’s a chance your kid will end up with two queens of hearts like this:

Here, even though the child has the same number of black and red cards as either parent, the child is much, much lighter than either parent because of those two queens of heart.

This may seem like a silly rule, but it’s actually how some genes work. In fact, it’s what happens for people with light skin and red hair.

There is a gene called MC1R that acts as an on switch for darker skin. Usually the sun is able to flick this switch and cause people to tan.

However, there is one type of this gene that doesn’t work. Like those two queens of hearts, if both of your copies of MC1R don’t work, you end up with way lighter skin. You score that 1,000 points!

When you need two copies of an allele to see a trait, this is called recessive. It takes two nonworking (recessive) MC1R alleles to give way lighter skin (the trait).

It turns out this switch doesn’t just change skin color. Hair color is also affected!

The rest of the person’s genes are saying, “make the hair colored!” so the person isn’t going to be blonde. But the person can’t flick the switch for brown, so their hair turns out red!

Genes Are Important, But You Still Have Control.

Your DNA contains all the information to make you. But that doesn’t mean it controls all of your future!

Genes, like MC1R, contain information about how a person will react to sun. Some people will burn while others will tan and still others will get covered in freckles. But each person can control how much he or she goes out into the sun.

Someone who likes to spend time in the sun will probably be darker than their parents who spend all their time indoors. Yes, they’re only tanner, but they could be significantly darker than their parents!


The Father of Genetics

Mendel did experiments with pea plants to show how traits such as seed shape and flower color are inherited. Based on his research, he developed his two well-known laws of inheritance: the law of segregation and the law of independent assortment. When Mendel died in 1884, his work was still virtually unknown. In 1900, three other researchers working independently came to the same conclusions that Mendel had drawn almost half a century earlier. Only then was Mendel's work rediscovered.

Mendel knew nothing about genes. They were discovered after his death. However, he did think that some type of "factors" controlled traits and were passed from parents to offspring. We now call these "factors" genes. Mendel's laws of inheritance, now expressed in terms of genes, form the basis of genetics, the science of heredity. For this reason, Mendel is often called the father of genetics.


Introduction to Heredity and Traits

Suggested Implementation

Below is a suggested sequence for implementing the activities contained in the unit. Please see each individual activity for implementation instructions, suggestions for adaptations and extensions, and applicable standards.

DayActivityNotes
Day 1 (40 mins.)An Inventory of My TraitsStudents take an inventory of their own easily-observable genetic traits and compare those inventories with other students in groups.
Observable Human CharacteristicsThis web page shows many of the traits included in An Inventory of My Traits.
A Tree of Genetic TraitsStudents find the most and least common combination of traits in the class by marking their traits for tongue rolling, earlobe attachment, and PTC tasting on paper leaf cut-outs. Students then organize the leaves on a large "tree of traits."
Family Traits Trivia (Homework)Students use game cards to inventory the traits in their family. (Note: individuals in families do not need to be related to participate in this activity.)
Day 2 (40 mins.)Generations of TraitsStudents track and record the passage of colored "pom-pom traits" through three generations of ginger-bread people.
Traits BingoIn this review activity, students cross off or color bingo squares in response to questions about their traits.
Handy Family Tree (Homework)Students distinguish between inherited and learned traits by creating a "family tree of traits" using handprints. (Note: Individuals in families do not need to be related to participate in this activity.)
Day 3 (40 mins.)A Recipe for TraitsStudents learn that differences in DNA lead to different traits by: 1) randomly choosing strips of paper that represent DNA, then 2) decoding the DNA strips to complete a drawing of a dog.
Family Traits and Traditions (Homework)Students and their families play a matching game with cards to identify traits that are inherited and traits that are learned or passed on through tradition.

An Inventory of My Traits

Students take an inventory of their own easily observable genetic traits. Working in small groups, they observe how their trait inventories differ from those of others. Students record their observations in a data table and make a bar graph to show the most and least common traits in the group.

Learning Objectives

  • Traits are observable characteristics that are passed down from parent to child.
  • An individual will have many traits they share in common with others.
  • An individual&aposs overall combination of traits makes them unique.
  • Some traits are more common in a population than others.

A Tree of Genetic Traits

Students mark their traits for tongue rolling, PTC tasting (a harmless, bitter chemical), and earlobe attachment on tree leaf cut-outs. They then place their leaves on a large tree whose branches each represent a different combination of traits. When completed, the tree forms a visual representation of the frequency of trait combinations within the class.

Learning Objectives

  • Traits are observable characteristics that are passed down from parent to child.
  • An individual will have many traits they share in common with others.
  • An individual&aposs overall combination of traits makes them unique.
  • Some traits are more common in a population than others.

A Word About PTC Safety

The 2004 publication Investigating Safety: A Guide for High School Teachers by Texley et al. has raised an alarm in the teaching community about the usefulness and safety of PTC taste testing. This has led to PTC being banned from many schools and districts - we believe unnecessarily.

Yes, PTC is toxic. In rats, the most sensitive animals tested, the oral LD50 of PTC (the amount that killed 50% of test animals) is 3 mg/kg. However, PTC is so intensely bitter that tasters can detect it in miniscule quantities. A single test paper from Carolina Biological Supply contains just 0.007 mg of PTC. And the amount that is licked off the paper by a test subject is much less than this. In addition, there has not been a single report of toxicity arising from PTC taste testing, which has been performed on tens of millions of individuals worldwide. To put the toxicity of PTC into perspective, we offer this quote (from Merritt et al., Am. Biol. Teacher online 70:4):

There is no question that PTC is toxic (LD50 in rat is 3mg/kg, in mouse 10mg/kg, and in rabbit 40mg/kg), but so is table salt (acute toxicity in humans at 500-1000mg/kg). The issue is how much PTC is on a taste paper. Texley et al. indicate that &ldquoa single strip contains about 0.3 mg&rdquo but the two suppliers we checked with indicate that a taste paper contains either 0.007 mg (Carolina Biological Supply Company) or 0.005 - 0.007 mg (ScienceStuff). Assuming a linear dose response curve, we calculate that the 230 mg of NaCl in a vending machine bag of potato chips is about 100 times more toxic than the 0.007 mg of PTC in a taste paper. We do not believe there is any reason for teachers to be concerned about the toxicity of PTC taste papers.

Choose either english versions.

Then download the leaves page and one of the following tree files.

Or english/spanish bilingual versions.

Then download the leaves page and one of the following tree files.

Family Traits Trivia

Take home game using picture cards that identify traits. A family or group can use this activity to see which traits they have in common.

Generations of Traits

In this hands-on activity students track and record the passage of colored "pompom traits" through three generations of ginger-bread people. In doing so, students learn that traits are passed from parents to offspring and that siblings may or may not receive the same traits from their parents.

Learning Objectives

  • Traits are observable characteristics that are passed down from parent to child.
  • An individual will have many traits they share in common with others, and more so with siblings and parents.
  • An individual&aposs overall combination of traits makes them unique.
  • An equal number of traits are passed on from each parent.

Traits Bingo

Students cross off or color bingo squares in response to questions about their traits. This activity is designed to be used as a review following An Inventory of My Traits, Generations of Traits, and A Tree of Genetic Traits.

Learning Objectives

  • Students will inventory their own inherited traits.
  • Students will compare traits to determine which are most and least common in the class.

Handy Family Tree (Homework)

An activity to catalog a family&aposs traits on a tree made of stacked handprints.

A Recipe for Traits

Students create and decode a "DNA recipe" for man&aposs best friend to observe how variations in DNA lead to the inheritance of different traits. Strips of paper (representing DNA) are randomly selected and used to assemble a DNA molecule. Students read the DNA recipe to create a drawing of their pet, and compare it with others in the class to note similarities and differences.

Learning Objectives

  • Every organism inherits a unique combination of traits.
  • DNA is a set of instructions that specifies the traits of an organism.
  • Variations in the DNA lead to the inheritance of different traits.

Family Traits and Traditions (Homework)

A memory match game in which participants must discern the differnce between a trait that is inherited or one that is learned/environmental.


Common Ancestry

Students sort images of seeds using a classification scheme of their own design. This exercise is intended to demonstrate how living things can be organized by similarities and differences in traits, preparing students to consider the similarities in living things in subsequent exercises.

  • Distribute sets of Seed Cards to individual or pairs of students, instructing them to make observations about the seeds then group them by a scheme of their choice.
  • Have students report about the scheme they used, discussing similarities and differences in schemes.

Example groupings: Size, color, shells, two distinct halves, type (nuts, beans, seeds), etc.

  • Humans are natural organizers.
  • Living things can be organized by their similarities and differences.

Students create their own organization and classification system based on observed characteristics of seeds.

Seed Cards and Teacher Guide (pdf) &mdash
Make one set per student or pair (card sets can be re-used).

Tree Diagrams

The video introduces tree diagrams. It prepares students for subsequent activities in which they will use tree diagrams in hypothesizing about common ancestry based on several lines of evidence.

Project to the whole class, pausing as needed to discuss.

  • Similarities among living things might indicate relatedness.
  • Organisms with the most similarities tend to be more closely related.
  • Tree diagrams are ways to organize hypotheses about the relationships among living things.

Tree diagrams are introduced as a system for organizing information and hypotheses about the relationships among organisms.

How do scientists use multiple lines of evidence to learn about common ancestry?

Fish or Mammals?

This series of activities explores the ancestry of cetaceans (whales, dolphins, and porpoises). The Case Study document presents data from comparative anatomy, fossils, embryological development, amino acid sequences, and DNA transposons.

The Evidence Organizer helps students follow the path that scientists took to understand the ancestry of cetaceans. Each new piece of evidence led to a more-detailed understanding: first that cetaceans are more similar to mammals than to fish then that they descended from a four-legged mammal that lived on land later still that they descended from an even-toed ungulate and finally that their closest living relative is the hippopotamus.

Tip: If students are still having trouble interpreting tree diagrams, go through the practice with trees extension.

Once students have finished filling in their Evidence Organizers (and they understand the evidence), give them a copy of the Argumentation document. Here they will match the appropriate pieces of evidence with the provided claims and reasoning.

  • Fossils, anatomy, embryos, and DNA sequences provide corroborative lines of evidence about common ancestry, with more closely related organisms having more characteristics in common.
  • (Argumentation) In a scientific argument, evidence is data or observations that support a claim.
  • (Argumentation practice) Choose evidence that supports a given claim and is consistent with a given line of reasoning.

Students interpret fossil, anatomical, embryological, and DNA data to determine the ancestry of cetaceans.

Students find patterns in fossil, anatomical, embryological, and DNA data to determine relatedness.

Students practice choosing the appropriate evidence that supports a claim and is in line with given reasoning.

Make one copy per student or pair (copies can be re-used), or have students view on tablets or computers

Make one copy per student

Make one copy per student.
Tip: If students are struggling to identify the appropriate evidence, tell them which type(s) of evidence to look for (i.e., A, E, F, or D provided on the Argumentation key).

Extension Activity: A Tale of Two Pandas

This second case study provides more practice with the evidence for common ancestry. In addition, it explores the scientific process, highlighting the fact that sometimes lines of evidence appear to contradict one another. The reading level and the evidence presented here are more challenging than in the Fish or Mammals case study.

The Tale of Two Pandas video introduces the question, "Is the giant panda a bear or a raccoon?"

The Case Study document presents evidence from behavior, anatomy, fossils, and DNA. Note that different lines of evidence support different conclusions.

The Teacher Guide describes how you can assign the lines of evidence to different groups of students to evaluate. Using the Evidence Organizer, students organize their evidence to support one of three claims.

To wrap up, present the Conclusion (pdf document) to summarize how more recent DNA evidence finally led to a scientific consensus: that the giant panda shares a more recent common ancestor with bears.

  • Fossils, anatomy, embryos, and DNA sequences provide corroborative lines of evidence about common ancestry, with more closely related organisms having more characteristics in common.
  • (Argumentation) In a scientific argument, evidence is data or observations that support a claim.
  • (Argumentation practice) Choose evidence that supports a given claim.

Students find patterns in anatomical, fossil, and DNA and protein data to determine relatedness.

Students interpret anatomical, fossil, and DNA and protein data to determine the evolutionary relationships of the giant panda.

Make one copy per student or pair (copies may be re-used), or have students view on tablets or computers

Make one copy per student

Evidence for Common Ancestry

With the Fish or Mammals? series, students have seen how multiple lines of evidence can help answer puzzling questions about common ancestry—and how multiple lines of evidence generally point to the same conclusion. This activity is intended to reinforce the idea that lines of evidence tend to corroborate one another, while also making the point that many questions about common ancestry are not so puzzling. Students explore a collection of inferences about the relationships among species, which are based on various lines of evidence.

Have students explore individually or in pairs. An optional guiding worksheet is provided.

  • Fossils, anatomy, embryos, and DNA sequences provide corroborative lines of evidence about common ancestry, with more closely related organisms having more characteristics in common.

Make one copy per student

Why does DNA evidence agree with the other lines of evidence for common ancestry?

Common Ancestry: It's in our DNA

This slide presentation circles back around to the DNA > Protein > Trait connection explored in the previous module (Shared Biochemistry) and puts it in context as the phenomenon that underlies all of the other lines of evidence for common ancestry.

Project to the whole class. You may wish to review the main science ideas.

  • DNA codes for proteins. Collectively, proteins are responsible for an organism's traits.
  • DNA underlies the similarities and differences in fossils, anatomy, and embryos.
  • More closely related organisms have more genes in common.

The DNA > Protein > Trait (cause) connection is put in context as the phenomenon that underlies all of the other lines of evidence (effect) for common ancestry.

Online Phylogenetic Tree

Choose any two species on the phylogenetic tree to see the relative sizes of their genomes, the number of shared and unique genes, and the amount of time that has passed since they diverged from a common ancestor.

After two organisms are selected, overlapping circles representing their genomes will appear.

Have students explore individually or in pairs as they fill in the worksheet.

  • All organisms have some genes in common.
  • More closely related organisms have more genes in common.
  • Tree diagrams are visual representations of evolutionary history that depict patterns of common ancestry and speciation over time.

Students use an interactive tree diagram to find general patterns in genetic data and the relationships among organisms.

Computers with internet access (online activity has no sound)

Make one copy per student

Formative Assessment

This quick formative assessment checks to see how well students understand tree diagrams and evidence for common ancestry.

Make one copy per student, or project to the class and have students submit answers in the format of your choice.


Character traits determined genetically? Genes may hold the key to a life of success, study suggests

Genes play a greater role in forming character traits -- such as self-control, decision making or sociability -- than was previously thought, new research suggests.

A study of more than 800 sets of twins found that genetics were more influential in shaping key traits than a person's home environment and surroundings.

Psychologists at the University of Edinburgh who carried out the study, say that genetically influenced characteristics could well be the key to how successful a person is in life.

The study of twins in the US -- most aged 50 and over- used a series of questions to test how they perceived themselves and others. Questions included "Are you influenced by people with strong opinions?" and "Are you disappointed about your achievements in life?"

The results were then measured according to the Ryff Psychological Well-Being Scale which assesses and standardizes these characteristics.

By tracking their answers, the research team found that identical twins -- whose DNA is [presumed to be] exactly the same -- were twice as likely to share traits compared with non-identical twins.

Psychologists say the findings are significant because the stronger the genetic link, the more likely it is that these character traits are carried through a family.

Professor Timothy Bates, of the University of Edinburgh's School of Philosophy, Psychology and Language Sciences, said that the genetic influence was strongest on a person's sense of self-control.

Researchers found that genes affected a person's sense of purpose, how well they get on with people and their ability to continue learning and developing.

Professor Bates added: "Ever since the ancient Greeks, people have debated the nature of a good life and the nature of a virtuous life. Why do some people seem to manage their lives, have good relationships and cooperate to achieve their goals while others do not? Previously, the role of family and the environment around the home often dominated people's ideas about what affected psychological well-being. However, this work highlights a much more powerful influence from genetics."

The study, which builds on previous research that found that happiness is underpinned by genes, is published online in the Journal of Personality.


Where Did You Get Your Genes?

You got all your genes from your parents. For each pair of their chromosomes, you get one chromosome from your mother and one from your father. When the egg and sperm cells come together, they create the full set of 46 chromosomes or 23 pairs.

So why aren’t your genes exactly the same as your siblings? Like you, your parents each have two copies of their chromosomes, which they got from their parents. When sperm and eggs are created, pairs of chromosomes separate independently and sort themselves at random into two eggs cells in your mom or two sperm cells in your dad. You might get one chromosome in one pair from your mom, and your sister might get the other chromosome from that pair. This means that there are 8,388,608 possible variations of egg and sperm. It’s really a wonder we look like our parents at all!


Nurture

On the other end of the spectrum are empiricists, who believe that the mind is a &lsquotabula rasa&rsquo or a clean slate, on that is then filled with learning and experience. This means that empiricists believe all psychological traits are learned from one&rsquos environment and the upbringing a child receives.

For example, Albert Bandura&rsquos &lsquoSocial Learning Theory&rsquo states that personality traits like aggression are gained through imitation, exemplified in his famous &lsquoBobo Doll&rsquo experiment. In this experiment, preschool children were shown a movie in which the actor was kicking a doll. After the movie, when the same doll was presented in the room, the children started kicking it too.

Children learn behavioral traits through imitation. (Photo Credit : Rozochka/Shutterstock)

The geography or the environment can impact how genes are expressed. A study of 13,000 pairs of twins by King&rsquos College London Institute of Psychiatry (2012) concluded that the place where one lives can actually influence genetic expression.


Genes don't just influence your IQ—they determine how well you do in school

If you sailed through school with high grades and perfect test scores, you probably did it with traits beyond sheer smarts. A new study of more than 6000 pairs of twins finds that academic achievement is influenced by genes affecting motivation, personality, confidence, and dozens of other traits, in addition to those that shape intelligence. The results may lead to new ways to improve childhood education.

“I think this is going to end up being a really classic paper in the literature,” says psychologist Lee Thompson of Case Western Reserve University in Cleveland, Ohio, who has studied the genetics of cognitive skills and who was not involved in the work. “It’s a really firm foundation from which we can build on.”

Researchers have previously shown that a person’s IQ is highly influenced by genetic factors, and have even identified certain genes that play a role. They’ve also shown that performance in school has genetic factors. But it’s been unclear whether the same genes that influence IQ also influence grades and test scores.

In the new study, researchers at King’s College London turned to a cohort of more than 11,000 pairs of both identical and nonidentical twins born in the United Kingdom between 1994 and 1996. Rather than focus solely on IQ, as many previous studies had, the scientists analyzed 83 different traits, which had been reported on questionnaires that the twins, at age 16, and their parents filled out. The traits ranged from measures of health and overall happiness to ratings of how much each teen liked school and how hard they worked. Then, the researchers collected data on how well each individual scored on the General Certificate of Secondary Education (GCSE) exam, an exam that all students in the United Kingdom must take and which is used for admission to advanced classes or colleges.

The team found nine general groups of traits that were all highly hereditary—the identical twins were more likely to share the traits than nonidentical twins—and also correlated with performance on the GCSE. Not only were traits other than intelligence correlated with GCSE scores, but these other traits also explained more than half of the total genetic basis for the test scores.

In all, about 62% of the individual differences in academic achievement—at least when it came to GCSE scores—could be attributed to genetic factors, a number similar to previous studies’ findings, the team reports online today in the Proceedings of the National Academy of Sciences.

“It’s really important to understand why children differ in academic achievement,” says developmental psychologist Kaili Rimfeld of King’s College London, an author of the new paper. “These twin studies show that there’s a genetic basis for the differences in how easy or enjoyable children find learning.” Understanding that there’s a genetic basis for why people differ in not only intelligence, but also their drive to learn, she says, underscores the need for personalized classrooms where students can learn in different ways—from computer programs to hands-on projects—that are most fitted to their own personalities.

The results, Thompson points out, would likely differ in less-developed countries where children don’t have equal access to education academic achievement in these places is shaped more by opportunities than genetics. And the new study gives little information on what the genes might be that influence test scores. “Each one of these traits is very complex,” she says, “so we’re talking about hundreds of genes that are acting together.” Future studies, she says, may be able to shed light on specific genes that affect academic achievement, which could help diagnose or treat learning disabilities.


The Debate

Do genetic or environmental factors have a greater influence on your behavior? Do inherited traits or life experiences play a greater role in shaping your personality? The nature versus nurture debate is one of the oldest issues in psychology. The debate centers on the relative contributions of genetic inheritance and environmental factors to human development.

Some philosophers such as Plato and Descartes suggested that certain things are inborn, or that they occur naturally regardless of environmental influences. Nativists take the position that all or most behaviors and characteristics are the results of inheritance.

Advocates of this point of view believe that all of our characteristics and behaviors are the result of evolution. Genetic traits handed down from parents influence the individual differences that make each person unique.

Other well-known thinkers such as John Locke believed in what is known as tabula rasa, which suggests that the mind begins as a blank slate. According to this notion, everything that we are and all of our knowledge is determined by our experience.

Empiricists take the position that all or most behaviors and characteristics result from learning. Behaviorism is a good example of a theory rooted in empiricism. The behaviorists believe that all actions and behaviors are the results of conditioning. Theorists such as John B. Watson believed that people could be trained to do and become anything, regardless of their genetic background.


Hershey and Chase Experiment

Even after the compelling evidence provided by the Avery, Macleod and McCarty experiment, there were still a few skeptics out there who weren&rsquot convinced. The debate still raged between proteins and DNA. However, the Hershey &ndash Chase experiment permanently put an end to this long-standing debate.

Alfred Hershey and Martha Chase in 1952, performed an experiment that proved, without a doubt, that DNA was the carrier of information. For their experiment, they employed the use of the bacteriophage T2. A bacteriophage is a virus that only infects bacteria. This particular virus infects Escherichia coli. T2 had a simple structure that consisted of just 2 components &ndash an outer protein casing and the inner DNA. Hershey and Chase took 2 different samples of T2. They grew one sample with 32 P, which is the radioactive isotope of phosphorus, and the other sample was grown with 35 S, the radioactive isotope of sulphur!

The protein coat has sulphur and no phosphorus, while the DNA material has phosphorus but no sulphur. Thus, the 2 samples were labelled with 2 different radioactive isotopes.

The viruses were then allowed to infect the E. coli. Once the infection was done, the experimental solution was subjected to blending and centrifugation. The former removed the ghost shells, or empty shells of the virus from the body of the bacteria. The latter separated the bacteria from everything else. The bacterial solution and the supernatant were then checked for their radioactivity.

Hershey &ndash Chase experiment

In the first sample, where 32 P was used, the bacterial solution showed radioactivity, whereas the supernatant barely had any radioactivity. In the sample where 35 S was used, the bacterial solution didn&rsquot show any radioactivity, but the supernatant did.

This experiment clearly showed that DNA was transferred from the phage to the bacteria, thus establishing its place as the fundamental carrier of genetic information.

Until the final experiment performed by Hershey and Chase, DNA was thought to be a rather simple and boring molecule. It wasn&rsquot considered structured enough to perform such a complicated and extremely important function. However, after this experiment, scientists started paying much more attention to DNA, leading us to where we are in research today!