Genetics

Genetics Focus Question: –If most organisms start from a single cell, than why don’t we all look the same? Prediction: –Why do you think species of organisms have different characteristics. For example I have blue eyes, but both of my parents have light green eyes.

The Father of Genetics The study of genetics is a very complicated and technical process, but the basic principal is quite simple. An Austrian Botanist is considered to be known as the “Father of Genetics” because of what he learned from his scientific experiments with pea pod plants. In the mid 1800’s Gregor Mendel carefully studied seven traits of the pea plant; seed shape, seed color, flower position, pod shape, seed coat color, stem length, and pod color. He discovered that crossing two plants with the same trait did not guarantee that those traits would show in their offspring. He discovered that if there were different traits in the plants’ history, those traits might eventually show up.

Pea Pod Experiment Mendel discovered that living organisms pass down traits to their offspring that do not physically show up from generation to generation. Mendel could not prove why this happened at the time, but it did set the stage for further investigation. Physical traits are observable characteristics determined by specific segments of DNA called genes. Multiple genes are grouped together to form chromosomes, thread-like parts which are found in the nucleus of the cell. Genes carry the information that determines the traits of an organism.

Basic Animal Cell Nucleus Chromosomes A chromosome is an organized package of DNA found in the nucleus of the cell. Different organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes. Each parent contributes one chromosome to each pair so that offspring get half of their chromosomes from their mother and half from their father Allele An allele is one of two or more versions of a gene. An individual inherits two alleles for each gene, one from each parent. Gene The gene is the basic physical unit of inheritance. They are arranged, one after another, on the chromosomes and contain the information needed to specify traits. Humans have approximately 23,000 genes arranged on their chromosomes. A a A A An example of possible variations

So How does Mendel's Peas Explain how we Inherit our Traits? If you think back to our cell investigation we said that organisms begin as one cell. Because of the way cells divide and join during reproduction, each new offspring created receives chromosomes (multiple groups of genes) for specific traits from the male and from the female. The example to the right demonstrates how Mendel’s pea pods could pass down genes for the specific trait of color. From this we discovered that some genes are recessive and some genes are dominate. Parent 1 st Generation 2 nd Generation

Recessive and Dominate Genes Parent 1 st Generation We discovered that some genes are recessive and some genes are dominate because most genes have two or more variations, called alleles Alleles: The variation of genes for a trait. The alleles for the color of a pea are referred to as G: green and Y: yellow. The green parent received 2 green alleles The yellow parent received 2 yellow alleles In this example each parent gives their offspring a copy of one of their alleles. Depending on what allele variations parents have to offer, offspring may inherit two identical or two different alleles. In this case each parent only had one type of allele to offer, one G and one Y As a result, all new 1 st generation offspring are yellow because the alleles interact in what is called a dominant or a recessive manner.

Recessive and Dominate Traits Parent 1 st Generation 2 nd Generation Dominate Traits: The trait observed because a dominant allele is present in the genes that the offspring received from its parents. In this example yellow color is a dominate trait Recessive Traits: Traits due to recessive alleles are only observed when two recessive alleles are present. Recessive alleles may exist in the genes of the offspring but the trait is not observed. In this example green is a recessive trait Depending on which alleles (gene variation) a pea receives, future offspring could be green although both parents are yellow. If you cross the 1 st generation of peas again, the second generation could receive any of the following allele combinations. 2 nd generation offspring could be yellow or green.

Inherited Traits You inherit many kinds of traits from your parents that determine your physical features. Many of these traits cannot be changed and may not even be present in your parents or grand parents because they are recessive genes. You are born with most of your traits, but some such as intelligence, personality, and athletic ability, may be inherited to a certain extent, but you are greatly influenced by your environment and your attitude. For example; If your parents were straight “A” students or professional athletes, you are not going to be just because you have their genes.

Inherited Traits There are thousands of genes that determine the traits each person has. We know that these traits are inherited from our parents and we know that some are dominate and some are recessive. Most physical traits result from a mix of genes, but scientists believe that some traits are due to one gene. When more than one gene determines a trait it is very difficult to predict an inheritance pattern. For example Mendel couldn’t easily predict the height and weight of pea pods, but he could predict their color. This chart contains traits that scientists have been able to study and predict inheritance patterns. You would assume that dominant alleles are the most common in a population, but we are going to complete an investigation to find out if this is always true.

Create a large version of this table below. For each of the traits we are going to identify and record the following: What is the Recessive or Dominate Trait? Fraction of Students With the Trait: Fraction of Students Without the Trait: Most common or least common in our population? Record the following in your scientist notebook What are examples of recessive and Dominate traits? Hairline ShapeEarlobe AttachmentTongue Rolling Cleft ChinDimplesHandedness FrecklesNaturally Curly HairHand Clasping Each step will be explained in the next slides

Hairline Shape Hairline shape is reportedly due to a single gene with a widow’s peak dominant and a straight hairline recessive. This image shows the possible combinations of alleles you could have received from your parents. The only way you can get a straight hairline is if both your parents gave you a recessive allele. Record and label in your table: What is the Recessive or Dominate Trait? Fraction Students With Widow Peak: Fraction Students Without Widow Peak: Most common or least common in our population?

Earlobe Attachment Some scientists have reported that this trait is due to a single gene for which unattached earlobes is dominant and attached earlobes is recessive. These are the possible combinations of alleles you could have received from your parents. If you have detached earlobes, both your parents gave you a recessive allele. Record and label in your table: What is the Recessive or Dominate Trait? Fraction Students With unattached earlobes: Fraction Students With attached earlobes : Most common or least common in our population? If earlobes hang free, they are detached. If they attach directly to the side of the head, they are attached earlobes. Results of Allele Combinations U is the Dominate Allele u is the recessive Allele Unattached = UU Unattached = Uu Detached = uu

Tongue Rolling Tongue rolling ability may be due to a single gene with the ability to roll the tongue a dominant trait and the lack of tongue rolling ability a recessive trait. These are the possible combinations of alleles you could have received from your parents. If you can’t roll your tongue, both your parents gave you a recessive allele. Record and label in your table: What is the Recessive or Dominate Trait? Fraction Students who can role tongue: Fraction Students who can’t role tongue: Most common or least common in our population? Can you roll your tongue? Results of Allele Combinations R is the Dominate Allele r is the recessive Allele Can Roll = RR Can Roll = Rr Can’t Roll = rr

Cleft Chin This trait is reportedly due to a single gene with a cleft chin dominant and a smooth chin recessive. These are the possible combinations of alleles you could have received from your parents. If you have a smooth chin, both your parents gave you a recessive allele. Record and label in your table: What is the Recessive or Dominate Trait? Fraction Students With Cleft Chin: Fraction Students Without Cleft Chin: Most common or least common in our population? Results of Allele Combinations C is the Dominate Allele s is the recessive Allele Cleft Chin = CC Cleft Chin = Cs Smooth Chin = ss

Dimples Dimples are reportedly due to a single gene with dimples dominant (people may exhibit a dimple on only one side of the face) and a lack of dimples recessive. These are the possible combinations of alleles you could have received from your parents. If you have no dimples, both your parents gave you a recessive allele. Record and label in your table: What is the Recessive or Dominate Trait? Fraction Students With Dimples: Fraction Students Without Dimples: Most common or least common in our population? Results of Allele Combinations D is the Dominate Allele d is the recessive Allele Dimples = DD Dimples = Dd No Dimples = dd

Handedness Some scientists have reported that handedness is due to a single gene with right handedness dominant and left handedness recessive. However, other scientists have reported that the interaction of two genes is responsible for this trait. These are the possible combinations of alleles you could have received from your parents. If you are left handed, both your parents gave you a recessive allele. Record and label in your table: What is the Recessive or Dominate Trait? Fraction Students who are Right Hand Dominate: Fraction Students who are Left Hand Dominate: Most common or least common in our population? Results of Allele Combinations R is the Dominate Allele l is the recessive Allele Right Handed = RR Right Handed = Rl Left Handed = ll

Freckles This trait is reportedly due to a single gene; the presence of freckles is dominant, the absence of freckles is recessive. These are the possible combinations of alleles you could have received from your parents. If you have no freckles, both your parents gave you a recessive allele. Record and label in your table: What is the Recessive or Dominate Trait? Fraction Students With Freckles: Fraction Students Without Freckles: Most common or least common in our population? Results of Allele Combinations F is the Dominate Allele f is the recessive Allele Freckles = FF Freckles = Ff No Freckles = ff

Naturally Curly Hair Early geneticists reported that curly hair was dominant and straight hair was recessive. More recent studies suggest that more than one gene may be involved. These are the possible combinations of alleles you could have received from your parents. If you have straight hair, both your parents gave you a recessive allele. Record and label in your table: What is the Recessive or Dominate Trait? Fraction Students With Curly Hair: Fraction Students Without Curly Hair: Most common or least common in our population? Results of Allele Combinations C is the Dominate Allele s is the recessive Allele Curly = CC Curly = Cc Straight = ss

Hand Clasping Record and label in your table: What is the Recessive or Dominate Trait? Fraction Students with Left Thumb on Top: Fraction Students with Right Thumb on Top: Most common or least common in our population? Fold your hands together by interlocking your fingers without thinking about it. Which thumb is on top – your left or your right? One study found that 55% of people place their left thumb on top and 45% place their right thumb on top. 1% have no preference. I was not able to find evidence that supports whether one is a dominate or recessive allele. A study of identical twins concluded that hand clasping has at least some genetic component. However, other scientists have not found evidence that genetics plays a significant role in determining this trait.

Hairline Shape Widows Peak Dominate _______ Widows Peak _______ No Widows Peak Which is most common in our Classroom Population? Earlobe Attachment Unattached is Dominate _______ Unattached _______ Attached Which is most common in our Classroom Population? Tongue Rolling Tongue Rolling Dominate _______ Roll Tongue _______ Can’t Roll Tongue Which is most common in our Classroom Population? Cleft Chin Cleft Chin Dominate _______ Cleft _______ No Cleft Which is most common in our Classroom Population? Dimples Dimples Dominate _______ Dimples _______ No Dimples Which is most common in our Classroom Population? Handedness Right Hand is Dominate Trait _______ Right Handed _______ Left Handed Which is most common in our Classroom Population? Freckles Freckles are Dominate Trait _______ Freckles _______ No Freckles Which is most common in our Classroom Population? Naturally Curly Hair Curly Hair Dominate Trait _______ Curly Hair _______ Straight Hair Which is most common in our Classroom Population? Hand Clasping Dominate vs. Recessive??? _______ Left Thumb _______ Right Thumb Which is most common in our Classroom Population? Our Class Data: Does the dominate trait express itself more frequently then the recessive?

Hairline Shape Widows Peak Dominate 8/21 Widows Peak 13/21 No Widows Peak No Widows Peak Frequent Earlobe Attachment Unattached is Dominate 14/21 Unattached 7/21 Attached Unattached Most Frequent Tongue Rolling Tongue Rolling Dominate 17/21 Roll Tongue 4/21 Can’t Roll Tongue Rolling is Most Frequent Cleft Chin Cleft Chin Dominate 6/21 Cleft 15/21 No Cleft No Cleft Most Frequent Dimples Dimples Dominate 11/21 Dimples 10/21 No Dimples Dimples Most Frequent Handedness Right Hand is Dominate Trait 14/15 Right Handed 1/15 Left Handed Right Handed Appeared More Freckles Freckles are Dominate Trait 13/17 Freckles 4/17 No Freckles Freckles Appeared Most Naturally Curly Hair Curly Hair Dominate Trait 3/17 Curly Hair 14/17 Straight Hair Straight Hair Appeared the Most Hand Clasping Dominate vs. Recessive Unsure??? 8/15 Left Thumb 7/15 Right Thumb Classroom A Data:

Hairline Shape Dominate: Widows Peak Recessive: Straight Line 13/25 Widows Peak 12/25 Straight Line Widows Peak Showed Most Earlobe Attachment Dominate: Unattached Recessive: Attached 15/25 Unattached 10/25 Attached Unattached Showed Most Tongue Rolling Dominate: Can Recessive: Can’t 18/25 Can 7/25 Can’t Can Showed Most Cleft Chin Dominate: Cleft Recessive: No Cleft 5/25 Cleft 20/25 No Cleft No Cleft Showed Most Dimples Dominate: Dimples Recessive: No Dimples 16/25 Dimples 9/25 No Dimples Dimples Showed Most Handedness Dominate: Right Recessive: Left 22/24 Right Handed 2/24 Left Handed Right Showed Most Freckles Dominate: Freckles Recessive: No Freckles 19/24 Freckles 5/24 No Freckles Freckles Showed Most Naturally Curly Hair Dominate: Curly Recessive: Straight 8/24 Curly 16/24 Straight Straight Showed Most Hand Clasping Dominate vs. Recessive Unsure?? 13/24 Left 11/24 Left Showed Most Classroom B Data:

Use the data you collected from the table… Did most of the students in your class display dominate or recessive traits? Why do you think this happened? Do you think the results would be different if you had surveyed the whole school? Explain your opinion… Do you think the results would be different if you surveyed people from different parts of the country or world? Explain your opinion… Answer the following questions in your scientist notebook

Claims and Evidence Focus Question: –If most organisms start from a single cell, than why don’t we all look the same? I claim that…I claim this because…

Conclusion Revisit your original prediction and explain whether the evidence from our investigation supports it or not. Reflection Respond to some of the following –What really surprised you –What new questions do you have –What would you really like to know more about