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

Genetics

GeneticsGenetics

• 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 GeneticsThe 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 ExperimentMendel 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

1st Generation

2nd Generation

Recessive and Dominate Genes

Parent

1st 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 1st generation offspring are yellow because the alleles interact in what is called a dominant or a recessive manner.

Recessive and Dominate Traits

Parent

1st Generation

2nd 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 1st generation of peas again, the second generation could receive any of the following allele combinations. 2nd 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 Shape Earlobe Attachment Tongue Rolling

Cleft Chin Dimples Handedness

Freckles Naturally Curly Hair Hand Clasping

Each step will be explained in the next slides

Hairline ShapeHairline 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 AttachmentSome 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 RollingTongue 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?


R is the Dominate Allele

r is the recessive Allele

Can Roll = RR

Can Roll = Rr

Can’t Roll = rr

Cleft ChinThis 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?


C is the Dominate Allele

s is the recessive Allele

Cleft Chin = CC

Cleft Chin = Cs

Smooth Chin = ss

DimplesDimples 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?


D is the Dominate Allele

d is the recessive Allele

Dimples = DD

Dimples = Dd

No Dimples = dd

HandednessSome 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?


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?


F is the Dominate Allele

f is the recessive Allele

Freckles = FF

Freckles = Ff

No Freckles = ff

Naturally Curly HairEarly 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?


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


Tongue Rolling

Tongue Rolling Dominate

_______ Roll Tongue

_______ Can’t Roll Tongue


Cleft Chin

Cleft Chin Dominate

_______ Cleft

_______ No Cleft


Dimples

Dimples Dominate

_______ Dimples

_______ No Dimples


Handedness

Right Hand is Dominate Trait

_______ Right Handed

_______ Left Handed


Freckles

Freckles are Dominate Trait

_______ Freckles

_______ No Freckles


Naturally Curly Hair

Curly Hair Dominate Trait

_______ Curly Hair

_______ Straight Hair


Hand Clasping

Dominate vs. Recessive???

_______ Left Thumb

_______ Right Thumb


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


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


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

Documents

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