Chapter 4 Lesson 2

Understanding Inheritance

Learning Objective:

Using your family history to predict genetic outcomes with phenotypes.

Modeling Inheritance

Two tools can be used to identify and predict traits among genetically related individuals.• Punnett square – using family histories to

predict genotypes and phenotypes.

• Pedigree – Creating a map using family histories to predict phenotypes.

One more thing about Punnetts

Human Gender XX = girl XY = boy You ALWAYS

have a 50% chance of having a boy or girl EVERY time.

X X

X

Y

XX XX

XY XY

Pedigrees

A pedigree shows genetic traits that were inherited by members of a family.

Pedigrees focus more on phenotypes. They are also used with Punnett

Squares to determine genotypes.

Normal

Affected

Female Male

Married

Children

11

3

9 10 11 12 1413

6 7 854

2

Pedigree chart

Pedigrees to evaluate

Go to page 201 and do problems #7 - 9

#7 = Not affected = dd = C

#8 = affected = Dd = B

#9 = not affected = dd = C

Draw a pedigree One couple has a son and a daughter with

normal pigmentation. Another couple has one son and two daughters with normal pigmentation. The daughter of the first couple has three children with the son of the second couple. Their son and one daughter have albinism; their daughter has normal pigmentation.

Is albinism, recessive or dominant?

It is recessive. What must the

genotype be of #2 and #3? (hint: make a Punnett Sq.)

Albino

Female Male

1st couple

6 87

3 4 521

2nd couple

Answer

Answer

Both parents must be Aa.

Not all their children are albino.

A a

A AA Aa

a Aa aa

Learning Objective – Part 2

By chance, Mendel studied traits only influenced by one gene with two alleles. However, we know now that some inherited traits have

There are more complex patterns.

Incomplete Dominance

Incomplete dominance produces a THIRD phenotype that is a blend of parents phenotype.

R = red flowers

W = white flowers

Red x white = 100% pink

R R

W RW RW

W RW RW

Codominance

When BOTH alleles can be observed in the phenotype.

Black horses (BB) are codominant to white horses (WW). The heterozygous horses (BW) is an appaloosa horse.

B B

W BW BW

W BW BW

Codominance continued

Blood types are unique because they are an example of:• Codominance: A and

B are both dominant.

AND

• Multiple Alleles: There are three different alleles.

Multiple Alleles

Some genes only have two alleles, like in Mendel’s experiments.

However, there are genes that have more then two alleles.

But remember you can still only inherit two of the alleles. One from each parent.

Multiple Alleles continued

In a Labrador retriever, coat color is determined by one gene with 4 alleles.

Black is dominant to chocolate = B or b.

Yellow is recessive epitstatic = E (when present, it blocks the black and chocolate alleles)

Phenotype Possible genotypes

Black BBEE, BdEE, BBEe, BbEe

Chocolate bbEE

bbEe

Yellow BBee

Bbee

bbee

Sex-linked

Because the Y chromosome is shorter than the X chromosome it has fewer genes.

Therefore if you are a boy you only get one copy of these genes. So you get what your Mom gives you.

Sex-linked continued

Examples in humans include:• Colorblindness

• Hemophilia

Polygenic Inheritance

When multiple genes determine the phenotype.

Many phenotypes are possible Examples in humans include:

• Height

• Weight

• Skin color

Polygenic - Skin color

There may be 100 different genes involved and many mutations.

Melanin is a pigment responsible for skin color and is a natural sunblock.

Lighter skin allows for more absorption of UV rays from sunlight. This is important for making vitamin D.

Darker skin allows for better sun protection.

Polygenic - Skin color

Polygenic - Skin color

Polygenic - Skin color

The long standing hypothesis is that . . . • If you lived near the equator you needed

darker skin to protect you from the intense UV rays

• If you lived farther north you needed lighter skin to help you get more UV rays because there is less sunlight.

The Environment and skin

Skin cells will produce more melanin within a few hours of exposure.

More exposure to the sun gives you a darker complexion, even for dark skinned individuals.

Some Northwest Europeans have lost the ability to tan. Their skin burns and peels rather than tans.

Genes and the Environment

Environment can affect an organisms phenotype.• Genes effect heart disease, but so do diet

and exercise.

• Genes affect skin color, so does exposure to sunlight.

• Go to page 189 and write down, on the left side of your notebook, two more examples of how the environment can affect genes.

To learn about different types of genetic disorders.

Learning Objective

Genetic Disorders

If a change occurs in a gene, the organism with the mutation may not be able to function as it should.

An inherited mutation can result in a phenotype called a genetic disorder.

Sickle Cell Anemia

This disease affects millions of people world wide.

About 2 million Americans have the sickle cell trait. About 1 in 12 are African Americans.

Sickle Cell Continued

Sickle Cell Continued

Sickle Cell Continued

Sickle Cell Continued

T-Boz Many people came to know

more about SCD through the efforts of Tionne “T-Boz” Watkins of the R&B group, TLC. Many people with SCD grow up knowing that this disease could greatly impact their life, but at 35, T-Boz is going strong and is an inspiration to many. Not only did she sing and dance her way to stardom with the pop group TLC, she gave birth to a child at 30. “Everything I ever wanted to do, I did. I'm all for taking over the disease instead of letting it take over me."