1. Understanding Inheritance
Chapter 4 Lesson 2
Understanding Inheritance

2. Learning Objective:
Using your family history to predict genetic outcomes with phenotypes.

3. 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.

4. 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

5. 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.

6. Pedigree chart Normal Affected 1 1 2 Female Male 3 4 5 6 7 8 Married
Children 12 13 14 9 10 11

7. 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

8. 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.

9. Answer 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
2nd couple 1 2 3 4 5 6 7 8

10. Answer Both parents must be Aa. Not all their children are albino. A a

11. 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.

12. 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 W RW

13. 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 W BW

14. 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.

15. 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.

16. 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

17. 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.

18. Sex-linked continued Examples in humans include: Colorblindness
Hemophilia

19. Polygenic Inheritance
When multiple genes determine the phenotype.
Many phenotypes are possible
Examples in humans include:
Height
Weight
Skin color

20. 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.

21. Polygenic - Skin color

22. Polygenic - Skin color

23. 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.

24. 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.

25. 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.

26. Learning Objective
To learn about different types of genetic disorders.

27. 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.

28. 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.

29. Sickle Cell Continued

30. Sickle Cell Continued

31. Sickle Cell Continued

32. Sickle Cell Continued

33. 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."