1. Genetics
The study of potentials of passing information from one generation to the next

2. Gregor Mendel “Father” of genetics Studied pea plants
Used contrasting features
Parents “bred true”
Kept good records
Studied one trait at a time

3. Mendel’s pea experiment
True breeding purple flower plants
True breeding white flower plants
F1 generation
F2 generation

4. Terminology Gene – unit of inheritance made of DNA
Genes occur in pairs except in the egg and sperm
An allele is a different form of the same gene
Black hair and brown hair are alleles of the hair color gene

5. Genes
Dominant gene is one that can overshadow another gene. Signified with capital letter, e.g. “A”
Recessive gene is the subordinate gene that can be suppressed by the dominant gene. Signified with a lower-case letter, e.g. “a”

6. Genes
Homozygous – since genes occur in pairs, this is when both genes for the trait are the same
AA is homozygous dominant
aa is homozygous recessive

7. Genes Heterozygous – genes are alleles or different for a given trait
Aa is heterozygous
Carrier is sometimes used to indicate that someone is heterozygous

8. Genes Genotype is your genetic makeup
For example, you might be heterozygous for hair color, Bb, one gene for black hair, and one for blonde hair

9. Genes Phenotype is your physical appearance
Your phenotype for hair color may be brown

10. One gene problem Let P = Purple flower plants, or
Let p = white flower plants, or
The parent generation included true breeding purple flower plants that must have been PP (homozygous dominant) in genotype
The parent generation included true breeding white flower plants that must have been pp (homozygous recessive) in genotype

11. Parents
PP plant can only make a gamete with the first “P” gene, or the second “P” gene
(See example using E instead of P)
pp plant can only make a gamete with its first “p” gene, or the second “p” gene
(See example using e instead of P)

13. F1 generation
If these two parents fertilize to create offspring, F1, or first generation, what genotypes and phenotypes would be possible in the F1 generation?
Use a mathematical Punnet square to find the probabilities

14. F1 generation Gamete with “P” gene – parent 1
Offspring is heterozygous – “Pp”

15. F1 generation
100% of the offspring would have a genotype of Pp, or be heterozygous
100% of the offspring would have a phenotype of purple flowers, since purple is dominant over white

16. F2 generation
If you take two plants from the F1 generation (Pp) and cross them, what would be the genotypic and phenotypic ratios of the next, or F2 generation?

17. F2 generation Gamete with “P” gene – parent 1
Offspring is homozygous dominant – “PP”
Offspring is heterozygous – “Pp”
Gamete with “p” gene – parent 2
Offspring is homozygous recessive – “pp”

18. F2 generation
Note that the four squares in the Punnet square do not represent four different offspring, but rather the statistical chances that any ONE offspring has a given trait
Genotypic ratios are 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive
Phenotypic ratios are 3 purple : 1 white

19. Try this problem E = unattached earlobes e = attached earlobes
Problem one: Both parents have unattached earlobes. However, they had a son with attached earlobes. What are the chances that their next child will have unattached earlobes?

23. Try this problem E = unattached earlobes e = attached earlobes
Problem two: One parent has unattached earlobes and the other has attached earlobes. They had a daughter with attached earlobes. What are the genotypes of the parents? What are the chances that their next child will have unattached earlobes?

25. Autosomal Dominant
The trait or disease is the result of a dominant gene

26. Autosomal Recessive
The trait or disease is the result of a recessive gene (e.g. cystic fibrosis)

27. Incomplete dominance
The dominant gene is not strong enough to completely overshadow the recessive gene
Example: If a red flower plant (dominant) crosses with a white flower plant (recessive) and the offspring have pink flowers (heterozygous).

28. Codominance No clear dominant or recessive gene
Genes are equal, or codominant
If genes for blood type A and blood type B are codominant and you have one gene of each, your blood type is AB

29. Blood typing practice
Genes for blood types A and B are dominant over type O
Genes for blood types A and B are codominant with each other
If mom has blood type A and dad has blood type B, and they have a son with blood type O, what are the genotypes of these 3 people? What are the statistical chances that their next child has blood type AB?

31. Sex-Linked traits
The sex of the person has not mattered up until this point working on the genetics problems. Now it does.
These sex-linked problems are such that the gene for the particular trait is located on the X chromosome only.
Recall that males are XY and females are XX.

33. Colorblindness is sex linked
Colorblind is a recessive trait
Carried on the X chromosome only
Let B = normal vision and b = color blind
Mom and dad both have normal vision. However, their second child was a colorblind son. What are the genotypes of the parents and what are the chances that their next son/daughter is colorblind?