1. Chapter 8 Mendel & Heredity

2. I. Terms
Heredity- the passing on of traits (color/shape of eyes, texture of hair) from parent to offspring
Genetics- the study of heredity
Genes- pieces of DNA that code for a certain trait (Mid-digital hair)
Alleles- alternative versions for each gene
(ex. hairy mid-digits, non hairy mid-digits)
1) Letters are used to represent alleles (Capital letters represent dominant trait, lower case represent recessive trait)

3. Terms continued
Homozygous- 2 alleles in an individual are the same (ex. HH, hh), pure bred
Heterozygous- alleles are different (ex. Hh), hybrid
Genotype- the set of alleles that an individual has (ex. HH, Hh, hh)
Phenotype- the physical appearance of a trait (ex. Hairy mid-digits, non hairy mid digits)

4. II. Gregor Mendel Gregor Mendel (1800’s) - Father of Genetics p.161

5. Mendel
Studied 7 traits in garden peas (grows quickly & produces many offspring)
***Traits- pod color, flower color, wrinkled, height, seed shape, etc.
-Self-pollination produced the same traits every time
Ex. Purple x Purple = All Purple flowers White x White = All White

7. Crossed 2 plants with contrasting traits (P1 x P1 = F1)
Ex. Pure white x Pure purple = All purple plants F1 (filial) generation
2nd cross between plants of F1 generation yielded the F2 generation
F1(purple) x F1 (purple) = F2 (75% purple & 25% white)
*(Before Mendel, people thought offspring were a blend of their parents
Ex. Tall x Short = Medium height)

9. C. Mendelian theory of heredity
1. For each trait, an individual has two copies of the gene—one from each parent
2. There are alternative versions of genes (alleles)
3. The allele that is displayed is called dominant; the allele that is present in the organism but has no effect on its appearance is called recessive

10. 1.Law of Segregation= the two alleles for the trait separate when gametes are formed. Gametes carry only one allele for each inherited trait

11. 2. Law of independent assortment= the alleles of different genes separate independently of one another when gametes are formed.

12. III.Punnett square
A. Tool used by scientist to predict the outcome of a genetic cross

13. Monohybrid sample problem: In roses, red is dominant over white.
Use R for the red gene.
Use r for the white gene.
Cross two heterozygous red roses, Rr X Rr
From the Punnett Square,
describe the phenotype of the offspring.
3/4 Red
1/4 White
describe the genotype of the offspring.
1/4 RR
1/4 rr
2/4 (or ½) Rr
</TD

14. IV. Beyond Complete Dominance
Incomplete dominance- when neither allele is dominant over the other; results in blending the heterozygous genotype (Rr)

15. Examples: Can they have an offspring that has straight hair?
Incomplete Dominance:
#1. One trait in humans that is displayed by incomplete dominance is hair texture. The heterozygous genotype (Hh) is expressed as wavy. If mom has curly hair, which is dominant to straight hair, and dad has wavy hair then what is the probability of them having an offspring that has curly hair?
Can they have an offspring that has straight hair?

16. B. Co-dominance- both alleles are expressed in the heterozygote equally
Ex. Multiple alleles inheritance (blood type)

17. Example
Co-dominance
#2. Roan cattle are a result of co-dominance. List the possible phenotypes of the offspring that would result from the crossing of 2 roan cattle.

18. C. Sex-linked inheritance- traits carried on the X chromosome
ex. color blindness (red/green),
hemophilia (blood clotting disorder)
Punnett Square Examples:
XX=female
XY=male

19. More Examples of Sex-Linked Recessive Disorders
Red/Green Colorblindness – Difficulty perceiving differences between colors (red or green, blue or yellow).
Hemophilia – Absence of one or more proteins necessary for normal blood clotting.
Deafness
Cataracts – opacity in the lens that can lead to blindness
Night blindness – (Nyctalopia) rods do not work so that can not see in the dark
Glaucoma – pressure in the eye that can lead to optic nerve damage and blindness
Duchenne Muscular Dystrophy – progressive weakness and degeneration of skeletal muscles that control movement due to absence of dystrophin (protein that maintains muscle integrity). Mainly in boys, onset 3-5 yrs, by 12 years can’t walk, and later needs respirator.

21. Example Sex-linked disorders:
#3. Hemophilia is a blood clotting disorder that is sex-linked recessive disorder (found on the X chromosome). Demonstrate a cross between a mom who is a carrier for the disorder and a dad who does not have hemophilia.
a) What percent of the offspring will have hemophilia?
b) What percent of the females are carriers?
c) What percent of the males have hemophilia?

22. Example Sex Linked Inheritance & Co-dominance:
#4. Coat color in cats is a co-dominant trait and is also located on the X chromosome. Cats can be black, yellow or calico. A calico cat has black and yellow splotches. In order to be calico, the cat must have an allele for the black color and an allele for the yellow color.

23. #4. A female calico cat is crossed with a male black cat.
a) What percent of the offspring are calico?
b) What percent of the females are calico?