G ENETICS

1. GENETICS Mendel’s Laws of Heredity

2. Mendel’s Laws • Law of segregation • The two alleles for each trait must separate when gametes are formed • A parent will pass down AT RANDOM, only one allele for each trait • Law of independent assortment • Genes for different traits are inherited independently of one another

3. Some Needed Vocabulary • Heredity • Passing on of characteristics from parent to offspring • Traits • Characteristics that are inherited • Genetics • The study of Heredity • Gametes • Sex cells • Sperm = male gamete • Egg = female gamete

4. Gregor Mendel • A monk who studied heredity using garden pea plants • Why garden peas? • They reproduce sexually • They have both male & female gametes on the same plant • What did he do? • He transferred pollen from one plant to another with different traits • This is called “making a cross” • Mendel first “crossed” tall plants with short plants

5. Mendel’s Monohybrid crosses • Monohybrid cross • Focuses on one (mono) trait • 1st generation • Crossed a tall pea plant with a short pea plant • All of the offspring were tall • 2nd generation • Crossing the offspring of the 1st generation • ¾ of the offspring were tall; ¼ of the offspring were short • 3:1 ratio (tall to short)

6. Mendel’s Findings • Mendel found that each chromosome has two factors for each traits… called alleles • Alleles = forms of genes • Types of alleles • Dominant • The trait that has the ability to mask the other • Represented with a capital letter (A) • Recessive • The trait that will be masked by the dominant trait… it will be there, but will not be expressed • Represented with a lowercase letter (a)

7. Phenotype vs. Genotype • Phenotype • The way that an offspring looks; how the trait appears • Tall, short • Genotype • The offspring’s genetic combination • TT, Tt, tt

8. Homozygous vs. Heterozygous • Homozygous (“homo” means “same”) • Having two identical alleles for a trait • TT, tt • Heterozygous (“hetero” means “different”) • Having two different alleles for a trait • Tt

9. Punnett square • Short way to find the expected proportions of possible genotypes in the offspring of a testcross

10. Mendel’s Punnett Square 1st generation T = Tall t = short TT x tt T T t T t T t t T t T t

11. Interpreting the Punnett Square T T t T t T t T t T t t • All offspring are heterozygous tall (Tt) • Ratio • 4:0 (Tall : Short) • Percentage • 100% Tall • Each offspring box represents 25% of the population of offspring produced Tall = T Short = t

12. Mendel’s Punnett Square 2nd generation • Homozygous Tall: • Genotype: _______ • How many? ______ • Heterozygous Tall: • Genotype: _______ • How many? ______ • Short: • Genotype: _______ • How many? ______ • TOTAL # OF TALL: _____ • TOTAL # OF SHORT: _____ • Ratio of Tall : Short  __________ • Percentages: • Percent Tall: ___________ • Percent Short: __________ Tall = ____ Short = ___ Parents: _______ x _______ T TT 1 t Tt 2 Tt Tt tt 1 T t 3 1 T TT Tt 3:1 t 75% Tt tt 25%

13. GENETICS Patterns of Heredity

14. Simple Mendelian Inheritance • The type of inheritance we have discussed thus far (Mendel’s peas) • Not all patterns in heredity are as simple… • There is more than just dominant and recessive

15. Incomplete Dominance • The phenotype of the heterozygote is intermediate (BLENDED) between those of the two homozygotes • For Example: • A cross between a particular Red flower and a Whiteflower will produce a Pink flower

16. Punnett Square for Incomplete Dominance Cross: (RR) Red flower X (R’R’) White flower RR = Red R’R’ = White RR’ = Pink R R R’ 100% PINK FLOWERS (RR') R R’ R R’ R’ R R’ R R’

17. Codominance • The phenotypes of both homozygotes is produced (SPOTTED) in the heterozygous individual • For Example: • A black rooster and a white hen might produce a chick with some black feathers and some white feathers (stripes, polka dots and patches are co-dominant)

18. Multiple Alleles • Traits controlled by more than 2 alleles … • For Example: • Multiple alleles are commonly seen in the coat color of rabbits • Also… Blood Typing…

19. Multiple Alleles – Blood Types • Human blood types are determined by the presence or absence of certain molecules on the surfaces of red blood cells • There are three alleles for blood type… • IA …………………… written as “A” • IB …………………… written as “B” • i …………………… written as “O”

20. Sex-linked traits • Traits that are controlled by genes located on sex chromosomes • These traits help explain why some characteristics and disorders are more common in one sex than in the other • Commonly referred to as “X-linked” because the trait is usually linked to the X-chromosome

21. Background Information • Humans have 46 chromosomes; or 23 pairs of chromosomes • Of these, 22 pairs are autosomes (self chromosomes) • The last (23rd) pair is different in males & females… these are the sex chromosomes • Females have two “X” chromosomes (XX) • Males have one “X” and one “Y” chromosome (XY)

22. “Sex-linked” traits Green-eyed male (XbY) X Heterozygous Blue-eyed female (XBXb) B = Blue eyes b = Green eyes Xb Y XB XBXb XBY Xb XbXb XbY

23. “Sex-linked” traits Green-eyed male (XbY) X Heterozygous Blue-eyed female (XBXb) B = Blue eyes b = Green eyes Xb Y XB XBXb XBY Xb XbXb XbY • OFFSPRING • MALES (XY) • Blue Eyes • Genotype _______ • How many? _____ • Green Eyes • Genotype _______ • How many? _____ • FEMALES (XX) • Blue Eyes • Genotype _______ • How many? _____ • Green Eyes • Genotype _______ • How many? _____ XBY 1 XbY 1 XBXb 1 XbXb 1

24. Sex-linked percentages Green-eyed male (XbY) X Heterozygous Blue-eyed female (XBXb) B = Blue eyes b = Green eyes Xb Y XB XBXb XBY Xb XbXb XbY • Percentages • When figuring percents for sex-linked punnett squares, you must be careful to only count what is asked for… • % of females with blue eyes • % of males with blue eyes • % of females with green eyes • % of males with green eyes 50% 50% Females Males 50% 50%

25. Polygenic Inheritance • When a trait is controlled by more than one gene • For Example: • Skin color is actually the accumulation of dominant genes for pigment in the skin