Probability & Genetic Crosses

1. Probability & Genetic Crosses

2. Probability If you roll one die, what’s the probability of rolling a 6? 1/6 (1 out of 6) If you pull one card from the deck, what’s the probability of getting the ace of hearts? 1/52 (1 out of 52) If you flip a coin, what’s the probability of landing on heads? 1/2 (1 out of 2)

3. A Genetic Cross • Gregor Mendel(1865) discovered that probability could be used to predict the results of agenetic cross (mating) • If you knowparentgenotypes, you can predictoffspringgenotypes

4. A Genetic Cross • If you knowparentgenotypes, you can predictoffspringgenotypes Example: • Brown hair (B) is dominant toblond hair (b). • What are the possible genotypes for their offspring? Bb bb ♀ Bb x ♂ bb Bb, Bb,bb, bb

5. A Genetic Cross • If you knowparentgenotypes, you can predictoffspringgenotypes Example: • Brown hair (B) is dominant toblond hair (b). • What is the probability that the Incredibles’ next child will have brown hair? Bb bb ♀ Bb x ♂ bb Bb, Bb,bb, bb 2/4 (50%) chance of brown hair

6. Practice • In pea plants, smooth peas (S) are dominant to wrinkled peas (s). • A homozygous smooth pea is crossed with a wrinkled pea. ♀ _____ x ♂ _____

7. Practice • In pea plants, smooth peas (S) are dominant to wrinkled peas (s). • A homozygous smooth pea is crossed with a wrinkled pea. • Determine the possible offspring genotypes & phenotypes. ♀ SS x ♂ ss Ss, Ss, Ss, Ss 100% chance of smooth peas

8. Practice • In guinea pigs, dark fur (D) is dominant to light fur (d). • Cross a heterozygous dark guinea pig with a light guinea pig. ♀ _____ x ♂ _____

9. Practice • In guinea pigs, dark fur (D) is dominant to light fur (d). • Cross a heterozygous dark guinea pig with a light guinea pig. • Determine the possible offspring genotypes & phenotypes. ♀ Dd x ♂ dd Dd, Dd, dd, dd 50% chance of dark fur 50% chance of light fur

10. A Genetic Cross • If you knowoffspringgenotypes, you can predictparentgenotypes Example: • Brown eyes (B) are dominant to blueeyes (b). • If Dash’s genotype is bb, what are his parents’ genotypes? Bb ? bb ? bb

11. Practice • In guinea pigs, dark fur (D) is dominant to light fur (d). • Two dark-fur guinea pigs produce a light-fur offspring. • What is the genotype of the offspring? dd

12. Practice • In guinea pigs, dark fur (D) is dominant to light fur (d). • Two dark-fur guinea pigs produce a light-fur offspring. • What must the parent genotypes be? Dd ? Dd ? dd

13. Punnett Squares • Created byReginald Punnett(1900) to makepredictingtheoutcomeof genetic crosses easier • show allthepossible outcomesof a genetic cross • show theprobability ofeach outcome 25% 25% 25% 25%

14. Punnett Squares • show all the possible outcomes of a genetic cross • show the probability of each outcome Example: • In dogs, short hair (S) is dominant to long hair (s). • Determine the possible offspring phenotypes. ♂ SS S S S s SS SS ♀ Ss Ss Ss 100% chance of short hair

15. Why Use a Punnett Square? Most scientists study MANY traits at one time It gets VERY confusing without a Punnett Square!

16. Practice • In humans, straight toes (S) is dominant to curled toes (s). • Determine the possible results for a cross between a recessive male & heterozygous female. ♂ ss s s Ss Ss S s ♀ Ss ss ss 50% chance of straight toes 50% chance of curled toes

17. Practice • In pea plants, yellow color (Y) is dominant to green (y). • Determine the possible results for a cross of 2 heterozygous plants. ♂ Ss S s SS Ss S s ♀ Ss Ss ss 75% chance of yellow peas 25% chance of green peas

18. Special Cases • Incompletedominance • Neitherallele is dominant • Heterozygous = inBETWEENphenotypes Example: Carnations CRCR = ? CRCW= CWCW=

19. Special Cases • Codominance • Neitherallele is dominant • Heterozygous =BOTHphenotypes Example: Cows HWHW= ? HWHB= HBHB=