Monohybrid cross

notes

1. Monohybrid Crosses

2. How do you solve a Punnett Square? Find the genotypes for both parents. Put the alleles for one parent on one side of the square. Put alleles for the other parent on the other side. Combine alleles inside the boxes. Write the fractions and %’s for the offspring (what’s inside the boxes). ¼ = 25% 2/4 = 50% ¾ = 75% 4/4 = 100%

3. Albinism is a Recessive Trait

4. Sample Problem 1 A = normal a = albino A heterozygous man and an albino woman have a child. What are the genotypes of the parents? ___________ Draw a Punnett square to represent this cross: What fraction of their kids are likely to be albino? _____ (This = ____%)

5. Sample Problem 2 A = normal a = albino A heterozygous man and a heterozygous woman have a child. What are the genotypes of the parents? ___________ Draw a Punnett square to represent this cross: What fraction of their kids are likely to be albino? _____ (This = ____%)

6. Sample Problem 3 A = normal a = albino A homozygous dominant man and an albino woman have a child. What are the genotypes of the parents? ___________ Draw a Punnett square to represent this cross: What fraction of their kids are likely to be albino? _____ (This = ____%)

7. What is a 1:3 ratio? 3/4 outcomes = dominant trait 1/4 outcome = recessive trait Processing Piece: G = green eyes Circle all outcomes that would result in green eyes.

8. Sample Question 4 Which of these are 1:3 ratios? Circle them. 1 has blue eyes, 3 have brown eyes 10 are tall, 10 are short 11 are short, 29 are tall 102 are albino, 98 are normal 297 are tall, 103 are short Hint: If one number is 3 times bigger , it’s a 1:3 ratio.

9. What does 1:3 ratio tell you? The parents are BOTH heterozygous!!

10. What is a 1:1 ratio? ½ the outcomes = dominant trait ½ the outcome = recessive trait Processing Piece: A = normal, a = albino Circle all outcomes that would result in being albino.

11. Sample Question 5 Which of these are 1:1 ratios? Circle them. 1 has blue eyes, 3 have brown eyes 10 are tall, 10 are short 11 are short, 29 are tall 102 are albino, 98 are normal 297 are tall, 103 are short Hint: If the numbers are the same , it’s a 1:1 ratio.

12. What does 1:1 ratio tell you? One parent is heterozygous ( Aa ), one parent is homozygous recessive ( aa )!

13. Sample Problem 6 Pea plant traits: G = green peas, g = yellow peas A green pea plant is crossed with a yellow pea plant. 104 of the offspring have yellow peas, and 96 have green peas. You know the genotype for the yellow pea parent is _____ . Compare 104 and 96. Is one 3 times bigger, or are they about the same? __________________ What kind of ratio is this? 1:1 or 1:3 (Circle one.) What are the genotypes for the two parents? __________ Draw a Punnett square to represent the children these parents could have : Circle the genotypes that would produce yellow flowers.

14. Who is the father of genetics? Gregor Mendel He experimented with pea plants. He noticed patters in the pea plants, like 1:1 ratios and 1:3 ratios. These ratios gave him ideas about alleles.

15. Exit Ticket In pea plants, G = green peas and g = yellow peas. 1) Two heterozygous pea plants are crossed. Draw a Punnett square to represent this. 2) What percentage of the offspring will be yellow ? 3) A farmer crosses 2 pea plants and finds that 51 have yellow peas and 49 have green peas. What must be the genotypes of the parents?