Monohybrids

For each cross determine the genotype, genotype terms, phenotypes as well as percentages of each.

1. A homozygous black rabbit is crossed with a heterozygous black rabbit. White is recessive.

2. A hybrid tall plant is crossed with a short plant. Short is recessive.

Dihybrids

3.In rattlesnakes brown diamonds is dominant (B) and gray diamonds is recessive. The ability to sidewind is dominant (S), the ability to crawl is recessive. If a gray diamond, crawling rattlesnake is crossed with a heterozygous brown diamond, sidewinding rattlesnake– what are the probabilities of the genotypes and phenotypes of the offspring.

Incomplete & Codominance

4. Lilies are incompletely dominant, so white (W) and purple (P) are both incompletely dominant traits. If a hybrid is present, one will see lilac tulips. What are the genotype and phenotype percentages of crossing a pure white with a lilac tulip.

5. In unicorns, both the horn and wings are codominannt. Assume that horns are expressed from the homozygous CH genotype, wings from the homozygous CW genotype, and both from the heterozygous genotype. What will be the phenotypic ratio of the F1 generation resulting from a cross of two unicorns, one with a horn & one with a horn & wings?

Blood Types

Person / Genotype / Blood type
Father / IAi / A+
Child / ii / O-
Mother #1 / IAIB / AB-
Mother #2 / IAi / B+

6. A lawyer is collecting evidence in a maternity case to determine who the child’s father is. The above table shows the people involved in the case as well as their genotypes & blood types. (10 pts.)

a. Using Punnett squares, show who would most likely be the mother of the child.

b. If Mother #1 and a O+ man were to have children, what are the possible blood types of their

children as well as the probabilities for each blood type?

Pedigree: Recessive Trait (Autosomal – body chromosome)

Cystic Fibrosis is a recessive trait (c) causing poor absorption due to pancreatic insufficiency and recurrent pulmonary infection with progressive respiratory insufficiency, usually leading to death in early adulthood.

7. Using a Punnet Square explain why none of the Generation II offspring have the disease?

8. Explain what the relationship is between Generation III #2 and Generation III #3?

9. What is the Punnett square for the marriage of Generarion III #2 & #3? What is the chance of having a child with cystic fibrosis? How does that percentage compare with the actual percentage of children with CF in generation IV?

Pedigree: Sex-linked Trait

Red-green color blindness is an X-linked, recessive trait (Xb).

10.What are the probabilities for each couple (#1 & 2) in generation II to have sons with colorblindness?

11. What are the probabilities for each couple in generation II (#1 & 2) to have daughters with colorblindness?

12. How does the actual risk for colorblindness for couple # 1 differ from what actually happened?

ANSWERS Part 2 Review

Monohybrids

For each cross determine the genotype, genotype terms, phenotypes as well as percentages of each.

1. A homozygous black rabbit is crossed with a heterozygous black rabbit. White is recessive.

B / B
B / BB / BB
b / Bb / Bb

50% Homozygous black (BB); 50% Heterozygous black

2. A hybrid tall plant is crossed with a short plant. Short is recessive.

T / t
t / Tt / tt
t / Tt / tt

50% heterozygous tall (Tt); 50% homozygous short (tt)

Dihybrids

3. In rattlesnakes brown diamonds is dominant (B) and gray diamonds is recessive. The ability to sidewind is dominant (S), the ability to crawl is recessive. If a gray diamond, crawling rattlesnake is crossed with a heterozygous brown diamond, sidewinding rattlesnake– what are the probabilities of the genotypes and phenotypes of the offspring. bbss X BbSs

bs / bs / bs / bs
BS / BbSs / BbSs / BbSs / BbSs
Bs / Bbss / Bbss / Bbss / Bbss
bS / bbSs / bbSs / bbSs / bbSs
bs / bbss / bbss / bbss / bbss

25% BbSs – brown, sidewinding 25% Bbss – brown, crawling

25% bbSs – gray, sidewinding 25% bbss – gray, crawling

Incomplete & Codominance

4. Lilies are incompletely dominant, so white (W) and purple (P) are both incompletely dominant traits. If a hybrid is present, one will see lilac tulips. What are the genotype and phenotype percentages of crossing a pure white with a lilac tulip.

W / W
P / PW / PW
W / WW / WW

5. In unicorns, both the horn and wings are codominannt. Assume that horns are expressed from the homozygous CH genotype, wings from the homozygous CW genotype, and both from the heterozygous genotype. What will be the phenotypic ratio of the F1 generation resulting from a cross of two unicorns, one with a horn & one with a horn & wings?

CH / CH
CH / CH CH / CH CH
CW / CH CW / CH CW

50% horns CH CH – & 50% Horns & wings CH CW Ratio 1:1

Blood Types

Person / Genotype / Blood type
Father / IAi / A+
Child / ii / O-
Mother #1 / IAIB / AB-
Mother #2 / IAi / B+

6. A lawyer is collecting evidence in a maternity case to determine who the child’s father is. The above table shows the people involved in the case as well as their genotypes & blood types.

a. Using Punnett squares, show who would most likely be the mother of the child.

Mother #2 to get the ii / O blood type.

IA / i
IA / IA IA / IA i
i / IA i / ii

b. If Mother #1 and a O+ man were to have children, what are the possible blood types of their

children as well as the probabilities for each blood type?

IA / IB
i / IAi / IBi
i / IAi / IBi

Pedigree: Recessive Trait (Autosomal – body chromosome)

Cystic Fibrosis is a recessive trait (c) causing poor absorption due to pancreatic insufficiency and recurrent pulmonary infection with progressive respiratory insufficiency, usually leading to death in early adulthood.

7.Using a Punnet Square explain why none of the Generation II offspring have the disease?

All carriers

C / C
c / Cc / Cc
c / Cc / Cc

8.Explain what the relationship is between Generation III #2 and Generation III #3? Cousins who got married

9. What is the Punnett square for the marriage of Generation III #2 & #3?

C / c
C / CC / Cc
c / Cc / cc

What is the chance of having a child with cystic fibrosis? 1 in 4

How does that percentage compare with the actual percentage of children with CF in generation IV?

Predicted is 25% actual is 67%

Pedigree: Sex-linked Trait

Red-green color blindness is an X-linked, recessive trait (Xb).

10.What are the probabilities for each couple (#1 & 2) in generation II to have sons with colorblindness?

#1 / Xr / Y / #2 / XR / Y
XR / XR Xr / XR Y / Xr / XR Xr / Xr Y
Xr / Xr Xr / Xr Y / Xr / XR Xr / Xr Y

Sons for colorblindness- Couple #1 – 50%. Couple #2 100%

11. What are the probabilities for each couple in generation II (#1 & 2) to have daughters with colorblindness? Daughters for colorblindness- Couple #1 – 50%. Couple #2 - 0%

12..How does the actual risk for colorblindness for couple # 1 differ from what actually happened?

#1 has a 50% chance of colorblind offspring- 50% normal. Actual 100% normal / carrier