DIHYBRID CROSSES – QUESTIONS

1. In mutant pseudo-punkers such as Prince, frizzy hair is dominant (F) and straight hair is recessive. Purple hair results from the action of a dominant allele (P) and orange air from the recessive allele. Determine the phenotypic and genotypic ratios if a heterozygous frizzy, purple haired male produced children with a straight, orange haired female?

2. Short hair in rabbits is governed by a dominant allele (S) and long hair by its recessive allele. Black hair results from the action of the dominant genotype (B) and brown from the recessive allele. In crosses between heterozygous short, black and homozygous short, brown rabbits, what genotype and phenotype ratios are expected among their progeny (offspring)?

3. Complete the crosses showing the phenotypic ratios, given the following information: Free earlobes are dominant to attached and tongue rolling is dominant to non-tongue rolling. A) A heterozygous male for both traits marries a woman with attached earlobes, who is heterozygous for tongue rolling. B) A man who is homozygous recessive marries a woman with attached earlobes who cannot roll her tongue.

4. In dogs, barking is dominant to non-barking and pointy ears are dominant to drooping ears. What pups could be expected from a cross between a heterozygous pointy eared barker and a droopy eared non-barker? Show your results in a phenotypic ratio.

5. A black smooth guinea pig was mated with an albino rough guinea pig. Their offspring were black rough and black smooth. If these were the only types produced over a period of years (hundreds of offspring) in a number of matings, determine: A) Which alleles are dominant and which are recessive. Explain. B) What was the probable genotype of each parent? Explain.

6. Mary is white skinned, but both of her parents are dark skinned. Mary has scaly skin, but her mother has normal skin and her father has scaly skin. The father is heterozygous for scaly skin. Joe is white skinned and has normal skin. A) Predict the genotypes of Mary and Joe. B) Predict the genotypic and phenotypic ratios of the offspring between Mary & Joe.

7. What kind of gametes (allele combinations) would be produced by organisms having the following genotypes?

a) AaBB b) aaBB c) AaBbCc (Hint: there are eight) d) AABBCc DIHYBRID CROSSES – Answers

#1. Phenotypic ratio: 1 : 1 : 1 : 1 frizzy/purple frizzy/orange straight/purple straight/orange Genotypic ratio: 1 : 1 : 1 : 1 FfPp Ffpp ffPp ffpp

#2. Phenotypic ratio: 1 : 1 short/black short/brown Genotypic ratio: 1 : 1 : 1 : 1 HhBb HHbb Hhbb Hhbb

#3. a) 5 : 1 : 1 : 1 free/rolling free/non-rolling attached/rolling attached/non-rolling

b) All attached and cannot roll their tongues. #4. 1 : 1 : 1 : 1 pointy/barker pointy/non-barker droopy/barker droopy/non-barker

#5. The black smooth guinea pig’s probable genotype is BBSs The albino rough guinea pig’s genotype is bbss

#6. a) Mary – ddSs Joe - ddss b) Phenotypic ratio: 1 : 1 white and scaly white and normal Genotypic ratio: 1 : 1 Ssdd ssdd

#7. a) AB and aB b) aB c) ABC, AbC, Abc, aBC, aBc, abc, abC, AbC d) ABC and ABc