GENETICS PROBLEMS - Part 2
BIOL 1406
 
 

Monohybrid problems:

 
1. In fruit flies (Drosophila melanogaster), red-eye is dominant to white-eye.  By crossing a heterozygous red-eyed male fly to a white-eyed female, 60 offspring were produced.  How many would you expect to be red-eyed and how many white-eyed?
 
2. Albinism occurs commonly in animals and it is always recessive to the normal.  Six brown and five albino mice were born to parents (one brown and one albino).  What is the genotype of the brown parent?
 
3. Supposing brown eyes (melanin pigment present) in people (B) is dominant to blue (b).  Could a marriage between two blue-eyed people produce a brown-eyed child?  Could a marriage between a homozygous brown-eyed person and a blue-eyed person result in blue-eyed children?  Could two brown-eyed people have a blue-eyed child?  Explain all of your answers by supplying the proper symbols.
 
4. In dogs, wire hair (S) is dominant to smooth hair (s).  In a cross of a wire hair (homozygous) and smooth haired dog, what will be the hair condition of the F1 generation?  By inbreeding litter mates, what phenotype ratio would you expect in the F2 generation?
 
5. Diabetes mellitus is thought to be inherited (in some cases) as a recessive gene (d).  Two normal people have a diabetic child.  What are the genotypes of the parents and offspring?
 
6. Short hair is dominant over long hair in guinea pigs.  A short-haired guinea pig, one of whose parents was long-haired, was mated with a long-haired guinea pig.  What are the phenotypes expected in the F1 generation?  In what ratio?
 
7. Polydactyly (presence of an extra finger) is due to a dominant factor.  When one parent is polydactylous, but heterozygous, and the other parent is normal, what would be the probability of their having a normal child?
 
 
Dyhybrid problems:
 
1. In cattle, polled (hornless) (H) is dominant over horned (h) and black coat (B) is dominant over yellow (b).  If the parental generation is homozygous polled black bulls and horned yellow cows, what is the genotype of the resulting F1 generation?  When these F1 generation cattle are permitted to inbreed (mated with one another), there are 18 polled black cattle produced.  How many horned black cattle should there be (assuming a large number of cattle are produced and an ideal ratio exists)?
 
2. If a heterozygous polled, yellow bull is crossed with a heterozygous polled, heterozygous black cow, what are the four phenotypes possible in the F1 generation and what is the probability of each being produced?
 
3. A solid-colored, short-haired female rabbit (ssLL) is mated to a spotted, long-haired male (SSll).  The F1 generation offspring are allowed to interbreed and 64 offspring are produced.  How many will be expected to be spotted with long hair?  How many will be solid-colored with short hair?
 
4. If a spotted, short-haired female rabbit is mated with a solid-colored, long-haired male and produces offspring that are half spotted with short hair and half solid with short hair, what is the genotype of the female rabbit?  This is an example of what type of cross?
 
5. In some dogs, barking when trailing is due to a dominant gene; others do not bark.  Also erect ears are dominant to drooping ears.  By crossing a heterozygous erect-eared barker with a droop-eared silent trailer, what kind of pups could you expect (phenotype & percent chance)?