Genetic Crosses that Involve 2 Traits - KEY
In rabbits, grey hair is dominant to white hair.
Also in rabbits, black eyes are dominant to red eyes.
| GG = gray hair Gg = gray hair gg = white hair |
BB = black eyes Bb = black eyes bb = red eyes |
1. What are the phenotypes (descriptions) of rabbits that have the following genotypes:
Ggbb ___gray hair, red eyes___ ggBB _white hair, black eyes_
ggbb ___white hair, red eyes____ GgBb __gray hair, black eyes__
2. A male rabbit with the genotype GGbb is crossed with a female rabbit with the genotype ggBb The square is set up below. Fill it out and determine the phenotypes and proportions in the offspring.
 |
How many out of 16 have grey fur and black eyes? _8__ How many out of 16 have grey fur and red eyes? ___8____ How many out of 16 have white fur and black eyes? _0____ How many out of 16 have white fur and red eyes? __0___ |
3. A male rabbit with the genotype GgBb . Determine the gametes produced by this rabbit (the sperm would have these combinations of alleles) Hint there are 4 combinations. GB, Gb, gB, gb
4. A female rabbit has the genotype ggBb. Determine the gamets (eggs) produced by this rabbit. gB, gb
5. Use the gametes from #4 and #5 to set up the punnet square below. Put the male's gametes on the top and the female's gametes down the side. Then fill out the square and determine what kind of offspring would be produced from this cross and in what proportion.
gray hair, black eyes =3/8
gray hair, red eyes =
1/8
white hair, black eyes = 3/8
white hair, red eyes = 1/8
6. An aquatic arthropod called a
Cyclops has antennae that are either smooth or barbed. The allele for barbs
is dominant. In the same organism, resistance to pesticides is a recessive trait.
Make a "key" to show all the possible genotypes (and phenotypes) of
this organism. Use the rabbit key to help you if you're lost.
AA = barbed, Aa = barbed, aa = smooth
RR = not, Rr = not, rr = resistant
7. A Cyclops that is resistant to
pesticides and has smooth antennae is crossed with one that is heterozygous
for both traits. Show the genotypes of the parents.
aarr x AaRr
8. Set up a punnet square for the cross.
9. What are the phenotypic ratios of the offspring?
1/4 resistant, barbed | 1/4 resistant smooth | 1/4 nonresistant, barbed | 1/4 nonresistant smooth