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Help with questions plz. - Dihybrid Crosses (Apr/26/2008 )

1.In pea plants, tallness (T) is dominant to shortness (t) and red flower ® is dominant to white ( r ). Two plants one heterozygous for both genes and the other homozygous short, white are crossed. What is the phenotypic ratio of the F1?

2.In horses, black coat colour (B) is dominant to chestnut colour ( b ) and trotting gait (T) is dominant to pacing ( t ). If a homozygous black pacer is mated to a homozygous chestnut trotter, what would be the phenotypes and genotypes of the F1? Show the phenotypic ratio of the F2

3.In guinea pigs, black coat colour is dominant to albino. Rough coat is dominant to smooth coat. 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 offspring produced over a period of years in a number of matings, what was the probable genotype of each parent? Show how you arrived at your answer.

4.In fruit flies, curly wings and ebony body are recessive alleles. The dominant alleles are normal wings and normal body colour. What type of offspring would you expect from a cross between a curly winged ebony female and a homozygous normal male?

5.Blue eyes and attached ear lobes are recessive while brown eyes and free hanging ear lobes are dominant. A woman who has blue eyes and attached ear lobes marries a man who has heterozygous brown eyes and free hanging ear lobes. What are the possible genotypes and phenotypes of their offspring? How many of each possible genotype is there?

can someone help me with atleast one or two so i can get some idea.. thanx


these are really very simple. you should try them yourself.

but, i will help you with #2:

since both are homozygous, but of the opposite phenotype, then all offspring will be heterozygous in both and the phenotype will be dominant in both.

now, if you can see how this happens then the other problems should be easy.

by the way, you could use punnett squares to determine the answers but my college genetics teacher threatened to fail any student who used one instead of calculating probabilities.