Genetics Answers

In peas, a gene for tall plants (T) is dominant over its allele for short plants (t). The gene for smooth peas (S) is dominant over its allele for wrinkled peas (s). The genes are not linked.

TtSs x TtSs

ttSs x Ttss 

TtsSS x ttss

Ttss x ttss

In peas, a gene for tall plants (T) is dominant over its allele for short plants (t). The gene for smooth peas (S) is dominant over its allele for wrinkled peas (s). The genes are not linked. Determine both phenotypic and genotypic ratios for the results of each of the following crosses:

In a pea plant that breeds true for tall, what possible gametes can be produced? Use the symbol D for tall, d for dwarf.

A. In a pea plant that breeds true for dwarf, what possible gametes will be produced?

B. What will be the genotype of F1 offspring from a cross between these two types?

C. Assuming that the allele for tall is dominant, what will be the phenotype of F1

offspring from a cross between these two types?

E. What will be the probable distribution of traits in the F2 generation? (Illustrate with a Punnett square).

a. In a pea plant that breeds true for tall, what possible gametes can be produced? Use

the symbol D for tall, d for dwarf.

c. What will be the genotype of F1 offspring from a cross between these two types?

d. Assuming that the allele for tall is dominant, what will be the phenotype of F1

offspring from a cross between these two types?

e. What will be the probable distribution of traits in the F2 generation? 

What is the probability that a women carrying an abnormal X-linked gene has three sons are unaffected?

What is the probability that a women carrying an abnormal X-linked gene has two sons unaffected an one affected? 

What is the probability that a women carrying an abnormal X-linked gene has two sons affected an one unaffected? 

What is the probability that a carrier women will transmit an abnormal X-linked gene to her 3 sons?

What is the probability that a carrier women will transmit an abnormal X-linked gene to her son? 

A 31 year old woman consults her physicain because she is concerned about developing breast cancer. She is currently in good health and she has never had any breast disease. Her concern arises bacause her sister has just been diagnosed as having breast cancer and her mother died of breast cancer.

• How can one determine if the cancer in this family is likely to be a dominantly inherited predisposition?
• What is the woman’s cahnce of developing breast cancer?