Question

Yellow fruit and dwarf vines are recessive traits in tomatoes. Red fruit and tall vines are dominant. Suppose a true-breeding dominant red and tall plant crossed with a heterozygous red and dwarf plant.

a. What is the phenotype ratio?
b. What percent of the offspring will have yellow fruit and dwarf vines?

a) Aa, Aa, aa, Aa
b) 25% yellow fruit and dwarf vines
c) 50% yellow fruit and dwarf vines
d) 75% yellow fruit and dwarf vines

Answer 1

The phenotype ratio is 4 red and tall plants : 2 red and dwarf plants. 25% of the offspring will have yellow fruit and dwarf vines.

Step-by-step explanation:

When a true-breeding dominant red and tall plant (RRTT) is crossed with a heterozygous red and dwarf plant (RrTt), the possible genotypes of the offspring are RRTT, RRtt, RrTT, RrTt, RRTt, and Rrtt.

The phenotype ratio is 4 red and tall plants : 2 red and dwarf plants. This is a result of the dominant red and tall traits showing Mendelian inheritance.

Since yellow fruit and dwarf vines are both recessive traits, the only genotype that can produce the phenotype of yellow fruit and dwarf vines is rrtt. Therefore, 25% of the offspring will have yellow fruit and dwarf vines.