Question

In peas, the round allele (r) is dominant to the wrinkled allele (r), and tall (t) is dominant to short (t). a pure-breeding round, tall strain is crossed to a wrinkled, short strain, and the f1 plants are crossed back to the wrinkled, short strain. what proportion of the offspring will be wrinkled and tall

Answer 1

When crossing a heterozygous round, tall F1 pea plant with a homozygous wrinkled, short pea plant, the probability of the offspring being wrinkled and tall is 1/4.

Step-by-step explanation:

In pea plants, we have two traits where round seed shape (R) is dominant to wrinkled seed shape (r), and tall height (T) is dominant to short height (t). When a homozygous round, tall plant (RRTT) is crossed with a homozygous wrinkled, short plant (rrtt), the resulting F1 generation will all have the genotype RrTt (heterozygous for both traits). If these F1 plants are then crossed back to the wrinkled, short strain (rrtt), we need to look at each trait separately to determine the phenotype ratios.

For the seed shape, the F1 plants (Rr) crossed with the wrinkled, short (rr) can produce offspring with either Rr or rr genotype. Therefore, the probability of having a wrinkled (rr) offspring is 1/2. For height, the F1 plants (Tt) crossed with the wrinkled, short (tt) can also produce offspring with either Tt or tt genotype. The probability of having a tall (Tt) offspring is 1/2 as well. To find the proportion of offspring that are wrinkled and tall, we multiply the probabilities of the independent events: 1/2 (chance of being wrinkled) × 1/2 (chance of being tall) which equals 1/4.

Therefore, the proportion of offspring that will be wrinkled and tall from this cross is 1/4.

Answer 2

The round allele is dominant (R)
The wrinkled allele is recessive (r)
The tall allele is dominant (T)
The short allele is recessive (t)

The genotype of the f1 generation would be RrTt.So if you cross that back to the wrinkled short then the Punnet of that cross would look like this:

RrTt x rrtt

RT Rt rT rt
rt RrTt Rrtt rrTt rrtt
rt RrTt Rrtt rrTt rrtt
rt RrTt Rrtt rrTt rrtt
rt RrTt Rrtt rrTt rrtt

The genotype for a wrinkled tall should be rrTt at least in this case because neither of the parents are pure-breed.

The proportion would then be then 4/16 or 1/4. There is a 25% chance of yielding a wrinkled tall.