Question

A plant with round seeds is crossed with another plant with round seeds. Round are dominant over oval seeds. When two heterozygous round-seeded plants are crossed, what is expected of their offspring, assuming random chromosome segregation?
Responses
A The oval-shaped plant will appear 50% of the time.The oval-shaped plant will appear 50% of the time.
B The round-shaped plant will appear 100% of the time.The round-shaped plant will appear 100% of the time.
C The oval-shaped plant will most likely appear 75% of the time.The oval-shaped plant will most likely appear 75% of the time.
D The round-shaped plant will most likely appear 75% of the time.

Answer 1

To determine the expected outcomes of the offspring when two heterozygous round-seeded plants are crossed, we can use a Punnett square to analyze the genetic combinations.

- Let's denote the dominant allele for round seeds as "R" and the recessive allele for oval seeds as "r".

When both parents are heterozygous (Rr):

- Possible gametes from each parent: R and r
- The Punnett square for the cross Rr x Rr is:

```
R | r
-----------------
R | RR | Rr
-----------------
r | Rr | rr
```

From the Punnett square, we can see the following genotypes for the offspring:

- 1 RR (homozygous round)
- 2 Rr (heterozygous round)
- 1 rr (homozygous oval)

This gives us the following ratio of phenotypes:

- Round (RR + Rr): 3 (1 RR + 2 Rr)
- Oval (rr): 1

Thus, the expected phenotypic ratio is:

- 75% round seeds (3 out of 4)
- 25% oval seeds (1 out of 4)

Based on this analysis, the correct response is:

**D** The round-shaped plant will most likely appear 75% of the time.