In a plant in which fuzzy leaves (F) are dominant over smooth leaves (f), which of the following crosses will produce only offspring with smooth leaves?
A.
ffx ff
B.
Ffx Ff-
C.
Ff x ff
D.
FFX FF
The Correct answer and Explanation is:
Correct Answer: A. ff x ff
Explanation:
To determine which cross will produce only offspring with smooth leaves, we need to understand the basic principles of Mendelian genetics, particularly dominant and recessive traits.
In this scenario, the trait for fuzzy leaves (F) is dominant, while the trait for smooth leaves (f) is recessive. This means that for a plant to have fuzzy leaves, it can either have the genotype FF (homozygous dominant) or Ff (heterozygous). On the other hand, a plant will only have smooth leaves if it is homozygous recessive, with the genotype ff.
Let’s examine each of the crosses provided:
A. ff x ff
- Both parents have the genotype ff, which means they both have smooth leaves.
- Since both alleles are recessive, all offspring from this cross will inherit an f allele from each parent, resulting in the genotype ff.
- Therefore, all offspring will have smooth leaves.
B. Ff x Ff
- Both parents are heterozygous (Ff), meaning they have one dominant (F) and one recessive (f) allele.
- The possible offspring genotypes from this cross are FF, Ff, and ff, with a 25% chance of ff (smooth leaves), 50% chance of Ff (fuzzy leaves), and 25% chance of FF (fuzzy leaves).
- This cross will produce some offspring with fuzzy leaves, so it does not meet the criteria.
C. Ff x ff
- One parent is heterozygous (Ff) and the other is homozygous recessive (ff).
- The possible offspring genotypes are Ff (fuzzy leaves) and ff (smooth leaves), with a 50% chance of each.
- This cross will also produce some offspring with fuzzy leaves.
D. FF x FF
- Both parents are homozygous dominant (FF), meaning they have only the dominant allele.
- All offspring will inherit an F allele from each parent, resulting in the genotype FF, so all offspring will have fuzzy leaves.
The only cross that will produce only offspring with smooth leaves is A. ff x ff, as both parents contribute only recessive alleles (f), ensuring that all offspring have the genotype ff and, consequently, smooth leaves.