What is the phenotypic ratio of a monohybrid cross?

(a) 1:3

(b) 3:1

(c) 1:2:2:1

(d) 9:3:3:1

To determine the phenotypic ratio of a monohybrid cross, we first need to understand what a monohybrid cross is. This type of genetic cross involves two organisms that are both heterozygous for a single trait. For example, if we consider a trait like flower color in pea plants, where purple (P) is dominant over white (p), a monohybrid cross would involve two plants with the genotype Pp.

Understanding the Basics of a Monohybrid Cross

In a monohybrid cross, we can use a Punnett square to visualize the possible combinations of alleles from the parents. When we cross two heterozygous plants (Pp x Pp), the possible gametes produced by each parent are P and p. The Punnett square for this cross looks like this:

• Parent 1: Pp
• Parent 2: Pp

	P	p
P	PP	Pp
p	Pp	pp

Analyzing the Results

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

• 1 PP (homozygous dominant)
• 2 Pp (heterozygous)
• 1 pp (homozygous recessive)

Now, let's translate these genotypes into phenotypes:

• PP and Pp will both exhibit the dominant phenotype (purple flowers).
• pp will exhibit the recessive phenotype (white flowers).

Calculating the Phenotypic Ratio

Now, we can summarize the phenotypes:

• 3 plants with purple flowers (1 PP + 2 Pp)
• 1 plant with white flowers (1 pp)

This gives us a phenotypic ratio of:

• 3 purple : 1 white

Final Thoughts

Therefore, the correct answer to the question regarding the phenotypic ratio of a monohybrid cross is (b) 3:1. This ratio is a fundamental concept in genetics and illustrates how dominant and recessive traits are expressed in offspring. Understanding this ratio is crucial for predicting the inheritance patterns of traits in various organisms.