Question

Part A: Punnett Squares

I. Monohybrid Crosses

1. In pea plants yellow peas (A) are dominant to green peas (a). Show a cross between two heterozygous yellow pea plants (Aa x Aa).

	A	a
A
a

What is the genotypic ratio of the offspring? _______ AA : _______ Aa: _________ aa

What is the phenotypic ratio of the offspring? _______ Yellow: ________ Green

Part B: Using the Chi-square (χ2) analysis

9. In Parent 1 (P1) corn plants, the color purple is dominant to yellow, and round shape is dominant to wrinkled, which is why both Filial (F1) generation corn plants have the purple and round phenotypes, even when one of the parents (P1) is yellow and wrinkled.

The cross below (F1 x F1) produced the F2 generation corn that you are seeing in Figure 1. Determine the phenotypic ratios of the offspring of this cross: A cross between two F1 generation (heterozygous purple and heterozygous round) corn plants.

Phenotypic Ratio: _____: _____:_____:_____ (This is your hypothesis: The corn in Figure 1 has this ratio.)

	PR	Pr	pR	pr
PR	PPRR	PPRr	PpRR	PpRr
Pr	PPRr	PPrr	PpRr	Pprr
pR	PpRR	PpRr	ppRR	ppRr
pr	PpRr	Pprr	ppRr	pprr

Answer 1

Ans1 : Genotypic ratio of the offspring : 1 :2 : 1

AA : 1 , Aa : 2 , aa : 1

Phenotypic ratio of the offspring : 3 : 1

Yellow : 3 , Green : 1

Explanation :

  

• Genotypic ration gives the ratio of different combinations of the two alleles in the offspring. When a gene has two alleles, they can be inherited as a homozygous pair or a heterozygous pair. The allele that is phenotypically expressed in a heterozygous pair is called the dominant allele and the other one is called the recessive allele. The given monohybrid cross gives offsprings with 1 homozygous dominant, 2 heterozygous and 1 homozygous recessive genotype.
• Phenotype is defines as the observable characteristics in the appearance of an organism formed due to its genotype. In the given monohybrid cross, yellow is dominant over green. Therefore, the ratio of yellow to green is 3 : 1 where there are 3 offsprings with yellow peas for 1 green offspring with green peas.

Ans 9. The phenotypic ratio for the given dihybrid cross is : 9 : 3 : 3 : 1

i.e. there are 9 Purple-Round, 3 Purple-Wrinkled, 3 Yellow-Round and 1 Yellow-Wrinkled seeds.

Explanation :

This is because, dominant allele is expressed over a recessive alle in a heterozygous pair of alleles.