Two pea plants heterozygous for the characters of pod color and pod shape are crossed

Two pea plants heterozygous for the characters of pod color and pod shape are crossed. Draw a Punnett square to determine the phenotypic ratios of the offspring.

The Correct Answer and Explanation is :

To determine the phenotypic ratios of the offspring from a cross between two pea plants that are heterozygous for pod color and pod shape, we first need to define the traits and their corresponding alleles.

Traits and Alleles:

1. Pod Color:

• Green (dominant) = G
• Yellow (recessive) = g

1. Pod Shape:

• Smooth (dominant) = S
• Wrinkled (recessive) = s

Since both parents are heterozygous for both traits, their genotypes are GgSs. To find the potential offspring, we will create a Punnett square.

Step 1: Determine Gametes

Each parent can produce the following gametes:

• For parent 1 (GgSs): GS, Gs, gS, gs
• For parent 2 (GgSs): GS, Gs, gS, gs

Step 2: Create the Punnett Square

       |   GS   |   Gs   |   gS   |   gs   
-------------------------------------------
   GS  | GGS S | GGS s | GgS S | GgS s 
-------------------------------------------
   Gs  | GGS s | GgS s | Gg s  | Gg s  
-------------------------------------------
   gS  | GgS S | GgS s | ggS S | ggS s  
-------------------------------------------
   gs  | GgS s | Gg s  | ggS s | ggs s  

Step 3: Determine the Genotypes

From the Punnett square, we can now analyze the offspring genotypes:

• GGS S (2): Green and smooth
• GGS s (2): Green and wrinkled
• GgS S (4): Green and smooth
• GgS s (4): Green and wrinkled
• ggS S (1): Yellow and smooth
• ggs s (1): Yellow and wrinkled

Step 4: Calculate Phenotypic Ratios

1. Green Smooth: 6 (GGS S + GgS S)
2. Green Wrinkled: 2 (GGS s + GgS s)
3. Yellow Smooth: 1 (ggS S)
4. Yellow Wrinkled: 1 (ggs s)

Phenotypic Ratio:

• Green Smooth: 6
• Green Wrinkled: 2
• Yellow Smooth: 1
• Yellow Wrinkled: 1

This results in a phenotypic ratio of 6:2:1:1.

Explanation

This Punnett square illustrates how Mendelian genetics predicts the inheritance of traits. The ratios observed reflect the combination of dominant and recessive alleles in the offspring. The higher occurrence of green pods demonstrates the dominance of the green allele over the yellow allele. Similarly, the smooth pods are more common than the wrinkled ones, highlighting the dominance of the smooth trait. The ratios show the expected outcomes based on the principles of segregation and independent assortment, showcasing the genetic variation that can arise from such crosses.