GENETICS REVIEW QUESTIONS (with possible answers)

QUESTIONS 

Hamisa had a garden of Pea plants, one day performed a work of crossing Red flowered Pea plants with white flowered Pea plant where she obtained all F1 plants had pink flowers. 

1. Give a biological reason to support above observation. 

2. From the above observation when two F1 plants were self-crossed, 800 F2 plants were produced by the help of illustration, show how many of F2 plants will have: 

1. Red flowers 

2. Pink flowers 

3. White flowers 

ANSWERS:

That's an interesting observation Hamisa made in her pea plant garden! Let's break down the genetics at play.

A. Biological Reason for Pink Flowers in F1:

The observation that crossing red-flowered pea plants with white-flowered pea plants resulted in all pink-flowered F1 plants suggests a phenomenon called incomplete dominance.

Here's why:

• In complete dominance, one allele completely masks the effect of the other allele in a heterozygous condition. For example, if red was completely dominant over white, the F1 generation would all have red flowers.

• However, in incomplete dominance, neither allele is completely dominant over the other. When a heterozygous individual inherits one allele for red flowers and one allele for white flowers, the resulting phenotype is a blend of the two parental phenotypes. In this case, the blend of red and white produces pink flowers.

B. Illustration of F2 Generation from Self-Crossing F1 Plants:

Let's use the following symbols for the alleles:

• R = allele for red flowers

• W = allele for white flowers

Since the F1 generation has pink flowers, their genotype must be RW (inheriting one R allele from the red parent and one W allele from the white parent).

Now, let's illustrate the self-crossing of two F1 plants (RW×RW) using a Punnett square:

       R       W

    -----------------

R   |   RR    RW

    |

W   |   RW    WW

    -----------------

From the Punnett square, we can see the following genotypes in the F2 generation:

• RR: 1 out of 4 offspring

• RW: 2 out of 4 offspring

• WW: 1 out of 4 offspring

Now, let's relate these genotypes to the flower colors based on incomplete dominance:

• RR genotype will result in Red flowers.

• RW genotype will result in Pink flowers.

• WW genotype will result in White flowers.

Given that 800 F2 plants were produced, we can calculate the expected number of each flower color:

I. Red flowers (RR): * The ratio of RR genotype is 1/4. * Number of red-flowered plants = (1/4) * 800 = 200 plants

II. Pink flowers (RW): * The ratio of RW genotype is 2/4 or 1/2. * Number of pink-flowered plants = (1/2) * 800 = 400 plants

III. White flowers (WW): * The ratio of WW genotype is 1/4. * Number of white-flowered plants = (1/4) * 800 = 200 plants

Therefore, in the F2 generation of 800 plants, we would expect approximately:

• 200 plants with red flowers

• 400 plants with pink flowers

• 200 plants with white flowers