Question

In a homozygous pea plant, axial flowers (A) are dominant over terminal flowers (a).

(i) What is the phenotype and genotype of the F, generation if a plant bearing pure axial flowers is crossed with a plant bearing pure temiinal flowers?

(ii) Draw a Punnett square board to show the gametes and offsprings when both the parent plants are heterozygous for axial flowers.

(iii) What is the phenotypic ratio and genotypic ratio of the above cross shown in (ii) ?

(iv) State Mendel's Law of Dominance.

(v) Name two genetic disorders commonly seen in human males.

Answer 1

(i) The phenotype of the F1 generation in plants with axial flowers will be produced. The genotype of F1 generation plants is Aa.

(ii)

Gametes	A	a
A	AA Axial Flowers	Aa Axial Flowers
a	Aa Axial Flowers	aa Terminal Flowers

Genotype of Offsprings:
AA, Aa, Aa, aa

(iii) From the above cross, 3 plants with axial flowers (Aa) and 1 plant with terminal flower (aa) is produced. So phenotypic ratio is 3 : 1. Genotypic ratio is 1 :2 : 1

(iv) Mendel's Law of Dominance states that - "Out of a pair of contrasting characters present together, only one is able to express itself while the other remains suppressed. The one that expresses itself is the dominant character and the one unerpressed is the recessive. The recessive character can express only when the pair is homozygous recessive".

(v) Haemophilia and colour blindness are two common genetic disorders commonly seen in human males.