Question

Five Mark Questions :
(a) Explain a monohybrid cross taking seed coat colour as a trait in Pisum Sativum. Work out the cross upto $F_2$ generation.
(b) State the laws of inheritance that can be derived from such a cross.
(c) How is phenotypic ratio of $F_2$ generation different in a dihybrid cross?

Answer 1

A) Mendel selected garden pea as his experimental material because of the following reason-

• It was an annual plant which had a short life cycle.
  
• It has bisexual flowers containing both male and female parts.
  
• He studied 7 pairs of character which are present on four different pairs of chromosome.
• The pair of traits works properly contrasting.

B) Law of dominance states that in a pair of alleles one is a dominant character and other is a recessive character. Only the dominant character will show itself in the heterozygous trait. The recessive character can show itself when it is present in a homozygotic condition. This is derived from the monohybrid cross.

C) In the F2 generation of a monohybrid cross, the phenotypic ratio is 3: 1 where three plants are tall and one is a dwarf plant. Whereas in the dihybrid cross which involves two pairs of contrasting characters the phenotypic ratio is in the ratio of 9:3:3:1.