Question

How does a monohybrid cross demonstrate the principle of segregation?

A. Crossing two F1 individuals produced F2 offspring that all had the same phenotype as the F1 parents

b Crossing two F1 individuals produced some F2 offspring with phenotypes seen only in the P generation

c Crossing two F1 individuals produced F2 offspring in the same ratio as the parent generation

d Crossing two F1 individuals produced some F2 offspring with new phenotypes not seen in any generation

Answer 1

Answer: “ d” Crossing two F1 individuals produced some F2 offspring with new phenotypes not seen in any generation.

Explanation: Monohybrid cross is done when two parents differing only in one pair of characters are crossed. If both the charcters are completely dominant or recseive then in the F1 generation , only the dominant character will be expressed. That is all the offsprings will show the dominant phenotype.

To know where the recessive character is gone, F2 cross is made between the F1 offsprings.

In the offsprings produced in the F2 cross, the recessive phenotype will be shown. This clearly indicates that the allele for the recessive phenotype was always there but it was not able to express in presence of the dominant allele. this also shows that when the alleles which are in pairs for a particular character enter into the gamates independent of each other and without blending with each other.

Mendel called the alleles as ‘factors’. This law of segregation of alleles is also known as ‘law of purity of gamates’

This can be also illustrated with the help of Mendel’s monohybrid cross.

If two pea plant differing only in the character of height, one being tall and other being dwarf

If they are crossed , the cross will be TT with tt

In F1 generation, the offsprings produced will be all tall

But their genotype will be ‘Tt’

To find out how the recessive charcter of dwarfness is expressed

F2 cross is made between Tt and Tt

gamates	T	t
T	TT tall	Tt tall
t	Tt tall	tt dwarf

The phenotypic ratio is 3 tall:1 dwarf

The expression of dwarf phenotype indicates that the alleles have segregated independent of each other( each gamate carries only one of the pairs of the alleles).