Now, we will consider 2 different characteristics of pea plant and analyse offsprings produced.
Let us consider Seed Shape and Seed Colour .
- Here - Round and Yellow are dominant traits.
Wrinkled and Green are recessive traits.
- As observed in the previous example, the F 1 generation shows dominant traits only - Yellow and Round.
- But the F 2 generation shows different traits :
- Yellow and Round seeds
- Green and Round seeds
- Yellow and Wrinkled seeds
- Green and Wrinkled seeds
The Phenotypic ratio of this cross is:
Yellow Round : Green Round : Yellow Wrinkled :Green Wrinkled
9 : 3 : 3 : 1
- A monohybrid cross is the cross of F 1 generation offspring of parents having two different forms of the same trait .
For Example - Homozygous tall X Homozygous short pea plant.
- A dihybrid cross is the cross of F 1 generation offspring which have different forms of two different traits .
For Example - Yellow and Round seeds X Green and Wrinkled seeds
What do we observe from these crosses?
- Characters are controlled by separate units called “ factors ” which are now known as genes .
- Genes occur in pairs .
- An individual inherits one gene for a particular trait from each parent.
- These genes are passed on from one generation to another without getting blended.
- If the pair of genes are not similar (heterozygous - Example - Tt) one member of the pair dominates ( dominant ) the other ( recessive ).
even when passed
are not observed in the offsprings
appear in the subsequent generations
For Example - In the cross between homozygous tall (TT) and homozygous short (tt) plants, though the gene from short plants did not appear in the F 1 generation, it appeared in the F 2 generation.
In the case of
traits are inherited independently
This is why we notice combinations in offspring that were not seen in the parents.