how are characteristics expressed (dihybrid cross)??
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Answer:
in this cross involve two pairs of alleles involve
A phenomenal typic ratio is 9:3:31
Application of the law of independent assortment is applicable in dihybrib cross
Dihybrid Cross - A cross which involves plants with two pairs of contrasting characters
Consider a cross of pea plants with round and yellow seeds and plants with wrinkled and green seeds. In this cross, the two pairs of characters involved are seed shape and seed colour.
The capital letter R is used to denote round-shaped seeds and capital Y to denote yellow-coloured seeds. The genotype of the parent plant is RRYY. The other parent has wrinkled seeds which are green in colour. The letter small r denotes wrinkled seeds and small y denotes green-coloured seeds. The genotype of the parent is rryy. The two parent plants are then crossed, RRYY × rryy.
Mendel observed that the F1 plants were with round yellow seeds phenotypically. The genotype of these F1 hybrids was RrYy.
When F1 plants are self-pollinated, the four types of male gametes and four types of female gametes produce in all 16 different mating combinations.
The F2 generation obtained by self-pollination of F1 plants exhibits 16 plants with different genotypes. Of a total of 16 plants, 9 plants are with round and yellow seeds RRYY, 3 are with wrinkled and yellow seeds rrYY, 3 are with round and green seeds RRyy and 1 is with wrinkled and green seed rryy. Thus, the phenotypic ratio of F2 plants is 9:3:3:1.
Genotypically, there are 9 different types of plant combinations—RRYY, RrYy, Rryy, rryy, RRYy, rrYy, Rryy, Rryy and rrYY. The genotypic ratio is 1:4:1:1:1:2:2:2:2.