determine the expected F1 and F2 result of cross between homozygous constricted pod, round seed and inflicted pod, wrinkled seed plant?

Dear Student,

Inheritance of traits over two generations
The appearance of F1 plants was similar to their parents i.e. they were tall, but were actually different from their parents. Mendel introduced the terms genotype and phenotype.
Genotype is the genetic constitution of an organism, which includes all genes that are inherited from both the parents. For example TT, Tt, and tt are genotypes of organisms with reference to their height.
Phenotype is the observable trait or characteristic of an organism, which is the result of genotype. For example, tallness and shortness are phenotypes resulting from different genotypes.
The above experiment of Mendel involved only one pair of contrasting characters (tall/short plant height), so it is called a monohybrid cross.
If two pairs of contrasting characters are involved, then the cross is termed as dihybrid cross
Inheritance of Two Genes (Dihybrid Cross)
  • In dihybrid cross, we consider two characters. (e.g., seed colour and seed shape)
  • Yellow colour and round shape is dominant over green colour and wrinkled shape.
 
The inflated pod and round seed are dominant traits while as constricted pod and wrinkled seed are recessive traits.
Suppose inflated pod is represented by 'I' and constricted pod by 'i'. Similarly round seed is represented by 'R' and wrinkled pod by 'i'.
The cross between two homozygous parents (iiRR  and IIrr) can be represented as

                            Constricted round       X            Inflated wrinkled

                                   iiRR                                                    IIrr


Gametes                        iR                                                     Ir

F1                                                             IiRr  (All plants with inflated pods with round seeds)
                                                              
                                                               Selfing
                                                IiRr            X              IiRr   
     
Gametes                            IR, Ir, iR, ir                IR, Ir, iR, ir​

F2 generation
  IR Ir iR Ir
IR IIRR IIRr IiRR IiRr
Ir IIRr IIrr IiRr Iirr
iR IiRR IiRr iiRR iiRr
ir IiRr Iirr iiRR Iirr

Inflated round seeds - 9
Inflated wrinkled - 3
Constricted round - 3
Constricted wrinkled - 1

Phenotypic ratio will be - 9:3:3:1
​​​​​​


At this level genotypic ratio is not required. You will learn them in your higher classes.





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