(a) Explain a monohybrid cross taking seed coat colour as a trait in Pisum sativum. Work out the cross upto F2 generation.
(b) State the laws of inheritance that can be derived from such a cross.
(c) How is the phenotypic ratio of F2 generation different in a dihybrid cross?
(a) Monohybrid cross is the cross in which only one trait is taken into account.
For example, if pea plant with yellow seed coat is crossed with pea plant having green seed coat then in the F1 generation all the plants produce yellow seeds.
(b) Two laws can be derived from such a cross
Law of Dominance- According to this law, characters are controlled by discrete units called factors, which occur in pairs with one member of the pair dominating over the other in a dissimilar pair. It explains the expression of only one of the parental character in F1generation and expression or appearance of both in F2 generation.
In the given cross, the allele for yellow seeds is dominant over the allele that produces green seeds. In F1 generation all offsprings showed yellow colour of seed (dominant character) and expression of both yellow and green in F2 generation.
Law of Segregation-This law states that the two alleles of a pair segregate or separate during gamete formation such that a gamete receives only one of the two factors. In homozygous parents, all gametes produced are similar; while in heterozygous parents, two kinds of gametes are produced in equal proportions. The alleles for yellow and green seeds in the F1 generation segregate and the gamete either contains yellow allele or green allele giving rise to different combination in the F2 generation. Thus, showing that the gametes receive only one of the two factors.
Explain the genetic basis of blood grouping in human population.
What is the inheritance pattern observed in the size of starch grains and seed shape of Pisum sativum? Workout the monohybrid cross showing the above traits. How does this pattern of inheritance deviate from that of Mendelian law of dominance?
(a) Why are thalassemia and haemophilia categorized as Mendelian disorders ? Write the symptoms of these diseases. Explain their pattern of inheritance in humans.
(b) Write the genotypes of the normal parents producing a haemophilic son.
A child by the family from Thalassemia is born to a normal couple. But the mother is being blamed by the family for delivering a sick baby. (a) What is Thalassemia?
(b) How would you counsel the family not to blame the mother for delivering a child suffering from this disease? Explain.
(c) List the values your counseling can propagate in the families.