Principles of Inheritance and Variation Test - 61

Mendel selected 14 true breeding pea plant varieties, as pairs which were similar except for one character with contrasting traits.

S.No    Character                    Dominant          Recessive

1.         Stem height                    Tall                     dwarf                           

2.         Flower position              Axial                 terminal                       

3.         Flower colour                 Violet                 white                          

4.        Pod shape                      Inflated              constricted              

5.        Pod colour                     Green                  yellow                          

6.        Seed colour                   Yellow                 Green                         

7.        Seed shape                    Round                  wrinkled                     

A.Polygenic character is controlled by multiple genes – True, because many genes control a single character.

B.Numerous intermediate types are found in between the two extremes in polygenic inheritance – True because many phenotypes are appear between the parental phenotypes.

C.Height, weight and skin colour are polygenic – True, because many genes control variety of phenotypes in the living organisms.

D.Polygenic traits is controlled by multiple alleles – False, because many genes control one trait. It is called Polygenic inheritance.

Mendel selected 14 true-breeding pea plant varieties, as pairs which were similar except for one character with contrasting traits.

S.No    Character                    Contrasting traits       Chromosome number

1.         Stem height                    Tall / dwarf                            4

2.         Flower position              Axial/terminal                       4

3.         Flower colour                 Violet/white                          1

4.        Pod shape                      Inflated/constricted              4

5.        Pod colour                     Green/yellow                          5

6.        Seed colour                   Yellow/Green                          1

7.        Seed shape                    Round/wrinkled                      7

In this 1 character is related to stem height, 2 characters are related to flower, 2 characters related to pod, 2 characters are related to seed.

A.Complmentary genes - Two genes present on separate loci that interact together to produce a dominant phenotype is called Complementary gene.

B.Pseudogenes – Genomic DNA sequences similar to normal genes but non-functional; they are regarded as defunct relatives of functional genes.

C.Pleiotrophic genes - The ability of a gene to have a multiple phenotypic effects is known as pleiotrophy and the gene is called Pleiotropic gene and the inheritance is called Pleiotropic inheritance. Eg:Sickle cell anaemia.

D.Cistrons – Functional parts of the DNA is called Cistron.

A.Dominance relationship - a relationship between alleles of one gene, in which the effect on phenotype of one allele masks the contribution of a second allele at the same locus. The first allele is dominant and the second allele is recessive.

B.Particulate inheritance - the inheritance of discrete characters via genes that are independently expressed without the blending of characters from one generation to the next generation.

C.Monogenic inheritance – inheritance, involves the transfer of a character by the involvement of a single gene. It produces only one type of phenotypes.

D.Polygenic inheritance - inheritance, involves the transfer of a character by the involvement of a more than one gene. It produces multiple phenotypes.

A.Human eye colour – polygenic inheritance.

   Sickle cell anaemia – Lethal genes.

B.Hair pigment of mouse – Lethal genes

   Tongue rolling in humans – Polygenic inheritance.

C.ABO blood groups in humans – Multiple alleles

    Flower colour of Mirabilis jalapa – Incomplete dominance.

D.Human height. – Polygenic inheritance

    Human skin colour – Polygenic inheritance

The ability of a gene to have a multiple phenotypic effects is known as pleiotrophy and the gene is called Pleiotropic gene and the inheritance is called Pleiotropic inheritance. In Drosophila, a gene is responsible in controlling the colour of the eye and depigmentation of body parts. It is a pleiotropic gene.

a)Dominance – In a heterozygous organism only one allele express itself

b)Codominance – in a heterozygous organism both alleles express themselves fully

c)Pleiotrophy – A single gene influences many characters.

d)Polygenic inheritance – Many genes govern a single character.