Principles of Inheritance and Variation

Question 1

Heredity or Inheritance

Answer 1

Transmission of traits from one generation to the other (Parents or Offspring)

Question 2

Variation

Answer 2

Difference in the genetic makeup of two individuals or between two organisms in a population

Question 3

Name Mendel’s laws

IN CORRECT ORDER

Answer 3

1. Law of dominance
2. Law of segregation
3. Law of independent assortment

Question 4

Law of dominance

Answer 4

Out of the pair of alleles that represent a trait, one is dominant and the other is recessive

Question 5

Law of segregation

Answer 5

When a pair of alleles are brought together, they remain together without blending, but separate completely during gamete formation

Question 6

Law of independent assortment

Answer 6

The law of independent assortment states that the alleles of different genes are inherited independently within the organisms that reproduce sexually.

Question 7

Reasons for success if using Pisum sativum for Mendel’s experiments

Answer 7

1. Easy to cultivate
2. Short life cycle
3. Bisexual flowes
4. True-breeding/pure plants that can be easily obtained through self-pollination

Question 8

Father of genetics

Answer 8

Gregor mendel

Question 9

Back cross

Answer 9

Crossing of a hybrid with any one of the parent

Question 10

Test cross

Answer 10

Crossing of a hybrid with a recessive parent

Question 11

Incomplete dominance

Answer 11

When a dominant allele, or form of a gene, does not completely dominate the effects of a recessive allele, and the organism’s resulting physical appearance shows a blending of both alleles

E.g. Incomplete dominance is exhibited in Snapdragon (Antirrhium) flower colour

Mirabilis jalapa

Question 12

Multiple allelism

Answer 12

Condition where three or more alles are present for a particular gene.
E.g. Human blood group is governed by 3 alleles
I^A, I^B, i

Question 13

Co-dominance

Answer 13

A condition wherein both alleles are equally expressed

E.g. Co-dominance is exhibited in AB blood group of ABO human blood group system

Question 14

Punnett square

Answer 14

Checkerboard representation of all the possible phenotype and genotype combinations that can be formed in the progeny of a particular generation

Question 15

Pleiotropy

Answer 15

The ability of a gene to influence more than one trait is called pleiotropy

E.g. Phenylketonuria
Starch synthesis in pea seeds

Question 16

Pleoitropy with reference to PKU

Answer 16

PKU- phenylketonuria
in gene that codes for phenylalanine hydroxylase

Mutations to the gene result in:
Hair loss, skin pigmentation, mental retardation

Question 17

Pleiotropy with reference to starch synthesis in pea seeds

Answer 17

BB: round, large seeds with more starch
Bb: round seeds with intermediate size starch grain
bb: wrinkled, small seeds with less starch

Question 18

Crossing over

Answer 18

Exchange of genetic material during sexual reproduction between 2 homologous chromosomes’ non-sister chromatids that results in recombinant chromosomes

Takes place in zygotene of prophase 1 of meiosis 1

Question 19

Linkage

Answer 19

Tendency of two or more genes of the same chromosome to remain together during the process of inheritance

Further the placement of genes in a chromosome less the chances of linkage

Question 20

Colour blindness

Answer 20

Sex linked inheritance
* X-linked inheritance means the gene causing the disorder is in the X-chromosome
* X (recessive) genes in females will be expressed ONLY
if there are two copies of the gene (one on each
chromosome).
* In males, only one copy of the gene is required for the
disorder to be expressed.

Question 21

Haemophilia

Answer 21

• Sex linked inheritance
• Blood borne disease
• Recessive trait (X- linked)
• Lacks the clotting factor (VII or IX) proteins responsible for clotting of blood.
• Prolonged bleeding leading to even death.
• Inheritance is similar, to that of Colour-blindness.

Question 22

PKU- hereditary disorder

Answer 22

• Autosomal-linked recessive disorder
• Phenylalanine—> Tyrosine (Phenylalanine hydroxylase - enzyme)

Question 23

Sickle cell anaemia

Answer 23

Autosomal-linked recessive disorder

Mutation in the 6th position of the Beta-globin chain of the haemoglobin molecule

Glutamic acid (GAG) —> Valine (GUG)
Base substitution- point mutation

Question 24

Thalassemia

Answer 24

Autosomal-linked recessive disorder
Inherited blood disorder which is caused due to less amount of haemoglobin protein in blood