Friday, 26 May 2017

CBSE CLASS 12 - Biology - CH 5 - Principles of Inheritance and Variation - Important Definitions (#cbseNotes)

Principles of Inheritance and Variation - Important Definitions


CBSE CLASS 12 - Biology

CBSE CLASS 12 - Biology - CH 5 - Principles of Inheritance and Variation - Important Definitions (#cbseNotes)


Q1: Define heredity.

Answer: It can be defined as the transmission of characters from one generation to successive generations of living organisms.


Q2: Define Alleles

Answer: The various forms of a gene are called alleles.


Q3: What are multiple alleles?

Answer: If a gene has more than two alleles then they are said to be multiple alleles. e.g. In humans ABO blood groups is an example for multiple allelism.


Q4: What is genotype?

Answer: The genetic constitution of an organism is its genotype.


Q5: What is phenotype?

Answer: The external / observable characteristics of an organism constitute its phenotype.




Q6: What is Pleiotropy?

Answer: The ability of a gene to have multiple phenotypic effects because it influences a number of
characters simultaneously is known as Pleiotropy. Eg: Phenylketonuria.


Q7: Define Homozygote.

Answer: A homozygote is an individual having two copies of the same allele at a locus. OR It is an individual organism in which the members of a pair of alleles for a character are same.


Q8: Define Heterozygote.

Answer: It is an individual organism in which the members of a pair of alleles of a character are different.


Q9: What is polygenic inheritance?

Answer: The cumulative effect of two or more genes on a single phenotypic character is known as
polygenic inheritance. e.g. skin colour in human beings.


Q10: Define Dominant characters.

Answer: The form of the character which is expressed in the F1 hybrid is called dominant character.


Q11: What is a recessive character?

Answer: The form of the character which is suppressed in the presence of the dominant character: character in a hybrid is called recessive character.


Q12: What is a Monohybrid cross?

Answer: It is a cross between individuals of the same species, in which the inheritance of contrasting pairs of a single trait is considered.


Q13: What is a Dihybrid cross?

Answer: It is a cross between two individuals of the same species, in which the inheritance of contrasting pairs of two traits is considered.


Q14: Define Epistasis.

Answer: Epistasis is the phenomenon where the effect of one gene (locus) is dependent on the presence of one or more 'modifier genes', i.e. phenotypic expression of a gene at one locus alters that of a gene at a second locus.


Q15: What is haplodiploidy?

Answer: It is a mechanism of sex determination. In this system the sex of the off spring is determined by the number of sets of chromosomes. E.g.: Honeybees.


Q16: What is Lyonization?

Answer: Lyonization is a process by which one of two copies of X – chromosome present in the body cells of female mammals is inactivated. The inactive X – chromosome is transcriptionally inactive called heterochromatic body.