NEET Biology Principles of Inheritance and Variation Important Questions Set 02

These Class 12 NEET Biology important questions on Principles of Inheritance and Variation give 22 questions with step-by-step answers, arranged as very short, short and long answer types, taken from a model test paper. They help NEET aspirants revise the definitions, structures, differences and key terms of the chapter.

Very Short Answer Type Questions

Question 1. What is the true breeding line?
Answer: A true breeding line is one that has undergone continuous self pollination, shows stable trait inheritance and expression for several generations.

Question 2. Name the cross in which Mendel crossed the tall plant from F₂ with a dwarf plant.
Answer: Test cross

Question 3. How many genotypes are possible in population for ABO blood group system?
Answer: Total 6 genotypes are possible

Question 4. Which type of sex determination is found in grasshopper?
Answer: XX-XO type (XO type)

Question 5. Who developed the graphical representation to calculate the probability of all possible genotypes of offspring in a genetic cross?
Answer: Reginald C. Punnett

Question 6. Mention the recessive traits of the following characters in garden pea.
(i) Flower position
(ii) Pod shape
Answer: (i) Terminal
(ii) Constricted

Question 7. Name the condition in which F₁ resembled either of the two parents.
Answer: Dominance

Question 8. Write down the karyotype of an individual affected with Turner's syndrome.
Answer: 44 + XO or 45 with XO

Short Answer Type Questions

Question 9. Differentiate between linkage and recombination.
Answer: Term linkage describes the physical association of genes on a chromosome while recombination decribes the generation of non-parental gene combinations.

Question 10. Write down the name of two most common and prevalent Mendelian disorders.
Answer: (i) Haemophilia
(ii) Cystic fibrosis

Question 11. What do you mean by the term heterozygous?
Answer: An individual having two different alleles (Tt) will be called heterozygous.

Question 12. Mention the two important symptoms of Down's syndrome.
Answer: (i) Short statured with small round head
(ii) Furrowed tongue and partially open mouth

Question 13. Write down the Mendel's laws of inheritance which is based on monohybrid cross.

Answer:

(i) Law of dominance

(ii) Law of segregation

Question 14. Differentiate between inheritance and variation.
Answer: Inheritance is the process by which characters are passed on from parent to progeny, while variation is the degree by which progeny differ from their parents.

Question 15. What is meant by Mendel's law of independent assortment?
Answer: The law of Independent Assortment states that when two pairs of traits are combined in a hybrid, segregation of one pair of traits is independent of the other pair of traits.

Short Answer Type Questions

Question 16. A diploid organism is heterozygous for three loci, how many types of gametes can be produced? Also write the genotypes of gametes.

Answer:

It can be calculated by using formula → 2n ∴ 2³ = 8

Individual = AaBbCc

ABC ABc AbC Abc aBC aBc abC abc

Question 17. (i) What is point mutation?
(ii) What is the cause of frame-shift mutations?

Answer:

(i) Mutation arises due to change in a single base pair of DNA, known as point mutation.

(ii) Deletions and insertions of base pairs of DNA, causes frame-shift mutations.

Question 18. Two heterozygous parents are crossed. If the three loci are linked completely what would be genotypic ratio in F₁ generation for a trihybrid cross? ABC/abc × ABC/abc

Answer:

i.e., Genotypic ratio = 1 : 2 : 1

Question 19. Make the comparision between parallel behaviour of chromosomes and genes.

Answer:

Segregate at the time of gamete formation Segregate at gamete formation and only such that only one of each pair is transmitted one of each pair is transmitted to a gamete to a gamete Independent pairs segregate independently of One pair segregates independently of another each other pair

Question 20. (i) Identify the following symbols used in human pedigree analysis.
(a) 5
(b)
(c)
(d)
(ii) Why polyploidy is rare in animals?
Answer: (i) (a) Five unaffected offspring
(b) Mating between relatives (consanguineous mating)
(c) Parents with male child affected with disease
(d) Affected female
(ii) In animals, polyploidy usually results in sterility therefore, it is rare.

Long Answer Type Questions

Question 21. Explain the concept of dominance.
Answer: Every gene contains information to express a particular trait. Diploid organisms have two copies of each gene, they are called alleles. These two alleles may be identical or non-identical. One of them may be different due to some changes that it has undergone which modifies the information that particular allele contains. Suppose that the normal allele produces the normal enzyme that is needed for the transformation of a substrate S. Theoretically, the modified or mutated allele could be responsible for production of:
(i) The normal/less efficient enzyme, or
(ii) A non-functional enzyme, or
(iii) No enzyme at all In case (i), the modified allele is equivalent to the unmodified allele, i.e., it will produce the same phenotype/trait. But, if the allele produces a non-functional enzyme or no enzyme [case (ii) & (iii)], the phenotype may be effected. The unmodified (functioning) allele, which represents the original phenotype is the dominant allele and the modified allele is generally the recessive allele. Hence, the recessive trait is due to non-functional enzyme or because no enzyme is produced. If the mutated allele forms an alterd but functional product, it behaves as incompletely or codominant allele. Let us take the example of tallness. Plant height depends on the amount of particular plant hormone. The amount of the plant hormone made will depend on the efficiency of the process for making it. Consider now an enzyme that is important for this process. If this enzyme works efficiently, a lot of hormone will be made, and the plant will be tall. If the gene for that enzyme has an alteration that makes the enzyme less efficient, the amount of hormone will be less, and the plant will be dwarf.

Question 22. Describe the chromosomal basis of sex determination with the help of examples.
Answer: According to chromosomal theory of sex-determination, the male and female individuals normally differ in their chromosomal constituent. On this basis in diploid organisms, there are two types of system.
(i) System in which male is heterogametic
(ii) System in which female is heterogametic In the first system, the female have XX-chromosomes while male have XY-chromosomes because of which males produce two types of sperms i.e. 50% carry X-chromosome and 50% carry Y-chromosome. This chromosomal pattern varies in different organism in the way that male either contain Y-chromosome (i.e., XX-XY system) or contain no chromosome along with X-chromosome (XX-XO type). XX-XY method is the most common method and is found in human, Drosophila. In this system female is homogametic and male is heterogametic i.e. two type of sperm (50% carry X-chromosome) and 50% carry Y-chromosome. Sex of embryo depends upon the kind of sperm. XX-XO method is found in insects (grasshopper). Again male is heterogametic i.e. 50% sperm has X-chromosome while 50% without any sex chromosome. In males, Y-chromosome is absent. In the second system ZW-ZZ method and ZO-ZZ method i.e., female is heterogametic (ZW) and male is homogametic (ZZ). ZW-ZZ type is found in birds and ZO-ZZ type in butterflies.