Principles of Inheritance and Variation
Short Questions and Answers
One mark questions with answers
1. Complete dominance is absent in
(a) Mirabilis jalapa
(b) Pisum sativum
(c) Lathyrus odoratus
(d) Oenothera lamarckiana
Answer: (a) Mirabilis jalapa
2. Ultimate source of variations is
Answer: (d) mutation
3. Father of genetics is
Answer: (a) Mendel
4. Discontinuous variations are due to
(a) crossing over
(c) segregation of chromosomes
(d) independent assortment
Answer: (b) mutation
5. Dihybrid test cross is
Answer: (a) 1:1:1:1
6. The recessive trait in garden pea is
(a) tall stem
(b) coloured flower
(c) wrinkled seed
(d) inflated pod
Answer: (c) wrinkled seed
7. A gene influencing many trait is
Answer: (b) plieotropic
8. Dihybrid ratio is connected with deduction of principle of
(a) purity of gametes
(c) independent assortment
(d) incomplete dominance
Answer: (c) independent assortment
9. Two genes present nearby on a chromosome will have
(a) double crossing over
(b) no crossing over
(c) hardly any crossing over
(d) regular crossing over
Answer: (c) hardly any crossing over
10. Exchange of segments between non-homologous chromosomes is called
(a) crossing over
Answer: (d) translocation
11. A couple has two girls the probability of a third girl baby is
Answer: (b) 50%
12. Sex chromosomes are also called as
Answer: (a) allosomes
13. Number of barr bodies present in Turner’s syndrome is
Answer: (a) 0
14. In a point mutation adenine is replaced by guanine. It is
(b) frameshift mutation
Answer: (d) transition
15. In an individual, haploid number is 10. Its tetrasomic number will be
Answer: (c) 22
Two marks questions with answers
1. What is Law of segregation?
Answer: Mendel’s law of segregation states that an individual organism has two alleles for every gene, one inherited from its mother and one from its father. When this organism forms its own gametes, each gamete will receive only one of these alleles, and this process is random.
The 2 alleles for each character segregate (separate) during gamete formation.
2. What is Co-dominance?
Answer: In co-dominance alleles express themselves independently even when present together. In heterozygous condition both alleles would be present and each would express independent of the other. While considering codominance different symbols are used. Capital letters are used for both the alleles with different subscripts for example, IA, IB, or HbA HbS or M and N (for MN blood system).
3. Mention two differences between incomplete dominance and codominance.
Answer: In incomplete dominance the phenotype of hybrid does not resemble either of the parent whereas in codominance the phenotype of hybrid resembles both the parents. In case of incomplete dominance hybrid causes a new phenotype whereas in case of codominance new phenotype is not formed.
4. Mention two differences between complete dominance and incomplete dominance.
Answer: In complete dominance F1 individuals have the same trait as that of one of the two parents where as in case of incomplete dominance F1 trait is different from either of the two parents. In case of complete dominance, in F2 generation 3/4 individuals show phenotype of F1 generation. In incomplete dominance, in F2 generation half individual show phenotype of F1 generation.
5. Differentiate between dominant and recessive factors.
Answer: Dominant factor generally produces a complete polypeptide, protein or enzyme for producing its effect where as a recessive factor generally forms an incomplete product so that its effect is due to non formation of material required for expressing the trait. Dominant factor does not require the company of another similar allele for producing its effect on the phenotype whereas recessive factor can produce its phenotyping effect only in the company of a similar allele.
Three marks questions with answers
1. What is Punnett square?
Answer: It was developed by a British geneticist, Reginald C. Punnett. It is a graphical representation to calculate the probability of all possible phenotypes of offspring in a genetic cross. The possible gametes are written on two sides, usually the top row and left column. All possible combinations are represented in boxes below in the squares. All the male gametes are entered in the vertical squares and all the possible female gametes are entered in the horizontal squares.
2. What is back cross?
Answer: It is a cross between the hybrid and one of its parents which can be repeated two or more times for obtaining the maximum number of traits of that parent. Backcross is a standard procedure in breeding programmes. The original process for obtaining hybrid is made to introduce one or more highly useful traits for example, disease resistance, pest resistance, high protein content, high vitamin content,. This however dilutes the good characters of original variety. Back crosses are made to reintroduce all the good characters of original variety.
3. What is test cross?
Answer: It is a special type of back cross which is made between individual with a dominant trait and its recessive parent in order to know whether the individual is homozygous or heterozygous for the trait. Offspring of a test cross will be hundred percent dominant if the individual was homozygous dominant. The progeny will consist of 50% dominant and 50% recessive for trait if the individual is heterozygous that is ratio is 1:1. In case of dihybrid the test ratio will give a ratio of 1:1:1:1.
4. What is Pedigree analysis? Suggest how such analysis can be useful.
Answer: The study of transmission of particular traits graphically over the present and the last few generations for finding out the possibility of their occurrence in the future generation is called pedigree analysis.
Pedigree analysis is important to know the impossibility of a recessive allele which may create disorder in the progeny example colour blindness, haemophilia, thalassemia etc. It can initiate the origin of a trait in the ancestors example Queen Victoria for haemophilia and royal families. It can indicate the usefulness or harm a marriage between close relatives will cause. The analysis is used for genetic counselling about the possibilities of prospective parents transmitting a disorder to the children. It is extensively used in medical research.
5. Briefly mention the contribution of Morgan in genetics.
Answer: TH. Morgan (1866 -945) was an American geneticist who was awarded Nobel Prize in 1933 for his work.
(a) Morgan found fruit fly Drosophila melanogaster to be better material for experiments on genetic as it was easy to rear and multiplied throughout the year.
(b) He established the presence of genes over the chromosomes.
(c) Morgan established the principle of linkage and crossing over.
(d) He discoverd sex linkage and cris cross inheritance.
(e) He developed a technique of chromosome mapping.
(f) He observed mutations.
(g) In 1926 Morgan wrote a book ‘The theory of Gene’.