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12th Standard English Medium Biology (Botany) Subject Chromosomal Basis of Inheritance Creative 3 Mark Questions with Solution Part - II updated Creative Questions

Published on: 13/05/2022

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Questions:

Generic 3

5 x 3 = 15

Study the figures given below and answer the questions.

Which type of cross produces higher recombinant percentage? Give reason in support of your answer.

In Drosophila melanogaster, there are four pairs of chromosomes. If there occurs chromosomal aberrations resulting in trisomic and monosomic condition, what will be the chromosomal count? Write the correct chromosomal count against respective chromosomal aberration.

What are the three types of synapsis? (or) Give the types of Synapsis.

Give a short note on incomplete linkage.

Compare Mendelian factors with chromosome.

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Answers Key:

Generic 3

5 x 3 = 15

(a) Cross B produces more recombinants.
(b) The gene e and f are located sufficiently apart leading to crossing over resulting in recombinant varieties.

Normal chromosome of Drosophila melanogaster (2n)   = 8
Trisomic condition (2n+ 1)   = 9
Monosomic condition (2n-l)   = 7

Pairing of homologous chromosomes during zygotene stage of prophase I of meiosis I is called synapsis. Synapsis of three types:
1. Procentric synapsis: Pairing starts from middle of the chromosome.
2. Proterminal synapsis: Pairing starts from the telomeres.
3. Random synapsis: Pairing may start from anywhere.

If two linked genes are sufficiently apart, the chances of their separation are possible. As a result, parental and non-parental combinations are observed. The linked genes exhibit some crossing over. This phenomenon is called incomplete linkage. This was observed in maize. It was reported by Hutchinson.

S. No.	Mendelian factors	Chromosomes behaviour
1.	Alleles of a factor occur in pair.	Chromosomes occur in pairs
2.	Similar or dissimilar alleles of a factor separate during the gamete formation.	The homologous chromosomes separate during meiosis.
3.	Mendelian factors can assort independently.	The paired chromosomes can separate independently during meiosis but the linked genes in the same chromosome normally do not assort independently.