Chromosomal Basis of Inheritance

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Questions:

Multiple Choice Question

10 x 1 = 10

Observe the gene sequence and identify the types of aberration ABC BCD E F?

(a)

Tandem duplication

(b)

Simple duplication

(c)

Reverse tandem duplication

(d)

Displaced tandem duplication

Assertion (A): Self-sterility is observed in Nicotiana species.
Reason (R): Because the genes are located on chromosome.

(a)

A is true R is false

(b)

Both A and R are false

(c)

A is true, R is not correct explanation for A

(d)

R explains A

Statement 1: Self-sterility in Nicotiana is controlled by multiple alleles.
Statement 2: Multiple alleles are always responsible for the same character.

(a)

Statement 1 is correct and Statement 2 is incorrect

(b)

Statement 1 is incorrect and Statement 2 is correct

(c)

Both the statements are correct

(d)

Both the statements are incorrect

Which one of the following ploidy is irrelevant to others?

(a)

Monosomy

(b)

Trisomy

(c)

Tetrasomy

(d)

Pentasomy

In a population of 250 progenies produced, only 120 resemble the parental forms. Calculate the recombinant frequency.

(a)

66%

(b)

52%

(c)

59%

(d)

49%

Identify the syntenic gene from the given genes sequence of a chromosome G-H-I-J-K-L-M-A-B

(a)

G and H

(b)

J, K and L

(c)

G and B

(d)

A and B

The following sequence represents the location of genes in a chromosome. A - B - C - M - R - S - y -Z. Which of the gene pairs will have least chance of getting inherited together?

(a)

A and M

(b)

Sand Y

(c)

M and Z

(d)

A and Y

Changing the codon AGC to AGA represents _______.

(a)

missense mutation

(b)

nonsense mutation

(c)

frameshift mutation

(d)

deletion mutation

Due to incomplete linkage in maize, the ratio of parental and recombinants are ______.

(a)

50:50

(b)

7:1:1:7

(c)

96.4: 3.6

(d)

1:7:7:1

10.

The A and B genes are 10 cm apart on a chromosome. If an AB/ab heterozygote is testcrossed to ab/ab, how many of each progeny class would you expect out of 100 total progeny?

(a)

25 AB, 25 ab, 25 Ab, 25 aB

(b)

10 AB, 10 ab

(c)

45 AB, 45 ab

(d)

45 AB, 45 ab, 5 Ab, 5aB

Generic 5

3 x 5 = 15

11.

What is translocation? Write about its types.

12.

Mention the name of man-made cereal. How it is formed?

13.

If you cross dominant genotype PV/PV male Drosophila with double recessive female and obtain F₁ hybrid. Now you cross F₁ male with double recessive female.
i) What type of linkage is seen?
ii) Draw the cross with correct genotype.
iii) What is the possible genotype in F₂generation?

Generic 2

4 x 2 = 8

14.

Mention the major stages involved in crossing over.

15.

Who coined the term crossing over? When does the crossing over occurs in a cell?

16.

What does the condition synteny refers to?

17.

What is the difference between missense and nonsense mutation?

Generic 3

6 x 3 = 18

18.

Why crossing over is important?

19.

Give a short note on incomplete linkage.

20.

State Coupling and Repulsion theory.

21.

Compare Mendelian factors with chromosome.

22.

What are the salient features of the chromosomal theory of inheritance ?

23.

Write the salient features of Sutton and Boveri concept.

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Answers Key:

Multiple Choice Question

10 x 1 = 10

(a)
Tandem duplication

(a)
Monosomy

(b)
52%

(d)
A and Y

(a)
missense mutation

(b)
7:1:1:7

10.

(d)
45 AB, 45 ab, 5 Ab, 5aB

Generic 5

3 x 5 = 15

11.

Translocation
The transfer of a segment of chromosome to a nonhomologous chromosome is called translocation. Translocation should not be confused with crossing over, in which an exchange of genetic material between homologous chromosome takes place. Translocation occurs as a result of interchange of chromosome segments in non-homologous chromosomes. There are three types:
i. Simple translocation
ii. Shift translocation
iii. Reciprocal translocation
i. Simple translocation
A single break is made in only one chromosome. The broken segment gets attached to one end of a non-homologous chromosome. It occurs very rarely in nature.
ii. Shift translocation
Broken segment of one chromosome gets inserted interstitially in a non-homologous chromosome.
iii. Reciprocal translocations
It involves mutual exchange of chromosomal segments between two non homologous chromosomes. It is also called illegitimate crossing over. It is further divided into two types.
a. Homozygous translocation: Both the chromosomes of two pairs are involved in translocation. Two homologous of each translocated chromosomes are identical.
b. Heterozygous translocation: Only one of the chromosome from each pair of two homologous are involved in translocation, while the remaining chromosome is normal.
Translocations playa major role in the formation of species.

12.

(i) Triticale (Hexaploid) (6x) is the first man made cereal.
(ii) It is obtained from a cross between tetraploid wheat Triticum durum and rye (diploid).

(iii) Triticale hybrid plants, have characteristics of both macroni wheat and rye.
(iv) They combine the high-protein content of wheat a high content of amino acid lysine of rye.

13.

(i) Incomplete linkage

Rano : 1:2:1

Generic 2

4 x 2 = 8

14.

Crossing over is a precise process that includes stages like synapsis, tetrad formation, cross over and terminalization.

15.

The term 'crossing over' was coined by Morgan (1912). It takes place during pachytene stage of prophase I of meiosis.

16.

The two genes that are sufficiently far apart on the same chromosome are called unlinked genes or syntenic genes. Such condition is known as synteny.

17.

Missense Mutation Non-sense Mutation The mutation where the codon for one amino acid is changed into a codon for another amino acid. The mutations where codon for one amino acid is changed into a termination or stop codon.

Generic 3

6 x 3 = 18

18.

1. Exchange of segments leads to new gene combinations which plays an important role in evolution.
2. Studies of crossing over reveal that genes are arranged linearly on the chromosomes.
3. Genetic maps are made based on the frequency of crossing over.
4. Crossing over helps to understand the nature and mechanism of gene action.
5. If a useful new combination is formed it can be used in plant breeding.

19.

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.

20.

The two dominant alleles or recessive alleles occur in the same homologous chromosomes, tend to inherit together into same gamete are called coupling or cis configuration. If dominant or recessive alleles are present on two different, but homologous chromosomes they inherit apart into different gamete are called repulsion or trans configuration.

21.

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.

22.

(i) Somatic cells of organisms are derived from the zygote by repeated cell division (mitosis). these consist of two identical sets of chromosomes. One set is received from female parent (maternal) and the other from male parent (paternal). These two chromosomes constitute the homologous pair.
(ii) Chromosomes retain their structural uniqueness and individuality throughout the life cycle of an organism.
(iii) Each chromosome carries specific determiners or Mendelian factors which are now termed as genes.
(iv) The behaviour of chromosomes during the gamete formation (meiosis) provides evidence to the fact that genes or factors are located on chromosomes.

23.

(i) Sutton and Boveri independently proposed the chromosome theory of inheritance.
(ii) Somatic cells of organisms are derived from the zygote by repeated mitotic division. These consist of two identical sets of chromosomes. One set is received from female parent and the other from male parent which constitute the homologous pair.
(iii) Chromosomes retain their structural uniqueness and individuality throughout the life cycle of an organism.
(iv) Each chromosome carries specific determiners or Mendelian factors which are now termed as genes.
(v) The behaviour of chromosomes during the gamete formation provides evidence to the fact that genes are located on chromosomes.