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Principles of Inheritance and Variation · Question 144

AIPMT 2003MCQMedium📈 Topic in 50% papers+4−1
1

Down's syndrome is caused by an extra copy of chromosome number 21. What percentage of offspring produced by an affected mother and a normal father would be affected by this disorder?

  1. 50%
  2. 100%
  3. 75%
  4. 25%

Answer

(1) 50%

Solution

An affected mother has three copies of chromosome 21 (trisomy 21).

⇒ At meiosis, half of her eggs receive two copies of chromosome 21 (n + 1) and half receive one copy (n).

Normal father ⇒ all sperms carry one copy (n).

∴ Egg (n + 1) × sperm (n) gives 2n + 1 (Down's syndrome) in 12 of the offspring, i.e. 50%.

Answer: (1)

AIPMT 2003

Keep practising — Principles of Inheritance and Variation

2

In Drosophila, the sex is determined by:

  1. X and Y chromosomes
  2. Whether the egg is fertilized or develops parthenogenetically
  3. The ratio of number of X-chromosomes to the sets of autosomes
  4. The ratio of pairs of X-chromosomes to the pairs of autosomes
AIPMT 2003
3

Christmas disease is another name for :-

  1. Hepatitis B
  2. Sleeping sickness
  3. Haemophilia B
  4. Down's syndrome
AIPMT 2003
4

Which of the following is the example of pleiotropy ?

  1. Thalassemia
  2. Haemophilia
  3. Sickle cell anaemia
  4. Colour blindness
AIPMT 2002
5

There are three genes a, b and c. The percentage of crossing over between a and b is 20%, b and c is 28% and a and c is 8%. What is the sequence of genes on chromosome?

  1. a, b, c
  2. b, a, c
  3. a, c, b
  4. None
AIPMT 2002
6

On selfing a plant of F1 generation with genotype “AABbCC”, the phenotypic ratio in F2 generation will be

  1. 1 : 1
  2. 3 : 1
  3. 9 : 3 : 3 : 1
  4. 27 : 9 : 9 : 9 : 3 : 3 : 3 : 1
AIPMT 2002
7

A gene is said to be dominant if : -

  1. It is expressed only in heterozygous condition
  2. It expresses its effect only in homozygous stage
  3. It is never expressed in any condition
  4. It is expressed both in homozygous and heterozygous condition
AIPMT 2002
8

A diseased man marries a normal woman. They get three daughters and five sons. All the daughters were diseased and sons were normal. The gene of this disease is : -

  1. Sex linked dominant
  2. Autosomal dominant
  3. Sex linked recessive
  4. Sex limited character
AIPMT 2002
9

Which of the following is a correct match -

  1. Sickle cell anaemia = X – Chromosome
  2. Down Syndrome = 21st Chromosome
  3. Haemophilia = Y – Chromosome
  4. Parkinson Disease = X & Y Chromosome
AIPMT 2002
10

Change in sequence of nucleotide in DNA is called as -

  1. Recombination
  2. Mutation
  3. Mutagen
  4. Translation
AIPMT 2002
11

If a diploid cell is treated with colchicine then it becomes : -

  1. Tetraploid
  2. Monoploid
  3. Diploid
  4. Triploid
AIPMT 2002

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