FREE NEET Biology Practice MCQ Test: Principles Of Inheritance And Variation Exercise 3 Questions Answers With Detailed Explanations [PDF]

Answer: (c)

Crossing of individuals having dominant phenotype with its homozygous recessive is a test cross, which can be represented as:

Answer: (c)

Answer: (a)

Statements I and II are correct. Statements III and IV are incorrect and can be corrected as

• Codominance cannot be manifested phenotypically in humans as ABO blood group in humans is three alleles of gene I ($I^A ,I^B$ ,i).
• ABO blood grouping system in humans does not follow Mendel's laws of inheritance.

Answer: (b)

Down’s syndrome is also known as Mongolian idiocy or mongolism. In Langdon Down of England (1866) studied the Mongolian idiocy and described the trisomic condition of their chromosomes. Down’s syndrome, a very common congenital abnormality arises due to the failure of separation of $21^{st}$ pair of autosomes during meiosis. Thus, an egg is produced with 24 chromosomes instead of 23. A Down’s syndrome has 3 autosomes in $21^{st}$ pair instead of 2. Total number of chromosome in this case is 2n + 1 (21st) = 47.

Answer: (c)

Answer: (a)

By introducing bone marrow cells producing ADA into cells at early embryonic stages, the genetic defect adenosine deaminase (ADA) deficiency may be cured permanently. It is due to mutation.

Answer: (a)

Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion.

Sickle-cell anaemia is an autosomal linked recessive disorder. The gene for this disorder is present on an autosome and an individual is said to be affected only when both the genes or a pair of allele (mutated or affected) are inherited from the carrier or affected parents.

Answer: (b)

If in a dihybrid test cross more parental combinations appear as compared to the recombinants in $F_2$ generation, then it is indicative of involvement of linkage. Linkage is the tendency of two different genes on the same chromosome to remain together during the separation of homologous chromosomes at meiosis. During complete linkage no recombinants are formed whereas in incomplete linkage few recombinants are produced along with parental combinations.

Answer: (a)

Colour blindness is an X-linked disease. So, a woman whose father is colourblind will be a carrier for the disease.

So, the possibility of a colourblind daughter (i.e. X Xc c) in $F_1$ -generation is 0%.

Answer: (d)

Answer: (a)

Genotype of carrier parents is

AA → normal child (25%)

Aa → carriers child (5%)

aa → affected child (25%)

Answer: (a)

Answer: (a)

According to Mendel's law of dominance, in heterozygous individuals a character is represented by two contrasting factors called alleles or allelomorphs which occur in pairs. Out of the two contrasting alleles, only one is able to express its effect in the individual. It is called dominant factor or dominant allele. The other allele which does not show its effect in the heterozygous individual is called recessive factor or recessive allele. The option (c) in the given question cannot be explained on the basis of law of dominance. It can only be explained on the basis of Mendel's law of independent assortment, according to which in a dihybrid cross, the two alleles of each character assort independently (do not show any blending) of the alleles of other character and separate at the time of gamete formation. Both the characters are recovered as such in $F_2$ generation producing both parental and new combinations of traits.

Answer: (b)

The type of inheritance shown in the given diagram is dominant X linked

Answer: (a)

Answer: (a)

Answer: (c)

Answer: (b)

Answer: (a)

In a cross between AABB × aabb, the ratio of $F_2$ genotypes between AABB, AaBB, Aabb and aabb would be 1 : 2 : 2 : 1.

Answer: (c)

Mutagens may be physical agents such as X-rays, α -rays, etc., which cause mutation and chemical agents such as mustard gas, etc., which cause changes in the DNA sequence in an organism.