A girl has blood group A and her brother has blood group B. Which combination of genotypes cannot belong to their parents ?

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Solution

If the mother has blood group I^AI^A and the father has blood group I^BI^O, then their children can only have genotypes I^AI^B or I^AI^O, which have the phenotypes blood group AB and blood group A respectively.

Which parental phenotypes would produce offspring with blood group phenotypes in the expected ratio of 1 type A : 1 type B ?

  Blood group of  Blood group of
      mother         father
(a)     A             B
(b)     AB            AB
(c)     AB            B
(d)     AB            O

Solution

The mother would have genotype I^AI^B and the father would have genotype I^OI^O. Thus, the two genotypes possible for their offspring would be I^AI^O and I^BI^O, with equal probability. Hence, the expected phenotypes would be 1 type A :1 type B.

A lawyer tells a male client that blood type cannot be used to his advantage in a paternity suit against the client because the child blood, in fact, be the client’s, according to blood type. Which of the following is the only possible combination supporting this hypothetical circumstance ?

(Answers are in the order mother : father:child)

A : B : O
A : O : B
AB : A : O
B : O : A

Among white human beings, when individuals with straight hair mate with those with curly hair, wavy-haired children are produced. If two individuals with wavy hair mate, what phenotypes and ratios would you predict among their offspring ?

3 curly : 1 wavy
1 curly : 1 wavy : 1 straight
1 straight : 1 curly : 2 wavy
3 wavy : 1 straight

Incomplete dominance occurs when

chromosomes are deleted.
heterozygotes synthesized a reduced amount of anenzyme, producing an intermediate phenotype.
the genes fail to segregate.
the law of independent assortment is upheld.

A woman with normal vision, but whose father was colour blind, marries a colour blind man. Suppose that the fourth child of this couple was a boy. This boy

may be colour blind or may be of normal vision
must be colour blind
must have normal colour vision
will be partially colour blind since he is heterozygous for the colour blind mutant allele

Solution

Since the woman’s father was colour blind. She would be a carrier of the colour blindness gene. When she marries a colour blind man. Their progeny could be

Which of the following is not a hereditary disease?

Cystic fibrosis
Thalassemia
Haemophilia
Cretinism

Solution

Cystic fibrosis : It is a common disorder of caucasian race in which thick and more salty mucus blocks the respiratory tract. The homozygous recessive condition produces the defective protein which regulates chloride transport channel.

Cretinism : In this disorder the physical growth, mental growth and sexual growth in children is retarded. Such a dwarf and sterile child is called a cretin.It is due to hyposecretion of thyroid hormones.

Thalassemia : Due to defective production of a or b chains of haemoglobin, autosomal recessive.

Haemophilia : Sex linked disorder due to defective recessive gene.

Haemophilia is more commonly seen in human males than in human females because:

a greater proportion of girls die in in fancy
this disease is due to a Y-linked recessive mutation
this disease is due to an X-linked recessive mutation
this disease is due to an X-linked dominant mutation

Solution

This disease is due to an X-linked recessive mutation. Males suffer this disorder since they have only one X chromosome and hence express any trait on this chromosome.

A women with 47 chromosomes due to three copies of chromosome 21 is characterized by:

super femaleness
triploidy
turner’s syndrome
down’s Syndrome

Solution

Down’s syndrome is caused by the presence of an extra chromosome number 21 and the offspring has 47 chromosomes.

One of the parents of a cross has a mutation in its mitochondria. In that cross, that parent is taken as a male. During segregation of F₂ progenies that mutation is found in

one-third of the progenies
none of the progenies
all the progenies
fifty percent of the progenies

Solution

Mitochondrion isan organelle present in the cytoplasm. A zygotereceives its cytoplasm from the female parentgamete. Hence in the given question, the F₂ progenies do not receive the mitochondrial genome from the male parent and mutation is not passed to progenies.

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