In Huntington’s disease, the unaffected persons are homozygous for normal allele h. The following is erroneous because

It shows both male and female affected by Huntingtons disease
Either person 6 or 7 should have the disease, if individual 11 shows the disease.
At least one of the 2 children (8, 9) should have the disease
All of these

Given pedigree shows that the trait is inherited as autosomal dominant. Trace the genotype of Mother and Father

Father AA, Mother aa
Father AA, Mother Aa
Father aa, Mother AA
Father aa, Mother Aa

Given below is a highly simplified representation of the human sex chromosomes from a karyotype. The gene a and b could be of

colour blindness and body height
attached ear lobe and Rhesus blood group
haemophilia and red-green colour blindness
phenylketonuria and haemophilia

Down’s syndrome in humans is due to

Two ‘Y’ chromosomes
Three ‘X’ chromosomes
Three copies of chromosome 21
Monosomy

Solution

Down’s syndrome is the chromosomal disorders due to the presence of an additional copy of the chromosome number 21 (trisomy of 21). The affected individual is short statured with small round head, furrowed tongue and partially open mouth and mental development is retarted.

In our society women are blamed for producing female children. Choose the correct answer for the sex-determination in humans

Due to some defect in the women
Due to some defect like aspermia in man
Due to the genetic make up of the particular sperm which fertilizes the egg
Due to the genetic make up of the egg

Solution

In case of humans, the sex determining mechanism is XY type. Out of 23 pairs of chromosomes, 22 pairs are exactly same in both males and females called autosomes. A pair of X-chromosomes present in the female, whereas the presence of an X and Y chromosome are determinant of male characteristic. In case the ovum fertilises with a sperm carrying X-chromosome the zygote develops into a female (XX) and the fertilisation of ovum with Y-chromosome carrying sperm results into a male offspring.

Which one is the incorrect statement with regards to the importance of pedigree analysis?

It helps to trace the inheritance of a specific trait
It confirms that DNA is the carrier of genetic information
It helps to understand whether the trait in question is dominant or recessive
It confirms that the trait is linked to one of the autosome

Solution

Pedigree is a chart showing the record of inheritance of certain genetic traits for two or more ancestral generations of an individual, abnormality or disease.

Genetic variation in a population arises due to

Mutations only
Recombination only
Mutations as well as recombination
Reproductive isolation and selection

Solution

Crossing over leads to recombination of genetic material on the two chromosomes. Mutation results in alternation of DNA sequences and consequently results in change in the genotype and the phenotype of an organism. In addition to recombination, mutation is another phenomenon that leads to variation in DNA.

The incorrect statement with regard to Haemophilia is :

It is a recessive disease
It is a dominant disease
A single protein involved in the clotting of blood is affected
It is a sex-linked disease

Solution

Haemophilia is sex linked recessive disease in which a simple protein that is a part of protein cascade involved in clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non stop bleeding.

Which of the following statements is not true of two genes that show 50% recombination frequency?

The genes are tightly linked
The genes show independent assortment
If the genes are present on the same chromosome, they undergo more than one crossovers in every meiosis
The genes may be on different chromosomes

Solution

Tightly linked genes show more linkage then crossing over.

If both parents are carriers for thalassemia, which is an auto-somal recessive disorder, what are the chances of pregnancy resulting in an affected child?

50%
25%
100%
no chance

Solution

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