Genetics and Human Reproduction

Monosomy means 2n - 1, i.e. (2 X 10) - 1 = 20 - 1 = 19. 

‘Gametes are never hybrid’. It is a statement of law of segregation. 

A normal female with XX chromosomes has one Barr body. A normal male (XY) has none. Abnormal males with three XXY (Klinefelters' syndrome) have one Barr body.

DNA generally acts as a template for the synthesis of DNA during replication and RNA during transcription. DNA does not act as a template for the synthesis of protein.

When chromosome sets are present in multiples of ‘n’, the condition is called euploidy.

A husband and wife have normal vision but father of both of them were colourblind. Probability of their first daughter to be colour blind is 0. Colour blindness is a sex linked recessively inherited disorder. Normal man has normal x and y chromosomes. Carrier female have one normal x and one abnormal x chromosome.The probability of their son to get colour blindness is 50%.

Secondary spermatocytes and spermatids are haploid.

Crossing over is advantageous because it brings about recombination or variation.

The average length of human ovary is 2-4 cm.

In human uterus, endometrium is maintained by the secretion of progesterone.

Leydig cells secrete testosterone.

Each testis has about 250 testicular compartments.

AaBb individual can produce 2² gametes, i.e. four gametes.

The genetic material in HIV is single stranded RNA.

Mendel's laws were rediscovered by Hugo de Vries, Correns and Tschermak.

The cross RRYY x rryy cannot have the ratio 1 : 1 : 1 : 1.

LNG-20 is a hormone releasing IUD.

The four nitrogenous bases in DNA are the purines: adenine (A), guanine (G), and the pyrimidines: cytosine (C) and thymine (T).

Spermatogenesis begins during puberty due to the increased secretion of GnRH.

Saheli is a once-in-a-week pill used by females.

Okazaki fragments are short DNA fragments on the lagging strand. Synthesis of the lagging strand requires working in relatively small, discontinuous stretches. These discontinuous stretches are synthesised just as the leading strand, by the addition of new nucleotides one at a time to the 3′ end of the new strand, but the synthesis of this new strand moves in the direction opposite to that in which the replication fork is moving. These stretches of new DNA for the lagging strand are called Okazaki fragments.

GIFT stands for “Gamete Intrafallopian Transfer”. 

In the F2 generation of a dihybrid cross, 4 phenotypes appear in the ratio 9 : 3 : 3 :1, if the loci are unlinked.

Skin colour inheritance in man is not monogenic, but it is polygenic, controlled by many genes like AABBCC, aabbcc, etc.

The seven characters studied by Mendel are: Plant height, Flower position, Pod shape, Pod colour, Flower colour, Seed shape and Seed colour. Shape of leaves is not considered by Mendel.

Blood group can either be A or B as both are dominant over O.

This is Turner's syndrome.

The sex of a fruitfly is determined by X and Y chromosomes, the male being XY.

The special unwinding enzyme that helps in breaking the weak hydrogen bond which holds the two strands of DNA is helicase.

Sometimes, a segment of a chromosome detaches and unites with another non-homologous chromosome. Such an inter-chromosomal rearrangement is called translocation.