Question

(i) What is a test cross? How can we find out the zygosity of a plant by the use of test cross? (ii) Why are human females rarely haemophilic?…

Accepted Answer

(a) (i) • It is a cross to determine unknown genotype of an organism showing dominant phenotype by crossing with a recessive parent. • A cross between plant with dominant phenotype (example violet colour flower) and plant with recessive phenotype( white colour flower )(monohybrid cross) is done - If the F1 individuals show 1: 1 ratio between dominant and recessive phenotype(violet flower: white flower),then the given plant is heterozygous (Vv) If the F1 individual show all dominant phenotype (all violet flower),then plant is homozygous (VV) / Cross can be explained by taking any other dominant phenotype (ii) • Haemohilia is a sex linked recessive trait and human females are rarely haemophilic because mother of such a female has to be at least carrier and father should be haemophilic. • Mother Father P1 generation - XXh x XhY F1 generation - XXh, XY, XhXh, XhY Carrier female, normal male, haemophilic female, haemophilic male / Mother Father P1 generation - XXh x XY F1 generation - XX, XY, XhX, XhY Normal female, normal male, carrier female,haemophilic male • A haemophilic female can be born if both the X chromosomes are having haemophilic gene / XhXh • clotting of blood is affected /In an affected individual a simple cut results in nonstop bleeding. OR (b) a – Transcription c – Translation (i) – ‘a’ in Nucleus of cell ‘c’ in Cytoplasm of cell (ii) • Changes in Event ‘b’ Splicing,–Removal of introns (non coding portions) and joining of exons (coding parts) from primary transcript. Capping –An unusual nucleotide methyl guanosine triphosphate is added at 5’ end of primary transcript. Tailing –200 – 300 Adenylate residues are added at 3’ end of primary transcript • These changes are needed to change the primary transcript (hnRNA) into a functional mRNA ready to make proteins.

(a)
What is a test cross ? How can we find out the zygosity of a plant by the use of test cross ?
(ii)
Why are human females rarely haemophilic ? Explain with the help of a cross. Under what conditions can a haemophilic female be born ? How do haemophilic patients suffer ?

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