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प्रश्न
Explain the mechanism of sex determination in birds.
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उत्तर
The sex chromosomes in birds are designated Z and W, and the male is the homomorphic sex (ZZ) and the female heteromorphic (ZW). In most avian species the Z chromosome is a large chromosome, usually the fourth or fifth largest, and it contains almost all the known sex-linked genes. The W chromosome is generally a much smaller microchromosome, containing a high proportion of repeat sequence DNA. Recently a gene encoding a protein involved in transcriptional activation of chromatin has been detected on the W chromosome. The weight of evidence suggests that sex determination in birds is by a genic balance mechanism, in which the ratio of autosomes to Z chromosomes is the crucial factor. DNA sequences homologous to the testis determining factor in humans have been detected in both male and female birds, but it is not clear that they have a sex-related function in birds. A number of different practical methods have been developed to distinguish the sex of birds, based on sex-linked genes, the amount of DNA per cell and using DNA probes for sex-linked sequences.
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संबंधित प्रश्न
Differentiate between ‘ZZ’ and ‘XY’ type of sex-determination mechanisms.
Does genetic combination of mother play a significant role in determining the sex of a new born baby?
A zygote which has inherited an X chromosome from the father will develop into :
(a) baby boy
(b) baby girl
(c) adult
(d) either boy or girl
A family consists of two parents and their five children and the pedigree chart below shows the inheritance of the trait colour blindness in them.
Who is colour blind in the parents – the Father or the Mother?
Define the following:
Autosomes
Explain the following terms:
Identical twins
Choose the correct answer:
Chromosomes identical in male and female are called __________
Choose the correct answer:
Males have more chances of suffering from sex-linked disease because of ___________
Write a short note on sex determination in man.
Complete the following sentence with appropriate word:
______are the alternative forms of a gene producing different effects.
Explain the haplo-diploid method of sex determination in the honey bee.
Chromosomal constitution of normal human females can be written as ______.
A trait in an organism is influenced by
Structures present in a cell which is responsible for determination of the sex of a baby is ______.
Female heterogamy is shown by
All human chromosomes ate not paired. Most human chromosomes have a maternal and a paternal copy, and we have 22 such pairs. But one pair called the sex chromosomes, is odd in not always being a perfect pair. Women have a perfect pair of sex chromosomes. But men have a mismatched pair in which one is normal sized while the other is a short one.
(a) In humans, how many chromosomes are present in a Zygote and in each gamete?
(b) A few reptiles rely entirely on environmental cues for sex determination. Comment.
(c) "The sex of a child is a matter of chance and none of the parents are considered to be responsible for it." Justify it through flow chart only.
OR
(c) Why do all the gametes formed in human females have an X chromosome?
Which term describes organisms where male and female reproductive organs are present in separate individuals?
Which organisms utilize the ZW–ZZ sex determination system?
If a male grasshopper with XO genotype produces sperm, what proportion of his sperm will carry the X chromosome?
