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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
In a human, how many chromosmes are present in a fertilised egg?
A normal cell of human body contains 23 pairs of chromosomes. The number of chromosomes in a sex cell (sperm or ovum) of a human being is most likely to be :
(a) 46
(b) 23
(c) 21
(d) 42
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
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- Which combination of genes in the zygote will produce children with blue eyes?
- Which combinations of genes in the zygote will produce children with brown eyes?
Does the sex of the child depend on the father or it is just a matter of chance? Discuss.
Choose the correct answer from the four options given below :
In a human male, a sperm will contain :
What is parthenogenesis?
Explain the mechanism of sex determination in birds.
Distinguish between heterogametic and homogametic sex determination systems.
If a normal cell of the human body contains 46 pairs of chromosomes then the numbers of chromosomes in a sex cell of a human being is most likely to be ______
A zygote which has an X-chromosome inherited from the father will develop into a
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In humans, males are heterogametic and females are homogametic. Explain. Are there any examples where males are homogametic and females heterogametic?
Does a male child inherit X chromosome from his father? Justify.
In the XX–XY sex determination system, which sex is considered heterogametic and produces two different types of gametes?
In the XX–XO sex determination system, what does the 'O' represent?
If a male grasshopper with XO genotype produces sperm, what proportion of his sperm will carry the X chromosome?
