Advertisements
Advertisements
प्रश्न
Explain the mechanism of sex determination in birds.
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.
APPEARS IN
संबंधित प्रश्न
Write the types of sex-determination mechanisms the following crosses show. Give an example of each type.
(i) Female XX with Male XO
(ii) Female ZW with Male ZZ
"The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it". Draw a flow chart showing determination of sex of a newborn to justify this statement.
In a human, how many chromosmes are present in a brain cell?
Name two animals which have nineteen pairs of chromosomes.
Give Reason:
Why X-linked recessive diseases are more common among males than females.
Kavitha gave birth to a female baby. Her family members say that she can give birth to only female babies because of her family history. Is the statement given by her family members true? Justify your answer.
What is male heterogamety?
How is sex determined in human beings?
Read the following statements and select the correct option.
i. If sperm containing Y chromosome fertilizes the ovum, then diploid zygote is formed that grows into a male child.
ii. If sperm containing X chromosome fertilizes ovum, then diploid zygote is formed, that grows into a female child.
The ‘X’ body of Henking was observed in ______.
Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution this means that
The belief that the mother is completely responsible for the sex of the child is wrong because the child
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.
How many types of gametes are produced by a human female?
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?
How is the sex of a newborn individual determined in different species of animals? Give three examples to support your answer.
A zygote which has Y chromosome inherited from the father will develop into a ______.
