Q.The cytological observations made in a number of insects led to the development of the concept of genetic/chromosomal basis of sex-determination mechanism. Honey bee is an interesting example to study the mechanism of sex-determination. Study the schematic cross between the male and the female honey bees given below and answer the questions that follow :
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Start your 14-day free trial to unlock the full solution →Honey bees exhibit haplodiploidy: females are diploid, males are haploid. Female gamete formation (A) involves meiosis, while male gamete formation (B) involves mitosis. Male drones develop from unfertilized eggs through parthenogenesis (C).
The honey bee's sex-determination system is a classic example of haplodiploidy, a mechanism where the sex of an individual is determined by the number of sets of chromosomes it possesses. Understanding this fundamental concept is key to identifying the cell divisions and processes involved.
In honey bees:
- Females (queens and workers) are diploid (2n), meaning they develop from fertilized eggs and have two sets of chromosomes.
- Males (drones) are haploid (n), meaning they develop from unfertilized eggs and have only one set of chromosomes.
This difference in ploidy directly dictates how gametes are formed and how individuals develop.
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Understanding Gamete Formation in Females (Cell Division A):
A female honey bee is diploid (2n). To produce eggs, which are gametes, the chromosome number must be halved to n so that upon fertilization with a sperm (also n), the resulting zygote is diploid (2n). The cell division process that reduces the chromosome number by half, producing haploid gametes from a diploid parent cell, is meiosis.
Diploid parent cell (2n) -- Meiosis --> Haploid gametes (n)
Therefore, cell division 'A' in the female honey bee, leading to egg formation, is meiosis.
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Understanding Gamete Formation in Males (Cell Division B):
A male honey bee (drone) is haploid (n). It needs to produce sperm, which are also gametes, and must maintain the haploid chromosome number (n). If a haploid organism were to undergo meiosis, it would result in cells with half the haploid number (n/2), which is not viable for gamete formation in this context. Instead, the male produces sperm through a process that maintains the chromosome number. The cell division process that produces genetically identical daughter cells with the same chromosome number as the parent cell is mitosis.
Haploid parent cell (n) -- Mitosis --> Haploid gametes (n) …
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