Questions and Answers
What determines the sex of the offspring in humans?
In honeybees, what is the consequence of an egg being fertilized?
What type of chromosome configuration do female honeybees possess?
What is the chromosomal composition of male humans?
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During spermatogenesis, what is the percentage of gametes that carry the Y chromosome?
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What unique reproductive characteristic do male honeybees exhibit?
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What is the term for chromosomes involved in sex determination?
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Who is credited with the discovery of the X chromosome?
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In which type of organisms does the XX-XO mechanism of sex determination occur?
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What is the term for chromosomes that are not involved in sex determination?
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In which type of organisms does the ZZ-ZW mechanism of sex determination occur?
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What is the characteristic of males in the XX-XY mechanism of sex determination?
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What is the characteristic of females in the XX-XO mechanism of sex determination?
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What is the term for the nuclear structure observed by Henking in 50% of sperm?
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Study Notes
Sex Determination Overview
- Sex chromosomes, also known as allosomes, are key in determining sex: includes X and Y chromosomes.
- Autosomes are chromosomes other than sex chromosomes, with equal numbers in males and females.
Historical Background
- Henking (1891) discovered the X body in insects during spermatogenesis, which is now recognized as the X chromosome.
Mechanisms of Sex Determination
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XX-XO Mechanism:
- Males are heterogametic (XO), producing gametes with X and those without X.
- Females are homogametic (XX), creating gametes only with X chromosomes.
- Example: Grasshoppers.
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XX-XY Mechanism:
- Males are heterogametic (XY), producing gametes with X and Y.
- Females are homogametic (XX), forming gametes only with X.
- Examples: Humans and Drosophila.
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ZZ-ZW Mechanism:
- Males are homogametic (ZZ), while females are heterogametic (ZW).
- Example: Birds.
Human Sex Determination (XX-XY Type)
- Humans have 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes.
- Females carry a pair of X chromosomes (XX), while males possess one X and one Y (XY).
- During male spermatogenesis, there is an equal production of sperm carrying either an X chromosome (50%) or a Y chromosome (50%).
- The type of sperm that fertilizes the ovum determines the offspring's sex.
Honeybee Sex Determination
- Based on the sets of chromosomes received:
- Fertilized eggs develop into females (queens or workers), while unfertilized eggs develop into males (drones).
- This reproductive strategy is referred to as parthenogenesis.
- In this haplodiploid system, females are diploid (32 chromosomes) and males are haploid (16 chromosomes).
- Male honeybees produce sperm through mitosis and do not have fathers, implying they cannot have sons, but they can have grandsons via their mothers.
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Description
Understand the basics of sex determination, including sex chromosomes, autosomes, and historical background, as well as mechanisms of sex determination, such as the XX-XO mechanism.
