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Questions and Answers
What is the primary signal for determining sex in Drosophila melanogaster?
What is the primary signal for determining sex in Drosophila melanogaster?
In Drosophila, individuals with one X chromosome and two sets of autosomes are classified as:
In Drosophila, individuals with one X chromosome and two sets of autosomes are classified as:
What does an X:A ratio greater than 1 result in?
What does an X:A ratio greater than 1 result in?
If the X:A ratio is less than 0.5 in Drosophila, what is formed?
If the X:A ratio is less than 0.5 in Drosophila, what is formed?
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Who drew the first set of cytogenetic maps of the D.melanogaster polytene chromosomes?
Who drew the first set of cytogenetic maps of the D.melanogaster polytene chromosomes?
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In Drosophila, what happens when the Sxl gene is activated?
In Drosophila, what happens when the Sxl gene is activated?
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What happens if there is inappropriate expression of the Sxl gene in Drosophila melanogaster?
What happens if there is inappropriate expression of the Sxl gene in Drosophila melanogaster?
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Which gene in Drosophila transforms females into sterile males?
Which gene in Drosophila transforms females into sterile males?
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What is the outcome when the X:A ratio is computed and the Sxl switch is flipped off?
What is the outcome when the X:A ratio is computed and the Sxl switch is flipped off?
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In environmental sex determination, what happens when turtles experience high temperatures?
In environmental sex determination, what happens when turtles experience high temperatures?
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What determines the sex of Bonellia worms?
What determines the sex of Bonellia worms?
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Which gene in Drosophila leads to the development of flies with intersex phenotypes?
Which gene in Drosophila leads to the development of flies with intersex phenotypes?
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In the XX-XO sex chromosomal system, which sex produces 2 types of gametes?
In the XX-XO sex chromosomal system, which sex produces 2 types of gametes?
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Which of the following systems is exhibited by birds, snakes, and butterflies?
Which of the following systems is exhibited by birds, snakes, and butterflies?
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In the XX-XY sex chromosomal system, which sex is the homogametic sex?
In the XX-XY sex chromosomal system, which sex is the homogametic sex?
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What type of embryos develop from fertilized eggs in haplodiploidy?
What type of embryos develop from fertilized eggs in haplodiploidy?
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Which of the following statements is true about the chromosomes in the XX-XO sex chromosomal system?
Which of the following statements is true about the chromosomes in the XX-XO sex chromosomal system?
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'Y' chromosome carries genes responsible for which trait in humans?
'Y' chromosome carries genes responsible for which trait in humans?
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Study Notes
Sex Determination in Drosophila Melanogaster
- Sex determination in Drosophila melanogaster is based on the X:A ratio, where X represents the number of X chromosomes and A represents the number of sets of autosomes.
- Individuals with one X chromosome and two sets of autosomes are male (X:A=0.5), whereas individuals with an equal number of X and autosomal chromosomes are female (X:A=1).
- If X/A ratio is greater than 1, metafemales are formed, and if X/A ratio is less than 0.5, metamales are formed.
- If X/A ratio is between 0.5 and 1, intersexes are formed.
Genic Balance and Sex-Lethal Gene
- The primary signal for sex determination is the X:A ratio, which activates or inactivates the Sex-lethal (Sxl) gene.
- In females, the Sxl gene is activated, and the Sxl protein is produced, whereas in males, the Sxl gene is inactive, and no Sxl protein is produced.
- Inappropriate expression of the Sxl gene leads to embryonic death.
Single Gene Effects
- The Transformer (tra) gene: autosomal recessive, transforms females into sterile males.
- The Doublesex (dsx) gene: transforms normal males and females into flies with intersex phenotypes.
Environmental Sex Determination
- Temperature-dependent sex determination (TSD): e.g., in turtles and crocodiles, where low temperatures produce females and high temperatures produce males.
- Location-dependent sex determination: e.g., in the echiuroid worm Bonellia, where sex is determined by where the larva settles.
Chromosomes Theory of Inheritance and Sex Chromosomes
- Chromosomes theory of inheritance: states that genes are located on chromosomes, which serve as vehicles for gene segregation in meiosis.
- Sex chromosomes: determine the sex and differ between males and females.
- Autosomes: non-sex chromosomes, same for males and females.
Haplodiploidy and Sex Chromosomal Systems
- Haplodiploidy: exhibited by bees, where 2n embryos develop from fertilized eggs and become females (workers), and 1n embryos develop parthenogenetically and become males (drones).
- XX-XO system: e.g., if 2n=12, males are heterogametic sex, and females are homogametic sex.
- ZZ-ZW system: exhibited by birds, snakes, and butterflies, where females are heterogametic sex, and males are homogametic sex.
- XX-XY system: e.g., in humans, females are XX and homogametic sex, and males are XY and heterogametic sex.
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Description
This quiz covers the topic of sex determination in Drosophila melanogaster, focusing on genic balance, sex chromosomes, autosomal balance, and the contributions of Calvin Bridges. Learn about the primary signal for sex determination based on the number of X chromosomes relative to sets of autosomes in a cell.
