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Questions and Answers
What is the primary function of the SRY gene?
What is the primary function of the SRY gene?
What is the genetic basis of androgen-insensitivity syndrome?
What is the genetic basis of androgen-insensitivity syndrome?
A person with XXXY sex chromosomes typically exhibits which condition?
A person with XXXY sex chromosomes typically exhibits which condition?
In Drosophila, if a white-eyed female is crossed with a red-eyed male, what was the genotype of the rare, red-eyed males in the F1 generation?
In Drosophila, if a white-eyed female is crossed with a red-eyed male, what was the genotype of the rare, red-eyed males in the F1 generation?
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If a woman with hemophilia has children with a man who has the normal blood clotting phenotype, what is the probability their child will have hemophilia?
If a woman with hemophilia has children with a man who has the normal blood clotting phenotype, what is the probability their child will have hemophilia?
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Which characteristic is unique to Y-linked traits?
Which characteristic is unique to Y-linked traits?
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What feature of the Y chromosome allows for some recombination?
What feature of the Y chromosome allows for some recombination?
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What happens to the Y chromosome over time?
What happens to the Y chromosome over time?
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What is a key characteristic of genic sex determination?
What is a key characteristic of genic sex determination?
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In Drosophila, what determines the sex of the organism?
In Drosophila, what determines the sex of the organism?
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An individual with an X:A ratio of 1.5 in Drosophila would most likely be classified as what?
An individual with an X:A ratio of 1.5 in Drosophila would most likely be classified as what?
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What role does the SRY gene play in human sex determination?
What role does the SRY gene play in human sex determination?
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Which of the following human conditions is characterized by an XO chromosome complement?
Which of the following human conditions is characterized by an XO chromosome complement?
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Which statement is true regarding the Y chromosome's role in humans?
Which statement is true regarding the Y chromosome's role in humans?
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What is a key distinction of environmental sex determination compared to chromosomal and genic systems?
What is a key distinction of environmental sex determination compared to chromosomal and genic systems?
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In humans, what phenotype is expected from an individual with an XXY chromosome complement, and what is the common name?
In humans, what phenotype is expected from an individual with an XXY chromosome complement, and what is the common name?
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Which of the following best describes the difference between male and female gametes?
Which of the following best describes the difference between male and female gametes?
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An organism that has both male and female reproductive structures is best described as:
An organism that has both male and female reproductive structures is best described as:
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Which chromosomal sex-determination system features an XO genotype that results in a male phenotype?
Which chromosomal sex-determination system features an XO genotype that results in a male phenotype?
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Which of these is a key characteristic of sexual reproduction regarding the genetic makeup of the offspring?
Which of these is a key characteristic of sexual reproduction regarding the genetic makeup of the offspring?
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In the ZZ-ZW system, which of the following is true?
In the ZZ-ZW system, which of the following is true?
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Which statement accurately describes a difference between dioecious and monoecious organisms?
Which statement accurately describes a difference between dioecious and monoecious organisms?
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Which sex determination system results in males being haploid and females being diploid?
Which sex determination system results in males being haploid and females being diploid?
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In mammals, the typical sex determination system is the:
In mammals, the typical sex determination system is the:
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What is a characteristic of gametes from the homogametic sex?
What is a characteristic of gametes from the homogametic sex?
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Which of the following is NOT a defining characteristic of the heterogametic sex?
Which of the following is NOT a defining characteristic of the heterogametic sex?
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In a ZZ-ZW system, which sex is considered the heterogametic sex?
In a ZZ-ZW system, which sex is considered the heterogametic sex?
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Which sex-determining system relies on genes located on undifferentiated chromosomes, rather than distinct sex chromosomes?
Which sex-determining system relies on genes located on undifferentiated chromosomes, rather than distinct sex chromosomes?
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In organisms that utilize environmental sex determination, what is the primary factor that determines sex?
In organisms that utilize environmental sex determination, what is the primary factor that determines sex?
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Which of the following is a characteristic of the XX-XO sex determination system?
Which of the following is a characteristic of the XX-XO sex determination system?
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What is unique about the sex determination in organisms that utilize the genic sex-determining system?
What is unique about the sex determination in organisms that utilize the genic sex-determining system?
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How does the heterogametic sex differ from the homogametic sex in terms of chromosome composition?
How does the heterogametic sex differ from the homogametic sex in terms of chromosome composition?
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Study Notes
Sex Determination and Sex-Linked Characteristics
- Multiple mechanisms exist for sex determination.
- The X and Y chromosomes pair during meiosis, even though they aren't homologous.
- Sexual reproduction alternates between haploid and diploid states.
- Most organisms have two sexual phenotypes: male and female.
- Male and female gametes differ in size (Fig. 4.4).
- Meiosis produces haploid gametes.
Chromosomal Sex-Determination Systems
-
XX-XO system:
- XX = female
- XO = male
- Example: Grasshoppers
-
XX-XY system:
- XX = female
- XY = male
- Example: Mammals
-
ZZ-ZW system:
- ZZ = male
- ZW = female
- Example: Birds, snakes, butterflies, some amphibians, and fishes
-
Haplodiploidy system:
- Haploid set = male
- Diploid set = female
- Example: Bees, wasps, and ants
Genic Sex-Determining System
- No sex chromosomes, only the sex-determining genes.
- Found in plants, fungi, protozoans, and fish.
Environmental Sex Determination
- Environmental factors influence sex determination:
- Limpet's position in the stack
- Temperature in turtles
Sex Determination in Drosophila melanogaster
- Genic balance system
- X:A ratio (X = number of X chromosomes, A = number of haploid sets of autosomes)
Sex Determination in Humans XX-XY
- SRY gene on the Y chromosome determines maleness
- Turner syndrome: XO; 1/3000 female births
- Klinefelter syndrome: XXY, XXXY, XXXXY, or XXYY; 1/1000 male births
- Poly-X females: 1/1000 female births
The Role of Sex Chromosomes
- The X chromosome contains essential genetic information for both sexes.
- At least one copy of an X chromosome is required.
- The male-determining gene is on the Y chromosome. A single Y chromosome produces a male phenotype even if multiple X chromosomes are present.
- The absence of a Y chromosome results in a female phenotype.
The Male-Determining Gene in Humans
- Sex-determining region Y (SRY) gene
- Androgen-insensitivity syndrome: caused by a defective androgen receptor
Sex-Linked Characteristics
- X-linked characteristics are determined by genes on the sex chromosomes:
- X-linked white eyes in Drosophila (Figures 4.12 and 4.13)
- X-linked color blindness in humans (Figure 4.14)
- Z-linked characteristics: traits are linked to the Z chromosome
Y-Linked Characteristics
- Only present in males.
- All male offspring exhibit the trait.
- Y chromosome lost DNA over time.
- Important for sex determination in SRY
X-Linked Characteristics (additional detail)
- Dosage compensation (amount of protein produced by X-linked genes and randomly inactivated in two sexes):
- Figure 4.17
- Lyon hypothesis
Concept Checks
- Several concept checks are provided for various aspects of sexual reproduction and sex determination.
Number of Barr Bodies
- A table lists the number of Barr bodies in cells with different sex chromosome complements.
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Description
Test your knowledge on various mechanisms of sex determination and the chromosomal systems involved. This quiz covers the XX-XO, XX-XY, ZZ-ZW, and haplodiploidy systems, along with the concept of genic sex determination. Dive into the intriguing world of sexual reproduction and gamete formation!
