BIO 222 Chap 4: Sex Determination Mechanisms

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Questions and Answers

What is the primary function of the SRY gene?

  • Regulation of blood clotting
  • Determination of sex in humans (correct)
  • Development of the female reproductive system
  • Production of androgens

What is the genetic basis of androgen-insensitivity syndrome?

  • A missing Y chromosome
  • A defective androgen receptor (correct)
  • A mutation in the SRY gene
  • An extra X chromosome

A person with XXXY sex chromosomes typically exhibits which condition?

  • XYY syndrome
  • Klinefelter syndrome (correct)
  • Turner syndrome
  • Poly-X female

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?

<p>X+Y (A)</p> Signup and view all the answers

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?

<p>50% (D)</p> Signup and view all the answers

Which characteristic is unique to Y-linked traits?

<p>They are only present in males. (B)</p> Signup and view all the answers

What feature of the Y chromosome allows for some recombination?

<p>Eight large palindromes (A)</p> Signup and view all the answers

What happens to the Y chromosome over time?

<p>It loses DNA. (B)</p> Signup and view all the answers

What is a key characteristic of genic sex determination?

<p>The chromosomes of males and females are indistinguishable. (D)</p> Signup and view all the answers

In Drosophila, what determines the sex of the organism?

<p>The ratio of X chromosomes to sets of autosomes (A)</p> Signup and view all the answers

An individual with an X:A ratio of 1.5 in Drosophila would most likely be classified as what?

<p>Metafemale (D)</p> Signup and view all the answers

What role does the SRY gene play in human sex determination?

<p>It determines maleness. (A)</p> Signup and view all the answers

Which of the following human conditions is characterized by an XO chromosome complement?

<p>Turner syndrome (D)</p> Signup and view all the answers

Which statement is true regarding the Y chromosome's role in humans?

<p>It contains the male-determining gene. (B)</p> Signup and view all the answers

What is a key distinction of environmental sex determination compared to chromosomal and genic systems?

<p>Sex is determined fully or in part by environmental influences. (C)</p> Signup and view all the answers

In humans, what phenotype is expected from an individual with an XXY chromosome complement, and what is the common name?

<p>Male, Klinefelter syndrome (A)</p> Signup and view all the answers

Which of the following best describes the difference between male and female gametes?

<p>Male and female gametes differ primarily in size. (B)</p> Signup and view all the answers

An organism that has both male and female reproductive structures is best described as:

<p>Monoecious (B)</p> Signup and view all the answers

Which chromosomal sex-determination system features an XO genotype that results in a male phenotype?

<p>XX-XO system (D)</p> Signup and view all the answers

Which of these is a key characteristic of sexual reproduction regarding the genetic makeup of the offspring?

<p>It introduces genetic variation through meiosis. (D)</p> Signup and view all the answers

In the ZZ-ZW system, which of the following is true?

<p>The homogametic sex is male, and the heterogametic sex is female. (D)</p> Signup and view all the answers

Which statement accurately describes a difference between dioecious and monoecious organisms?

<p>Monoecious organisms have both male and female reproductive structures in a single individual, while dioecious organisms have separate individuals with male or female structures. (B)</p> Signup and view all the answers

Which sex determination system results in males being haploid and females being diploid?

<p>Haplodiploidy system (D)</p> Signup and view all the answers

In mammals, the typical sex determination system is the:

<p>XX-XY system. (A)</p> Signup and view all the answers

What is a characteristic of gametes from the homogametic sex?

<p>They all contain the same type of sex chromosome. (D)</p> Signup and view all the answers

Which of the following is NOT a defining characteristic of the heterogametic sex?

<p>It is always the male in all species. (D)</p> Signup and view all the answers

In a ZZ-ZW system, which sex is considered the heterogametic sex?

<p>The ZW sex. (B)</p> Signup and view all the answers

Which sex-determining system relies on genes located on undifferentiated chromosomes, rather than distinct sex chromosomes?

<p>Genic sex-determining system. (A)</p> Signup and view all the answers

In organisms that utilize environmental sex determination, what is the primary factor that determines sex?

<p>External conditions like temperature or location. (A)</p> Signup and view all the answers

Which of the following is a characteristic of the XX-XO sex determination system?

<p>Females are XX and Males are XO (B)</p> Signup and view all the answers

What is unique about the sex determination in organisms that utilize the genic sex-determining system?

<p>Sex is determined by specific genes on undifferentiated chromosomes. (B)</p> Signup and view all the answers

How does the heterogametic sex differ from the homogametic sex in terms of chromosome composition?

<p>The heterogametic sex has two different sex chromosomes; the homogametic sex has two copies of the same sex chromosome. (A)</p> Signup and view all the answers

Flashcards

Heterogametic Sex

The sex that produces gametes with different sex chromosomes (e.g., male: XY).

Homogametic Sex

The sex that produces gametes with the same sex chromosomes (e.g., female: XX).

Environmental Sex Determination

Sex determined by environmental factors like temperature or position.

XX-XY System

A system where females are XX and males are XY, common in many organisms.

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ZZ-ZW System

Females are ZW and males are ZZ, found in birds and butterflies.

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Genic Sex Determination

No distinct sex chromosomes; sex determined by genes on undifferentiated chromosomes.

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Chromosomal Sex Determination

Sex is determined by specific combinations of sex chromosomes (XX, XY).

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Sex-Determining Systems

Systems that categorize sex based on chromosomes or environmental factors.

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Meiosis

A process that causes genetic variation in offspring during sexual reproduction.

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Hermaphroditism

A condition where an organism has both male and female reproductive structures.

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Haplodiploidy

A reproductive system where males are haploid (one set of chromosomes) and females are diploid (two sets).

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Monoecious

An organism that has both male and female reproductive structures in the same individual.

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SRY gene

The gene responsible for male sex determination in humans.

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Androgen-insensitivity syndrome

A condition caused by a defective androgen receptor, resulting in male phenotype despite XY chromosomes.

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Klinefelter syndrome

A genetic condition in males caused by an extra X chromosome (XXY or more).

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X-linked characteristics

Traits determined by genes located on the X chromosome, can exhibit unique inheritance patterns.

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Hemophilia

An X-linked recessive disease that affects blood clotting, primarily in males.

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Y-linked characteristics

Traits determined by genes found exclusively on the Y chromosome and passed from father to son.

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Palindromes on Y chromosome

Eight large palindromic sequences that facilitate some recombination on the Y chromosome.

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F1 generation

The first filial generation derived from the cross of parental generations in Mendelian genetics.

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X:A Ratio

Ratio of X chromosomes to haploid sets of autosomes in Drosophila.

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Turner Syndrome

A condition in females resulting from a single X chromosome (XO).

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Poly-X Females

Females with more than two X chromosomes (XXXY).

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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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