BIO 222 Chap 4: Sex Determination in Drosophila and Humans
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Questions and Answers

Which of the following is a key difference between chromosomal and genic sex determination systems?

  • Chromosomal systems are found in mammals, while genic systems are exclusive to insects.
  • In chromosomal systems, males and females have distinguishable chromosomes, while in genic systems, they do not. (correct)
  • Genic systems always result in a 1:1 sex ratio, while chromosomal systems do not.
  • Chromosomal systems rely on environmental factors, while genic systems do not.

    • In Drosophila melanogaster, sex is determined by the X:A ratio. What does 'A' represent in this ratio?

  • The number of sex chromosomes.
  • The number of haploid sets of autosomes. (correct)
  • The number of X chromosomes.
  • The number of Y chromosomes.

    • According to the provided information on Drosophila, what sexual phenotype would an individual with an X:A ratio of 1.5 likely exhibit?

  • Metafemale (correct)
  • Intersex
  • Male
  • Female

    • What is the role of the SRY gene in human sex determination?

    <p>It is located on the Y chromosome and determines maleness. (D)</p> Signup and view all the answers

    Which of the following genotypes in humans results in Turner syndrome?

    <p>XO (C)</p> Signup and view all the answers

    What is a common characteristic of individuals with Klinefelter syndrome?

    <p>They are phenotypically male and have an XXY chromosome complement. (B)</p> Signup and view all the answers

    Based on the principles of sex chromosome function, what phenotype would you expect in an individual with an XXYY chromosome complement in humans?

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

    What is the most accurate interpretation of the statement: 'The absence of Y results in a female phenotype'?

    <p>Without a Y chromosome, the default developmental pathway in mammals leads to female development. (B)</p> Signup and view all the answers

    In a species with an XX-XY sex-determination system, how do the gametes produced by the heterogametic sex differ from those produced by the homogametic sex?

    <p>Heterogametic gametes have different sex chromosomes, while homogametic gametes have the same sex chromosome. (D)</p> Signup and view all the answers

    Which statement best describes the genic sex-determination system?

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

    In environmental sex determination, what primarily influences the sex of an offspring?

    <p>External conditions such as temperature or position in a stack. (A)</p> Signup and view all the answers

    A species of fish relies on a genic sex-determination system. What would you expect to find regarding sex chromosomes in this species?

    <p>There are no distinct sex chromosomes present. (B)</p> Signup and view all the answers

    How does the ZZ-ZW sex-determination system differ from the XX-XY system?

    <p>In the ZZ-ZW system, the female is the heterogametic sex, while in the XX-XY system, the male is the heterogametic sex. (D)</p> Signup and view all the answers

    In a turtle species with environmental sex determination, warmer incubation temperatures produce females. If a nest of eggs is consistently incubated at cooler temperatures, what would be the likely outcome?

    <p>Primarily males. (C)</p> Signup and view all the answers

    Consider a newly discovered insect species where sex determination is suspected to be genic. Which observation would best support this hypothesis?

    <p>Males and females have the same set of chromosomes, with sex linked to specific autosomal genes. (C)</p> Signup and view all the answers

    A researcher is studying a population of grasshoppers with an XX-XO sex-determination system. What chromosomal composition would you expect to find in the male grasshoppers?

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

    What is the direct function of the SRY gene in humans?

    <p>Determination of maleness. (B)</p> Signup and view all the answers

    A person with Androgen-insensitivity syndrome is genotypically male (XY). Which of the following best describes why they develop a female phenotype?

    <p>Their cells are unable to respond to testosterone due to a defective androgen receptor. (D)</p> Signup and view all the answers

    Someone with Klinefelter syndrome has a XXXY genotype. Which of the following statements is most accurate regarding this condition?

    <p>They exhibit a phenotypic presentation that deviates from the typical binary sex presentation. (A)</p> Signup and view all the answers

    In Drosophila, white eyes is an X-linked recessive trait. If a white-eyed female is crossed with a wild-type red-eyed male, what proportion of the male offspring will have white eyes?

    <p>100% (D)</p> Signup and view all the answers

    In an experiment involving eye color in Drosophila, Bridges crossed a white-eyed female with a red-eyed male and observed a small number of red-eyed males in the F1 generation. What was the genotype of these exceptional red-eyed males?

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

    A woman with hemophilia, an X-linked recessive trait, has children with a man who does not have hemophilia. What is the probability that their daughters will be carriers of hemophilia?

    <p>100% (B)</p> Signup and view all the answers

    Considering the general trend of Y chromosome evolution, what is the most likely outcome for Y-linked genes over a long evolutionary timescale?

    <p>Y-linked genes will be lost or rendered non-functional due to a lack of recombination. (A)</p> Signup and view all the answers

    What is the significance of palindromic sequences found on the Y chromosome?

    <p>They facilitate gene conversion, which can correct mutations and maintain gene function. (A)</p> Signup and view all the answers

    Which of the following statements correctly describes the relationship between ploidy and sex determination in a haplodiploidy system?

    <p>Females are diploid, arising from fertilized eggs, while males are haploid, arising from unfertilized eggs. (B)</p> Signup and view all the answers

    In species with XX-XY sex determination, what would be the result of a mutation that causes the SRY gene on the Y chromosome to be non-functional?

    <p>An XY individual would develop as female. (D)</p> Signup and view all the answers

    A researcher discovers a new insect species. Females are ZZ and males are ZW. Is this statement correct?

    <p>No, in the ZZ-ZW system, males are typically ZZ and females are ZW. (A)</p> Signup and view all the answers

    Which of the following statements accurately compares the XX-XO and XX-XY sex-determination systems?

    <p>In the XX-XO system, females have two X chromosomes, while males have only one, whereas in the XX-XY system, females have two X chromosomes and males have one X and one Y chromosome. (D)</p> Signup and view all the answers

    In a dioecious plant species with an XX-XY sex-determination system, a mutation arises that prevents meiosis during pollen formation. What would be the resulting pollen grain's chromosomal content?

    <p>Each pollen grain would contain a complete diploid set of chromosomes, either XX or XY. (C)</p> Signup and view all the answers

    How does sexual reproduction contribute to genetic diversity, and why is this diversity important for the long-term survival of a species?

    <p>Sexual reproduction increases genetic diversity through meiosis, which allows populations to adapt to changing environmental conditions. (C)</p> Signup and view all the answers

    A species of fish is discovered to be hermaphroditic. Which of the following is a valid conclusion based on this information?

    <p>Individual fish possess both male and female reproductive structures. (B)</p> Signup and view all the answers

    In bees, haplodiploidy determines sex. Queen bees are diploid and lay both fertilized and unfertilized eggs. What will be the sex of the offspring from each type of egg?

    <p>Fertilized eggs become females, unfertilized eggs become males. (C)</p> Signup and view all the answers

    Flashcards

    Heterogametic sex

    The sex with different sex chromosomes in gametes (XY).

    Homogametic sex

    The sex with the same sex chromosomes in gametes (XX).

    Chromosomal sex determination

    Determination based on sex chromosomes (XX-XY, ZZ-ZW).

    Genic sex determination

    Sex determined by genes without distinct sex chromosomes.

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    Environmental sex determination

    Sex determined by environmental factors rather than genetics.

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    XX-XY system

    Females are XX, males are XY; common in mammals and many others.

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    ZZ-ZW system

    Females are ZW, males are ZZ; found in birds and some reptiles.

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    Factors for environmental sex determination

    Includes temperature, position in species like limpets or turtles.

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    Sex Determination

    The process by which sex is determined in organisms, often involving chromosomes.

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    Haploid and Diploid States

    Haploid cells have one set of chromosomes, diploid cells have two sets.

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    Hermaphroditism

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

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    Monoecious

    An organism that has both male and female reproductive structures.

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    Dioecious

    Organisms that have either male or female reproductive structures.

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    Haplodiploidy

    A sex-determination system where haploid males and diploid females exist.

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    X:A ratio in Drosophila

    Ratio of X chromosomes to haploid sets of autosomes determining sex phenotype.

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    SRY gene

    Gene on the Y chromosome that determines male sex characteristics.

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    Turner syndrome

    Genetic disorder in females with a single X chromosome (XO).

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    Klinefelter syndrome

    Genetic disorder in males typically characterized by an XXY configuration.

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    Role of X chromosome

    Essential genetic information present on the X chromosome required for both sexes.

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    Androgen-insensitivity syndrome

    A condition where the body cannot respond to male hormones due to defective receptors.

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    X-linked characteristics

    Traits determined by genes located on the X chromosome.

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    Hemophilia

    An X-linked recessive disorder characterized by impaired blood clotting.

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    Y-linked characteristics

    Traits determined by genes found solely on the Y chromosome.

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    Palindromes in Y chromosome

    Eight large palindromes allowing some crossing over on Y chromosome.

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    Probability of hemophilia inheritance

    The chance that children will inherit hemophilia from a carrier mother and normal father is 1/2.

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    Study Notes

    Chapter 4: Sex Determination and Sex-Linked Characteristics

    • Sex determination is a complex process involving various mechanisms.
    • Different organisms use different mechanisms for sex determination.
    • Sexual reproduction alternates between haploid and diploid states, producing genetic variation.
    • Most organisms have male and female phenotypes.
    • Male and female gametes often differ in size.
    • Meiosis produces haploid gametes.
    • Fertilization restores the diploid state.

    Sex Determination Mechanisms

    • Hermaphroditism: both sexes in one organism
    • Monoecious: both male and female reproductive structures in one organism
    • Dioecious: either male or female reproductive structures in one organism

    Chromosomal Sex-Determining Systems

    • XX-XO system: XX - female, XO - male (e.g., grasshoppers)

    • XX-XY system: XX - female, XY - male (e.g., mammals)

    • ZZ-ZW system: ZZ - male, ZW - female (e.g., birds, snakes, some amphibians, and fishes)

    • Haplodiploidy system: haploid set - male, diploid set - female (e.g., bees, wasps, and ants)

    • In the XX-XY system, the SRY gene on the Y chromosome is crucial for maleness.

    • Absence of the Y chromosome results in female phenotype.

    Concept Checks

    • Concept Check 1: Meiosis is the process causing genetic variation in offspring produced by sexual reproduction.
    • Concept Check 2: The heterogametic sex typically differs from the homogametic sex in having different sex chromosomes. The heterogametic sex is usually male, and the homogametic sex is often female.
    • Concept Check 3: Chromosomal sex determination involves different chromosomes for males and females, genic sex determination involves genes determining sex without obvious chromosome difference, and environmental sex determination involves environmental factors influencing an organism's sex.
    • Concept Check 4: XXXY is a Klinefelter syndrome.
    • Concept Check 5: The genotype of the few live F1 red-eyed males obtained by Bridges in a cross of a white-eyed female and a red-eyed male is XY.
    • Concept Check 6: The probability that a child born to a hemophilic woman and a normal man will have hemophilia is 1/2.
    • Concept Check 7: Eight large palindromes in the Y chromosome allow recombination.
    • Concept Check 8: A male with XXXYY chromosomes has two Barr bodies in each cell.

    X-Linked Characteristics

    • X-linked characteristics are determined by genes on the X chromosome. Examples include X-linked white eyes in Drosophila and X-linked color blindness in humans.
    • Dosage compensation: the amount of protein produced by X-linked genes is equalized in both sexes.
    • Lyon hypothesis: one X chromosome is inactivated randomly in female cells.

    Genic Sex Determination in Drosophila Melanogaster

    • The X:A ratio helps determine the sex.

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    Sex Determination Lecture Slides PDF

    Description

    Explore key concepts of sex determination systems, focusing on both chromosomal and genic systems found in Drosophila melanogaster and humans. This quiz covers important genetic features, including the roles of specific genes and the implications of different sex chromosome configurations.

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