Biology Chapter 7 & 4: Sex Determination
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Questions and Answers

What does the XX/XY mode of sex determination indicate about female and male gametes?

  • Male gametes have either an X or Y chromosome. (correct)
  • Female gametes have one X chromosome. (correct)
  • Male gametes have one X chromosome.
  • Both female and male gametes contain Z chromosomes.

    • What chromosomal arrangement characterizes female mammals?

    XX

    What chromosomal arrangement characterizes male mammals?

    XY

    The ZW sex determination system has males with ZW chromosomes.

    <p>False</p> Signup and view all the answers

    What are Klinefelter and Turner syndromes characterized by?

    <p>Aberrant sexual development</p> Signup and view all the answers

    Triplo-X syndrome involves three Y chromosomes.

    <p>False</p> Signup and view all the answers

    In humans, how many pairs of autosomal chromosomes are present?

    <p>22</p> Signup and view all the answers

    The Y chromosome is _____ compared to the X chromosome.

    <p>very small</p> Signup and view all the answers

    What is the primary characteristic of individuals with 47,XXX syndrome?

    <p>Three X chromosomes</p> Signup and view all the answers

    Males are consistently characterized by the 47, _____ syndrome.

    <p>XYY</p> Signup and view all the answers

    What is dosage compensation?

    <p>A genetic mechanism balancing the expression of X-linked genes.</p> Signup and view all the answers

    What is a Barr body?

    <p>An inactive X chromosome</p> Signup and view all the answers

    All females are homogametic.

    <p>True</p> Signup and view all the answers

    In X-inactivation, what is the rule followed?

    <p>N − 1 rule</p> Signup and view all the answers

    A trait controlled by genes on the sex chromosome (X) is called _____ linkage.

    <p>X</p> Signup and view all the answers

    What is the genetic status of males in terms of gene dosage on the X chromosome?

    <p>Hemizygous</p> Signup and view all the answers

    What determines the sex of offspring in the XX/XO mode of sex determination?

    <p>Random distribution of X chromosomes</p> Signup and view all the answers

    What describes the homogametic sex in mammals?

    <p>Has two like chromosomes</p> Signup and view all the answers

    How do heterogametic sexes in mammals differ from homogenetic sexes?

    <p>They have two unlike chromosomes</p> Signup and view all the answers

    In the ZZ/ZW sex determination system, which statement is true about male gametes?

    <p>They can only carry Z chromosomes</p> Signup and view all the answers

    How many X chromosomes must be present in a zygote for female offspring to be produced in the XX/XY sex determination system?

    <p>Two X chromosomes</p> Signup and view all the answers

    Which statement accurately describes the role of the Y chromosome in humans?

    <p>It is responsible for maleness when present with an X chromosome</p> Signup and view all the answers

    What is the chromosomal arrangement of males in terms of sex chromosomes?

    <p>XY</p> Signup and view all the answers

    What defines the primary characteristic of the ZZ/ZW sex determination system in birds?

    <p>Females possess the W chromosome</p> Signup and view all the answers

    In the context of ZW sex determination in birds, what is the heterogametic sex?

    <p>ZW</p> Signup and view all the answers

    Which of the following is NOT true about the XX/XY mode of sex determination?

    <p>Female offspring arise from the presence of one Y chromosome</p> Signup and view all the answers

    What genetic anomaly is primarily associated with having three X chromosomes?

    <p>Triplo-X syndrome</p> Signup and view all the answers

    Which syndrome is characterized by a male having two Y chromosomes?

    <p>XYY syndrome</p> Signup and view all the answers

    Which of the following syndromes is most likely to occur due to nondisjunction of X chromosomes during meiosis?

    <p>All of the above</p> Signup and view all the answers

    Individuals with Klinefelter syndrome are characterized by which of the following chromosomal configurations?

    <p>47,XXY</p> Signup and view all the answers

    What is a common feature shared by individuals with Triplo-X syndrome?

    <p>They may have underdeveloped secondary sex characteristics.</p> Signup and view all the answers

    What is the typical height characteristic associated with the 47,XYY syndrome?

    <p>Over 6 feet tall</p> Signup and view all the answers

    What aspect of the Y chromosome is highlighted in its comparison to the X chromosome?

    <p>It is smaller and has fewer genes than the X chromosome.</p> Signup and view all the answers

    What is a noted mental health issue associated with the XYY syndrome?

    <p>Personality disorders</p> Signup and view all the answers

    What is the primary function of dosage compensation in mammals?

    <p>To balance the expression of X-linked genes</p> Signup and view all the answers

    What characterizes Barr bodies in human somatic cells?

    <p>They are condensed inactive X chromosomes</p> Signup and view all the answers

    What does the Lyon Hypothesis state about X chromosome inactivation?

    <p>It is random and affects all descendant cells</p> Signup and view all the answers

    Which of the following best exemplifies the Lyon Hypothesis in practice?

    <p>Calico cats displaying varied fur color patterns</p> Signup and view all the answers

    How does X-inactivation contribute to dosage compensation?

    <p>By randomly silencing one X chromosome in females</p> Signup and view all the answers

    What is the N − 1 rule in the context of X-inactivation?

    <p>It indicates how many X chromosomes can be inactivated</p> Signup and view all the answers

    What occurs to the X chromosome during the early stages of embryonic development, according to the Lyon Hypothesis?

    <p>One X chromosome is randomly inactivated</p> Signup and view all the answers

    In terms of genetic mechanisms, what role do Barr bodies play in females?

    <p>They prevent excessive expression of X-linked genes</p> Signup and view all the answers

    Study Notes

    Mode of Sex Determination

    • XX/XO, XX/XY, and ZZ/ZW are different modes of sex determination.
    • XX/XY: Female gametes contain one X chromosome; male gametes have either X or Y chromosome.
    • ZZ/ZW: Females are ZW (heterogametic) and males are ZZ (homogametic); Z chromosome is larger than W, which is smaller.

    Homogametic and Heterogametic Sex

    • Homogametic sex has two like chromosomes and produces identical gametes.
    • Heterogametic sex has two unlike chromosomes, producing two types of gametes (e.g., 50% X and 50% Y in males; 50% Z and 50% W in females).

    Y Chromosome and Maleness

    • The presence of a Y chromosome determines maleness in humans.
    • Humans have 22 pairs of autosomal chromosomes and one pair of sex chromosomes; females are XX and males are XY.

    Klinefelter and Turner Syndromes

    • Klinefelter syndrome (47,XXY) and Turner syndrome (45,X) result from nondisjunction during meiosis, leading to atypical sexual development.

    Triplo-X Syndrome

    • Triplo-X syndrome (47,XXX) features three X chromosomes; many individuals are normal, while some may show underdeveloped secondary sex characteristics. Possible sterility and cognitive impairment.

    XYY Syndrome

    • XYY syndrome (47,XYY) is characterized by tall stature (often over 6 feet) and potential subnormal intelligence; also associated with personality disorders.

    Y Chromosome Characteristics

    • Y chromosome is smaller and contains fewer genes than X chromosome.
    • Pseudoautosomal regions (PARs) on both ends of the Y chromosome allow for pairing with X during meiosis.

    Dosage Compensation

    • Dosage compensation balances the expression of X-linked genes between males and females.
    • Inactive X chromosomes condense into Barr bodies, which are present in females.

    Lyon Hypothesis

    • Lyon hypothesis states that X-inactivation is random in somatic cells early in embryonic development, resulting in uniform X-expression in descendant cells.
    • Example: Calico cats display varied fur patterns due to random X-inactivation affecting color genes.

    X-Inactivation

    • X-inactivation is the genetic mechanism explaining dosage compensation and follows the N - 1 rule, where N equals the total number of X chromosomes.

    X-Linkage

    • X-linkage refers to traits determined by genes on the X chromosome, differentiating them from autosomal traits.
    • Females can be homozygous or heterozygous for X-linked traits, while males are hemizygous (one dosage).

    Color Blindness

    • Red/green color blindness is a common X-linked trait in the USA, impacting males more frequently due to their single X chromosome.

    Modes of Sex Determination

    • XX/XO system: Gender determined by X chromosome dosage; female zygotes have two Xs, males have one X.
    • XX/XY system: Female gametes carry one X, while male gametes can carry either X or Y chromosomes.
    • ZZ/ZW system: Z chromosome (large) and W chromosome (small); females are ZW and males are ZZ. Example: Chickens.

    Homogametic and Heterogametic Sex

    • Homogametic sex has two identical chromosomes (e.g., females XX) and produces like gametes.
    • Heterogametic sex has two different chromosomes (e.g., males XY) and produces unlike gametes (50% X and 50% Y).

    Human Y Chromosome and Maleness

    • Human karyotype features 22 pairs of autosomes and one pair of sex chromosomes.
    • Females have XX chromosomes, while males have XY chromosomes, with the presence of the Y chromosome determining maleness.

    Klinefelter and Turner Syndromes

    • Klinefelter syndrome (47,XXY) and Turner syndrome (45,X) result from nondisjunction, leading to abnormal sexual development.
    • Nondisjunction is the failure of chromosomes to separate properly during meiosis.

    Triplo-X Syndrome

    • Characterized by the presence of three X chromosomes (47,XXX) and normal autosome count.
    • Can lead to underdeveloped secondary sex characteristics, sterility, and mental retardation in some cases, often due to nondisjunction.

    XYY Syndrome

    • Notable for males being often over 6 feet tall, along with possible subnormal intelligence and personality disorders.
    • Occurs from nondisjunction during meiosis, where Y chromosome sister chromatids fail to separate.

    Y Chromosome Characteristics

    • The Y chromosome is smaller and contains fewer genes compared to the X chromosome.
    • Pseudoautosomal regions (PARs) are found on both ends of the Y chromosome, allowing for pairing and recombination with the X chromosome during meiosis.

    Dosage Compensation Mechanism

    • Dosage compensation is a genetic mechanism to balance the gene expression of X chromosomes in both males and females.
    • Prevents excessive expression of X-linked genes, utilizing Barr bodies (inactive X chromosomes).

    Lyon Hypothesis and X-Inactivation

    • The Lyon Hypothesis states that X chromosome inactivation is random and occurs early in embryonic development.
    • Once an X chromosome is inactivated, all descendant cells retain that inactivation pattern, affecting traits like fur color in calico cats.
    • X-inactivation follows the N − 1 rule, where N is the total number of X chromosomes.

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    Description

    Explore the mechanisms of sex determination in this quiz covering Chapter 7 and Chapter 4. Learn about the XX/XO and XX/XY modes of sex determination, as well as the role of sex chromosomes and sex-linkage. Test your understanding of these foundational concepts in genetics.

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