Questions and Answers
What does the XX/XY mode of sex determination indicate about female and male gametes?
What chromosomal arrangement characterizes female mammals?
XX
What chromosomal arrangement characterizes male mammals?
XY
The ZW sex determination system has males with ZW chromosomes.
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What are Klinefelter and Turner syndromes characterized by?
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Triplo-X syndrome involves three Y chromosomes.
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In humans, how many pairs of autosomal chromosomes are present?
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The Y chromosome is _____ compared to the X chromosome.
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What is the primary characteristic of individuals with 47,XXX syndrome?
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Males are consistently characterized by the 47, _____ syndrome.
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What is dosage compensation?
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What is a Barr body?
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All females are homogametic.
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In X-inactivation, what is the rule followed?
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A trait controlled by genes on the sex chromosome (X) is called _____ linkage.
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What is the genetic status of males in terms of gene dosage on the X chromosome?
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What determines the sex of offspring in the XX/XO mode of sex determination?
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What describes the homogametic sex in mammals?
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How do heterogametic sexes in mammals differ from homogenetic sexes?
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In the ZZ/ZW sex determination system, which statement is true about male gametes?
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How many X chromosomes must be present in a zygote for female offspring to be produced in the XX/XY sex determination system?
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Which statement accurately describes the role of the Y chromosome in humans?
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What is the chromosomal arrangement of males in terms of sex chromosomes?
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What defines the primary characteristic of the ZZ/ZW sex determination system in birds?
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In the context of ZW sex determination in birds, what is the heterogametic sex?
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Which of the following is NOT true about the XX/XY mode of sex determination?
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What genetic anomaly is primarily associated with having three X chromosomes?
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Which syndrome is characterized by a male having two Y chromosomes?
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Which of the following syndromes is most likely to occur due to nondisjunction of X chromosomes during meiosis?
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Individuals with Klinefelter syndrome are characterized by which of the following chromosomal configurations?
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What is a common feature shared by individuals with Triplo-X syndrome?
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What is the typical height characteristic associated with the 47,XYY syndrome?
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What aspect of the Y chromosome is highlighted in its comparison to the X chromosome?
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What is a noted mental health issue associated with the XYY syndrome?
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What is the primary function of dosage compensation in mammals?
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What characterizes Barr bodies in human somatic cells?
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What does the Lyon Hypothesis state about X chromosome inactivation?
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Which of the following best exemplifies the Lyon Hypothesis in practice?
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How does X-inactivation contribute to dosage compensation?
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What is the N − 1 rule in the context of X-inactivation?
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What occurs to the X chromosome during the early stages of embryonic development, according to the Lyon Hypothesis?
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In terms of genetic mechanisms, what role do Barr bodies play in females?
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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.
