Sex Determination in Mammals
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Questions and Answers

Which duct system is associated with the development of testes?

  • Müllerian duct
  • Wolffian duct (correct)
  • Oviduct
  • Cloacal duct

    • What role do Lhx9 and Gata4 play in gonadal sex determination?

  • They function solely in the development of Wolffian ducts
  • They promote only ovary formation
  • They inhibit the SRY gene
  • They activate Wnt and Rspo1 (correct)

    • What does the SRY gene influence in male sex determination?

  • Initiates gonadal sex differentiation (correct)
  • Promotes Wolffian duct formation
  • Inhibits Müllerian duct development
  • Regulates hormone levels only

    • What is the primary role of the Y chromosome in male sex determination?

    <p>It initiates the development of testes.</p> Signup and view all the answers

    Which of the following best defines primary sex determination?

    <p>Determined by the chromosomal constitution.</p> Signup and view all the answers

    What outcome is associated with XX humans who have RSPO1 mutations?

    <p>They develop as phenotypic males</p> Signup and view all the answers

    What happens in XY individuals with a duplication of the region containing WNT4 and RSPO1?

    <p>Male-to-female sex reversal occurs</p> Signup and view all the answers

    What is true about individuals with XY chromosomes?

    <p>They usually develop testes and produce sperm.</p> Signup and view all the answers

    What does the term 'bipotential' refer to in early embryonic gonads?

    <p>The potential to differentiate into testes or ovaries.</p> Signup and view all the answers

    What is secondary sex determination primarily influenced by?

    <p>The level of hormones and responses to them.</p> Signup and view all the answers

    What is the primary role of estrogens in females during secondary sex determination?

    <p>Differentiation of Müllerian ducts</p> Signup and view all the answers

    Which phenotype is associated with individuals who are XXY?

    <p>They are males with testes structures.</p> Signup and view all the answers

    What effect does testosterone have on the development of male genitalia?

    <p>It promotes the development of Wolffian ducts.</p> Signup and view all the answers

    Why is the second X chromosome critical in the context of sex determination?

    <p>It is necessary for ovarian development.</p> Signup and view all the answers

    Which of the following is a potential application of stem cells?

    <p>Disease modeling.</p> Signup and view all the answers

    What is the result of the secretion of Müllerian-inhibiting substance by Sertoli cells in males?

    <p>Regresses the Müllerian ducts.</p> Signup and view all the answers

    What distinguishes primary sex determination from secondary sex determination?

    <p>Primary sex determination is chromosomal, whereas secondary is hormonal and phenotypic.</p> Signup and view all the answers

    How do females compensate for having two X chromosomes compared to males in terms of gene transcription?

    <p>Through X-chromosome inactivation.</p> Signup and view all the answers

    What primary sex characteristic is typically present in individuals with androgen insensitivity syndrome?

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

    In which taxonomic group is sex determination primarily influenced by temperature during embryonic development?

    <p>Turtles and crocodilians</p> Signup and view all the answers

    What process is primarily responsible for gonadal differentiation into either testes or ovaries?

    <p>Primary sex determination influenced by genetic and chromosomal factors.</p> Signup and view all the answers

    What is primarily affected in individuals with Androgen Insensitivity Syndrome (AIS)?

    <p>Recognition of testosterone by cells.</p> Signup and view all the answers

    What key function does dihydrotestosterone (DHT) serve in male development?

    <p>Facilitates testicular descent.</p> Signup and view all the answers

    Which of the following statements about secondary sex determination is accurate?

    <p>It pertains to hormonal levels and responses to those hormones.</p> Signup and view all the answers

    What is the difference between primary and secondary sex determination?

    <p>First involves hormone production, while second involves development of sex characteristics.</p> Signup and view all the answers

    In terms of sex determination systems, which of these is not typically characterized as an example of environmental sex determination?

    <p>Chromosomal sex determination in mammals.</p> Signup and view all the answers

    What is the role of the Sry gene on the Y chromosome?

    <p>Initiates testis formation in mammals</p> Signup and view all the answers

    What result occurs when the Sry gene is translocated to the X chromosome in an XX individual?

    <p>Testis formation is initiated</p> Signup and view all the answers

    What primary sexual characteristic is expected in an XX/Sry mouse?

    <p>Testis formation</p> Signup and view all the answers

    Which of the following statements about men with ovotestes is true?

    <p>Sry activation later than normal can result in their formation</p> Signup and view all the answers

    What does secondary sex determination involve?

    <p>Hormonal response from testes and ovaries</p> Signup and view all the answers

    What is a characteristic of the external genitalia in an XX/Sry mouse compared to an XY mouse?

    <p>They are essentially the same</p> Signup and view all the answers

    What effect does the presence of two X chromosomes have on the seminiferous tubules in an XX mouse with Sox9 transgene?

    <p>They will lack sperm production</p> Signup and view all the answers

    What happens in mammals when Sry is activated late during development?

    <p>Both ovarian and testicular tissues can form</p> Signup and view all the answers

    Study Notes

    Sex Determination in Mammals

    • The presence of a Y chromosome initiates the development of testes.
    • The gonads in early embryonic mammals are bipotential meaning they can develop into either testes or ovaries.
    • The Y chromosome contains the SRY gene, which is a transcription factor that activates the Sox9 gene.
    • Sox9 is a key gene for testis formation.
    • In the absence of a Y chromosome, the gonads develop into ovaries. During this process, a transcription factor called Wnt4 is activated, which inhibits Sox9 expression.
    • The presence of WNT4 and RSPO1 genes on chromosome 1 can cause a male-to-female sex reversal.

    Secondary Sex Determination in Mammals

    • Secondary sex determination in mammals is regulated by hormones secreted by the testes and ovaries.
    • These hormones influence the development of male or female phenotypes, including the internal reproductive organs, external genitalia, and other secondary sexual characteristics.
    • Testosterone determines male secondary sex determination, and estrogens determine female secondary sex determination.

    Environmental Sex Determination

    • Some animals, like reptiles, use temperature cues to determine sex.
    • This mechanism is known as temperature-dependent sex determination (TSD).
    • The sex of the offspring is determined by the temperature at which the embryos are incubated during a specific period of development.
    • Some reptile species, like turtles and crocodilians, have a specific temperature range for male development and another range for female development.
    • Different species have different temperature thresholds for sex determination.

    Key Takeaways

    • Sex determination in mammals is a complex process involving genetic and hormonal cues.
    • Primary sex determination depends on the presence or absence of the Y chromosome.
    • Secondary sex determination is regulated by specific hormones, resulting in male or female phenotypes.
    • Environmental sex determination, seen in reptiles and some other species, uses temperature as a cue for determining sex.

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    Related Documents

    L9 Sex Determination Lecture Notes PDF

    Description

    Explore the mechanisms of sex determination in mammals, focusing on the role of the Y chromosome and key genes such as SRY and Sox9. Understand how hormones influence secondary sex characteristics and the implications of gene interactions in sex reversal. Ideal for biology students studying mammalian development.

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