MBG: BLOCK 2: TOPIC 6: SEX-LINKED HEREDITY AND SEX DETERMINATION
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Questions and Answers

What term describes an organism that has two of the same type of sex chromosomes?

  • Hemizygous
  • Heterogametic
  • Homogametic (correct)
  • Haploinsufficient

    • In temperature-dependent sex determination, which factor is typically crucial for determining the biological sex of offspring?

  • Incubation temperature (correct)
  • Parental age
  • Nutritional availability
  • Photoperiod

    • How does climate change potentially affect the sex ratios of certain reptiles like turtles?

  • By shifting the incubation temperatures of eggs (correct)
  • By changing the geographic distribution of species
  • By increasing the number of offspring produced
  • By altering the mating rituals of males

    • What is the primary difference between X-linked and Y-linked inheritance?

    <p>X-linked traits can be expressed in both males and females.</p> Signup and view all the answers

    Which of the following is a characteristic of mammals regarding sex determination?

    <p>Sex determination is primarily chromosomal.</p> Signup and view all the answers

    What characterizes genic sex determination?

    <p>Involves multiple genes determining sex without visible sex chromosomes.</p> Signup and view all the answers

    How does temperature affect sex determination in reptiles like turtles?

    <p>Warmer temperatures lead to increased female production.</p> Signup and view all the answers

    What is the concept of sequential hermaphroditism?

    <p>An organism can change its sex depending on environmental factors.</p> Signup and view all the answers

    In mammals, which sex is typically heterogametic?

    <p>Males, with XY sex chromosomes.</p> Signup and view all the answers

    Which of the following statements accurately describes temperature-based sex determination in alligators?

    <p>Colder temperatures produce more females while warmer temperatures create more males.</p> Signup and view all the answers

    Which factor influences the sex ratios in certain species as global temperatures rise?

    <p>Rising temperatures can skew sex ratios towards one gender.</p> Signup and view all the answers

    What term describes a chromosome configuration where an organism has two different sex chromosomes?

    <p>Heterogametic.</p> Signup and view all the answers

    What mechanism must occur to ensure proper gene dosage for certain genes on the X chromosome?

    <p>X chromosome inactivation must take place.</p> Signup and view all the answers

    Which reproductive strategy describes organisms that do not have distinguishable sex chromosomes?

    <p>Genic sex determination.</p> Signup and view all the answers

    How do environmental factors influence sex determination in slipper limpets?

    <p>They exhibit sequential hermaphroditism based on environmental changes.</p> Signup and view all the answers

    What happens to ZZ individuals if they are incubated at high temperatures?

    <p>They develop as phenotypically female.</p> Signup and view all the answers

    At what temperature do male crocodiles typically develop?

    <p>32-33°C</p> Signup and view all the answers

    How does global warming impact sex determination in species that rely on temperature for sex determination?

    <p>It disrupts the reproductive potential of these species.</p> Signup and view all the answers

    Which of the following is essential for male mammalian sex determination?

    <p>The activation of the SRY gene</p> Signup and view all the answers

    What is the consequence of losing key genes from the Y chromosome in an XY individual?

    <p>They can develop as phenotypically female.</p> Signup and view all the answers

    What initiates the development of testes in mammals?

    <p>Activation of the SRY gene</p> Signup and view all the answers

    Which of the following statements about the pseudoautosomal region (PAR) is true?

    <p>PARs are regions of crossing over during male meiosis.</p> Signup and view all the answers

    What is a hallmark of X-linked inheritance as demonstrated by Morgan's fruit fly experiments?

    <p>Differential expression of traits between genders.</p> Signup and view all the answers

    What was one of the main goals of Thomas Hunt Morgan’s experiments?

    <p>To demonstrate gene linkage.</p> Signup and view all the answers

    In the absence of the SRY gene, which reproductive organs are most likely to develop?

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

    What does hemizygous mean in the context of male inheritance patterns?

    <p>Males have only one copy of certain genes on the X chromosome.</p> Signup and view all the answers

    What kind of inheritance pattern is primarily associated with the X chromosome?

    <p>X-linked inheritance</p> Signup and view all the answers

    Study Notes

    Terminology

    • Sex Chromosomes: Chromosomes that determine biological sex and influence secondary sexual characteristics.
    • Homogametic: Individuals with gametes containing the same sex chromosomes.
    • Heterogametic: Individuals with gametes containing different sex chromosomes.
    • Hemizygous: Containing only one copy of a chromosome that is typically observed in a pair.
    • Haploinsufficiency: Loss of one copy of a gene results in insufficient product, leading to reduced function.
      • Genes exclusive to the Y or X in humans are NOT haploinsufficient as proper gene dosage is 1.
    • Nondisjunction: Failure of chromosomes to separate properly during meiosis, resulting in an abnormal number of chromosomes in gametes.

    Sex Chromosomes and Sex Determination

    • Sex determination can vary across organisms.
    • Difference in biological sex is established by key genes.
    • Sex chromosomes do not always involve two distinct chromosome types.
      • Humans: XX (female) vs XY (male)
      • Grasshoppers: XX (female) vs XO (male) - males have fewer chromosomes.
    • In organisms with unequal chromosome numbers, meiosis results in gametes with unequal chromosome counts.

    Heterogametic Sex

    • The sex with two different sex chromosomes.
    • ZZ vs ZW: In many species, the female is the heterogametic sex (ZW).
      • Found in birds, snakes, butterflies, amphibians, and some fish.

    XY Heredity (Humans)

    • Males are heterogametic (XY).
    • X and Y can pair during meiosis due to structural similarity (regions of homology).
      • Pseudoautosomal regions.
    • Crossing-over occurs in these regions.
    • These homologous regions contain genes that are NOT inactivated in women, ensuring proper gene dosage.

    Sex Determination without Sex Chromosomes

    • Biological sex can be determined by genes or the environment, even in the absence of sex chromosomes.
    • Genic Determination: Genes at specific loci determine sex.
    • Environmental Sex Determination: Environment partially or completely determines sex.
      • Example: Slipper limpet (Crepidula fornicata) - sequential hermaphroditism.
      • Example: Reptiles including turtles, crocodiles, and alligators.
        • Temperature-based sex determination.
        • Turtles: warmer temperatures = females, colder temperatures = males
        • Alligators: colder temperatures = females, warmer temperatures = males

    Global Warming and Sex Determination

    • Increasing global temperatures are affecting male:female ratios in temperature-dependent sex determination, potentially impacting reproductive potential.

    Mammalian Biological Sex Determination

    • Genes on the Y chromosome are crucial for testes development.
      • Loss of these genes in an XY individual leads to female phenotypic development.
      • Presence of a small portion of the Y chromosome in XX individuals can cause male phenotypic development, indicating a small region of the chromosome is vital for sex determination.

    Human Biological Sex Determination

    • SRY gene on the Y chromosome triggers testes development.
      • Transcription factor activated at around 6 weeks of development.
      • Before SRY activation, gonads are undifferentiated.
    • Testes secrete testosterone (promotes male characteristics) and Mullerian Inhibitory Substance (MIS) (suppresses female reproductive ducts).
    • In the absence of SRY, ovaries develop (estrogen and no MIS).
    • Improper gene activity can hinder development and lead to sterility.

    The X and Y Chromosomes

    • Contain genes not associated with sexual development.
    • Inheritance of these genes does not follow Mendel's laws.
    • Males in XY inheritance are hemizygous for genes on the X chromosome.

    Pseudoautosomal Regions

    • Located on the distal ends of the short and long arms of X and Y chromosomes.
    • These regions contain highly similar DNA sequences (PAR1 & PAR2).
    • Crossing-over occurs in these regions during male meiosis.
    • All genes within PAR1 are NOT inactivated in women, ensuring proper gene dosage.
    • High recombination frequency in PAR1.

    Sex-Linked Inheritance

    • Inheritance patterns for genes on sex chromosomes differ from those on autosomes.
    • Most sex-linked inheritance is X-linked, due to the X chromosome having more genes.
    • Results in differential expression of traits between males and females.

    Morgan’s Fruit Fly Experiments

    • Demonstrated X-linked inheritance and differential expression of traits between males and females.
    • Parental Generations:
      • Red-eyed female x White-eyed male: All offspring red-eyed (no difference between males and females).
      • White-eyed female x Red-eyed male: All females red-eyed, all males white-eyed.
    • F1 Crosses:
      • Heterozygous female x Red-eyed male: All females red-eyed, half the males white-eyed.
      • Heterozygous female x White-eyed male: 50% red-eyed males and females, 50% white-eyed males and females.
    • The discrepancy between males and females in phenotype presentation is a hallmark of X-linked inheritance.

    Morgan’s Fruit Fly Experiments Summary

    • Sex-linked inheritance based on mutations observed in males only.
    • Gene linkage based on the inheritance of genes as a single unit.
    • Chromosome mapping based on recombination frequencies between linked genes.

    X-Linked Inheritance in Humans

    • Can cause various genetic disorders, including hemophilia and color blindness.

    Nondisjunction

    • Can lead to sex chromosome aneuploidy (abnormal number of sex chromosomes).
    • Impact on genotype and phenotype depends on the specific chromosomes involved and the dosage of genes.

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    Related Documents

    Sex-Linked Heredity and Sex Determination BMS 532 PDF

    Description

    Test your knowledge on sex chromosomes and their role in biological sex determination. This quiz covers key terms such as homogametic, heterogametic, and nondisjunction. Explore the complexities of chromosome behavior during meiosis and how it affects genetic functions.

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