G214 SU2 Sex Chromosomes

• What are the 2 categories of sex determination

  Genotypic and environmental
• What type of chromosomes characterize sex and are referred to as sex chromosomes

  heteromorphic
• What system is XX/XO

  Protenor
• What system is XX/XY

  Lygaeus
• What type of sex determination does insects (eg butterflies) have?

  XX/XO
• What type of sex determination does mammals and some insects have?

  XX/XY
• What type of sex determination does birds, fish, reptiles etc have?

  ZZ/ZW
• What type of sex determination does bees and ants have?

  Haplodiploidy
• What is a heterogametic sex?

  Forming different gametes, for example males
• What is a homogametic sex?

  Forming 1 type of gamete, for example females
• What determines the sex of a foetus?

  The male gamete
• What causes Klinefelter syndrome?

  More than 1 X chromosome with Y present
• What causes Turner syndrome?

  Only 1 X chromosome
• What is a pseudoautosomal region on the Y chromosome?

  Homology with X chromosome allowing recombination during meiosis
• Where is the pseudoautosomal region located on the Y chromosome?

  On the tips
• Where is the nonrecombining (male specific) region located on Y chromosome?

  In the middle
• Where is the sex determining region on Y?

  Between the nonrecombining and pseudoautosomal regions
• In which phase does dosage compensation occur?

  Interphase
• What is a sex chromatin body (Barr body)

  inactivated X chromosome
• What concept does the Lyon hypothesis support?

  Dosage compensation
• According to Lyon hypothesis, which stage does X deactivation occur?

  Blastocyst
• What is sex linkage?


  If the gene is on the X chromosome the female parent will have 2 copies of the gene and the male parent only one copy
• In sex linkage, males are not homozygous or heterozygous but

  hemizygous
• What are autosomal genes responsible for in sex linkage?

  existence of contrasting phenotypes
• What is sex limited?


  Both sexes carry the alleles for a trait but they are only expressed in one sex and no penetrance in the other
• What is sex influenced?


  Sex of individual influences the expression of phenotype that is not limited to one sex, therefore dependent on hormone constitution which results in a higher penetrance in one or other sex
• Does Y chromosome play a role in sex determination in drosophila?

  1. Offspring produced by female with nondisjunction of X chr during meiosis
  2. Progeny of triploid females
• What is XXY classified as

  trisomic female
• What is XO classified as

  monosomic sterile male
• Does Y chr cause maleness in drosophila?

  No
• What is the formula for triploid?

  3n
• Sex determination in drosophila

  Ratio of X chr to the number of haploid sets of autosomes determines sex
• What determines sex in drosophila?

  Lack of X chromosome and genes on autosomes
• What determines femaleness in drosophila?

  Extra X chr and genes on X chr
• What is the genic balance theory

  Threshold for maleness is reached when X:A ratio is 1:2 (0.5)
• What is the sex-lethal X linked gene

  Activation of gene if sex ratio = 1.0 (female) and non-activation of gene if sex ratio < 1.0 (male)
• Dosage compensation in drosophila

  No X chr inactivatioon and transcription of male X linked genes doubles
• What is environmental sex determination

  Sex is governed by internal and external environmental conditions
• What animals rely on temperature dependent sex determination

  Crocodiles, turtles and lizards
• What has an effect on sex differentiation with temperature dependent sex determination

  Effects on temperature on androgens, estrogens and their synthesis enzymes