Chapter 4 Flashcards
Sex
refers to sexual genotype; male or female; XX or XY (not including rare exceptions)
Sex Determination
the mechanism by which sex is established; the sex of an individual organism refers to it’s phenotype;
sometimes an individual can have genes that are associated with one sex but a morphology corresponding to the opposite sex
Sex Chromosome
a pair of chromosomes in many organisms that differ between males and females
Autosome
nonsex chromosomes, which are the same for males and females
Heterogametic Sex
males, because males produce 2 different types of gametes with respect to the sex chromosomes
Homogametic Sex
females, because females produce gametes that are all the same with respect to the sex chromosomes
Pseudoautosomal Region
a small region that allows the X and Y chromosomes to pair and segregate into different cells, in which they have the same genes; it’s essential for the X-Y pairing in meiosis for the male;
in humans, there are pseudoautosomal regions at both tips of the X and Y chromosomes (on the telomeres)
Sex-Determining Region Y (SRY) Gene
the male-determining gene in humans; it encodes a transcription factor (a protein) that binds to the DNA and stimulates other genes that promote the differentiation of the testes
it is not the entire Y chromosome that determines the sex of an organism, it is only this gene
males with XX chromosomes have this gene, females with XY chromosomes do not
Sex-Linked Characteristics
characteristics determined by genes located on the sex chromosomes
X-Linked Characteristics
genes on the X chromosome; most sex-linked characteristics found are X-linked
Y-Linked Characteristics
genes on the Y chromosome; Y chromosome typically contains little genetic information
Hemizygosity
Possession of a single allele at a locus
males of organisms with XX-XY sex determination are hemizygous for X-linked loci because their cells only possess a single X chromosome
Nondisjunction
failure of homologous chromosomes or sister chromatids to separate in anaphase in either mitosis or meiosis
Dosage Compensation
equilizes the amount of protein produced by X-linked genes in the 2 sexes
it is necessary for species with XX-XY sex determination because females produce 2x as much gene product as males
gene product (proteins) play a crucial role in development
Barr Body
darkly staining body in the nuclei; found in cells of female placental mammals; it is an inactivated X chromosome
females are hemizygous at the cellular level for X-linked genes; cells in these females are not identical with respect to the expression of genes on the X chromosome; females are mosaics for the expression of X-linked genes