Chapter 7 Flashcards
heteromorphic, chromosomes
Dissimilar chromosome pairs that characterize one sex or the other in a wide range of species, e.g., XY in mammals and ZW in chickens.
Y chromosome
The sex chromosome in species where the male is heterogametic (XY).
heterogametic sex
The sex that produces gametes containing unlike sex chromosomes. In mammals, the male is the heterogametic sex.
homogametic sex
The sex that produces gametes with identical sex-chromosome content; in mammals, the female is homogametic.
ZZ/ZW
Sex-determining chromosomes in animals such as chickens, frogs, and certain fish, where the maleness is determined by homomorphic chromosomes (ZZ) and females by heteromorphic chromosomes (ZW).
nondisjunction
A cell division error in which homologous chromosomes (in meiosis) or the sister chromatids (in mitosis) fail to separate and migrate to opposite poles; responsible for defects such as monosomy and trisomy.
mosaics
Refers to individuals with cell types that contain different karyotypes (for example, in Turner syndrome, cells with 45,X and cells with 46,XY) and thus often show mixed phenotypes for a particular genetic condition compared with non-mosaics (for example, 45,X individuals with Turner syndrome).
gonadal (genital) ridges
In mammalian embryos, a precursor to gonads are the gonadal or genital ridges, described as bipotential gonads because they can develop into male or female gonads based on genetic and hormonal influences.
bipotential gonads
In mammalian embryos, a precursor to gonads are the the gonadal or genital ridges, described as bipotential gonads because they can develop into male or female gonads based on genetic and hormonal influences.
pseudoautosomal regions
(PARs) A region on the human Y chromosome that is also represented on the X chromosome. Genes found in this region of the Y chromosome have a pattern of inheritance that is indistinguishable from genes on autosomes.
male-specific region of the Y chromosome
(MSY) Region of the Y-chromosome that does not recombine with the X-chromosome; contains a majority of genes specific to the Y-chromosome.
sex-determining region Y chromosome
(SRY) Essential gene on the human Y chromosome that controls male sexual development; encodes TDF protein.
testis-determining factor
(TDF) Protein encodes by SRY gene; causes bipotential gonads of an embryo to form testes.
Müllerian inhibiting substance
(MIS) Protein produced by the developing mammalian testis; causes atrophy of embryonic tissue (Müllerian duct) that forms female reproductive tissues.
primary sex ratio
(PSR) Ratio of males to females at fertilization, often expressed in decimal form (e.g., 1.06).
secondary sex ratio
The ratio of males to females at birth, usually expressed in decimal form (e.g., 1.05).
Barr body
sex chromatin body
Densely staining DNA-positive mass seen in the somatic nuclei of mammalian females. Discovered by Murray Barr, this body represents an inactivated X chromosome.
Lyon hypothesis
The proposal that there is random inactivation of the maternal or paternal X chromosome in somatic cells of mammalian females early in development. All daughter cells will have the same X chromosome inactivated as in the cell they descended from, producing a mosaic pattern of expression of X chromosome genes
clone
Identical molecules, cells, or organisms derived from a single ancestor by asexual or parasexual methods; for example, a DNA segment that has been inserted into a plasmid or chromosome of a phage or a bacterium and replicated to produce many copies, or an organism with a genetic composition identical to that used in its production
genomic imprinting
The process by which the expression of an allele depends on whether it has been inherited from a male or a female parent.
epigenetics
The study of the effects of reversible chemical modifications to DNA and/or histones on the pattern of gene expression. Epigenetic modifications do not alter the nucleotide sequence of DNA.
X-inactivation center
(Xic) Region of the p-arm of the X-chromosomes in humans which produces a non-coding RNA (Xist) that is essential for X-inactivation mechanisms.
X-inactive specific transcript
(Xic) Region of the p-arm of the X-chromosomes in humans which produces a non-coding RNA (Xist) that is essential for X-inactivation mechanisms.
transgenes
A DNA sequence, often containing a gene or part of a gene, which is isolated from one organism and introduced into a different organism or cells of a different organism.
metafemales
In Drosophila, a poorly developed female of low viability with a ratio of X chromosomes to sets of autosomes that exceeds 1.0. Previously called a superfemale.
metamales
In Drosophila, a poorly developed male of low viability with a ratio of X chromosomes to sets of autosomes that is below 0.5. Previously called a supermale.
genic balance theory
In Drosophila, sex is determined by the ratio of X-chromosomes and autosomes.
RNA splicing
The processing of a nascent transcript of RNA by the removal of introns and the joining together of exons.
alternative splicing
Generation of different protein molecules from the same pre-mRNA by incorporation of a different set and order of exons into the mRNA product.
primordial germ cells
(PGCs) Precursor cells in the early embryo that migrate into gonads and develop to form gametes.
Facts about the Y-chromosome
Y chromosome has at least 75 genes
Fewer genes than X chromosome (900 – 1400 genes)
Located adjacent to PAR of the short arm of Y chromosome
Controls male development
Encodes protein: Testis-determining factor (TDF)
MSY on the Y-chromosome
Male-specific region of the Y
Nonrecombining region of Y chromosome
Encodes proteins specific to development and function of testis
Txis
Prevents X-chromosome compaction on one X-chromosome
