Chapter 3: Sex Determination Mechanisms in Humans and Animals

Non-chromosomal sex determination

Sex determined by environmental factors, not chromosomes.

Temperature-dependent sex determination

Sex determined by incubation temperature during development.

Population-dependent sex determination

Sex determined by social structure within a population.

Blue-headed wrasse

Fish species with unique male-female transformation. When head male dies, largest female becomes male.

Chromosomal sex determination

Sex determined by specific chromosomes present.

Platypus sex chromosomes

Females: 10 Xs; Males: 5 Xs, 5 Ys.

Lygaeus mode

Most common XX/XY heterogametic sex determination system.

Protenor mode

XX/XO system; no Y chromosome present.

Homogametic sex

Produces gametes with identical sex chromosomes. XX.

Heterogametic sex

Produces gametes with different sex chromosomes. XY.

Human chromosomal sex determination

Determined by presence of X and Y chromosomes.

Klinefelter syndrome

47,XXY; male with extra X chromosome.

Turner syndrome

45,X; female with missing second X chromosome.

Jacob's syndrome

47,XYY; male with extra Y chromosome.

Y chromosome function

Presence determines maleness in humans.

Barr bodies

Visible in Interphase eon nucleus. Inactive X chromosomes (except one) in female cells. Creates Dosage compensation.

Dosage compensation

Equal expression of X-linked genes in females.

Mary Lyon hypothesis

Random X inactivation in early embryonic development. All descendants from each cell will have same X chromosome inactivated. Females become mosaics for all heterozygous X-linked loci.

Tortoiseshell cat

Female with orange and black fur patches. X linked. XXY

Calico cat

Tortoiseshell with additional white spotting due to expression of separate white spotting gene.

Anhidrotic ectodermal dysplasia

X-linked disorder causing lack of sweat glands in males and mosaic skin in females with. Affects hair and nails too.

X-linked inheritance

Traits determined by genes on X chromosome.

Drosophila white locus

Gene affecting eye color in fruit flies. Thomas H. Morgan

Punnett square

Tool for predicting genetic cross outcomes.

ZW system in birds

Females are ZW; males are ZZ.

Ca+ allele in peacocks

Z-linked allele causing blue feather color while ca allele causes cameo color.

Scalloped mutation in Drosophila

X-linked mutation causing irregular wing margins.

Sex-determining region of Y (SRY)

locus that controlsmale sexual development in humans

Primary and secondary pseudoautosomal region (PAR)

only area where X and Y chromosomes are homologous

holandric traits

Traits that are linked to genes in the nonpseudoautosomalregions (non-PAR) of the Y chromosome. Only in males.

Mosaics