Sex Determination and Sex Chromosomes

Vocabulary flashcards related to sex determination and sex chromosomes, covering topics from phenotypic dimorphism to temperature-dependent sex determination.

Phenotypic Dimorphism

Differences in physical shape between the sexes in animals.

Heteromorphic Chromosomes

Dissimilar chromosomes, such as sex chromosomes X and Y.

Sex Chromosomes

Chromosomes that characterize one sex or the other in a wide range of species.

Sex Determination

Determination of sex by specific genes, not entire chromosomes.

Homogametous

Producing like gametes; zygotes with two X chromosomes, resulting in female offspring (e.g., Protenor and Lygaeus).

Heterogametous

Producing unlike gametes; zygotes with one X and one Y chromosome, resulting in male offspring (e.g., Protenor and Lygaeus).

Klinefelter Syndrome

A human abnormality (47,XXY) characterized by tall stature, long arms and legs, rudimentary testes, and often feminine development.

Turner Syndrome

A human abnormality (45,X) characterized by phenotypically female traits, underdeveloped breasts, short stature, and cognitive impairment.

Gonadal Primordia

The tissues that will form the gonad during early embryonic development.

Bipotential Gonads

Gonads in the early embryo (5th week) that can form either ovaries or testes.

Pseudoautosomal Regions (PARs)

Regions present on both ends of the Y chromosome that share homology with regions on the X chromosome, allowing them to synapse and recombine during meiosis.

Male-Specific Region of the Y (MSY)

The nonrecombining region of the Y chromosome.

Sex-Determining Region Y (SRY)

A gene located adjacent to the PAR of the short arm of the Y chromosome that controls male development; encodes the testis-determining factor (TDF).

Testis-Determining Factor (TDF)

A protein encoded by the SRY gene that triggers testes formation in XY embryos around 6–8 weeks of development.

Primary Sex Ratio

Reflects the proportion of males to females conceived in a population.

Secondary Sex Ratio

Reflects the proportion of each sex born.

Dosage Compensation

A genetic mechanism that balances the dose of X chromosome gene expression in males and females, preventing excessive expression of X-linked genes.

Barr Bodies

Inactive X chromosomes that are highly condensed and darkly stained in interphase nerve cells; a mechanism for dosage compensation.

Lyon Hypothesis

The inactivation of the X chromosome is random and occurs in somatic cells at an early stage of embryonic development; all descendant cells have the same X-inactivation.

X Inactivation Center (Xic)

A region active only on the inactive X chromosome, containing the X-inactive specific transcript (XIST) gene critical for X inactivation.

X-Inactive Specific Transcript (XIST)

A gene within the Xic that is critical for X inactivation; RNA might physically interfere with gene transcription.

Temperature-Dependent Sex Determination (TSD)

A mode of sex determination in reptiles where the incubation temperature of eggs during embryonic development determines sex.