Chapter 5 Sex Determination and Sex Chromosomes

What are the two main types of reproductive modes in organisms?

Asexual reproduction and sexual reproduction.

What is the significance of meiosis in sexual reproduction?

Meiosis produces gametes for fertilization and contributes to sexual differentiation.

What are sex chromosomes?

Heteromorphic or dissimilar chromosomes (e.g., XY in mammals) that characterize one sex or the other.

Who first linked X and Y chromosomes to sex determination?

Edmund B. Wilson in 1906.

What did Wilson discover about female and male somatic cells in Protenor?

Females have 14 chromosomes with two X chromosomes, while males have 13 chromosomes with one X chromosome.

How do fertilization outcomes differ based on sperm type in Protenor?

Fertilization by X-bearing sperm results in female offspring, while X-deficient sperm results in male offspring.

What is the difference in chromosome composition between male and female somatic cells in Lygaeus?

Females have 14 chromosomes with two X chromosomes, while males have 14 chromosomes with one X and one Y chromosome.

What is the homogametic and heterogametic sex in Protenor and Lygaeus?

Females are homogametic (XX), and males are heterogametic (XY).

What does the Y chromosome determine in humans?

Maleness.

What is Klinefelter syndrome?

A condition in males with a 47,XXY karyotype, resulting in rudimentary testes and male genitalia but often no sperm production.

What are the characteristics of Turner syndrome?

A condition in females with a 45,X karyotype, resulting in rudimentary ovaries, short stature, and normal intelligence.

What happens in the absence of a Y chromosome during sexual differentiation?

The cortex of the gonadal ridge forms ovarian tissue.

What is the 47,XXX syndrome?

A condition where females have three X chromosomes, often resulting in normal differentiation but can include underdeveloped secondary sex characteristics.

What is the 47,XYY condition?

A condition where males have an additional Y chromosome, often associated with tall stature and potential behavioral issues.

What is the role of the Y chromosome in early embryonic development?

It houses genetic information for maleness and signals the development of testes.

How many genes does the Y chromosome have compared to the X chromosome?

The Y chromosome has at least 75 genes, while the X chromosome has 900-1400 genes.

What is the gonadal phenotype during the early embryonic development period?

It is sexually indifferent (hermaphroditic) until the 5th week.

What occurs by the 5th week of embryonic development regarding gonadal ridges?

Gonadal ridges form either ovaries or testes, depending on the presence of the Y chromosome.

What are pseudoautosomal regions (PARs)?

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

What is the significance of the pairing region in male gametogenesis?

It is critical for the segregation of X and Y chromosomes.

What does MSY stand for in genetics?

Male-Specific Region of Y.

What are the two types of regions in the Male-Specific Region of Y (MSY)?

Euchromatic regions (functional genes) and heterochromatic regions (lacking genes).

What is the SRY gene and its role?

The SRY gene, located adjacent to the PAR on the Y chromosome, is critical for controlling sexual development and is not found on the X chromosome.

What does the Testis-Determining Factor (TDF) do?

The TDF, encoded by the SRY gene, triggers the formation of testes in all mammals.

What anomaly can occur in sex determination related to the SRY gene?

Males can have two X chromosomes and no Y chromosome if one X contains the SRY gene.

Why is the male-to-female birth ratio not equal?

Despite equal production of X- and Y-bearing sperm, the reasons for the discrepancy are still under investigation.

What is dosage compensation?

A mechanism that balances the expression of X chromosome genes in both males and females.

What are Barr Bodies?

Inactive X chromosomes that are highly condensed and lie against the nuclear envelope in interphase cells.

How many Barr bodies are present in a normal female and male?

Normal females have one Barr body (XX), while normal males have none (XY).

What is the N - 1 rule regarding Barr bodies?

The number of Barr bodies is equal to the number of X chromosomes minus one.

What is the Lyon hypothesis?

The hypothesis that X chromosome inactivation is random in somatic cells early in embryonic development.

What is an example of the Lyon hypothesis in cats?

Heterozygous female cats show mottled coat colors due to different X chromosomes being inactivated in adjacent patches of cells.

What is the mechanism of X chromosome inactivation?

It involves chemical modifications of DNA and histone proteins, silencing most genes on the inactivated chromosome.

What is the X-inactivation center (Xic)?

A major control unit on the X chromosome that regulates inactivation, consisting of the XIST gene.

What determines sex in Drosophila despite the presence of a Y chromosome?

The Y chromosome has no role in sex determination in Drosophila.

What is Temperature-Dependent Sex Determination (TSD)?

A mechanism where environmental temperature influences sex determination in reptiles.

What are the three patterns of temperature sex determination in reptiles?

1) Low temperatures yield 100% females; high temperatures yield 100% males. 2) The opposite occurs. 3) Low and high temperatures yield 100% females; intermediate temperatures yield various proportions of males.