ch 8 g

What is a unisexual organism?

An organism containing only male or female reproductive organs.

What is a hermaphrodite?

An organism containing both male and female reproductive organs that can produce both types of gametes.

What is a supermale and super female?

Supermale = 47,XYY; Super female = 47,XXX.

What is a Barr body?

A highly condensed, inactivated X chromosome.

What is primary sexual differentiation?

Present at birth (the reproductive organs and genitalia) and further matured during puberty (such as the growth of the testes, penis, uterus, and ovaries)

What is secondary sexual differentiation?

Features that emerge later during puberty (such as facial hair, voice deepening, breast development, and hip rounding)

Differentiation involving the overall appearance of an organism, including mammary glands and external genitalia.

Does sex determination occur the same way in all species?

No, sex determination varies between species.

What are the four genetic sex-determination systems?

XY, XO, ZW, and no special sex chromosomes.

What does homogametic mean?

An individual that produces gametes with the same type of sex chromosome.

What does heterogametic mean?

An individual that produces gametes with different sex chromosomes.

What is the XY system and what organisms use it?

Females are XX and males are XY; found in mammals and some insects.

In the XY system, which sex is homogametic and which is heterogametic?

Females (XX) are homogametic; males (XY) are heterogametic.

What is the XO system and what organisms use it?

Females are XX and males are XO; found in some insects.

What gametes do XO males produce?

Half contain an X chromosome and half contain no sex chromosome.

What is the ZW system and what organisms use it?

Females are ZW and males are ZZ; found in birds, some reptiles, amphibians, and insects.

In the ZW system, which sex is heterogametic and which is homogametic?

Females (ZW) are heterogametic; males (ZZ) are homogametic.

What organisms may lack special sex chromosomes?

Some plants and fungi.

What is haplodiploid sex determination?

Haploid individuals are male and diploid individuals are female.

• Male = Haploid (n): Develops from an unfertilized egg.

• Female = Diploid (2n): Develops from a fertilized egg.

What is temperature-dependent sex determination (TSD)?

Sex is determined by the incubation temperature of eggs during embryonic development.

Which organisms exhibit TSD?

All crocodiles, most turtles, and some lizards.

What are the three patterns of temperature-dependent sex determination?

Case I: Low = female, high = male; Case II: Low = male, high = female; Case III: Low and high = female, intermediate = male.

What enzyme is involved in temperature-dependent sex determination?

Aromatase, which converts androgens into estrogens.

What is Genic Balance Theory?

Sex is determined by the ratio of X chromosomes to haploid sets of autosomes (X:A).

What organism demonstrates Genic Balance Theory?

Drosophila (fruit flies).

Does the Y chromosome determine sex in Drosophila?

No, the X:A ratio determines sex; Y is required for male fertility.

What X:A ratio produces a normal female in Drosophila?

1.0 (XX:2A).

What X:A ratio produces a normal male in Drosophila?

0.5 (X:2A).

What X:A ratio produces an intersex in Drosophila?

Between 0.5 and 1.0, such as 0.67 or 0.75.

What X:A ratio produces a metafemale or metamale in Drosophila?

Metafemale = 1.5; Metamale = 0.33.

How is X-linked gene expression balanced in male Drosophila?

The single X chromosome is upregulated to match expression in XX females.

What are the two sexual phenotypes of C. elegans?

XO males and XX hermaphrodites.

What are the typical male and female sex chromosomes in humans?

Male = XY; Female = XX.

What are bipotential gonads?

Embryonic gonads capable of developing into either testes or ovaries.

What is MSY?

Male-specific region of the Y chromosome; the nonrecombining region.

What is PAR and why is it important?

Pseudoautosomal region; allows X and Y chromosomes to pair and recombine during meiosis.

What is SRY?

Sex-determining region Y; a gene located near the PAR on the short arm of the Y chromosome.

What is TDF?

Testis-determining factor; a protein encoded by SRY that triggers testes formation.

What is the relationship between MSY, SRY, and TDF?

MSY is the male-specific region of Y; SRY is the sex-determining gene; SRY encodes TDF.

When does SRY become active during human development?

Approximately 6–8 weeks of embryonic development.

What happens when SRY/TDF is expressed versus not expressed?

Expressed = testes develop; Not expressed = ovaries develop.

How can an XX individual develop a male phenotype?

The SRY region is translocated from the Y chromosome onto an X chromosome.

How can an XY individual develop a female phenotype?

The SRY gene is missing or deleted.

What is androgen insensitivity syndrome?

An XY condition caused by a mutation in the X-linked testosterone receptor gene, resulting in an externally female phenotype.

What is dosage compensation?

A mechanism that balances X-linked gene expression between males and females.

What is the Lyon hypothesis?

One X chromosome is randomly inactivated in female somatic cells early in embryonic development.

When does X-inactivation occur and is it random?

Early embryonic development; either the maternal or paternal X is randomly inactivated.

What happens to X-inactivation after mitosis?

Daughter cells retain the same inactivated X chromosome.

Why are females genetic mosaics?

Different cell populations express genes from different active X chromosomes.

Why do calico cats have patches of different fur colors?

Random X-inactivation causes different X-linked coat-color alleles to be expressed in different areas.

What is an example of X-inactivation mosaicism in humans?

Patchy sweat gland development in females heterozygous for X-linked ectodermal dysplasia.

What is the N−1 rule?

The number of Barr bodies equals the number of X chromosomes minus one.

How many Barr bodies are found in XX, XY, XO, XXY, XXX, and XXXX?

XX = 1; XY = 0; XO = 0; XXY = 1; XXX = 2; XXXX = 3.

What is Klinefelter syndrome and its genetic basis?

A male condition involving extra X chromosomes, usually 47,XXY.

What are characteristics of Klinefelter syndrome?

Tall stature, long limbs, underdeveloped testes, infertility, and possible breast enlargement.

What is Turner syndrome and its genetic basis?

A condition involving only one X chromosome (45,XO).

What are characteristics of Turner syndrome?

Short stature, rudimentary ovaries, broad chest, skin folds on the neck, and underdeveloped breasts.

One thing I would definitely practice beyond memorizing these cards: Your professor's slides include a chart of X:A ratios and a diagram of the N−1 rule. Make sure you can calculate the ratio or number of Barr bodies when given an unfamiliar genotype, not just recognize the examples on the cards.