Chapter 4: Sex Determination and Sex-Linked Characteristics

A comprehensive vocabulary review set for Chapter 4 covering sex determination mechanisms, sex chromosome abnormalities, sex-linked traits, and dosage compensation mechanisms.

Hermaphroditism

A condition in which both male and female sexual phenotypes are present within the same organism.

Monoecious

Refers to organisms that possess both male and female reproductive structures in the same individual, such as earthworms, jellyfish, and planarians.

Dioecious

Refers to species in which an individual organism has either male or female reproductive structures, such as mammals, birds, reptiles, and insects.

XX-XO Sex-Determination System

A chromosomal sex-determination system in which females have two X chromosomes ($XX$) and males have a single X chromosome ($XO$), common in grasshoppers.

XX-XY Sex-Determination System

A chromosomal sex-determination system in which females have two X chromosomes ($XX$) and males have one X and one Y chromosome ($XY$), found in mammals and many other organisms.

ZZ-ZW Sex-Determination System

A chromosomal sex-determination system where males are the homogametic sex ($ZZ$) and females are the heterogametic sex ($ZW$), found in birds, snakes, butterflies, and some amphibians and fishes.

Haplodiploidy System

A sex-determination system in which males develop from unfertilized eggs and are haploid, while females develop from fertilized eggs and are diploid, as seen in bees, wasps, and ants.

Pseudoautosomal Region

Homologous regions at the ends of the X and Y chromosomes that allow them to pair and segregate during meiosis in males.

Genic Sex-Determining System

A sex-determination system in which sex is determined by specific genes on undifferentiated chromosomes without morphologically distinct sex chromosomes.

Environmental Sex Determination

A process in which sex is determined fully or in part by environmental factors, such as positional cues in limpets or incubation temperature in turtles and alligators.

Genic Balance System

A sex-determination system in Drosophila melanogaster in which sex is determined by the ratio of X chromosomes to haploid sets of autosomes ($X:A$ ratio).

Metafemale

A Drosophila phenotype resulting from an $X:A$ ratio of $1.5$ (such as $XXX\,AA$ or $XXXY\,AA$), typically exhibiting developmental abnormalities and low viability.

Intersex

A Drosophila phenotype resulting from an $X:A$ ratio between $0.5$ and $1.0$ (specifically $0.67$, such as $XX\,AAA$), displaying characteristics intermediate between male and female.

Metamale

A Drosophila phenotype resulting from an $X:A$ ratio of $0.33$ (such as $XO\,AAA$), characterized by low viability.

Turner Syndrome

A human condition caused by monosomy X ($XO$), resulting in a female phenotype; occurs in approximately $1$ in $3000$ female births.

Klinefelter Syndrome

A human condition in males characterized by the presence of one Y chromosome and two or more X chromosomes (such as $XXY$, $XXXY$, $XXXXY$, or $XXYY$); occurs in approximately $1$ in $1000$ male births.

SRY Gene

The sex-determining region Y gene located on the short arm of the Y chromosome that triggers male development in humans and other mammals.

Androgen-Insensitivity Syndrome

A condition caused by a defective androgen receptor in which an $XY$ individual with functional SRY develops testes and produces testosterone, but target tissues cannot respond, resulting in female external physical characteristics.

Dosage Compensation

A genetic mechanism that equalizes the amount of protein expressed from X-linked genes in males and females.

Lyon Hypothesis

The proposal that one X chromosome in each female somatic cell is randomly inactivated early in development, forming a Barr body.

Barr Body

A condensed, inactivated X chromosome observed in the interphase nuclei of female somatic cells and individuals with multiple X chromosomes.

Random X Inactivation

The random inactivation of one of the two X chromosomes in female mammalian cells, resulting in patchy phenotypic patterns such as tortoiseshell coats in cats.

Y-Linked Palindromes

Eight large repetitive sequences on the Y chromosome that allow internal recombination between duplicate regions, helping to maintain gene structure in the absence of recombination with an X chromosome.