BIOL3304 Ch06

Sex Chromosomes

Chromosomes that determine the sex of an individual; X and Y chromosomes in humans.

X chromosome

A sex chromosome that contains over 1500 genes and is larger than the Y chromosome.

Y chromosome

A sex chromosome that contains 231 genes and is responsible for male sex determination.

SRY gene

The gene on the Y chromosome that determines male characteristics and stimulates development of male structures.

Gonads

The reproductive organs that develop into either testes or ovaries.

X inactivation

The process by which one of the two X chromosomes in a female is randomly inactivated.

Homogametic sex

Refers to females (XX), as they have two identical sex chromosomes.

Heterogametic sex

Refers to males (XY), as they have two different sex chromosomes.

Androgen insensitivity syndrome

A condition caused by a mutation that prevents the formation of androgen receptors, affecting male development.

Pseudohermaphroditism

A condition where an individual has both male and female sexual structures at different life stages.

Intersex

Refers to individuals whose internal structures are inconsistent with their external genitalia.

Sex-influenced trait

A trait that is expressed differently in males and females due to hormonal differences.

Pattern baldness

An example of a sex-influenced trait where males exhibit baldness while females do not.

X-linked dominant inheritance

A pattern of inheritance where a single copy of an allele on the X chromosome can cause the trait in both males and females.

X-linked recessive inheritance

A pattern of inheritance where two copies of an allele are necessary for females to express the trait, but one copy is sufficient for males.

Barr body

An inactivated X chromosome found in the cells of females.

Genomic imprinting

The process by which genes are expressed in a parent-of-origin-specific manner, often influenced by methylation.

Epigenetic change

A change in gene expression that does not involve alterations to the underlying DNA sequence.

XY genotype

The genetic configuration that indicates a male individual in humans.

XX

The genetic configuration that indicates a female individual in humans.

Embryonic sexual development

The process by which embryos develop male or female characteristics based on their sex chromosomes.

Sex ratio

The ratio of males to females in a population, often expressed as the number of males per 1000 females.

Primary sex ratio

The sex ratio at conception.

Secondary sex ratio

The sex ratio at birth.

Tertiary sex ratio

The sex ratio at maturity.

Hermaphroditism

A condition where an individual possesses both male and female reproductive structures.

Dihydrotestosterone (DHT)

A potent androgen that contributes to the development of male characteristics.

5-alpha reductase deficiency

A genetic condition where testosterone cannot be converted to DHT, affecting male sexual development.

Congenital adrenal hyperplasia

A genetic disorder affecting adrenal gland hormones, potentially leading to ambiguous genitalia in females.

Sex-limited traits

Traits that are expressed in only one sex despite being inherited from both parents.

Fate of Müllerian ducts

These ducts develop into female reproductive structures in the absence of male hormones.

Fate of Wolffian ducts

These ducts develop into male reproductive structures in the presence of male hormones.

Pseudoautosomal regions

Regions on the X and Y chromosomes that are homologous and can recombine.

Maternally-influenced traits

Traits that are affected by the genes inherited exclusively from the mother.

Preeclampsia

A pregnancy complication characterized by high blood pressure and signs of damage to another organ system.

Inheritance pattern

The manner in which a particular genotype is transmitted from parents to offspring.

Sperm and oocyte formation

The processes that produce male and female gametes, respectively.

X-linked disorders

Genetic disorders that are caused by mutations in genes located on the X chromosome.

Manifesting heterozygote

A female who exhibits a phenotype linked to an X-linked disorder due to X inactivation patterns.

XIST gene

A gene encoding an RNA molecule responsible for X inactivation in females.

Mosaic expression

The state where different cells in a female express different X-linked alleles due to X inactivation.

Transcription factor

A protein that controls the transcription of specific genes, such as the one encoded by the SRY gene.

Hemizygous

Having only one allele of a gene, as male individuals do for X-linked traits.

Age of onset

The age at which symptoms of a genetic condition first appear.

Severe symptoms

More pronounced or damaging effects experienced by individuals with certain genetic conditions.

Imprinted genes

Genes that are expressed in a parent-of-origin-specific manner due to epigenetic modifications.