Lecture 26: Sex Determination Flashcards

What is a gene?

A DNA sequence on a chromosome that encodes proteins or traits.

What is an allele?

A version of a gene created by DNA mutations.

What is a chromosome?

A long linear DNA molecule that contains many genes.

What does it mean to be diploid?

A cell with two of each chromosome type (from both parents).

What does it mean to be haploid?

A cell with one of each chromosome type (as in gametes).

What are homologous chromosomes?

Chromosome pairs with the same genes, one from each parent.

Are most human cells diploid?

Yes.

Are gametes (sex cells) haploid?

Yes.

How many autosomal chromosome pairs do humans have?

22 pairs.

How many sex chromosome pairs do humans have?

1 pair.

What are sex chromosomes?

A chromosome pair that determines biological sex.

Which sex chromosomes indicate male?

XY.

Which sex chromosomes indicate female?

XX.

Which parent determines the offspring’s sex?

The father (sperm can carry X or Y).

Do you need at least one X chromosome to live?

Yes.

Do you need a Y chromosome to live?

No.

What is the SRY gene and where is it located?

A gene on the Y chromosome; it triggers male development.

What does the SRY gene produce?

TDF (Testes Determining Factor), a DNA-binding protein.

What does TDF do?

Activates male development genes; causes gonads to become testes.

How do Sertoli and Leydig cells influence development?

Sertoli cells secrete anti-Müllerian hormone (destroys female ducts), Leydig cells secrete testosterone and DHT (form male structures).

Do X and Y chromosomes behave like homologous chromosomes in male meiosis?

Yes.

What is nondisjunction?

Failure of chromosomes to separate during meiosis.

What disorders result from nondisjunction?

Klinefelter’s Syndrome (XXY): Male with some female traits, often sterile; Turner’s Syndrome (XO): Female, sterile, with mild developmental issues.

How is gene dosage handled in XX females?

One X becomes a Barr body (inactivated).

What is a mosaic expression pattern in females?

Random X inactivation causes different cells to express different X-linked traits.

When is the “sex indifference stage”?

Around 5 weeks of embryonic development.

What is the default developmental pathway?

Female (XX).

What are gonads?

Undifferentiated tissue that can develop into testes or ovaries.

What are Müllerian ducts?

Potential female ducts; develop if no SRY/AMH is present.

What are Wolffian ducts?

Potential male ducts; need testosterone to survive and develop.

What hormones do Sertoli cells secrete and what’s their function?

Anti-Müllerian hormone → degrades Müllerian ducts.

What hormones do Leydig cells secrete and what’s their function?

Testosterone → promotes Wolffian ducts; DHT → develops external genitalia.

What does the genital tubercle become?

Penis (male) or clitoris (female).

What do urethral folds become?

Male: Fuse to form spongy urethra; Female: Form labia minora.

What does the urethral groove become?

The vestibule in females.

What do labioscrotal swellings become?

Male: Scrotum; Female: Labia majora.

What are examples of homologous sex structures?

Testes / Ovaries; Penis / Clitoris; Scrotum / Labia majora.