Chromosomal Inheritance

What does the chromosomal theory of inheritance state?

Genes are located on chromosomes, and their behavior during meiosis explains inheritance patterns.

What did T.H. Morgan’s fruit fly experiments show?

Eye color is linked to the X chromosome, proving genes reside on chromosomes.

What notation did Morgan use for alleles?

Mutant = w, Wild type = w⁺

What gene determines male development?

SRY gene — triggers testes formation.

What happens if SRY is missing?

XY embryo develops ovaries.

What gene promotes ovary development?

WNT4 gene on chromosome 1.

Why are X-linked traits more common in males?

Males have only one X (hemizygous), so recessive alleles are expressed.

What is X inactivation?

Random inactivation of one X in females to form a Barr body.

What gene controls X inactivation?

XIST gene — produces RNA that coats and inactivates one X chromosome.

How do tortoiseshell cats demonstrate X inactivation?

Random patches of color express different active X chromosomes.

What are linked genes?

Genes close together on a chromosome, inherited together.

What are unlinked genes?

Genes on different chromosomes that assort independently.

What is recombination frequency?

Percentage of recombinant offspring; reflects gene distance.

What is nondisjunction?

Failure of chromosomes to separate during meiosis.

What is aneuploidy?

Abnormal number of chromosomes.

What is genomic imprinting?

Only one parental allele expressed; the other silenced.

How are mitochondria inherited?

From the mother only.