Genetics 311 Indiana University

Pseudoautosomal regions (PARs)

Homologous segments on the tips of the X and Y chromosomes that allow them to pair and recombine during meiosis. The two PARs contain about 30 genes total.

SRY

A protein that activates testes development and prevents the formation of ovaries. Sex determining region of Y.

Sex Reversal

(XX with SRY+ is male) and (XY with SRY- is female)

Sex Chromosomes

X(large amount of protien-coding genes) and Y(much smaller amount)

Thomas Hunt Morgan

Established a firm experimental base for the chromosome theory. (Specifc genes reside on specific chromosomes.

Crisscross inheritance

Males inherit eyecolor mutation from their mothers.

X-Linked

The gene is carried by the X chromosome and the Y chromosome carries no allele of the gene. 

w+

normal / wild type allele

w

mutant allele

hemizygous

an individual who has only one member of a chromosome pair or chromosome segment rather than the usual two. Often used to describe X-linked genes in males who have only one X chromosome.

Nondisjunction

where the X chromsomes fail to seperate during meiosis in fmeales. Failure in chromsome segregation. Occurs in meiosis I or meiosis II.

All possible products of nondisjunction + fertilization

XXY

XXX

XO

OY (these die in embryonic development)

Kinetochore

A structure in the centromere region of each chromatid that is specialized for conveyance. Each kinetochore contains protein that enable the chromsome to slide along the microtubule.

Pedigree

A diagram of a family’s relevant genetic features, extending back through as many generations as possible.

Family pedigree diagram symbols

Squares = males

Circles = females

Diamonds = unspecified sex

Late-onset genetic trait

Symptoms are not present at birth and manifest themselves later in life. example = huntington disease

Incomplete Dominance

Codominance

Variable Expression

Incomplete penetrance