Chapter 4.1: Sex Chromosomes and Sex Determination

sex determination

the set of events that govern whether a zygote will develop as a male or female

s ex linked traits

s ex chromosomes can carry these genes taht are not s ex specific

Nettie Stevens

the first cytologist to demonstrate that chromosomes determine s ex

Noted gemales had 20 large chromosomes and males had 19 plus an unmatched pair.

how did stevens determine chromosomes determined s ex?

Physical characteristics of a male

Any person carrying the Y chromosome will have:

Females with Turner syndrome. Develops as female because no Y

Humans carrying one X chromosome and no second s ex chromosome

SRY (s ex determining region of Y)

Y chromosome specific gene that is the primary determinant of maleness

S ex reversal (transgenic mice)

how was SRY determined as necessary and sufficient for maleness?

Male specific region of Y (MSY)

Region of the X chromosome that carries the SRY gene together with genes required for spermatogenesis (and thus fertility) that is not found anywhere else in the genome

Y chromosome evolved from the X chromosome in an ancient mammal. Y gradually lost almost all its genes except those few required in two copies and those such as SRY

the fact that the X and Y chromosomes share several genes suggests that what?

PAR1 and PAR2 are homologous regions of the X and Y chromosomes that together contain about 30 genes.

Human S ex chromosomes have both shared and unique genes, including:

Birds and butterflies

Examples of variation of s ex determining mechanisms: [2]

ZZ (matching)

Male chromosomes in birds and butterflies

ZW (unmatched)

Female chromosomes in birds and butterflies

Heterogamatic s ex

the s ex having two different s ex chromosomes because it gives rise to two different types of gametes

Homogamatic s ex

the s ex with two similar s ex chromosomes it the