Ch 4: Sex Determination and Sex Related Traits (Bio 375 - Genetics) Flashcards
sex chromosome
chromosome involved in sex determination; X and Y chromosomes in humans
autosomal chromosome (autosome)
chromosome which is not a sex chromosome
sex determination by sex chromosomes: XX-XY
for humans – XY = males = heterogametic sex, XX = females = homogametic sex
heterogametic sex
two different sex chromosomes
homogametic sex
two identical sex chromosomes
sex determination by sex chromosomes: ZZ-ZW
for birds – ZZ = male = homogametic, ZW = females = heterogametic
sex determination by sex chromosomes: XX-XO
for grasshoppers, no “male” chromosome… the O represents a lacking sex chromosome
crossing over involves
the exchange of similar genetic material in equal amounts
primary/secondary pseudoautosomal regions on sex chromosomes
where crossing over can occur during spermatogenesis
hermaphroditism
both sexes are present in same organism
monoecious
organisms with both male and female reproductive structures
dioecious
organism has either male or female reproductive structures; sex may be determined chromosomally/genetically/environmentally
X chromosome
at least one copy required for human development; abnormal copies beyond normal number result in developmental disorders
Y chromosome
single copy of this chromosome is all that is required for male development due to SRY gene
SRY gene
gene causes gonads to develop into testes which secrete: testosterone (inducing development of male characteristics) and mullerian inhibiting substance (degenerates female reproductive ducts)
turner syndrome
XO; only a single X chromosome; sterile female with underdeveloped secondary sex characteristics
klinefelter syndrome
XXY; feminized male phenotype; multiple X chromosomes and/or 1+ Y chromosomes
dosage compensation
equalizes amount of protein produced by X-linked genes in two sexes; one X chromosome is inactivated in female cells to become a Barr body; this results in only one active X chromosome in each cell, or one “dose” of X-linked genes
lyon hypothesis
during early development one X chromosome is inactivated in each cell during dosage compensation -> X to inactivate is determined at random in each cell and the inactivation is permanent (inactivated X remains inactivated in all descendant cells)
mosaics
an individual consisting of cells of more than one chromosomal composition; of differing genetic composition; expression of X-linked genes is different in different cells; some cells express maternal X and others express paternal X (heterozygotes, tortoiseshell cats)
sex linked traits
determined by genes located on sex chromosomes; first described by Thomas Hunt Morgan (using fruit fly genetics and winning the nobel prize in 1933 for his work)
hemizygous
males having only one single allele for X-linked loci
+ symbol on a gene
wild type, not mutated
reciprocal cross
used to determine if a trait is influenced by the sex of the parent/is sex linked
sex limited traits
autosomal traits that are only expressed in one sex even though the genes are present in both sexes; tend to be hormonally regulated (ex: milk production, egg production, multiple ovulation/twinning allele)
sex influenced traits
autosomal traits which are due to genes whose expression depends on hormonal background; exhibits a different expression pattern in different sexes – an allele may be dominant in one sex and recessive in another (ex: pattern baldness is dominant in males but recessive in females, longer index finger length is dominant in females but recessive in males)
completely dominant allele
what is expressed phenotypically in heterozygotes
