Sex Determination and Sex linked traits

sexual reproduction

different sexes produce different gamete types

mechanisms of sex determination

• Chromosomal

• Genic

• Environmental

chromosomal

different sexes have different “sex” chromosomes

genic

not different chromosome, rather sex determined by different genes across genome

environment

sex is determined by environment (rather than by DNA)

chromosomal sex determination types

• XX-XO system

• ZZ-ZW system

• XX-XY system

XX-XO system

• XX (homogeneous, female)

• XO (heterogeneous, produces 1 gamete with no sex cells, male)

• these are found mostly in insects

ZZ-ZW system

• ZW (heterogenous, female)

• ZZ (homogenous, male)

• found in birds, reptiles and some fish species.

XX-XY system

• XX (homogenous, 2 same gametes)

• XY (heterogenous, produce 2 different types of gametes)

The sex chromosomes are so different. How do they pair??

pseudautosomal regions

pseudautosomal regions

regions of similar genes between X&Y allow them to pair during meosis

when does homologous pair (tetrad)

prophase I in meiosis

genic sex determination

• no “sex” chromosomes

  • some plants, fungi, protozoans, fish

• genotype determine sex

environmental sex determination

• photoperiod

• food shortage

• population density

temperature-dependent sex determination

• temperature rises in favor of males

• temperature decreases in favor of females

what chromosome determines sex

Y chromosome

SPY

sex-determination region of y

what is the expression of TDF

testis-determining factor gene

MSY

male-specific region of the y

X/Y Chromosomal Abnormalities

• nondisjunction

• can occur in Anaphase of Meiosis I, Anaphase of Meiosis II, Anaphase in Mitosis

nondisjunction

results in daughter cells with unequal # of chromosomes

what are some types of sex chromosome abnormalities

• Turner Syndrome

• Klinefelter Syndrome

• Poly-X Syndrome

• Jacob Syndrome

Turner Syndrome

• XO

• occurs in females

• most sterile

Klinefelter Syndrome

• XX+Y

• occurs in males

• most sterile

Poly-X Syndrome

• XXX

• occurs in females

Jacob Syndrome

• XYY

• occurs in males

Males have been identified who are XX

SPY attached to another chromosome

Femalesave have been identified as XY

Y chromosome is missing the SPY

Androgen

insensitive females externally female, internally male

androgen insensitivity syndrome

a rare genetic disorder that affects a person's ability to respond to male hormones (androgens)

what happens in androgen insensitivity syndrome

• Uterus, oviducts, ovaries are absent

• Testis produce testosterone; cells are insensitive

x linked characteristics

Red-green color-blindness, hemophilia, Duchenne muscular dystrophy,
ocular albinism, Severe Combined Immunodeficiency (SCID)++

y linked characteristics

Males; most are reproductive-related