chapter 7 Flashcards
Zygote
a fertilized egg that develops into a new individual
Gametes
Unfertilized germ cells
Sperm
Male gamete
Oocyte
Female gamete (egg)
Gonads
organs where gametes are produced
Testes
Male gonads that produce spermatoa and male sex hormones
Ovaries
Female gonads that produce oocytes and female sex hormones
Teratogen
any physical or chemical agent that brings about an increase in congenital malformations
SRY gene
sex-determining region of the Y chromosome
Testosterone
a steroid hormone produced by the testis
Mullerian inhibiting hormone (MIH)
A hormone produced by developing testis that causes the breakdown of Mullerian (female) ducts in the embryo
Androgen Insensitivity
X-linked genetic trait that causes XY individuals to develop into phenotypic females
Barr body
a densely staining mass in the somatic nuclei of mammalian females, inactivated X chromosome, tightly coiled
X inactivation center (Xic)
region on the x chromosome where inactivation begins
sex-influenced traits
Traits controlled by autosomal genes that are usually dominant in one sex but recessive in the other sex
sex-limited traits
inherited by both males and females but generally expressed in only one sex. Genes that deal with secondary sex characteristics are sex-limited
Explain the main differences in the timing of gamete formation between sperm and oocytes
- The meiotic division produces 4 sperm
- Meiotic division produces 1 oocyte and 2 polar bodies
what happens in the first trimester of embryonic and fetal development
1.) Basic tissue layers form; most of the body is divided into paired segments
2.) Most major organ systems are formed
3.) Embryo becomes a fetus; sexual development is initiated
what happens in the second trimester of embryonic and fetal development
1.) Increase in size and organ-system development
2.) Body parts of skeleton form
3.) Heartbeat is heard with a stethoscope
4.) Fetal movements begin
what happens in the third trimester of embryonic and fetal development
1.) rapid growth
2.) Circulatory and respiratory systems mature
3.) Birth is a hormonally induced process at the end of the 3rd trimester
which trimester is the fetus most sensitive to teratogens? give examples
- Most sensitive in 1st trimester (8 weeks)
Examples: Radiation, viruses, medications (Thalidomide), alcohol
what are the three levels at which the sex of an individual is defined
Chromosomal Sex, Gonadal Sex, and Phenotypic Sex
Chromosomal Sex definition
established at fertilization
Gonadal Sex Definition
7 or 8 weeks sex undefined, genes cause gonads to form testis or ovaries
Phenotypic Sex Definition
Sex determined by internal and external genitalia
Pathways to sexual differentiation
1.) Gene action
2.) Interactions within the embryo
3.) Interactions with other embryos in the uterus
4.) Interactions with the maternal environment
How does the chromosomal sex of an individual differ from their phenotypic sex
- chromosomal sex is found in their genes, having XX or XY chromosomes
- Phenotypic Sex is determined by their internal and external genitalia like ovaries and testis
Example of chromosomal sex differing from phenotypic sex
Androgen Insensitivity: mutation x-linked androgen receptor gene causes XY males to females phenotypically
How does dosage compensation work for the X chromosome
Random inactivation of one x chromosome in females equalizes the activity of x-linked genes in males and females
