Chapter 26 Development and Inheritance

zygote

a diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum; it enters a 2-week period of rapid cell division and develops into an embryo

embryo

the developing human organism from about 2 weeks after fertilization through the second month (8 weeks)

fetus

the developing human organism from 9 weeks after conception to birth

zona pellucida

A thick, transparent coating rich in glycoproteins that surrounds a secondary oocyte.

corona radiata

The protective layer of follicular granulosa cells that surround a secondary oocyte after it has been ovulated.

oocyte activation

-contact and fusion of cell membranes of sperm and oocyte triggers depolarization (influx of Na+)
-follows fertilization; hardens zona pellucida, inactivates sperm receptors
-oocyte completes meiosis II, becomes mature ovum

amphimixis

Fusion of female pronucleus and male pronucleus
Moment of conception
Cell becomes a zygote with 46 chromosomes
Fertilization is complete

blastomeres

individual cells of the blastula

blastula (blastocyst)

A hollow ball of cells that marks the end of the cleavage stage during early embryonic development in animals.

morula

a solid ball of cells resulting from division of a fertilized ovum, and from which a blastula is formed.

blastocoel

the fluid-filled cavity inside a blastula

inner cell mass

The mass of cells in the blastocyst that ultimately give rise to the embryo and other embryonic structures (the amnion, the umbilical vessels, etc.)

amnion

Membrane that encloses the embryo in protective amniotic fluid

chorionic villi

These are finger like projections that form the fetal portion of the placenta.

placentation

the development and differentiation of the fetal and maternal portions of the placenta

embryogenesis

the formation and development of an embryo

gastrulation

The process by which a blastula develops into a gastrula with the formation of three embryonic layers

cytotrophoblast

inner cellular layer of the trophoblast

Syncytiotrophoblast

Found as thin, non-distinct lateral barrier, outer layer of chorionic villi in the placenta. Are supplied with new cells via the cytotrophoblast. Secrete human chorionic gonadotrophin (hCG) to preserve corpus luteum (the presence of this hormone is used to test for pregnancy).

amniotic cavity

the fluid-filled space between the embryo and the amniotic sac

amniotic fluid

fluid within the amniotic sac that surrounds and protects the fetus

yolk sac

The yolk sac is an extra-embryonic membrane that provides food for the embryo.

ectopic pregnancy

implantation of the fertilized egg in any site other than the normal uterine location, usually in a fallopian tube

ectoderm

outermost germ layer; produces sense organs, nerves, and outer layer of skin

mesoderm

the middle layer of an embryo in early development, between the endoderm and ectoderm.
develops into muscle, bone, and connective tissues.

endoderm

innermost germ layer; develops into the linings of the digestive tract and other visceral organs

allantois

begins as an outpocketing of the yolk sac
Forms the foundation for the umbilical cord
Becomes part of the urinary bladder

body stalk

The structure connecting the embryo to the chorion. Eventually develops into the umbilical cord

placenta

A structure that allows an embryo to be nourished with the mother's blood supply

Braxton Hicks contractions

irregular false labor contractions of the uterus

dilation stage of labor

Cervix dilates (to ~10 cm) & effaces (thins), due to contractions pushing infant head against cervix. Water breaks (amnion ruptures)

expulsion stage of labor

birthing stage during which a baby travels through the birth canal and exits the mother's body

placental stage of labor

uterus continues contracting to expel placenta and attached fetal membranes

Oxytocin (OT)

secreted by the posterior lobe of the pituitary gland; stimulates contraction of the uterus during labor and childbirth
Increases the contractions of the uterus during birth and promotes the release of breast milk

Organogenesis

organ formation that takes place during the first two months of prenatal development

Teratogens

agents, such as chemicals and viruses, that can reach the embryo or fetus during prenatal development and cause harm

homologous chromosomes

Pair of chromosomes that are the same size, same appearance and same genes.

dominant allele

An allele whose trait always shows up in the organism when the allele is present.

recessive allele

An allele that is masked when a dominant allele is present

homozygous dominant

Both alleles (factors) for a trait are the same and dominant (AA)

Heterozygous

An organism that has two different alleles for a trait

homozygous recessive

Both alleles (factors) for a trait are the same and recessive (aa)

Co-dominant alleles

Pairs of alleles that both affect the phenotype when present in a heterozygote

sex-linked traits

Traits controlled by genes located on sex chromosomes.

incomplete dominance

Situation in which one allele is not completely dominant over another allele