CH 29 Flashcards
what is inheritance?
passing of genes and traits from one generation to the next
what is genetics?
study of genes and inheritance
what is genetic counselling?
medical branch of study that tests, detects fetal abnormalities, and provides advice accordingly
what is a genotype?
combination of genes
does every human have the same genotype?
No, all humans have the same set of genes but each person may differ by the sequence of those genes
what are alleles?
genes that encode the same protein product but differ in sequence, they are alternate versions of genes
what is a phenotype?
physical and observed expression of a particular trait/genotype
why do genotypes determine one’s phenotype?
central dogma of biology
(genes → RNA → proteins)
how many alleles per gene do humans have?
humans are diploid so they have two maximum alleles per gene (1 from dad, 1 from mom)
what are dominant alleles?
alleles that need only one copy to be expressed
what are recessive alleles?
alleles that need two copies to be expressed
what is autosomal inheritance?
alleles are found on non-sex chromosomes and can be inherited to offspring
what are homozygotes?
individuals with two of the same alleles
what are heterozygotes?
individuals with two different alleles
who do homozygotes for a dominant disease allele usually die in utero?
100% of proteins coded by the alleles are of disease variant, no functional copies made
why are individuals who express the traits of a dominant disease usually heterozygotes for that allele?
50% of proteins coded by the gene are functional, and that is enough for normal functioning
why are most disease alleles carried on the X chromosome?
there are very few genes on the Y chromosome
what sweeps secondary oocytes down the uterine tubes?
cilia on the mucosa of the uterine tubes
when is pregnancy most likely to occur?
if intercourse occurs within 3-day window of ovulation
what moves sperm through uterine tubes?
their flagellum, and peristaltic contractions of the uterine tubes
describe the path of sperm to fuse with the oocyte
corona radiata → zona pellucida → plasma membrane of oocyte → cytoplasm of oocyte
why can’t sperm fertilize oocyte within hours after coitus?
they must undergo capacitation
what is capacitation?
changes to sperm’s plasma membrane and increased flagellar whipping due to conditions of the vagina
what happens to the plasma membrane of the sperm during capacitation?
anything besides phospholipids and glycolipids from membranes are stripped for easier fusion with the oocyte plasma membrane
how does the sperm go through the corona radiata and zona pellucida?
sperm releases acrosomal enzymes that digest them, flagellar motility pushes the sperm into the secondary oocyte further
what is ZP3?
a protein on the zona pellucida that is a receptor for a sperm plasma membrane
what happens when a sperm-ZP3 complex binds oocyte plasma membrane receptors?
an acrosomal reaction is triggered, and the acrosome releases digestive enzymes that digests the surrounding zona pellucida
what happens when the plasma membranes of the sperm and oocyte fuse?
the newly fertilized ovum is depolarized
which ion enters the cytoplasm after depolarization of the newly fertilized ovum?
calcium, through the the opening of VGCCs
what does depolarization of the fertilized egg do?
intracellular Ca2+ triggers exocytosis of secretory vesicles that block ZP3 receptors and crystallize zona pellucida
what is a slow block to polyspermy?
the process of blocking ZP3 receptors and crystallizing the zona pellucida to prevent multiple sperm fusing with the oocyte
why is slow block to polyspermy important? what would happen if every egg were fertilized by multiple sperm?
- slow block to polyspermy prevents every sperm trying to fuse w/ oocyte
- too many chromosomes is fatal for an embryo
what is syngamy?
the fusion of the female and male pronuclei to form a single diploid nucleus
(different from fertilization)
what structures are found upon fertilization?
- large ovum w/ female pronuclei
- second polar body
- male pronuclei
what is cleavage?
rapid mitotic division of the zygote after ~24 hours post fertilization
how is cleavage different from normal mitotic divisions?
it increases the number of cells without a significant increase in size
when is a morula formed?
~4 days after fertilization
what is a morula?
solid mass of cells formed through cleavage of a zygote
what is uterine milk?
glycogen-rich fluid formed by the uterus that enters zona pellucida of a morula and rearranges its cells, forming a blastocyst cavity
what is a blastocyst cavity?
uterine milk-filled pouch
what does formation of a blastocyst cavity mean for the morula
the morula is now a blastocyst
what are the two parts of a blastocyst?
- embryoblast
- trophoblast
what is the embryoblast?
inner cell mass in the blastocyst that gives rise to embryo
what is the trophoblast?
outer cell mass of the blastocyst that forms fetal portion of the placenta
what happens to the blastocyst on the 5th day after fertilization?
blastocyst secretes an enzyme that digests through zona pellucida and it hatches out the hole
what is implantation?
blastocyst implanting on the endometrium of the uterus, with the embryoblast oriented towards endometrium
when does implantation occur?
7 days after fertilization
why does the embryoblast orient itself toward the endometrium in implantation?
to be closer to nutrients provided by the endometrium
what are some histological changes to the endometrium and blastocyst during implantation?
endometrium becomes more vascularized, endometrial glands enlarged, blastocyst is engulfed in endometrial tissue
what happens to the trophoblast 8 days after fertilization?
- trophoblast differentiates into two layers
- secretes enzymes that liquefy the endometrium for nourishment
- secretes hCG, preventing CL degeneration
what happens to the embryoblast 8 days after fertilization?
embryoblast differentiates into two layers
what is the bilaminar embryonic disc?
flat disc structure formed from the two layers that came from the embryoblast
what is the amniotic cavity?
cavity formed by the cells of the bilaminar embryonic disc containing amniotic fluid
what is the function of amniotic fluid?
cushions and protects the fetus during pregnancy, absorbs shock, moisturizes the fetus
where does amniotic fluid come from?
- filtered from maternal capillaries
- fetal urine
why does the umbilical vesicle shrink as development progresses?
its nutrient-providing function is replaced by the placenta
what are the functions of the umbilical vesicle?
- nourishes embryo during week 2/3
- forms first blood cells
- contains primordial germ cells of the developing fetus
- cushions embryo and prevents dessication
what two structures sandwich the bilaminar embryonic disc 8 days after fertilization?
- amniotic cavity
- umbilical vesicle
when does the chorion develop?
~12 days post-fertilization, the two layers of the trophoblast develop into the chorion
what does the chorion eventually become
the fetal portion of the placenta
what are the functions of the chorion?
- Secretes proteins that block maternal antibody production
- Secretes hCG
- Promotes the production immuno- suppressing T lymphocytes in endometrium