Human Development And Human Genetics Flashcards
Where do sperm undergo final maturation?
W/in female reproductive tract
What happens during fertilization?
- Sperm nucleus enters the ovum
- Fusion of egg and sperm nuclei occurs
-> 23 chromosomes of egg + 23 chromosomes of sperm - 46 chromosomes in zygote
-> Zygote: 22 pairs of autosomes and a pair of sex chromosomes
What are the stages of human development starting with the Zygote?
1.) Zygote begins mitosis divisions (forms 2 cells,4, 8,etc)
2.) Morula forms
- SOLID sphere of cells
- divides further to form a HOLLOW sphere (blastocyst)
3.) Blastocyst: made of…
- Trophoblast (outer layer of cells)
- Embryoblast (inner cell mass containing potential embryo) - stem cells, not yet specialized
- Surface proteins of blastocyst fit with “docking” molecules on endometrium
- Trophoblast secretes enzymes to form depression in endometrium that blastocyst sinks into
Implantation occurs 5-8 days after fertilization
After implantation…
4. Trophoblast becomes chorion -> develops into fetal portion of placenta
Zygote -> morula -> blastocyst -> Trophoblast (outer layer of blastocyst) BECOMES chorion -> fetal portion of placenta
What is the embryo?
Embryo: from zygote through 8 wks gestation
- 3 primary germ layers develop
1. Ectoderm
2. Mesoderm
3. Endoderm
- by 8th wk of gestation, all organ systems are formed
What structures are derived from the ectoderm?
- Epidermis; hair and nail follicles; sweat glands
- Nervous system, pituitary gland, adrenal gland
- Lens and cornea of eye; internal ear
- Mucosa of oral and nasal cavities; salivary glands
What structures are derived from the mesoderm?
- Dermis; bone and cartilage
- Skeletal muscles; cardiac muscle; most smooth muscle
- Kidneys and adrenal cortex
- Bone marrow and blood; lymphatic tissue; lining of blood vessels
Structures derived from the endoderm?
- Mucosa of esophagus, stomach, and intestines
- Epithelium of respiratory tract, including lungs
- Liver and mucosa of gallbladder
- Thyroid gland; pancreas
What are the layers of the embryonic membranes?
Yolk sac
- Forms the first blood cells and cells that become spermatogonia or oogonia
Amnion (surrounds the fetus)
- Contains amniotic fluid
-> Absorbs shock around the fetus
Chorion
- Develops chorionic villi that contains blood vessels for fetal portion of placenta
What happens to the fetus in wks 9-40 of gestation?
- Organ systems grow and mature
- Growing fetus brings about structural and functional changes in the mother
Umbilical cord and placenta
- Umbilical cord connects fetus to placenta
- Placenta: formed by chorion of embryo and uterine endometrium
-> Functions: site of exchanges b/w maternal and fetal blood; produce hormones to maintain pregnancy
- FETAL BLOOD DOESNT mix with maternal blood
- Fetal capillaries are w/in maternal blood sinuses
-> site of exchanges b/w maternal and fetal blood sinuses
Umbilical arteries and veins
2 umbilical arteries
- carry blood from fetus to the placenta
Exchange in maternal blood sinuses
- Fetal CO2 and waste products diffuse into maternal blood
- O2 and nutrients enter fetal blood enter fetal blood
Umbilical vein returns blood from placenta to fetus
How many chromosomes do we have?
23 homologous pairs = 46 total per human cell
- 22 pairs of autosomes
- 1 pair of sex chromosomes (XX or XY)
DNA: hereditary material of chromosomes
Gene: genetic code for one protein
- An individual has 2 genes for each protein or trait
- 1 maternal and 1 paternal
Genotype and Phenotype
Alleles
- Versions of a gene (possibilities for how a gene may be expressed)
Genotype
- Actual genetic makeup
- The alleles present
Phenotype
- Appearance or how the alleles are expressed
- Depends on dominance or recessiveness of alleles, or pattern of inheritance
A gene has 2 or more alleles
-> some alleles may be dominant and others recessive
Heterozygous vs. Homozygous
Heterozygous
- 1 dominant allele and 1 recessive allele
- Dominant allele appears in the phenotype
- Recessive allele is not expressed in phenotype
-> May be passed to children
Homozygous
- 2 similar alleles
- Can be homozygous dominant or homozygous recessive
- Expression of recessive alleles requires homozygous recessive
Inheritance
Dominant recessive
- Dominant gene will appear in phenotype of a heterozygous
- Recessive gene will appear in phenotype only if the individual is homozygous recessive
Multiple alleles
- More than 2 possible alleles for each gene
- An individual will have only two of the alleles (same or different)
Inheritance: sex linked (x linked) traits
Genes are found only on the X chromosome
- No corresponding genes on the Y chromosome
Women with 1 gene for the trait and 1 gene not for the trait are called carriers
Men cannot be carriers
- Either have he trait or do not have it
Example of Inheritance Patterns
Autosomal recessive
- sickle cell anemia
- cystic fibrosis
Autosomal dominant
- Huntington’s disease
- Polycystic kidney disease
- Marfan syndrome
Sex linked
- Duchenne’s muscular dystrophy
- Hemophilia A and B
- Red green color blindness
