Genetics Compendium

Early Fetal Development

Fertilization-occurs when a sperm makes it's way through the corona radiata where the acrosomal membrane digests through the zona pellucida and binds to and fuses with the egg's plasma membrane. When the sperm enters the egg, and the sperm nucleus joins with the egg nucleus to form a zygote.

Processes required for development are cleavage when the zygote divides by mitiotic divisions. Each cell has the full amount of chromosones (23 pairs). The mass of cells now called a morula increases in size and the inner cell mass becomes present to become a blastocyst. Identical twins are formed when if the morula splits. Fraternal twins are formed by two separate eggs and sperm.The blastocyst implants in the uterus and is then called an embryo. Embryo experiences growth, increase in size; morphogenisis where the embryo assumes different shapes; and differentiation when the cells start to specialize in function and structure.

Extraembyonic membranes- are outside the embryo and consist of the chorion, the fetal half of the future placenta that gets nourishment from mom, and rids waste from fetus. The allantois develops into placenta arteries, veins, and bladder.The umbilical arteries and veins exchange blood. The yolk sac is where blood cell formation and blood vessels form. And the amnion is the fluid that cushions and protects the fetus from temperature extremes and shock.

Gestation period-is 280 days normally, from start of last menstrual period to the expected date of delivery. It's in the first week of gestation that the blastocyst implants into the uterus, clinically known as pregnancy.

Embryonic development-

2nd week of gestation, HCG is secreted by the chorion and affects the corpus luteum which secretes hormones that ends the menstrual cycle and is also the hormone to determine pregnancy. The inner cell mass becomes an embryonic disc in a process called gastrulation. The yolk sac forms the first sight of blood vessel formation, the amniotic cavity fills with amniotic fluid and the cells of the inner mass differentiate into 3 primary germ layers: ectoderm, mesoderm, and endoderm. 

3rd week, nervous system and circulatory system start to develop including the heart

4th and 5th week, the body stalk becomes the future umbilical cord that connects the embryo to the chorion, the future placenta. The allantois becomes the umbilical artery and veins. At this time limb buds appear, the head enlarges: and the eyes, ears, and nose appear.

6th-8th week,embryo starts to resemble a human, reflexes develop.

Fetal developement- After 2 months the embryo becomes a fetus.

3rd-4th month, the head becomes larger in proportion to the rest of the body, and the fingernails, nipples, eyelashes, eyebrows, and hair on the head appear. Cartilage begins to be replaced by bone. Fetal sex can be seen on ultrasound and the heartbeat can be heard with a stethoscope on mom's abdomen.

5th-7th month, movement can be felt, eyelids open. The baby can survive if it is born at the end of this period.

8th-9th month, full term babies have the best chance to survive and premature babies can suffer from respiratory distress syndrome, jaundice, and infections.

Genes/Chromosones in Inheritance

Every cell has 46 chromosomes. a chromosome has two sister chromatids held together by a centromere. Chromosomes  are paired, males have XY and females have XX. 

The Cell Cycle- consists of interphase, 90percent of the cycle and cell division. There are 3 stages in interphase: G1stage the cell doubles, S stage it replicates. and G2 the cell breaks down proteins for cell division.  There are 2 types of cell division, Mitosis and meiosis, and 2 stages mitotic and cytokinesis.

Mitosis-when the parent cell divides into two daughter cells that are identical to the parent cell through the process of prophase, metaphase, anaphase, and telophase. 

Meiosis-when cell divides into four daughter cells that are not identical. Spermatogenisis and oogenisis involve meiosis.

Chromosome inheritance-A chromosome carries genetic information in a certain order. When nondisjunction occurs it results in  trisomy, 24 chromosomes or monosomy 22 chromosomes. Nondisjunction can result in too many or too few sex chromosomes. Example is Turner Syndrome were only one chromosome is apparent. Certain syndromes can be traced to chromosome structure changes. The kinds of changes include<>

DNA/genes in cell metabolism

DNA is a found in the nucleus of the cell and stores gene information, can replicate, and undergo mutation. It has a double helix and is comprised of a series of nucleotides. The phosphate and sugar molecules are the backbone of the paired bases. Replication occurs creating two identical molecules. RNA are made up of sugar ribose and assists DNA in protein synthesis. Three types of RNA assist in the process: rRNA found in ribosomes, mRNA which act as messengers, and tRNA which tranfers amino acids to ribosomes. Protein synthesis requires transcription when a copy is made and translation that occurs when a codons from MRNA match up to a sequence of amino acids.

Cellular basis for cancer

Cancer develops in various stages and is a cellular disease. The cells replicate divide unlimited times. Cacinogenisis  starts with initiation when the cell starts to divide, promotion when the tumor develops, and progression when the cells mutate and starts to invade other cells.

Recombinant DNA- Genetically modified form of DNA created by the insertion of DNA into an "existing organismal genome.  A restriction enzyme is used to fuse a human DNA with a plasmid DNA. Another enzyme DNA ligase seals the opening and the rDNA molecule is ready. Bacteria take up the plasmid.  when plasmid replicate it becomes a clone. The resulting bacteria can also result  in becoming a product.