8.02

 Body is made up of millions of tiny structural units called cells.  The cell is the basic unit of the body the supports and sustains life of an animal.

CELL PARTS  Protoplasm- the material or contents inside of a cell.  Cell Membrane- a thin layer of protein and fat that surround the cell. Some substances can pass into the cell and the membrane blocks others materials from entering.  Centrosome- small body where the microtubules are made. The centrosome divides during mitosis.  Nucleus- gives cell ability to grow, digest food and divide. Contains chromosomes and DNA.  Cytoplasm- a jellylike substance that gives the cell shape and contains components necessary for cell functions.

 Golgi body- located near the nucleus and produces the membrane that surrounds the lyosomes.  Lyosome- round shaped organelles that contain digestive enzymes that allow for digestion of cell nutrients.  Mitochondrion- rod-shaped organelles that convert the energy stored in glucose into ATP (adenosine triphosphate).  Nuclear membrane- the membrane that surround the nucleus.  Nucleolus- organelle found inside the nucleus. Produced ribosomal RNA.  Endoplasmic Reticulum- transports materials through the cell.  Vacuole- fluid filled membrane that fills with food and waste products inside the cell.  Ribosome- site of protein synthesis.

 Type of cell division that increases the total number of cells and results in animal growth with the chromosome pairs being duplicated in each new cell.  Results in animal growth.  Animals begin as a single cell.  Chromosomes are duplicated in each new cell as division occurs.  There are four typical stages in mitosis cell division:  Prophase- the nucleolus disappears and centrioles move to opposite ends of the cell. Fibers begin to form and extend from the centromeres.  Metaphase- spindle fibers align the chromosomes along the middle of the cell nucleus.  Anaphase- the paired chromosomes separate and move to opposite sides of the cell.  Telophase- nuclear membrane forms around the newly divided chromosomes and cell membrane begins to contract.

MEIOSIS  Type of cell division that produces the sex cells or gametes that have ½ the number of chromosomes that body cells have.  Gamete Formation  One set of chromosomes come from the sperm and one from the ovum.  The zygote that is created during fertilization has chromosomes from each parent. Chromosomes match up with one another based on the genetic information they carry.  Sex cell formation of the sperm and ova are also produced through meiosis:  Production of sperm is called spermatogenesis.  Male animals begin producing sperm at sexual maturity.  Spermatocytes divide into spermatids through meiosis.  Production of an ovum is called oogenesis.  Females also begin producing ova at sexual maturity.  The oocytes divide and form an ovum. The ovum contains cytoplasm and stored food. It provides nourishment for the zygote and embryo.

 Chromosomes- rod-shaped bodies that are in pairs.  Cattle- 30 pairs.  Hogs- 19 pairs.  Chickens- 39 pairs.  Genes- located on chromosomes, control characteristics that are inherited from parents.

 Dominant Genes- hide the effect of recessive genes (covers recessive traits). Represented by a capital letter.  Recessive Genes- mask dominant genes, but can show up when heterozygous gene pairs (Pp x Pp) combine as homozygous recessive “pp”. In this case if “p” is the recessive trait for horns, the calf will have horns.  Homozygous- genes are the same on each allele.  Heterozygous- gene pairs that carry two different genes that affect a trait.

 Heritability- the likelihood of a trait being passed on from parent to offspring.  Heritability estimates vary from 0% to about 70%.  If a trait is highly heritable, a producer will see improvements faster than traits that have a low heritability estimate.  Heritability estimates for traits in beef cattle are generally higher than for traits in swine.  Heritability traits are usually higher for carcass quality traits than for reproduction traits in both swine and beef cattle.  Traits with low heritability estimates are improved most through environment, and those traits with high heritability estimates are improved most by selective breeding and environmental improvements.