Genetics and Cell Cycle Chapter 18

Objectives Explain how the structure and replication of DNA are essential to heredity and protein synthesis, that changes in DNA may alter genetic expression. Understand the steps in mitosis and meiosis Predict and interpret patterns of inheritance. Understand that genetic information coded in DNA is passed from parents to offspring by sexual reproduction.

Chromosomes In each of your cells is found a nucleus. Inside the nucleus is found chromatin, or spaghetti looking DNA. During times of cell division, chromatin bunches together into 46 chromosomes, or colored stained x shaped structures.

Autosomes and Sex chromosomes 22 pairs are autosomes, Homologous- same shape 1 pair is the gender or sex chromosome. Males have an X and y shaped pair. Females have two X shaped chromosomes.

Karyotype White Blood Cells separate from blood using centrifuge. Cells are placed in a petri dish. Cells are stimulated to divide. Chromatin condenses to a chromosome. Nucleus dissolves. A chemical stops division and a picture is taken. The similar size chromosomes are placed together.

Diploid Having two sets of chromosomes 46 chromosomes Each pair has genes that code for a trait in the body, one on each side. Each side is called a sister chromatid. They are joined at a centromere.

Cell Cycle and Mitosis The process to divide cells to grow and heal. Interphase Cell division or Mitosis

Interphase Most of the life of the cell is spent making proteins, carbs, etc. Three stages G1 phase- Growth phase or Gap 1 Organelles are doubled, makes proteins needed for DNA replication. S phase- DNA replication or synthesis. DNA is copied or doubled. Chromosomes will have two sister chromatids. G2 phase- Gap 2 or Growth phase. Makes proteins in microtubules which pull apart chromatids.

Mitosis and Cytokinesis Division of the nuclear material or sister chromatids. Each new cell will have the same number of chromatin or DNA strands. 46 chromosomes. Two daughter cells will result after cytokinesis or cell division. Takes about 4 hours in humans. In RBCs, WBCs, skin, etc.

Mitosis Prophase Metaphase Anaphase Telophase Cytokinesis Interphase- cell growth

Prophase Spindle fibers are made of microtubules made of tubulin proteins

Metaphase

Anaphase

Telophase and Cytokinesis and Interphase Actin filaments form a ring that contracts.

Single cells only do Binary Fission Bacteria only have one chromosome so don’t do Mitosis. They just split one circular chromosome.

Control of Cell Cycle Apoptosis: programmed cell death. Destroys cells that divide when they shouldn’t Controlled by hormones in checkpoints in G1, G2, and Mitosis Human growth hormone. G1 checkpoint is when the cell will divide. If the cell is checked before this the cell will grow but not divide. DNA integrity is checked. If damaged then protein P53 stops the cycle and starts repair. If DNA can’t be repaired then cell will go through apoptosis. G2 checkpoint verifies DNA has duplicated. Allows damage from UV or X rays to be repaired

Control of Cell cycle Mitosis check 2 places to ensure chromosomes are properly attached and separated

Hormones control cell cycle Hormones attach to receptors on the cell membrane, signal genes inside the cell to make proteins to start division. Epidermal growth factors- cause skin to repair around an injury. Progesterone- helps cells to line uterus

Meiosis Increases variety in offspring. Called Reduction division. Parent makes 4 different sex cells. Makes sex cells which have half the number of chromosomes as other body cells. 46 chromosomes reduce to 23 chromosomes Diploid is reduced to Haploid gametes 2n becomes n Gametes are Sperm in males, Eggs in females

Homologous chromosomes Similar shaped chromosomes pair up. 4 chromatids together in synapsis in Prophase I Spindle appears Crossing over may happen between similar shaped chromosomes Allows exchange of traits

Crossing over can increase variety During Meiosis I, homologous chromosomes may exchange genes. Brown and blonde genes may switch

Meiosis Meiosis has two phases of mitosis called Meiosis I & II which reduces number of chromosomes in half from 46 to 23 Interkinesis: time between Meiosis I and II

Meiosis

Result of meiosis 4 gametes are formed, with different combinations of genes Humans have 23 chromatids so that is 2*23 possibilities of genes or 8,388,608 possible combinations of traits. Sperm joins with egg to form a diploid cell that grows into a new baby.

Compare Mitosis & Meiosis Mitosis has same number of chromosomes as parent cell. Mitosis makes two daughter cells Meosis begins with 4 sets of chromosomes, ends with half the number of chromosomes as parent cell, chromosomes can cross over in metaphase I. Meiosis makes four daughter cells