Biology Chapters 6 & 7 Chromosomes Mitosis and Meiosis 1

DNA Deoxyribonucleic Acid is made up of building blocks called nucleotides (A, T, G, C) DNA directs all activities in a cell and determines characteristics of an organism There are 46 pieces of DNA in a normal human nucleus making up the 46 chromosomes There are only 23 pieces of DNA (chromosomes) in a human egg (ovum) and 23 pieces of DNA (chromosomes) in a human sperm 2

Genes Genes are sections of the DNA molecule that direct the production of a specific protein Genes on chromosomes are units of inheritance Humans have about 30,000 genes in the 46 chromosomes Genes can become detached from the DNA then reattach in reverse, resulting in a mutation 3

Mitosis Mitosis is the division of the cell nucleus right before a normal cell divides during growth and repair of an organism After cell division each cell is identical and contains the same genetic information Cell division is called cytokinesis Each new cell formed from mitosis has a complete set of the parent cell’s chromosomes Four stages of Mitosis (Prophase, Metaphase, Anaphase, and Telophase) P-M-A-T 4

Meiosis Meiosis is the process of forming gametes (egg) and (sperm) for reproduction Human sperm and egg cells have 23 chromosomes Meiosis produces 4 nuclei that have ½ (haploid) the number of chromosomes as the parent cell Two parents form haploid gametes which join to form a cell with ( = 46) chromosomes in sexual reproduction 5

Mutations Mutations are errors in the DNA, some are Bad, some are Good, and most are minor Examples: 1.Down Syndrome an extra #21 chromosome in each cell of the body (47 chromosomes), caused by non disjunction of the #21 during meiosis 2.Dwarfism 6

Terms of Genetics Mitosis – duplication of DNA and division of the nucleus Cytokinesis – division of the cell after Mitosis Diploid – When chromosomes are paired in humans that would be 23 pairs = 46 total Haploid – When chromosomes are not paired, in humans that would be 23 (egg and sperm) Crossover – chromosomes exchange corresponding sections of DNA during MEIOSIS 7

Genetic Diseases Down Syndrome – 47 chromosmes Hemophilia – sex-linked recessive gene Sickle Cell Anemia – one base pair wrong Color Blindness – sex-linked recessive gene 8

Stages of Mitosis (nucleus divides) 1.Prophase – DNA replicates to make 46 x 2 = 92 chromosomes in the nucleus 2.Metaphase – Chromosomes double up forming chromatids 3.Anaphase – Chromatids align on the cell equator 4.Telophase – Chromosomes separate with 46 going to each end of the cell 9