Chromosomes & Mitosis and Meiosis Chapter 7 Chromosomes & Mitosis and Meiosis

DNA Coiled around Proteins Chromosomes DNA coiled around proteins forms chromosomes DNA -Double Helix- DNA Coiled around Proteins Chromatid Super Coil Chromosome

DNA Coiling

Parts of a Chromosome Each half of a chromosome is called a chromatid Chromatids are held together at a point called the centromere

Genes Genes are segments of DNA in chromosomes that code for proteins Each chromosome contains hundreds of genes

Gametes Gametes are an organisms sex cells or reproductive cells Male gamete = sperm Female gamete = egg Each gamete only contains half the number of chromosomes of regular cells

Sets of Chromosomes Humans have 23 pairs of chromosomes, 46 total chromosomes Humans have 2 copies of each chromosome 2 exact copies of a chromosome are called Homologous Pairs

Fertilization Fertilization is the joining of male and female gametes, egg + sperm

Haploid & Diploid Cells Haploid Cells(n) - have ½ the number of chromosomes of other cells (egg&sperm) Diploid Cells(2n) - have 2 copies of all chromosomes (regular human cells) - Sperm haploid(n) Egg – haploid(n) - Fertilized Egg Diploid(2n)

Types of Chromosomes Autosomes- the 22 pairs of chromosomes that do NOT determine the sex of an organism Sex Chromosomes- the 23rd pair of chromosomes that determines the sex of an individual (X & Y chromosome) XX = female XY = male

Changes in Chromosome # If an individual has more or less than 46 chromosomes, a genetic disorder may result Ex: Trisomy-21 (Down Syndrome) - a person with trisomy-21 has 3 copies of chromosome #21 - Mutations in chromosomes may also cause genetic disorders

Trisomy-21

Karyotype A karyotype is a picture of an organisms chromosomes Karyotypes can be used to detect genetic disorders and chromosome abnormalities

The Cell Cycle The cell cycle is a repeating process in which a cell grows, copies it’s DNA, and then divides

Cell Cycle Diagram G1- cell grows S- DNA is copied G2- growth & preparation for mitosis M- cell divides Cytokinesis- point when 2 new cells split apart Apoptosis- cell death G1 (gap 1) - Cell Growth S (synthesis) - DNA Synthesis Cytokinesis G2 (gap 2) - Cell Growth M (mitosis) - Cell Division

Cancer Normal body cells that begin to grow & divide uncontrollably become cancer cells Carcinogen- a substance that causes cancer Ex: radiation(x-ray, UV-rays), chemicals, viruses

* * Mitosis Mitosis is the process of making exact copies of cells Phases of Mitosis: Prophase- - - * *

Phases of Mitosis 2) Metaphase- - * *

Phases of Mitosis 3) Anaphase- - * *

Phases of Mitosis 4) Telophase- -

Cytokinesis 2 exact copies of the original are formed

Interphase Interphase is the phase when a cell is resting and growing, not dividing Cells spend most of their time in interphase

Meiosis Meiosis is the process of forming sex cells (gametes) Gametes: Male = sperm Female = egg Meiosis produces haploid(n) cells, cells that have only one copy of each chromosome Egg & Sperm cells only have 23 chromosomes each

Spermatogenesis Spermatogenesis makes 4 sperm cells in males Diploid(2n)Parent Cell Meiosis I Immature Sperm Cells Meiosis II Haploid(n) Sperm Cells

Oogenesis Oogenesis makes egg cells in females makes 1 egg Diploid(2n)Parent Cell Meiosis I Polar Body Secondary Egg Cell Meiosis II Polar Bodies Haploid(n) Egg Cell * All Polar Bodies Die

Genetic Recombination Often during meiosis pairs of homologous chromosomes exchange pieces of DNA before they separate into daughter cells This exchange of genetic material is called Crossing Over Crossing over results in variation in the traits passed on to offspring

Crossing Over

END OF CHAPTER 7 NOTES