Chapter 7 Chromosomes Mitosis and Meiosis Chromosomes DNA

Chapter 7 Chromosomes & Mitosis and Meiosis

Chromosomes • DNA coiled around proteins forms chromosomes DNA Double Helix- DNA Coiled Chromatid around Proteins 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(2 n) - have 2 copies of all chromosomes (regular human cells) Egg – haploid(n) - Sperm haploid(n) - Fertilized Egg Diploid(2 n)

Types of Chromosomes • Autosomes- the 22 pairs of chromosomes that do NOT determine the sex of an organism • Sex Chromosomes- the 23 rd 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 G 1 (gap 1) - Cell Growth S (synthesis) - DNA Synthesis Cytokinesis G 2 (gap 2) M (mitosis) - Cell Division - Cell Growth • G 1 - cell grows • S- DNA is copied • G 2 - growth & preparation for mitosis • M- cell divides • Cytokinesis- point when 2 new cells split apart • Apoptosis- cell death

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: 1) 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(2 n) Parent Cell Meiosis II Immature Sperm Cells Haploid(n) Sperm Cells

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

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