Chapter 8 Cell Reproduction

Table of Contents Section 1 Chromosomes Section 2 Cell Division Section 3 Meiosis

Section 1: Chromosomes Objectives Describe the structure of a chromosome. Identify the differences in structure between prokaryotic chromosomes and eukaryotic chromosomes. Compare the numbers of chromosomes in different species. Explain the differences between sex chromosomes and autosomes. Distinguish between diploid and haploid cells.

DNA Recall: DNA stands for Deoxyribonucleic acid. DNA stores genetic information, synthesizes proteins, and controls cellular activities. DNA is a polymer. Its monomer is a nucleotide.

DNA DNA is a long thin molecule. It is organized into long structures called chromosomes. DNA is packed and coiled in a complicated but organized manner.

Chromosome structure Chromosomes are rod-shaped structures made of DNA and protein. In eukaryotes, DNA wraps around proteins called histones to help maintain the compact structure of chromosomes and aid in the tight packaging of DNA. Nonhistone proteins are involved in controlling specific regions of the DNA.

Chromosome Structure

Chromosome Structure Between cell divisions, DNA isn’t so tightly coiled into chromosomes. Regions of DNA uncoil in between cell divisions so they can be read. The less tightly coiled DNA-protein complex is called chromatin.

Parts of a chromosome

Parts of a chromosome ..\..\Abir School CD copy\Biology\Teacher's one stop\Powernotes presentations\ch_ppts\Ch08\60116.html

Chromosome Structure Chromosomes in prokaryotes are simpler in structure than chromosomes in eukaryotes. DNA of most prokaryotes consists of only one chromosome, which is attached to the inside of the cell membrane. Prokaryotic chromosomes consist of a circular DNA molecule.

Chromosome Numbers Each species has a characteristic number of chromosomes in each cell.

Chromosome Numbers Chromosome numbers of various organisms

Chromosome Numbers Sex Chromosomes and Autosomes Sex chromosomes are chromosomes that determine the sex of an organism. All of the other chromosomes in an organism are autosomes.

Chromosome Numbers Every cell of an organism produced by sexual reproduction has two copies of each autosome. The organism receives one copy of each autosome from each parent. The two copies of each autosome are called homologous chromosomes or homologues. Homologous chromosomes are the same size and shape and carry genes for the same traits.

Sex Chromosomes and Autosomes ..\..\Abir School CD copy\Biology\Teacher's one stop\Powernotes presentations\ch_ppts\Ch08\60121.html

Karyotype Karyotypes are used to examine an individual’s chromosomes. Karyotypes are made from a sample of person’s Blood. WBCs are treated chemically to stimulate then arrest mitosis in Metaphase. The chromosomes are photographed, cut out, and arranged by size and shape into pairs.

Karyotype

Chromosome Numbers Diploid and Haploid Cells Cells having two sets of chromosomes are diploid (2n). Haploid cells (1n) have only one set of chromosomes.