Chapter 8

Cell Reproduction

Section 8.1

Chromosomes

DNA- deoxyribonucleic acid

Consists of six billion pairs of nucleotides

Eukaryotic Cells

During cell division, DNA is coiled into compact chromosomes

Chromosomes are rod-shaped structures made of DNA and proteins

Each chromosome is a single DNA molecule wrapped around proteins called histones

Histones maintain the shape of the chromosome

Nonhistone proteins are involved in controlling the activity of specific regions of the DNA

Chromosome Structure

Each half is called a chromatid

The constricted area is called a centromere

When a cell divides, each of the two new cells receives one chromatid from each chromosome

Prokaryotic Cells

DNA usually consists of only one chromosome

DNA molecule is circular

Chromosome Numbers

Each species has a characteristic number of chromosomes

Examples: fruit fly 8 cat 32 human 46

Sex Chromosomes

Determine the sex of an organism

In humans, sex chromosomes are either X or Y

Normal females are XX Normal males are XY

Autosomes

The other 44 chromosomes are autosomes

Every cell of an organism produced by sexual reproduction has two copies of each autosome (one from each parent)

Homologous Chromosomes

Refers to the two copies of each chromosome

Same size and shape Carry genes for the same trait

Karyotype

A photomicrograph of the chromosomes in a dividing cell found in a normal human

46 human chromosomes exist as 22 homologous pairs of autosomes and two sex chromosomes

Diploid

Cells that have two sets of chromosomes

All normal human cells, except for reproductive cells, are diploid

Abbreviated as 2n

For humans, the diploid (2n) number is 46

Haploid

Cells that contain only one set of chromosomes

Includes sperm and egg cells

Abbreviated as 1n The haploid number (1n) of humans is

23

Introduction to Cell Reproduction http://www.youtube.com/watch?v=vjA

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