Download Bio Ch 8-1 Notes

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
cat
human
8
32
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
diUMc96w