Chapter 8Cell Reproduction

Introduction to Chromosomes

Important Words

Chromosomes – tightly coiled packages of DNA; they are rod shaped and proteins hold them together.

Strands of DNA wrap around proteins called Histones.

Important Words

Chromatid – each half of a chromosome; forms as DNA copies itself before cell division

Centromere – holds the chromatids together until they separate

Important Words

Each species has a unique number of chromosomes.

How many chromosomes do humans have?

46 chromosomes or 23 pairs.

Types of Chromosomes

2 Types of Chromosomes: 1. Sex Chromosomes – are the chromosomes that

determine the sex of an organism.

Female: XX

Male: XY

2. Autosomes – all other chromosomes Humans: 44 autosomal chromosomes

Karyotype: Picture of Chromosomes. What do you notice about the arrangement?

Chromosomes

Karyotype – is a picture of the chromosomes in a somatic (body) cell.

22 homologous pairs of autosomes.

2 sex chromosomes Is this person male

or female? Male: XY Normal or abnormal Normal: 23 pairs

Chromosomes

Homologous chromosomes – two copies of each autosome (maternal and paternal)

Homologous chromosomes are the same size, shape, and carry genes for the same trait.

Final pair is not numbered: Sex Chromosomes.

Compare the karyotypes. Record your observations

Karyotype A Karyotype B

Comparisons

Karyotype A 19 pairs: Not Human Sex: Male (XY) Sister chromatids are still

attached at their centromeres (these are double copies of each chromosome).

This is a picture BEFORE the cell divided!

Karyotype B 23 pairs: Human Sex: Female (XX) Single Copy of each

chromosome. This picture was taken

AFTER the cell divided! Be prepared to analyze a

karyotype regardless of when the picture of the chromosomes was taken.

Human Karyotype: Male

Human Karyotype: Female

Chromosomes

Diploid – cells have two sets (maternal and paternal) of chromosomes. Have all 46 chromosomes. Represented by 2n (means a full set of DNA) Somatic Cells (cells making up the body)

Haploid – cells have one set of chromosomes. Have 23 chromosomes. Represented by n (means a half set of DNA) Gametes (reproductive cells : egg and sperm)

Haploid Cells

Reproductive Cells Gametes - sperm and

egg cells; they have 23 chromosomes

Fertilization 23 in sperm + 23 in egg = 46 in zygote

Gametes are produced through Meiosis (cell division results in 4 genetically different cells)

Diploid Cells

Somatic Cells Cells that make

up the body of organisms.

Somatic Cells are produced through Mitosis (cell division results in 2 genetically identical cells).