4.1-Cell Division & Genetic Material cont’d:

Chromosomes and Karyotypes

SBI3U

Asexual Reproduction• Reproduction requires

only one parent ▫ produces genetically

identical offspring.

• Single-cell organisms can reproduce asexually through mitotic division

• (ie. Bacteria, protists, fungi)

Sexual Reproduction•Two parents give rise to an

offspring

•Offspring have a unique combination of genes from both parents

•Offspring is genetically distinct from siblings and parents

Sexual Reproduction Cont’d•Requires fusion of male and female gametes

•GAMETE: male or female reproductive cell (i.e. egg or sperm)

•When the male and female gamete join (fertilization), a ZYGOTE is formed.

Chromosomes•Human Somatic Cells

▫46 chromosomes (23 from each parent)

•Each chromosome is paired▫one chromosome from the father

and one from the mother.

maternal paternal

Chromosomes Cont’d•1 of the 23 pairs of chromosomes are

called sex chromosomes, the remaining pairs are called autosomes

•Sex chromosome: an X or Y chromosome that determines the genetic sex of an organism.

•Females: XX

•Males: XY

Chromosomes Cont’d

sex chromosome

s

Homologous Chromosomes•Pairs of chromosomes that appear similar.

•Similarities:▫length▫centromere location▫banding patterns

•Each chromosome has genes (sections of DNA) ▫Genes contain specific genetic information for traits

Similarities:

1) Length

2) Banding patterns (genes)

3) Centromere location

Homologous Chromosomes

Homologous Chromosomes Cont’d

•Homologous chromosomes have several characteristics in common.

•However, they are not identical

•They can carry different forms of the same gene, called alleles.

•The different alleles allow the variation in the population.

GENE ALLELE•Section of DNA that controls a specific trait.•Ex. eye colour, blood type, skin colour

•Specific variation of a gene.•Ex. blue eyes, green eyes, type A blood, black skin, white skin

Examining Chromosomes…•Karyotype is a photograph used to

examine pairs of homologous chromosomes in a cell

•Cell sample is collected and stopped during metaphase

•The sample is stained and viewed under a microscope

KaryotypeChromosomes are ordered from largest to smallest, and paired with other chromosomes that have the same banding pattern

Autosomes are numbered from 1-22.

Sex chromosomes are identified as X or Y

A B

C

D E

F G

Why study karyotypes?•Karyotypes help to determine

chromosome abnormalities

•Can indicate genetic disorders such as Down syndrome or Turner syndrome.

• .

Check your Understanding…

Identify the abnormalities in the following karyotypes…

Homework•Read pgs. 166-168•Complete pg. 168 Q# 1, 4 , 5, 9, 14, 17•Karyotype Assignment