4 1 Cell Division Genetic Material contd Chromosomes

4. 1 -Cell Division & Genetic Material cont’d: Chromosomes and Karyotypes SBI 3 U

Asexual Reproduction • Reproduction requires only one parent ▫ produces genetically identical offspring. • Single-cell organisms can reproduce asexually

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 chromosomes

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

Karyotype Chromosomes 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 B A C D F E 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