CHROMOSOMES AND CELL REPRODUCTIONSECTION 1: CHROMOSOMES

Chapter 6

Grade 10 BiologyFall 2010

Bell Ringer

1. What is the difference between prokaryotes and eukaryotes?

2. Do all cells divide in the same manner?

Objectives

Identify four examples of cell division in eukaryotes and one example in prokaryotes

Differentiate between a gene, a DNA molecule, a chromosome, and a chromatid

Differentiate between homologous chromosomes, autosomes, and sex chromosomes

Compare haploid and diploid cells Predict how changes in chromosome number

or structure can affect development

Formation of New Cells

About 2 trillion cells are produced by an adult human body every day

New cells are formed when older cells divide Cell division, aka cell reproduction

Formation of New Cells

Different types of cell division The type of cell division differs depending on

the organism and why the cell is dividing Prokaryotes: bacteria reproduce asexually Eukaryotes: undergo growth, development, repair, or

asexual reproduction, formation of gametes

Formation of New Cells

Gametes: are an organism’s reproductive cells Sperm or eggs

Formation of New Cells

Regardless of the type of cell division occurring, information stored in DNA must be present in each of the resulting cells DNA directs cells activities and

determines its characteristics

When a cell divides, DNA is first copied and then distributed

Each cell ends up with a complete set of the DNA

Prokaryotic Cell Division

DNA- circular, attached to inner cell membrane

Reproduce by binary fission Binary Fission: form of asexual

reproduction that produces identical offspring Single parent passes exact copies of

all of its DNA to its offspring

Prokaryotic Cell Division

Binnary Fission Stages:1.DNA is copied 2.Cell divides

Adds new cell membrane to the point on the membrane between the two DNA copies

New cell wall forms around membrane

Pinch in two

Eukaryotic Cell Reproduction

Genes: segments of DNA that codes for a protein or RNA molecule

Single molecule of DNA has thousands of genes lined up like train cars

Eukaryotic Cell Reproduction

Chromosomes: consists of DNA tightly coiled around proteins, condensed form of DNA DNA and proteins become visible

Chromatids: the 2 exact copies of DNA that make up each of the chromosomes

Centromere: the point where two chromatids of a chromosomes are attached

Activity Time!

Design a chromosome of your own. Label and colour:

Chromosome Centromere Chromatids 2 Gene regions

Eukaryotic Cell Reproduction

2 chromatids get separated during cell division and placed into each new cells Ensures that each new

cells will have the same genetic information as the original cell

Chromosome Number and Structure

Somatic Cell: body cell, any cell other than sperm or egg Has 2 copies of 23 different chromosomes Total of 46 chromosomes 23 chromosomes differ in size, shape and set of genes

Sets of Chromosomes

Homologous chromosomes: chromosomes that are similar in size, shape, and genetic contents

Each of 23 pairs of chromosomes consists of two homologous chromosomes

Each homologue in a pair of homologous chromosomes comes from one of the two parents

Sets of Chromosomes

Diploid: contains 2 sets of chromosomes, somatic cells 2n = (23 x 2) = 46

Haploid: contains 1 set of chromosomes, gamete cells n = 23

Each organism has characteristic number of chromosomes

Sets of Chromosomes

Fertilization: fusion of 2 haploid (n) gametes (sperm and egg) Forms diploid (2n) zygote

Zygote: a fertilized egg cell

Sex Chromosomes

Autosomes: chromosomes not directly involved in determining the sex of an individual 22 pairs in humans

Sex Chromosomes: contain genes that will determine the sex of an individual 1 pair out of 23 in humans

Sex Chromosomes

Human sex chromosomes: X Y- genes that cause fertilized egg to develop into a

male located here XX- female XY- male Sex determined by male since females only have X

X X

X XX XX

Y XY XY

Change in Chromosome Number

Presence of all 46 chromosomes is essential for normal development and function

Trisomy: humans with more than two copies of a chromosome Will not develop

properly

Change in Chromosome Number

Karyotype: a photo of a chromosome in a dividing cell that shows the chromosome arranged by size

Change in Chromosome Number

Down syndrome: Trisomy 21 Short stature, round

face with slanted eyes, varying degrees of mental retardation

How does this happen?

Change in Chromosome Number

Disjunction: if one or more chromosomes fail to separate properly One new gamete ends up receiving both chromosomes

and other gamete receives none

Trisomy occurs when gamete with both chromosomes fuses with a normal gamete

Activity Time!

Karyotype activity with a friend!Label:

Haploid number Diploid number

Indicate: Autosomes Sex cells If male or female

Change in Chromosome Structure

Mutation: changes in chromosome structure

Change in Chromosome Structure

Deletion: a piece of chromosome breaks off completely After cell division the new cell will lack a certain set of

genes

Change in Chromosome Structure

Duplication: chromosome fragment attaches to its homologous chromosome Carries two copies of a certain set of genes

Change in Chromosome Structure

Inversion mutation: chromosome piece reattaches to the original chromosome but in a reverse orientation

Translocation mutation: if the piece reattaches to a nonhomologous chromosome

Activity Time!

Modeling Chromosomal Mutations 11 note cards Label:

1 – 5 Centromere 1 – 2 6 – 8

Demonstrate the 4 types of mutations