Chapter 6
CHROMOSOMES AND CELL REPRODUCTION
SECTION 1: CHROMOSOMES
Grade 10 Biology
Fall 2010
Bell Ringer
What is the difference between prokaryotes and
eukaryotes?
2. Do all cells divide in the same manner?
1.
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:
DNA is copied
2. Cell divides
1.



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


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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