Chapter 10Chromosomes andCell Reproduction

Chromosomes

Organisms grow by dividing of cellsBinary Fission – form of asexual

reproduction that produces identicaloffspring (Bacteria)

Eukaryotes have two types of celldivision, Mitosis and Meiosis

Somatic Cell – a cell other than asperm or egg cell (Mitosis)

Gamete – a sperm or egg cell(Meiosis)

Before a cell divides, chromosomesare made

Chromosome – when the DNA andproteins associated with DNA coil

Gene – segment of DNA that codesfor a protein

Before chromosomes are created,DNA is copied

The two exact copies are calledchromatids

Two chromatids are held togetherby a centromere

Chromosome #

Diploid – somatic cell contains twosets of chromosomes (2n)

Haploid – when a gamete cellcontains one set of chromosomes(n)

Fusing two gametes creates adiploid zygote (fertilized egg cell)

Homologous Chromosomes are likea pair of shoes

You get one “shoe” from yourmother and one “shoe” from yourfather

n + n = 2n

Chromosomes determine the sex ofoffspring

X and Y chromosomes are the sexchromosomes

All others are called autosomesXX = Female (humans)XY = Male

Some organisms have differenttypes of sex chromosomecombinations

XX = Male BirdX = Female Bird

Changing Chromosome #

Each chromosome had thousandsof genes

Things go wrong if missing orhaving extra chromosomes

Example is trisomy (three copies ofa chromosme)

Trisomy 21 causes Down syndrome

Trisomy 13 causes Patau Syndrome

A karyotype is a picture of thechromosome #

Used to detect abnormalities inchromosome #

Change in Structure

Mutation – change in chromosomestructure

Four types of mutationsDeletion – Deletes informationDuplication – Adds extra

information

Inversion – Changes order ofinformation

Translocation – moves informationto a different chromosome

The Cell Cycle

Is a repeating sequence of cellulargrowth and division during the life ofan organism

Broken down into 3 main phases:Interphase, Mitosis, Cytokinesis

90% of the time, a cell is inInterphase

Interphase

Can be broken down intosmaller phases: G1, S, G2

G1 Phase

Cell grows rapidly andcarries out routine functions

Cell spends most of its life inthis phase

S or Synthesis Phase

A cell copies its DNAEach chromosome consists

of two chromatids attachedat a centromere at the endof S Phase

G2 Phase

Nucleus prepares to divideProteins called microtubules

form (used to movechromosomes duringmitosis)

Mitosis

The process of cell divisionin which the nucleus of a celldivides into two nuclei

Produces exact copies

Cytokinesis

The process during celldivision when the cytoplasmdivides

Controlling the Cell Cycle

Controlled by many proteinsUse checkpoints to regulate the

cycle

G1 Checkpoint

Decides whether a cell willdivide

If conditions are favorable,proteins will stimulate the cellinto starting the S Phase

Only when conditions arefavorable

DNA Synthesis or G2 Checkpoint

DNA replication is checked by DNArepair enzymes

If checkpoint is passed, proteins helptrigger mitosis

Mitosis Checkpoint

Triggers the exit from mitosisSignals the beginning of the G1

Phase

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Cancer

Certain genes contain theinformation for makingcheckpoint proteins

If one of these genes getsmutated, the check points maynot function

Cancer is the uncontrolledgrowth of cells

Some mutations cause cells togrow to rapidly byoverproducing growthmolecules

Some mutations causeinactivation of checkpointproteins

Some mutations occurspontaneously

Others are caused byenvironmental influences

Mitosis

Mitosis is the division of onenuclei into two

Each contains a completeset of the cell’schromosomes

Structures called centrioles arereplicated during G2 Phase in animalcells

These centrioles migrate towards thepoles during mitosis

When they move, spindle fibers begin toform

Spindle fibers are made of microtubules

Spindle fibers areresponsible for separatingchromatids during mitosis

Prophase

Chromosomes coil up andbecome visible

The nuclear envelopedissolves and the spindleforms

Metaphase

The chromosomes move to themiddle of the cell and line up onthe equator

Spindle fibers link to thechromatids of eachchromosome

Anaphase

Centromeres divideTwo chromatids move towards

opposite polesThese chromatids are now

called chromosomes

Telophase

A nuclear envelope formsaround the chromosomes ateach pole

Chromosomes at each poleuncoil and the spindle dissolves

Mitosis is now complete

Cytokinesis

The cytoplasm of the cell divides inhalf

Cell membrane grows to encloseeach cell

End result is two identical cells In animal cells, a belt of proteins

threads pinches the cell in halfPlant cells use a cell plate to split a

cell into two

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