Homo sapiens (human) 46 Mus musculus (house mouse) 40Zea mays(corn or maize) 20Drosophila melanogaster (fruit fly) 8Xenopus laevis (South African clawed frog) 36Caenorhabditis elegans (microscopic roundworm) 12Saccharomyces cerevisiae (budding yeast) 32Canis familiaris (domestic dog) 78Arabidopsis thaliana (plant in the mustard family) 10Muntiacus reevesi (the Chinese muntjac, a deer) 32Muntiacus muntjac (its Indian cousin) 6Myrmecia pilosula (an ant) 2Parascaris equorum var. univalens (parasitic roundworm) 2Cambarus clarkii (a crayfish) 200Equisetum arvense (field horsetail, a plant) 216

Chromosome Number of Chromosome Number of Different SpeciesDifferent Species

Chromosome VocabularyChromosome Vocabulary

DNADNA Doubles during Doubles during

interphase (S interphase (S phase)phase)

ChromosomeChromosome Forms during Forms during

prophaseprophase Become sister Become sister

chromatidschromatids

Homologous Homologous ChromosomesChromosomes: :

Members of a pair of Members of a pair of chromosomeschromosomes One – MomOne – Mom One – DadOne – Dad

Same sizeSame size Same shape Same shape

(centromere location)(centromere location) Same number and Same number and

type of genestype of genes

Homologous Homologous ChromosomesChromosomes::

Specific gene Specific gene information may information may differdiffer (brown eyes from (brown eyes from

mom, blue eyes mom, blue eyes from dad)from dad)

Homologous Homologous ChromosomesChromosomes::

Same banding Same banding pattern when pattern when stained and viewed stained and viewed under a under a microscope. microscope. Bands DO NOT Bands DO NOT

indicate genes. indicate genes.

Types of Chromosomes:Types of Chromosomes:

Humans have 23 Humans have 23 pairs of pairs of chromosomes. chromosomes.

Types of Chromosomes:Types of Chromosomes:

2 Types:2 Types: Autosomes:Autosomes:

Members of Members of chromosome chromosome pairs #1-22.pairs #1-22.

Types of Chromosomes:Types of Chromosomes:

2 Types:2 Types: Sex Sex

Chromosomes:Chromosomes: Members of Members of

chromosome pair chromosome pair #23#23

Females = XXFemales = XX Males = XYMales = XY

Sex ChromosomesSex Chromosomes

ALL pairs are ALL pairs are homologous in homologous in females because they females because they have two X have two X chromosomeschromosomes

The sex The sex chromosomes of chromosomes of males are NOT males are NOT homologous, they homologous, they have one X and one Yhave one X and one Y

Diploid vs. Haploid

DiploidDiploid: two sets of chromosomes: two sets of chromosomes Each chromosome has a homologous Each chromosome has a homologous

pair– there is one from each parent!pair– there is one from each parent! They have the same type of genes They have the same type of genes

but are not identicalbut are not identical

Human body cells:

23 PAIRS 46 total

Diploid vs. Haploid

HaploidHaploid: one set of chromosomes: one set of chromosomes Why would you want just one set of Why would you want just one set of

chromosomes in a cell?chromosomes in a cell?

SEXUAL REPRODUCTION!SEXUAL REPRODUCTION!

Human gametes: 23 total

Why do we need Why do we need meiosis?meiosis?

Meiosis is necessary to halve the Meiosis is necessary to halve the number of chromosomes going number of chromosomes going into the sex cellsinto the sex cells Gametes are haploid (1n)Gametes are haploid (1n)

1 N egg1 N sperm

2N zygote

Why do we need Why do we need meiosis?meiosis?

FertilizationFertilization Male and female sex cells will Male and female sex cells will

provide provide ½ of the chromosomes½ of the chromosomes each each Offspring has genes from both Offspring has genes from both

parentsparents 1n + 1n = 2n1n + 1n = 2n

1 N egg1 N sperm

2N zygote

Video ClipVideo Clip

Worksheet 17: Meiosis OverviewWorksheet 17: Meiosis Overview

Two divisionsTwo divisions

- - Meiosis 1Meiosis 1::

- like mitosis, but not quite- like mitosis, but not quite

- creates 2 cells (haploid)- creates 2 cells (haploid)

- - Meiosis 2Meiosis 2::

- divides again- divides again

- creates 4 gametes (haploid)- creates 4 gametes (haploid)

2N

1N

1N 1N

1N

Meiosis SummaryMeiosis Summary

Meiosis SummaryMeiosis SummaryParent cell – chromosome pair

Chromosomes copied

1st division - pairs split

2nd division – produces 4 gamete cells with ½ the original # of chromosomes

Meiosis I – Prophase IMeiosis I – Prophase I

Nuclear envelope Nuclear envelope dissolvesdissolves

Meiosis I – Prophase IMeiosis I – Prophase I

TetradsTetrads form form Homologous pair Homologous pair

links togetherlinks together Crossing OverCrossing Over

Crossing Over in Prophase ICrossing Over in Prophase I Homologues break at Homologues break at

identical locations, identical locations, Rejoin opposite Rejoin opposite

partnerspartners Occurs randomly Occurs randomly

several times on several times on every chromosome every chromosome Results in mixing of Results in mixing of

the genes you the genes you inherited from your inherited from your parentsparents

Crossing over is NOT Crossing over is NOT a mutationa mutation

Meiosis I – Metaphase IMeiosis I – Metaphase I

Tetrads line up in Tetrads line up in middlemiddle

Spindle fibers Spindle fibers attachattach

Independent Independent AssortmentAssortment

Independent AssortmentIndependent AssortmentMetaphase IMetaphase I

Principle of Independent Assortment—Genes for different traits (on differentchromosomes) can separate independently of each other. --Happens because homologous pairs line up in random order on random sides during Metaphase I

Meiosis I – Anaphase IMeiosis I – Anaphase I

Fibers pull Fibers pull homologous homologous chromosomes chromosomes apartapart

Sister chromatids Sister chromatids are still connected!are still connected!

(2 X’s are (2 X’s are separating from separating from each other)each other)

Meiosis I – Telophase IMeiosis I – Telophase I

Cell separated into two cells

Nuclear membrane forms

Meiosis II – Prophase IIMeiosis II – Prophase II

Nuclear membranes dissolve

New spindle fibers form

Meiosis II – Metaphase IIMeiosis II – Metaphase II

• Sister chromatids connect to spindle fibers

• Line up in the middle

Meiosis II – Anaphase IIMeiosis II – Anaphase II

Sister chromatids separate

Meiosis II – Telophase IIMeiosis II – Telophase II

Cells divide Now there are 4

haploid cells!

Steps of Meiosis I and IISteps of Meiosis I and II

Video ClipVideo Clip

Worksheet 18: Animal Cell MeiosisWorksheet 18: Animal Cell Meiosis

http://www.johnkyrk.com/meiosis.html

Cell DivisionCell Division

Products of Products of MitosisMitosis::

Two identical Two identical cellscells

Somatic cellsSomatic cells

AKA body cellsAKA body cells DiploidDiploid

Products of Products of MeiosisMeiosis::

Four different Four different cellscells

GametesGametes

AKA sex cellsAKA sex cells HaploidHaploid

Comparing Meiosis and Comparing Meiosis and MitosisMitosis

Your Turn!Your Turn!

Mitosis and Meiosis WorksheetMitosis and Meiosis Worksheet