homo sapiens (human)46 mus musculus (house mouse)40 zea mays(corn or maize)20 drosophila...
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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
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
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 II – Metaphase IIMeiosis II – Metaphase II
• Sister chromatids connect to spindle fibers
• Line up in the middle
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