Chromosomes and Chromosomes and Meiosis Meiosis

UnitUnit

Cell TypesCell Types

1) Somatic Cells (aka: body cells)1) Somatic Cells (aka: body cells)

- are diploid (2n)- are diploid (2n)

- DNA not passed on- DNA not passed on

Cell TypesCell Types

2) Gametes (aka: sex cells)2) Gametes (aka: sex cells)

- ex: ova (egg) and - ex: ova (egg) and spermatozoa (sperm)spermatozoa (sperm)

- are haploid (1n)- are haploid (1n)

- DNA passed on- DNA passed on

Egg and Sperm Comparative SizeEgg and Sperm Comparative Size

Diploid vs. HaploidDiploid vs. HaploidDiploid cells have two Diploid cells have two copies of each copies of each chromosome: one copy chromosome: one copy from the mother and from the mother and one from the father.one from the father.

Haploid cells have only Haploid cells have only one copy of each one copy of each chromosomechromosome

Look at the following Look at the following chromosome numbers of chromosome numbers of these living things.these living things.

Do you notice anything Do you notice anything about the numbers?about the numbers?

Chromosome Numbers of Various Chromosome Numbers of Various Living ThingsLiving Things

Algae Algae

148148CowCow

6060Dog Dog

7878EarthwormEarthworm

3636

KangarooKangaroo

1212MosquitoMosquito

66PigeonPigeon

8080TigerTiger

3838

ShrimpShrimp

254254DeerDeer

7070TurkeyTurkey

8282Horse Horse

6464

HedgehogHedgehog

9090GiraffeGiraffe

6262CabbageCabbage

1818CarpCarp

104104

ChromosomesChromosomes

Each species has a Each species has a characteristic number of characteristic number of chromosomeschromosomes

That fact prevents this from That fact prevents this from happeninghappening

That fact allows this to happenThat fact allows this to happen

That fact allows this to happenThat fact allows this to happen

That fact allows this to happenThat fact allows this to happen

Mule = male donkey and a Mule = male donkey and a female horsefemale horse

That fact allows this to happenThat fact allows this to happen Liger TigonLiger Tigon

ChromosomesChromosomes (cont) (cont)

TypesTypes

1) Autosomes1) Autosomes

2) Sex Chromosomes2) Sex Chromosomes

- female = XX- female = XX

male = XYmale = XY

The sex of some species is The sex of some species is determined by the temperature of determined by the temperature of the environment during incubationthe environment during incubation

(mostly occurs in reptiles) (mostly occurs in reptiles)

ChromosomesChromosomes (cont) (cont)

Humans have 46 chromosomes Humans have 46 chromosomes (23 pairs)(23 pairs)

- 44 autosomes (22 pairs) and - 44 autosomes (22 pairs) and 2 sex chromosomes (1 pair)2 sex chromosomes (1 pair)

- a diploid # (2n) of 46 and a - a diploid # (2n) of 46 and a haploid # (1n) of 23haploid # (1n) of 23

Karyotype = picture of an Karyotype = picture of an individual’s chromosomesindividual’s chromosomes

Homologous Chromosomes vs. Homologous Chromosomes vs. Sister ChromatidsSister Chromatids

Homologous Chromosomes = Homologous Chromosomes = two separate chromosomes, two separate chromosomes, one from mom and one from one from mom and one from daddad

- very similar in size and carry - very similar in size and carry the same genes, but they are the same genes, but they are not copies of one anothernot copies of one another

Homologous Chromosomes vs. Homologous Chromosomes vs. Sister ChromatidsSister Chromatids (cont)

In contrast, each half of a In contrast, each half of a duplicated chromosome is called a duplicated chromosome is called a chromatidchromatid- together, the two chromatids are - together, the two chromatids are called sister chromatidscalled sister chromatids- thus, sister chromatids refers to - thus, sister chromatids refers to the duplicated chromosome that the duplicated chromosome that remain attached (by the remain attached (by the centromere)centromere)

Homologous Homologous chromosomes chromosomes (shown (shown duplicated) are duplicated) are two separate two separate chromosomes – chromosomes – one inherited one inherited from the mother from the mother and one from and one from the fatherthe father

Homologous Chromosomes

Sister Chromatids

Sister Chromatids

Homologous Chromosomes vs. Homologous Chromosomes vs. Sister ChromatidsSister Chromatids (cont)

Homologous chromosomes Homologous chromosomes split in Meiosis Isplit in Meiosis I

Sister chromatids split in Sister chromatids split in Meiosis IIMeiosis II

MeiosisMeiosis

= a form of nuclear division = a form of nuclear division that divides a diploid cell into that divides a diploid cell into a haploid cella haploid cell

- makes egg and sperm- makes egg and sperm

- 2 rounds of division (Meiosis I - 2 rounds of division (Meiosis I and Meiosis II)and Meiosis II)

MeiosisMeiosis (cont)

Meiosis I – divides Meiosis I – divides homologous chromosomeshomologous chromosomes

Meiosis II – divides sister Meiosis II – divides sister chromatidschromatids

The overall process The overall process produces haploid cells.produces haploid cells.

Meiosis IMeiosis I

Meiosis IIMeiosis II

GametogenesisGametogenesis

1) spermatogenesis = sperm 1) spermatogenesis = sperm production (4 haploid cells)production (4 haploid cells)

- even distribution- even distribution

SpermatogenesisSpermatogenesis

GametogenesisGametogenesis (cont) (cont)

2) oogenesis = egg production 2) oogenesis = egg production (1 haploid cell)(1 haploid cell)

- uneven distribution (polar - uneven distribution (polar bodies created)bodies created)

OogenesisOogenesis

Comparing Mitosis and MeiosisComparing Mitosis and MeiosisMitosisMitosis - Produces - Produces

genetically genetically identical cells identical cells

- Results in diploid - Results in diploid cells cells

- Takes place - Takes place throughout an throughout an organism’s life organism’s life

- Involved in asexual - Involved in asexual reproductionreproduction

MeiosisMeiosis

- Produces - Produces genetically unique genetically unique cells cells

- Results in haploid - Results in haploid cells cells

- Takes place only at - Takes place only at certain time in life certain time in life cycle cycle

- Involved in sexual - Involved in sexual reproductionreproduction