meiosis 5.3. i. cell division replaces worn out or damaged cells replaces worn out or damaged cells...

MeiosisMeiosis5.35.3

I. Cell DivisionI. Cell Division

Replaces worn out or damaged cellsReplaces worn out or damaged cells Frequency of division varies by cell typeFrequency of division varies by cell type

Prokaryotes every 30 minutesProkaryotes every 30 minutes Nerve cells virtually neverNerve cells virtually never

Reproduction depends on cell divisionReproduction depends on cell division

II. Two Types of ReproductionII. Two Types of Reproduction

Asexual ReproductionAsexual Reproduction reproduction of offspring from one parentreproduction of offspring from one parent offspring have identical genetic material as offspring have identical genetic material as

the parentthe parent binary fissionbinary fission

a. the simplest form of asexual reproductiona. the simplest form of asexual reproduction

b. most common among prokaryotesb. most common among prokaryotes

c. occurs in two stagesc. occurs in two stages

- copy the single circular DNA molecule- copy the single circular DNA molecule

- a new cell wall forms between DNA copies- a new cell wall forms between DNA copies


Asexual Reproduction – Binary FissionAsexual Reproduction – Binary Fission


Spores Spores a. a single spore will develop into an adult without a. a single spore will develop into an adult without

combining with another cellcombining with another cell

b. common among molds and fungib. common among molds and fungi

c. important in the life cycle of plantsc. important in the life cycle of plants

BuddingBuddinga. a cell’s nucleus divides and the cytoplasm a. a cell’s nucleus divides and the cytoplasm

divides unequallydivides unequally

b. common among yeasts and simple animalsb. common among yeasts and simple animals


Vegetative PropagationVegetative Propagationa.a. some plants produce organisms that some plants produce organisms that

are initially attached to the parent plantare initially attached to the parent plant

b.b. i.e. strawberry runners (horizontal i.e. strawberry runners (horizontal underground stems) & spider plantsunderground stems) & spider plants

Regeneration (fragmentation)Regeneration (fragmentation)a.a. ability to develop lost body parts or to ability to develop lost body parts or to

form new individuals from a single form new individuals from a single fragmentfragment

b.b. i.e. starfish & some plantsi.e. starfish & some plants


Sexual ReproductionSexual Reproduction formation of a new individual from the union formation of a new individual from the union

of two specialized parental cells (gemetes) of two specialized parental cells (gemetes)

a. female gamete = ovum or egga. female gamete = ovum or egg

b. male gamete = sperm cellb. male gamete = sperm cell

always requires TWO parentsalways requires TWO parents


Sexual ReproductionSexual Reproduction offspring usually show some offspring usually show some

characteristics of both parentscharacteristics of both parents fertilizationfertilization – fusion of 2 gametes (1n) – fusion of 2 gametes (1n)

(ovum and sperm) to form a zygote (ovum and sperm) to form a zygote (2n)(2n)

zygotezygote – first cell of a new individual – first cell of a new individual

III. DNA and ChromosomesIII. DNA and Chromosomes

DNADNA segments of DNA that code for a segments of DNA that code for a

protein or one RNA molecule is called protein or one RNA molecule is called a genea gene

one molecule of DNA is made up of one molecule of DNA is made up of 1,000s of genes1,000s of genes

genes determine how a body develops genes determine how a body develops and functionsand functions

is stretched out while being usedis stretched out while being used


ChromosomesChromosomes is TWO exact copies called chromatidsis TWO exact copies called chromatids is made up of DNA wrapped around proteinsis made up of DNA wrapped around proteins chromatids are held together at the chromatids are held together at the

centromerecentromere chromatids separate during cell divisionchromatids separate during cell division called called chromatinchromatin when not coiled around when not coiled around

proteinsproteins


ChromosomesChromosomes


Chromosome Chromosome Number and Number and TypeType

Number is different Number is different

for each type of for each type of organismorganism

a.a. Human – Human –

b.b. Housefly – Housefly –

c.c. Dog – Dog –


Chromosome Number and TypeChromosome Number and Type Number is different for each type of Number is different for each type of

organismorganisma.a. Human – 46Human – 46

b.b. Housefly – 12Housefly – 12

c.c. Dog – 78Dog – 78

Within an organism; each chromosome Within an organism; each chromosome is different in size, shape, and set of is different in size, shape, and set of genesgenes


Chromosome Number and TypeChromosome Number and Type Homologous ChromosomesHomologous Chromosomes

a. Pairs of chromosomes that have similar size, a. Pairs of chromosomes that have similar size, shape, & set of genesshape, & set of genes

b. One of the pair comes from one of the two parentsb. One of the pair comes from one of the two parentsc. …..sooooo 46 chromosomes are really two sets of c. …..sooooo 46 chromosomes are really two sets of

23 chromosomes; one set from each parent23 chromosomes; one set from each parent

AutosomesAutosomesa. The chromosomes not directly responsible for a. The chromosomes not directly responsible for

determining the sex of the individual (22 pair in determining the sex of the individual (22 pair in humans)humans)

III. DNA and ChromosomesIII. DNA and Chromosomes Chromosome Number and TypeChromosome Number and Type

Sex ChromosomesSex Chromosomesa. Responsible for determining the sexa. Responsible for determining the sexb. Female = XXb. Female = XXc. Male = XYc. Male = XY

Diploid (2n)Diploid (2n)a. Means two sets of chromosomesa. Means two sets of chromosomes

b. All cells in your body (somatic cells) except sex cells are b. All cells in your body (somatic cells) except sex cells are diploiddiploid

Haploid (1n)Haploid (1n)a. Means one set of chromosomesa. Means one set of chromosomesb. Sex cells (gametes) are haploidb. Sex cells (gametes) are haploid


Chromosome Number and TypeChromosome Number and Type KaryotypeKaryotype

a. A photo of a dividing cell that is used to a. A photo of a dividing cell that is used to match chromosomes by size and shapematch chromosomes by size and shape

b. Matching of chromosomes are used for b. Matching of chromosomes are used for diagnosis of medical abnormalitiesdiagnosis of medical abnormalities

c. c. Trisomy Trisomy – condition of 3 chromosomes; – condition of 3 chromosomes; Down’s syndrome – 3 - #21 chromosome Down’s syndrome – 3 - #21 chromosome pairspairs


KaryotypeKaryotype

IV. MeiosisIV. Meiosis

Sex cells (gametes) are formed by this type of Sex cells (gametes) are formed by this type of nuclear divisionnuclear division

Reduces the number of chromosomes to half Reduces the number of chromosomes to half the number in somatic cellsthe number in somatic cells

Somatic cells:Somatic cells:a.a. 46 chromosomes46 chromosomesb.b. 23 homologous pairs23 homologous pairsc.c. diploid number (2n)diploid number (2n)

GametesGametesa.a. 23 chromosomes23 chromosomesb.b. haploid number (1n)haploid number (1n)


Phases in MeiosisPhases in MeiosisMeiosis is preceded by the synthesis of DNA Meiosis is preceded by the synthesis of DNA

and the replication of the chromosomes.and the replication of the chromosomes.Has 8 main phases:Has 8 main phases:

a. First 4 phases separate homologous a. First 4 phases separate homologous chromosomes into 2 different cells chromosomes into 2 different cells

b. Last 4 phases separate sister b. Last 4 phases separate sister chromatids, just like mitosis chromatids, just like mitosis


Phases in MeiosisPhases in MeiosisMeiosis IMeiosis I

a. Phases of Meiosis Ia. Phases of Meiosis I

i. Prophase Ii. Prophase I

1. chromosomes become visible1. chromosomes become visible

2. the nuclear membrane disappears2. the nuclear membrane disappears

3. 3. crossing overcrossing over occurs occurs

* portions of one chromosome * portions of one chromosome are broken and exchanged are broken and exchanged with the other with the other


ii. Metaphase Iii. Metaphase I

1. homologous chromosomes line up 1. homologous chromosomes line up along the equator (meet in the middle) along the equator (meet in the middle)

iii. Anaphase Iiii. Anaphase I

1. homologous chromosomes move to 1. homologous chromosomes move to opposite ends of the cell (poles) opposite ends of the cell (poles)

2. chromatids DO NOT separate at the 2. chromatids DO NOT separate at the centromeres centromeres


iv. Telophase Iiv. Telophase I

1. chromosomes gather at the poles 1. chromosomes gather at the poles of of the cell the cell

2. cytokinesis takes place and the 2. cytokinesis takes place and the cell cell divides into two daughter cells divides into two daughter cells


b. At the end of Meiosis I, each daughter cell b. At the end of Meiosis I, each daughter cell contains one of each chromosome (half contains one of each chromosome (half the number)the number)

c. Meiosis I is the reductive division; it c. Meiosis I is the reductive division; it reduces the number of chromosomes from reduces the number of chromosomes from diploid (2n) to the haploid (1n) numberdiploid (2n) to the haploid (1n) number


Meiosis IIMeiosis II

Each daughter cell produced in Meiosis I Each daughter cell produced in Meiosis I undergoes another nuclear and cytoplasmic undergoes another nuclear and cytoplasmic division in Meiosis IIdivision in Meiosis II

Meiosis II is similar to Mitosis, but is NOT Meiosis II is similar to Mitosis, but is NOT preceded by the replication of DNApreceded by the replication of DNA


Phases of Meiosis IIPhases of Meiosis II

i. Prophase IIi. Prophase II

1. telophase I leads directly into prophase 1. telophase I leads directly into prophase IIII

2. a new spindle forms around the 2. a new spindle forms around the chromosomes chromosomes


ii. Metaphase IIii. Metaphase II

1. chromosomes line up along the cell’s equator1. chromosomes line up along the cell’s equator

2. spindle fibers attach at the centromere2. spindle fibers attach at the centromere

iii. Anaphase IIiii. Anaphase II

1. chromosomes separate at the centromere1. chromosomes separate at the centromere

2. each chromatid in the pair moves to opposite sides of 2. each chromatid in the pair moves to opposite sides of the cell the cell


iv. Telophase IIiv. Telophase II

1. nuclear membrane forms around each 1. nuclear membrane forms around each set set of new chromosomes of new chromosomes

2. cytokinesis takes place and the cell 2. cytokinesis takes place and the cell divides divides into two daughter cells into two daughter cells

d. Meiosis II gives four daughter cells that d. Meiosis II gives four daughter cells that are haploidare haploid


Meiosis in Males and FemalesMeiosis in Males and FemalesMalesMales

a. results in four cells that a. results in four cells that differentiate into sperm cells differentiate into sperm cells

b. b. SpermatogenesisSpermatogenesis – the – the production of sperm cells production of sperm cells


Meiosis in Males and FemalesMeiosis in Males and FemalesFemalesFemales

a. Results in four cells; only one of a. Results in four cells; only one of which becomes an ovum which becomes an ovum

b. During Meiosis I, the cytoplasm b. During Meiosis I, the cytoplasm divides unequally; the smaller cell is divides unequally; the smaller cell is called the 1 called the 1stst polar body polar body

c. In Meiosis II, the division is again c. In Meiosis II, the division is again unequal; the smaller cells die (2 unequal; the smaller cells die (2ndnd polar body) polar body)


Meiosis in Males and FemalesMeiosis in Males and FemalesFemalesFemales

d. Because of its larger cytoplasm, the d. Because of its larger cytoplasm, the mature ovum has a rich storehouse mature ovum has a rich storehouse of nutrients. These nutrients nourish of nutrients. These nutrients nourish the young organism that may the young organism that may develop if the ovum is fertilized. develop if the ovum is fertilized.

e. e. oogenesisoogenesis – the formation of female – the formation of female egg cells (ovum) egg cells (ovum)

MeiosisMeiosis

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meiosis 5.3. i. cell division replaces worn out or damaged cells replaces worn out or damaged cells...

Documents

dna copiesii

chromosomesdnasegments

geneone molecule of

single circular dna

minutesnerve cells

sex cells gametes

chromosomeschromosome

body somatic cells