Asexual Reproduction

Asexual ReproductionSingle parent – complete copy of DNA

Offspring is identical to parentProkaryotes

Advantages:

Disadvantages:

Types of Asexual ReproductionBinary fission –

Fragmentation –

Budding –

Parthenogenesis -

Sexual Reproduction

Sexual ReproductionEukaryotesTwo parents give genetic material to produce

offspring that are genetically different from parents

Gamete – Zygote – Germ cell – Somatic cell –

Advantages /disadvantages of sexual reproduction

Chromosome NumberEach chromosomes contains thousands of

genes that control development and function of organisms.

Humans have _____ (diploid)Mom gives ____ and Dad gives ____ (haploid)Chromosome reduction is MEIOSIS!

Meiosis means reduction division – halves the number of chromosomes

Diploid – 2n (human 2n=46)Haploid - n (human n=23)

Homologous ChromosomesHomologous chromosomes – similar in size,

shape, and genes. A diploid cell contains pairs of chromosomes made up of two homologous chromosomes. One set comes from mom, and one set comes from dad.

Autosomes and Sex ChromosomesAutosomes – DO NOT determine sex of

individualSex Chromosomes – DETERMINE sex of

individualMALE – XY (Mom donates the X, father

donates the Y)FEMALE – XX (Mom donates the X, Father

donates the other X)

Sex ChromosomesSex Chromosomes

XX chromosome - femaleXY chromosome - male9

Karyotype (Human)Karyotype (Human) AAn organized organized

picture picture of the chromosomes of a human arranged arranged in pairs by size in pairs by size from largest to smallest.

PPairs 1-221-22 called AUTOSOMESAUTOSOMES

LLast pair are SEX SEX CHROMOSOMESCHROMOSOMES

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Male - XYMale - XY

Human Chromosomes

12Female - XXFemale - XX

Gamete Production

Interphase IInterphase I Similar to mitosismitosis interphase. CHROMOSOMESCHROMOSOMES (DNA)(DNA) replicate in the

S phaseS phase Each duplicated chromosomechromosome consist

of twotwo identicalidentical SISTER SISTER CHROMATIDS CHROMATIDS attached at their CENTROMERESCENTROMERES.

CENTRIOLECENTRIOLE pairs also replicate.

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Interphase IInterphase I

Nucleus and nucleolus visiblevisible.

Nucleus

nucleolus

cell membrane

chromatin

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MeiosisMeiosisSimilar in many ways to mitosisSimilar in many ways to mitosisSeveral differences howeverSeveral differences however

Involves 2 cell divisionsInvolves 2 cell divisionsResults in 4 cells with 1/2 the normal genetic information.Results in 4 cells with 1/2 the normal genetic information.

Vocabulary:Vocabulary:Diploid (2N)Diploid (2N) - Normal amount of genetic material - Normal amount of genetic materialHaploid (N)Haploid (N) - 1/2 the genetic material. - 1/2 the genetic material.

Meiosis results in the formation of haploid cells.Meiosis results in the formation of haploid cells.In Humans, these are the In Humans, these are the OvaOva (egg) and (egg) and spermsperm..Ova are produced in the Ova are produced in the ovariesovaries in females in females

Process is called Process is called oogenesisoogenesisSperm are produced in the Sperm are produced in the testestestes of males. of males.

Process is called Process is called spermatogenesisspermatogenesisMeiosis occurs in 2 phases: Meiosis occurs in 2 phases: Meiosis 1Meiosis 1 & & Meiosis 2Meiosis 2

Meiosis I (four phases)Meiosis I (four phases)

Cell division Cell division that reduces the chromosome number chromosome number by one-half.one-half.

Four phasesFour phases:

a.a. Prophase IProphase I

b.b. Metaphase IMetaphase I

c.c. Anaphase IAnaphase I

d.d. Telophase ITelophase I

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Prophase IProphase I

Prophase IProphase I LongestLongest and and most complex most complex phase (90%).phase (90%).

ChromosomesChromosomes condense. SynapsisSynapsis occurs - Homologous chromosomesHomologous chromosomes come togetherto form a tetradtetrad.

TetradTetrad is two chromosomestwo chromosomesor four chromatids four chromatids (sister and non-sister chromatids).

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Non-Sister Chromatids-Non-Sister Chromatids-HOMOLOGSHOMOLOGS

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•Homologs contain DNA that codes for the same genes , but different versions of those genes

•Genes occur at the

same loci

Meiosis I.Meiosis I.Prior to division, amount of DNA doublesPrior to division, amount of DNA doubles

Overview of MeiosisOverview of Meiosis

Prophase 1Prophase 1

During prophase 1 During prophase 1 homologous homologous chromosomes line-chromosomes line-up along the up along the metaphase platemetaphase plate

Areas of Areas of homologous homologous chromosomes chromosomes connect at areas connect at areas called called chiasmatachiasmata

Crossing OverCrossing OverSegments of Segments of

homologous homologous chromosomes break chromosomes break and reform at similar and reform at similar locations.locations.

Results in new Results in new genetic combinations genetic combinations of offspring.of offspring.

This is the main This is the main advantage of sexual advantage of sexual reproductionreproduction

Non-Sister Chromatids-Non-Sister Chromatids-HOMOLOGSHOMOLOGS

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•Homologs contain DNA that codes for the same genes , but different versions of those genes

•Genes occur at the

same loci

Genetic Recombination Genetic Recombination

nonsister chromatids

chiasmata: site of crossing over

variation

Tetrad

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Metaphase IMetaphase IShortest phaseTetrads align on the equator.Independent assortment occurs –

chromosomes separate randomly causing GENETIC RECOMBINATION

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Metaphase IMetaphase I

Homologs line up at equator or

metaphase plate

OR

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Question:Question:

In terms of In terms of Independent Independent AssortmentAssortment -how many -how many different combinations of different combinations of sperm could a sperm could a humanhuman malemale produce? produce?

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AnswerAnswer

Formula: 2Formula: 2nn

Human chromosomes:Human chromosomes: 2n = 2n = 4646

n = 23n = 23 222323 = ~8 million combinations = ~8 million combinations

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Anaphase 1Anaphase 1 During anaphase 1, each homologous chromosome is pulled to opposite During anaphase 1, each homologous chromosome is pulled to opposite

sides of the cell. Unlike mitosis, sides of the cell. Unlike mitosis, THE CENTROMERES DO NOT THE CENTROMERES DO NOT BREAKBREAK..

Nuclei may or may not reform following division.Nuclei may or may not reform following division. Cytokenesis may or may not occur.Cytokenesis may or may not occur.

Telophase ITelophase I

Each pole now has haploidhaploid (1n) set of chromosomeschromosomes.

CytokinesisCytokinesis occurs and two haploid daughter cells are formed.

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Telophase ITelophase I

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cytokinesis

Meiosis IIMeiosis II

DNA DNA does notdoes not double doubleChromosomes randomly line-up along metaphase plate Chromosomes randomly line-up along metaphase plate

like regular mitosis.like regular mitosis.During anaphase 2, During anaphase 2, CENTROMERES BREAKCENTROMERES BREAK and and

each chromosome is pulled to opposite sides of the cell.each chromosome is pulled to opposite sides of the cell.Nuclei reform and cytokenesis usually occurs (although it Nuclei reform and cytokenesis usually occurs (although it

is often unequal).is often unequal).

Telophase ITelophase I

Each pole now has haploidhaploid (1n) set of chromosomeschromosomes.

CytokinesisCytokinesis occurs and two haploid daughter cells are formed.

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Telophase ITelophase I

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cytokinesis

Meiosis IIMeiosis II

No Interphase II No Interphase II or very shortor very short ****No DNA ReplicationNo DNA Replication Remember: Meiosis II is similar Remember: Meiosis II is similar

to mitosisto mitosis

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Prophase IIProphase II Same as Same as ProphaseProphase in in mitosismitosis

Nucleus & nucleolus disappearNucleus & nucleolus disappear Chromosomes condenseChromosomes condense Spindle formsSpindle forms

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Metaphase IIMetaphase II

Same as Metaphase in mitosis

Chromosomes (not homologs) line up at equator38

Anaphase IIAnaphase II

Same as AnaphaseAnaphase in mitosismitosis **SISTER CHROMATIDS **SISTER CHROMATIDS separateseparate

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Telophase IITelophase II Same as Same as TelophaseTelophase in mitosis. in mitosis. Nuclei and Nucleoli Nuclei and Nucleoli reform, reform,

spindle disappearsspindle disappears CYTOKINESISCYTOKINESIS occurs. occurs. Remember: Remember: FOUR HAPLOID FOUR HAPLOID

DAUGHTER cells DAUGHTER cells are produced.are produced.

Called Called GAMETESGAMETES (eggs and sperm) (eggs and sperm)

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1n Sperm cell

fertilizes 1n egg to form 2n zygote

Telophase IITelophase II

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VariationVariation Also known as Also known as GENETIC GENETIC

RECOMBINATIONRECOMBINATION Important to population as the raw Important to population as the raw

material for material for NATURAL SELECTION.NATURAL SELECTION. All organisms are All organisms are NOTNOT alike alike StrongestStrongest “ “most fit” most fit” survive to survive to

reproduce & pass on traitsreproduce & pass on traits

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Question:Question: What are the What are the 33 sources of sources of genetic recombination genetic recombination or or variation? variation?

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Answer:Answer:

1.1. CROSSING OVER CROSSING OVER (prophase (prophase I)I)

2.2. INDEPENDENT INDEPENDENT ASSORTMENT ASSORTMENT (metaphase (metaphase I)I)

3.3. RANDOM FERTILIZATIONRANDOM FERTILIZATION

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Question:Question:

A cell containing 20 20 chromosomeschromosomes (diploid)(diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomeschromosomes?

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Answer:Answer:

1010 chromosomes (haploid chromosomes (haploid or 1n)or 1n)

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Haploid

Diploid

Meiosis and Gamete formationOogenesis

Ovum and 3 polar bodiesUn-equal distribution of the cytoplasm

Spermatogenesis4 sperm

MeiosisMeiosis Sex cells divide to produce

GAMETESGAMETES (sperm or egg)(sperm or egg). Gametes have HALFHALF the # of chromosomes.

Occurs only in GONADSGONADS (testes (testes or ovaries).or ovaries).

Male: Male: SPERMATOGENESIS -SPERMATOGENESIS -spermsperm

Female: Female: OOGENESIS - OOGENESIS - egg or egg or

ovaova 50

SpermatogenesisSpermatogenesis

2n=46

humansex cell

diploid (2n)

n=23

n=23

Meiosis I

n=23

n=23

n=23

n=23

sperm

haploid (n)

Meiosis II 51

OogenesisOogenesis

2n=46

humansex cell

diploid (2n)

n=23

n=23

Meiosis I

n=23

eggHaploid (1n)

Meiosis II52

Polar Bodies (die)

Spermatogenesis & Oogenesis

Egg/Ova4 sperm

University of Arizona Biology Pagehttp://www.biology.arizona.edu/cell_bio/tutori

als/meiosis/main.html

Cell’s Alivehttp://www.cellsalive.com/meiosis.htm

55Female - XXFemale - XX

FertilizationFertilization The fusion of a spermsperm and eggegg to form a zygotezygote.

A zygote is a FERTILIZED FERTILIZED EGGEGG

n=23egg

sperm n=23

2n=46zygote

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Question:Question:

A cell containing 40 40 chromatidschromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomeschromosomes?

(Tricky! Think!)

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Answer:Answer:

10 chromosomes10 chromosomes

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Multicellular Life CyclesLIFE CYCLE – events in the growth and

development of an organism until it reaches sexual maturity.

Most animals have a DIPLOID LIFE CYCLEDuring meiosis, germ cells undergo meiosis to produce haploid gametes.

Fertilization – joining of 2 haploid cells to form a zygote which then undergoes mitosis to grow and develop into a new organism.

Haploid Life Cycle

Alternation of Generations