1 Reproduction and Meiosis. 2 Reproduction Reproductionthe process of producing offspring...

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Reproduction Reproduction and and

MeiosisMeiosis

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ReproductionReproduction• Reproduction—the process of producing

offspring– Asexual—one parent, offspring are

genetically identical to parent•Budding, fission, fragmentation,

parthenogenesis

– Sexual—two parents, offspring genetically different from parents•Parents produce gametes

– Females=egg– Males=sperm

•Two gametes combine=fertilization; produces first cell called the zygote

•Offspring will have traits of both parents

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Homologous ChromosomesHomologous Chromosomes

• Each species has a characteristic number of chromosomes– Humans=46; dogs=78; fruit flies=8

• Chromosomes come in pairs—homologous chromosomes– Chromosomes with the same size,

shape, and carry the codes for the same genes

– Each chromosome in a homologous pair comes from one of the parents• In humans, 23 chromosomes come from

mom and 23 from dad

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MeiosisMeiosis• Form of cell division that produces 4

daughter cells with half the number of chromosomes as the parent cell

• 2 distinct stages– Meiosis I

• Prophase I, Metaphase I, Anaphase I, Telophase I

– Meiosis II• Prophase II, Metaphase II, Anaphase II,

Telophase II

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Meiosis IMeiosis I• Prophase I

– Chromosomes condense– Homologous chromosomes pair up– Crossing over

•Chromatids exchange genetic material• Increases genetic variability

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Meiosis IMeiosis I• Metaphase I

– Homologous chromosomes line up along equator of cell

• Anaphase I– Homologous

chromosomes move apart, pulled by spindle fibers

• Telophase I– Cytoplasm divides,

resulting in two cells with the same number of chromosomes as parent

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Meiosis IIMeiosis II

Prophase Prophase IIII

MetaphaMetaphase IIse II

AnaphasAnaphase IIe II

TelophasTelophase IIe II

4 different 4 different haploid haploid

cellscells

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Results of MeiosisResults of MeiosisGametes (egg & Gametes (egg & sperm) formsperm) form

Four haploid cells Four haploid cells with one copy of each with one copy of each chromosome chromosome

One allele of each One allele of each genegene

Different Different combinations of combinations of alleles for different alleles for different genes along the genes along the chromosomechromosome

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MitosisMitosis MeiosisMeiosisNumber of Number of

divisionsdivisions 1122

Number of Number of daughter cellsdaughter cells 22 44

Genetically Genetically identical?identical? YesYes NoNo

Chromosome #Chromosome # Same as Same as parentparent Half of parentHalf of parent

WhereWhere Body cellsBody cells Sex cellsSex cells

WhenWhen Throughout Throughout lifelife

At sexual At sexual maturitymaturity

RoleRole Growth and Growth and RepairRepair

Sexual Sexual ReproductionReproduction

Mitosis vs MeiosisMitosis vs Meiosis

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Gamete ProductionGamete Production• Gametes have half the number of

chromosomes of the organism– Sperm (23 chromosomes) + Egg (23

chromosomes) = Human (46 chromosomes)

• Diploid (2n)– A cell with two of each chromosome,

which are in pairs {FULL set}

• Haploid (n)– A cell with only one of each

chromosome {half set}

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Gamete Production: SpermGamete Production: Sperm

• Occurs in the Occurs in the testestestes

• Two divisions Two divisions produce 4 produce 4 spermatidsspermatids

• Spermatids Spermatids mature into spermmature into sperm

• Men produce Men produce about 250,000,000 about 250,000,000 sperm per daysperm per day

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Gamete Production: EggGamete Production: Egg• Occurs in the ovariesOccurs in the ovaries• Two divisions Two divisions

produce 3 polar produce 3 polar bodies that die and bodies that die and 1 egg1 egg

• Polar bodies die Polar bodies die because of unequal because of unequal division of division of cytoplasmcytoplasm

• Immature egg called Immature egg called oocyteoocyte

• Starting at puberty, Starting at puberty, one oocyte matures one oocyte matures into an ovum (egg) into an ovum (egg) every 28 daysevery 28 days