Cellular Cellular ReproductionReproduction

Unit 4 (Ch.9, 10.1)Unit 4 (Ch.9, 10.1)

TYPES OF REPRODUCTIONTYPES OF REPRODUCTION• AsexualAsexual

– Relies on MITOSISRelies on MITOSIS– All of the parent’s DNA goes to the All of the parent’s DNA goes to the

offspringoffspring– Bacteria reproduce through Bacteria reproduce through binary fissionbinary fission

• SexualSexual– Relies on MEIOSISRelies on MEIOSIS– Used to create sex cellsUsed to create sex cells

TYPES OF CELLSTYPES OF CELLS• Body CellsBody Cells

– Includes all cells that are not sex cells Includes all cells that are not sex cells • i.e. skin, liver, muscle, etc…i.e. skin, liver, muscle, etc…

– Also called somatic cells (soma- Also called somatic cells (soma- means “body”)means “body”)

– Made by MITOSISMade by MITOSIS– Contain 2 copies of each chromosome Contain 2 copies of each chromosome

• Called homologous chromosomesCalled homologous chromosomes• Have a diploid # (2n) Have a diploid # (2n)

– Ex. Humans = 46Ex. Humans = 46

TYPES OF CELLSTYPES OF CELLS• Sex CellsSex Cells

– Include egg cells and sperm cells Include egg cells and sperm cells – Also called gametesAlso called gametes– Made by MEIOSISMade by MEIOSIS– Contain 1 copies of each Contain 1 copies of each

chromosome chromosome • Have a haploid # (n) Have a haploid # (n)

– Ex. Humans = 23Ex. Humans = 23

Chromosome NumbersChromosome NumbersSperm Sperm

(haploid # of 23)(haploid # of 23)

Egg Egg

(haploid # of 23)(haploid # of 23)

Zygote Zygote

(diploid # of 46)(diploid # of 46)

FertilizationFertilization

MeiosisMeiosis• Produces Sex CellsProduces Sex Cells• Reduction division Reduction division

– Starts with 1 diploid cell and ends Starts with 1 diploid cell and ends up with 4 haploid cellsup with 4 haploid cells

• Occurs in TWO stepsOccurs in TWO steps– Meiosis IMeiosis I– Meiosis IIMeiosis II

InterphaseInterphase• Chromosomes replicateChromosomes replicate• Chromatin condensesChromatin condenses

Interphase

Homologous Homologous ChromosomesChromosomes

• One of two paired One of two paired chromosomes, one chromosomes, one from each parentfrom each parent

• Same lengthSame length• Same centromere Same centromere

positionposition• Carry genes that Carry genes that

control the same control the same inherited traitsinherited traits

Homologous Homologous ChromosomesChromosomes

Prophase IProphase I• Pairing of Pairing of

homologous homologous chromosomes occurschromosomes occurs– Each chromosome Each chromosome

consists of two consists of two sister chromatidssister chromatids

• The nuclear The nuclear envelope breaks envelope breaks downdown

• Spindles formSpindles form

Prophase I

Crossing OverCrossing Over• The exchange of material between The exchange of material between

homologueshomologues– Occurs during Prophase IOccurs during Prophase I– Tetrads are formed and DNA is Tetrads are formed and DNA is

exchangedexchanged– Produces chromosomes that contain Produces chromosomes that contain

genes from both parents… GENETIC genes from both parents… GENETIC DIVERSITYDIVERSITY

Metaphase IMetaphase I

Metaphase I

• Chromosome Chromosome centromeres centromeres attach to attach to spindle fibersspindle fibers

• Homologous Homologous chromosomes chromosomes (tetrads) line up (tetrads) line up at the equatorat the equator

Independent AssortmentIndependent Assortment• The random distribution The random distribution

of genes located on of genes located on different chromosomes.different chromosomes.

• Since each homologous pair assorts Since each homologous pair assorts independently from all others, the independently from all others, the process produces 2process produces 2nn possible possible combinations of maternal and combinations of maternal and paternal chromosomes in gametes paternal chromosomes in gametes (where n is the haploid number) (where n is the haploid number)

• In humans, the possible In humans, the possible combinations would be 2combinations would be 22323, or eight , or eight million – there are eight million million – there are eight million possible assortments of possible assortments of chromosomes from the parentschromosomes from the parents

Independent AssortmentIndependent Assortment

Anaphase IAnaphase I• Homologous Homologous

chromosomes chromosomes separate and separate and spindle fibers spindle fibers move them move them towards opposite towards opposite poles of the cell poles of the cell

Anaphase I

Telophase I

Telophase I & CytokinesisTelophase I & CytokinesisTelophase ITelophase I• Spindles break downSpindles break down• Chromosomes uncoil to Chromosomes uncoil to

form two nucleiform two nuclei

CytokinesisCytokinesis• The cell divides into two The cell divides into two

new daughter cellsnew daughter cells

Each pole now has a Each pole now has a haploid set of haploid set of chromosomes that are chromosomes that are still composed of two still composed of two sister chromatids sister chromatids attached at a centromereattached at a centromere

MEIOSIS IIMEIOSIS II• This second division separates sister This second division separates sister

chromatids of each chromosome chromatids of each chromosome (virtually identical to Mitosis)(virtually identical to Mitosis)

Prophase IIProphase II• Spindle apparatus forms and Spindle apparatus forms and

chromosomes condensechromosomes condense

Prophase II

Metaphase IIMetaphase II• A haploid number of chromosomes A haploid number of chromosomes

align along the metaphase platealign along the metaphase plate

Metaphase II

Anaphase IIAnaphase II• Chromosomes are pulled apart Chromosomes are pulled apart

producing sister chromatids.producing sister chromatids.– Each chromatid is pulled (by the Each chromatid is pulled (by the

spindles) towards the opposite spindles) towards the opposite poles of the cell poles of the cell

Anaphase II

Telophase II & CytokinesisTelophase II & CytokinesisTelophase IITelophase II• Chromatids reach the polesChromatids reach the poles• Nuclear membranes and nuclei reformNuclear membranes and nuclei reform

CytokinesisCytokinesis• Results in four haploid cells, each with n Results in four haploid cells, each with n

number of chromosomes. number of chromosomes.

Telophase II Cytokinesis

Gamete Development Gamete Development in Malesin Males

• ““SPERMATOGENESISPERMATOGENESIS”S”

• Meiosis occurs in Meiosis occurs in testes at puberty testes at puberty and then occurs as and then occurs as neededneeded

• 1 spermatocyte = 4 sperm 1 spermatocyte = 4 sperm cellscells

Gamete Development Gamete Development in Femalesin Females

• ““OOGENESIS”OOGENESIS”• Meiosis occurs Meiosis occurs

in the ovaries in the ovaries before birthbefore birth

• 1 oocyte = 1 egg & 3 polar 1 oocyte = 1 egg & 3 polar bodiesbodies

HUMAN LIFE CYCLEHUMAN LIFE CYCLEUses both meiosis & mitosisUses both meiosis & mitosis