Meiosis (necessary for sexual reproduction)

Reduction Division sex cells egg/sperm (germ cells) 2N diploid N haploid ???why??

Humans 46 chromosomes 23 chromosomes Sexual Reproduction (N) gametes combine 2N diploid # restored)

↑ Diversity (combine 2 sets of genes) ?effects on evolution

Shuffling during synapsis Xing over of homologous prs in Prophase 1

Draw egg (N) + sperm (N) cell fertilization

2N diploid # restored

Meiosis# of chromosomes is cut in 1/2 thru separation of homologous chromosomes in a diploid 2N cell

2N diploid cell contains 2 complete sets of chromosomes (1 set of chromosomes/genes from each parent)

Mendel: All of an organisms cells except gametes contain 2 alleles for a trait

Sex cells undergo meiosis to produceGametes (ovum/egg and sperm)

Symbols ________ ________

Somatic/Body cells 46 chromosomes (23prs)

22 prs/44 autosomes –not sex chromosomes (#’s1-22) 1 pr/2 sex chromosomes (#23)

Homologous Chromosomes: Corresponding chromosomes between male + female

Homologs: chromosomes themselves

Cell that contains both sets of homologous chromosomes (from each parent) = 2N diplod

2N diploid cells contain 2 complete sets of genes- 1 from each parentGametes/Sex cells contain only a single copy (1 set) of genes b/c alleles (forms of a gene) are separated during gamete formation (oognesis _____ and spermatogenesis ________)

Meiosis: produces 4 haploid cells (N) Genetically different from each other & original

Stages of MeiosisMeiosis IInterphase 1: Chromosomes replicate (S Phase) Growth & development (G1 phase)

Organelle synthesis (G2 phase)

Chromosomes condense & coil Centrioles replicate

Prophase 1: Chromosomes visible Each chromosome seeks its homologous pr to form tetrad in synapsis (maternal + paternal) Shuffling: way/side homologous pr ends up on CHANCE!

Xing over: between homologus prs exchange of genetic info on chromatids new combos of genesCentrioles migrate & spindles formHomologous prs migrate to spindle fibers Nuclear membrane breaks ↓

Shuffling demo- line students up on opposite sidesInclude Xing over using appendages

Metaphase 1: Spindle fibers attached to chromosomes – at kinetocore Tetrads (homologous prs) line up on equator **Chance which side maternal/paternal pr ends up on (w/ rest of genes on chromosomes on that side)

Anaphase 1: Dysjunction Homologous chromosomes (each w/ 2 chromatids) move to opposite poles along spindle fibers Nondysjunction: homologous pr(s) fail to separate gametes w/ too many/few chromosomes Ex. Trisomy 21 Down Syndrome Kleinfleter’s 47XXY Turner’s 45XO Jacob’s 47XYY Polyploidy: nondysjunction of entire set of chromosomes 3N, 4N, etc Fatal in animals Can be in plants hearty, disease resistant, big!

Telophase 1: Followed by cytokinesis (division of cytoplasm) Chromosomes gather in nuclei Nuclear membrane reforms

Cells contain a single set of chromosomes/genes (N-haploid) 2, haploid, (N) Daughter cells

Meiosis II (like mitosis- w/ no DNA replication)

Interphase II: No DNA Replication Synthesis of organelles Chromatin mesh

Prophase II: Chromosomes condense, coil visible Centrioles migrate & spindles form Chromosomes migrate to spindles attach at kinetocore

Metaphase II: Chromosomes line up on equator

Anaphase II: Sister chromatids separate & move towards opposite poles along spindle (Nondysjunction can occur here also)** b/c of shuffling & Xing over in Prophase I each cell has a different genetic makeup- combo of genes in each gamete Random

**chromosomes carry genes & genes carry alleles (forms of a gene) for specific trait (chromosome carry genes for specific traits DNA)

Earth

Country

State

City

People

Cell

Chromosome

Chromosome fragment

Gene

Nucleotide base pairs

Section 11-5

Comparative Scale of a Gene Map

Mapping of Earth’s Features

Mapping of Cells, Chromosomes, and Genes

Telophase II: followed by Cytokinesis Chromosomes gather & Nuclear membrane reforms

Produces 4 haploid (N) gametes/sex cells for sexual reproduction

Go to Section:

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

How does Xing over affect inheritance?It changes the combo of alleles on the chromosomes Ex. fruit fly w/ red eyes & brown body or white eyes & yellow body

Xing over red eyes w/ yellow body and white eyes w/ brown body

Xing over used to map genes closer 2 genes are located on a chromosome the Less likey they’ll be separated by xing over By observing how frequently Xing over separates any 2 genes helps determine genes relative position on chromosome

Go to Section:

Exact location on chromosomes Chromosome 2

Section 11-5

Figure 11-19 Gene Map of the Fruit Fly

Mitosis vs Meiosis

Mitosis vs Meiosis

2 identical daughter cells 4 genetically different cells

2N diploid 2N diploid 2N diploid N haploid

Asexual Sexual

1 division 2 divisions

Body/Somatic cells Sex Cells

Growth Development Repair Produce gametes (egg/ovum & sperm)

Less genetic diversity↑ genetic diversity (genes from 2 parents combine, Prophase 1 shuffling (in synapsis), Xing over

Occurs after fertilization/ formation of Zygote growth & differentiation

Occurs at puberty

Gametogenesis: formation of gametes 2N diploid N haploid

Spermatogenesis Sperm Formation

Oogenesis Egg (ovum) Formation

Spermatogenesis: males, in the testes produces 4 viable sperm cells (small)

Oogenesis: females in the ovaries (follicle in ovary is where mature egg develops) produces 1 egg/ovum (lgst cell in body) + 2 or 3 polar bodies≠ division of cytoplasm ovum gets all the nutrients (why)?Travels thru fallopian tube (propeled by cilia) for fertilization by sperm

Spermatogenesis vs Oogenesis

Spermatogenesis vs Oogenesis

Males Females

4 viable haploid sperm cells 1 viable haploid egg/ovum + 2 or 3 polar bodies

Small Largest cell in human body

Motile Non motile

Produced in testes Produced in ovaries (*follicle)

Produce millions at a time Produce 1/month

= division of cytoplasm ≠ division of cytoplasm

Occurs at Puberty

Karyotype: Chromosome map

Cells must be undergoing mitosis for chromosomes to be visible.Count chromosome prs, look for abnormalities Ex. Nondysjunction, Translocation, Inversion of chromosomes

Normal male

Normal female