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 sperms) 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)

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

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