Find someone with the opposite color paper. Use your notes to come with anything you remember about mitosis: Purpose What you start with, what you end up with Are the daughter cells identical to or different from the parent cells? 4 phases? What happens in them (keep it simple) Mitosis Review First!

Meiosis

What differences do you notice? Asexual Sexual 46 23 46 46 46

2 Types of Reproduction 1. Asexual One parent produces genetically identical offspring Ex: Body cells (during mitosis) & bacteria No genetic diversity! 2. Sexual Two parents produce genetically different offspring through fertilization Uses meiosis – type of cell division used to create gametes (egg & sperm) Produces genetic variation

Budding Binary Fission

Genetic Variation (diversity) Differences in DNA = differences in our traits Need variation If habitat changes, populations are more likely to survive if traits/skills are varied

Haploid (n or 1n) Haploid (n) – cell that has 1 set of chromosomes n = # of chromosomes Gametes/sex cells (egg & sperm) are haploid- 23 chromosomes Meiosis- type of cell division used to make haploid cells

Haploid

Haploid vs. DIploid

Haploid vs. diploid Diploid (2n) - cell that contains 2 sets or pairs of chromosomes (1 from mom and dad) Referred to as 2n 2x haploid #

Contains homologous pairs of chromosomes Analogy- like pairs of shoes Somatic (body) cells are diploid  46 chromosomes or 23 pairs Contains homologous pairs of chromosomes Analogy- like pairs of shoes

DIploid

Homologous Chromosomes Pairs of chromosomes that are the same size, shape and gene pattern Made of 2 chromatids They are NOT identical  one from each parent Ex: 2 Chromosome 10’s

C4U

Why Meiosis? Purpose: Sexual reproduction (make gametes) and to create genetic diversity/variation Location: Reproductive organs/cells Produces: 4 genetically unique, haploid (gametes) Variation from crossing over (prophase I) & independent assortment (metaphase I)

Process of Meiosis Meiosis occurs in 2 rounds- Meiosis 1 and meiosis 2 Before Meiosis I, DNA replication occurs Human cell: Normally 23 pairs  46 pairs before Meiosis starts (92 total) McGraw Hill Animation

Meiosis I Purpose: To create genetic diversity variation and reduce chromosome number in half

Meiosis I – Prophase I Synapsis occurs – when homologous chromosomes line up next to each other forming tetrads Tetrads- pair of homologous chromosomes ( 4 chromatids) (2n)

Remember! Chromatid = ½ of a chromosome

Meiosis I – Prophase I Crossing over occurs – exchange genetic info by exchanging matching sections of chromatids This produces genetic diversity and unique chromatids (2n) Crossing Over CC 4-6:30

Tetrads vs homologous chromosomes X Homologous chromosome - 2 chromatids

This again causes genetic diversity Metaphase I Independent assortment occurs – when the tetrads line up randomly at metaphase plate This again causes genetic diversity Independent assortment

Tetrads separate to opposite ends of cell Anaphase I Tetrads separate to opposite ends of cell

Telophase I Cell splits into 2 diploid cells Remember we started with 46 pairs (92 total) chromosomes  now we have 23 pairs (46 total) in each cell The cells are NOT identical – Why??

Why do we still need meiosis II? Because the chromosomes are still replicated  sister chromatids (46 chromosomes) . We need individual chromatids in gametes

Answer these questions in notebook 1. What’s the purpose or result of meiosis? 2. When does independent assortment occur? 3. When does crossing over occur? 4. How does meiosis introduce genetic diversity? 5. What has to happen before meiosis can occur?

Meiosis II The 2 diploid cells are divided- like mitosis Produces: 4 haploid cells, each containing a single copy of each chromosome Those haploid cells are the egg & sperm cells

Meiosis II – Prophase II No crossing over Sister chromatids are still replicated Nuclear membrane disappears again

Metaphase II Sister chromatids line up at metaphase plate

ANAphase II Sister chromatids separate

TeloPHASE II McGraw Hill Animation Cells split, producing 4 genetically unique haploid daughter cells

Meiosis I vs. Meiosis II During Meiosis I _____________________ divide. During Meiosis II _____________________ divide Metaphase 1 Anaphase 1 Homologous chromosomes Sister chromatids Metaphase 2 Anaphase 2

Comparing Mitosis and Meiosis

Comparing Mitosis and Meiosis C4U Produces identical daughter cells, produces unique daughter cells, occurs in eukaryotic cells, two round of cell division, one round of cell division, occurs in multi-cellular organisms, produces haploid cells, produces diploid cells, produces body cells, produces gametes, is a multi-step process, involves crossing-over and independent assortment

Produces identical daughter cells, (MT) occurs in multi-cellular organisms, (B) produces haploid cells, (MS) produces diploid cells, (MT) produces body cells, (MT) produces gametes, (MS) is a multi-step process, (B) involves crossing-over and independent assortment (MS) Produces identical daughter cells, (MT) produces unique daughter cells, (MS) occurs in eukaryotic cells, (B) two round of cell division, (MS) one round of cell division, (MT)

Mutations in Meiosis Do mutations in body cells have an effect on the offspring? How about in sex cells? Explain. Body cells  only affect cells produced from mitosis from this cell Sex cells  Used to make offspring; mutations are passed on

Are most of the genetic differences in the world attributed to mutations or shuffling DNA in meiosis?

This picture shows a type of mistake that can occur during meiosis. On your paper write down what you think is happening.

This can result in gametes that have too many or too few chromosomes. Non-disjunction is an error during meiosis in which the chromosomes fail to separate properly. This can result in gametes that have too many or too few chromosomes. Step-through Mistakes in Meiosis Animation

Nondisjunction can be detected through a Karyotype. A Karyotype is - a picture of one’s 46 chromosomes. It allows us to detect abnormal numbers of chromosomes as well as chromosomal mutations.

Healthy Female: 46 chromosomes  XX Healthy Male: 46 chromosomes  XY

Down Syndrome Trisomy 21- 3 copies of the chromosome 21 47 total chromosomes instead of 46 Caused by nondisjunction Effects: Characteristic facial features, heart defects, susceptibility to leukemia & Alzheimer’s Varying degrees of intellectual disability

Klinefelter’s Males with extra X chromosome Reduced facial & body hair Breast enlargement Infertility Some learning disabilities and difficulty with speech

Jacob’s Syndrome Males with extra Y chromosome Taller than average Learning or speech difficulties Weaker bones or muscles

Turner’s syndrome Female with only 1X chromosome Short height Lack hormones for menstruation and breast growth Infertility Drooping eye lids, low hair line Kidney & heart problems, diabetes

Mitosis Meiosis Purpose Takes place in… Produces how many cells? What happens to chromosome number? How do parents and daughter cells differ genetically? Variation between daughter cells?