Biology Meiosis Remember from Chapter 1 CHARACTERISTICS OF

Biology Meiosis

Remember from Chapter 1: CHARACTERISTICS OF LIVING THINGS REPRODUCE ALL LIVING THINGS _____

Remember from Chapter 7, there are EUKARYOTIC basically 2 types of cells_____ PROKARYOTIC and ______

Now let’s review Ch 10. . Mitotic Cell Division • Mitosis makes two identical daughter cells from one Parent cell • Bacteria and other prokaryotes may use mitosis to reproduce – called Binary Fission • This is asexual reproduction

ASEXUAL REPRODUCTION Bacteria reproduce using BINARY FISSION This is mitosis!

Budding is used by plants and some animals to reproduce asexually (mitosis) Hydra Regeneration is another way some animals reproduce asexually (mitosis) Planaria

MITOSIS identical Produces cells that are _____ copies of parent cell

Major Events in Mitosis

• Chromosome number must be maintained in animals. • Many plants have more than two copies of each chromosome.

• Mitosis and meiosis are types of nuclear division that make different types of cells. • Mitosis makes more diploid cells.

MITOSIS-in conclusion 2 cells genetically • Makes ___ identical to parent cell & to _____ each other 2 n (diploid) • Makes _____ cells SOMATIC (body) • Makes _____ • Used by organisms to: increase size of organism, repair injuries, and replace worn out cells

ADVANTAGES OF ASEXUAL REPRODUCTION Can make offspring faster Don’t need a partner

ADVANTAGES OF ASEXUAL REPRODUCTION Works great for making new skin cells, blood cells, and any of the other body cells that need to be replaced Our body cells are called Somatic cells (repeat word)

DISVANTAGES OF ASEXUAL REPRODUCTION ALL ALIKE No genetic diversity within a population One disease can wipe out whole population

Question…. if not asexual, then how can we reproduce?

Sexual Reproduction Sexual reproduction is when two gametes (sex cells) fuse together to make a zygote.

SEXUAL REPRODUCTION In humans, (and in many other organisms), sexual reproduction combines the genetic material from the gametes of 2 parents (sperm & egg) into a zygote -develops into offspring that are genetically DIFFERENT _____ from parents

• Let’s review sexual reproduction • In sexual reproduction, there are two parents. • Each parent has a gamete, or sex cell to donate to the offspring. • Each gamete has one set of chromosomes. • The two gametes come together (fertilization) to form one new cell called a Zygote. • This Zygote will grow and divide to become a unique organism.

ADVANTAGES OF SEXUAL REPRODUCTION Allows for variation in population Individuals can be different Provides foundation for EVOLUTION Allow species adapt to changes in their environment

EGG + SPERM If egg and sperm cells had the same number of chromosomes as other body cells. . . baby would have too many chromosomes!

MEIOSIS is the way we can avoid this problem. Meisosis makes cells with half the number of chromosomes for sexual reproduction

Sex Cells (also called germ cells) • Germ cells develop into_ gametes. – Germ cells are located in the ovaries and testes of humans and other animals. egg and sperm – Gametes are sex cells: _____. – Gametes have DNA that is passed to the offspring. sex cells (sperm) (egg)

• Haploid (n) cells have one copy of every chromosome. (Remember diploid cells have two copies) – Gametes are haploid. – Human gametes have 22 autosomes and 1 sex chromosome.

Haploid cells develop into mature gametes. • Gametogenesis is the production of gametes. • Gametogenesis differs between females and males. – Sperm become streamlined and motile. – Sperm primarily contribute DNA to an embryo.

Haploid cells develop into mature gametes. • Gametogenesis differs between females and males. – Eggs contribute DNA, cytoplasm, and organelles to an embryo. – During meiosis, the egg gets most of the contents; the other cells form polar bodies.

KEY CONCEPT Gametes have half the number of chromosomes that body cells have.

DIPLOID & HAPLOID Most cells have 2 copies of each chromosome DIPLOID 2 n = _______ (one from mom; one from dad) HOMOLOGOUS CHROMOSOMES SOMATIC All BODY (______) cells are diploid

HOMOLOGOUS Chromosomes • SAME SIZE • SAME SHAPE • CARRY GENES for the SAME TRAITS IDENTICAL • BUT NOT _______! (Don’t have to have the SAME CHOICES)

DIPLOID & HAPLOID Some cells have only one copy of each HAPLOID 1 n chromosome = _______ Fertilization between egg and sperm occurs in sexual reproduction. All gametes (sperm and egg) cells are haploid

SO……what is a chromosome? • main organelle involved in the Cell Cycle • Found in the nucleus • Contains genetic material (DNA) • Has 2 major parts-a centromere and sister chromatids

There are two types of Chromosomes. • Your body cells have 23 pairs of chromosomes. – Homologous pairs of chromosomes have the same structure. – For each homologous pair, one chromosome comes from each parent.

There are two types of Chromosomes. • Chromosome pairs 1 -22 are autosomes. • Sex chromosomes, X and Y, determine gender in mammals.

• • • Humans have 46 chromosomes (23 pair) Cats have 38 chromosomes (19 pair) Chickens have 78 chromosomes (39 pair) Horses have 64 chromosomes (32 Pair) Potatoes have 48 chromosomes (24 pair) Goldfish have 100 chromosomes (50 pair) Fruit fly has 8 (4 pair) Corn has 20 (10 pair) Peas have 14 (7 pair) Mosquitoes have 6 chromosomes (3 pair) Mice have 40 chromosomes (20 pair) Elephants have 56 chromosomes (28)

So Again…… • The zygote of humans have 23 pairs of chromosomes (or 46 individual chromosomes) • 23 chromosomes come from each parent • 23 + 23 = 46 • Humans have 46 chromosomes

The process of Meiosis- The Formation of Sex Cells

• Meiosis makes haploid cells from diploid cells. – Meiosis occurs in sex cells. – Meiosis produces gametes.

I. Introduction to Meiosis A. Purpose - to make sex cells for reproduction. B. Why can’t mitosis do this? Remember…. mitosis would make too many chromosomes.

MEIOSIS 4 cells • Makes ____ genetically different from parent cell & from each other 1 n cells • Makes _____ Germ cells • Makes _______ OR Gametes (sperm & eggs) sexual • Used for ______ reproduction

WHAT MAKES MEIOSIS DIFFERENT ? Crossing Over, Segregation, and Independent Assortment ALL are ways MEIOSIS results in GENETIC RECOMBINATION =_______________ different So daughter cells are _______ from parents and from each other

WHAT MAKES MEIOSIS DIFFERENT ? 1. Homologous chromosomes pair up during ________ PROPHASE I SYNAPSIS = _______ This group of FOUR (4) chromatids is called a TETRAD _________

WHAT MAKES MEIOSIS DIFFERENT? 1. Exchange of DNA between OVER homologous pairs = CROSSING _______ during PROPHASE I Separates gene choices and Allows shuffling of genetic material

CROSSING OVER rearranging of DNA • Allows for_________ in different combinations • After crossing over, chromatid arms NOT IDENTICAL anymore are________

WHAT MAKES MEIOSIS DIFFERENT ? Separation during ANAPHASE I -chromosome pairs separate SEGREGATION & INDEPENDENT ASSORTMENT

SEGREGATION & CROSSING OVER together make even more combinations

INDEPENDENT ASSORTMENT

INDEPENDENT ASSORTMENT at ANAPHASE I Lots of different combinations are possible! This is why you don’t look exactly like your brothers and sisters even though you share the same parents!

SO WHAT MAKES MEIOSIS DIFFERENT ? 1. SYNAPSIS & CROSSING OVER (PROPHASE I) 2. SEGREGATION & INDEPENDENT ASSORTMENT in Anaphase I create genetic recombination 3. Skip INTERPHASE II (NO S) CELL DIVIDES TWICE, BUT… ONLY COPIES DNA ONCE

WHAT MAKES MEIOSIS DIFFERENT ? 3. Skip INTERPHASE II (No S) CELL DIVIDES TWICE, BUT … ONLY COPIES ITS DNA ONCE MITOSIS: G 1 S G 2 P MEIOSIS: G 1 S M G 2 P M P M A T C (I) C ( II ) A T

Workings of Meiosis A. Meiosis is - the formation of sex cells (eggs and sperm) 1. Gametes - another name for sex cells. A. Gametes have haploid chromosome number

B. Meiosis is the making of eggs and sperm with half the number of chromosomes as the parent cell. 1. Female egg = 23 2. Male sperm = 23

C. Two Main Stages of Meiosis 1. Meiosis I a. Prophase I b. Metaphase I c. Anaphase I d. Telophase I

2. Meiosis II a. Prophase II b. Metaphase II c. Anaphase II d. Telophase II D. There is only one interphase

Cells go through two rounds of division in meiosis. • Meiosis reduces chromosome number and creates genetic diversity.

• Meiosis I and meiosis II each have four phases, similar to those in mitosis. – Pairs of homologous chromosomes separate in meiosis I. – Homologous chromosomes are similar but not identical. – Sister chromatids divide in meiosis II. – Sister chromatids are copies of the same chromosome. homologous chromosomes sister chromatids

• Meiosis I occurs after DNA has been replicated. • Meiosis I divides homologous chromosomes in four phases.

• Meiosis II divides sister chromatids in four phases. • DNA is not replicated between meiosis I and meiosis II.

Meiosis I A. Interphase 1. Replication of chromosomes occurs. 2. This is the only interphase.

B. Prophase I 1. Chromatids appear 2. Centrioles split. 3. Centrioles move to the opposite poles. 4. Spindle fibers appear

5. Nucleolus disappears 6. Nuclear membrane disappears 7. Tetrads form - two pairs of homologous chromosomes joining together.

8. Crossing-over occurs here - genes are exchanged between homologous chromsomes. a. Creates variation in new offspring

C. Metaphase I 1. Tetrads line up at the equator.

D. Anaphase I 1. Tetrads separate. 2. Chromatids are pulled to the opposite poles.

E. Telophase I 1. Chromatids still visible. 2. Nucleolus and Nuclear Membrane reforms. 3. Centrioles replicate 4. Two new cells.

IV. Meiosis II A. No interphase begins this phase. 1. 2 cells with the haploid chromosome number begin this stage. 2. Meiosis II will always have two cells in each phase.

B. Prophase II 1. Nuclear membrane and nucleolus disappear. 2. Centrioles split 3. Centrioles move to the poles.

4. Spindle fibers form. 5. Chromatids are visible and attach to spindle fibers.

C. Metaphase II 1. Chromatids line up on the equator.

D. Anaphase II 1. Centromeres separate. 2. Chromotids are pulled to opposite poles.

E. Telophase II 1. Centrioles replicate 2. Nuclear membrane and nucleolus reappear. 3. Spindle fibers disappear.

4. 4 new cells are formed a. Only have half the number of chromosomes as the parent cell. b. Males - all 4 remain alive and viable. c. Females – one egg grows rest (polar bodies) die off.

V. Meiosis-Mitosis Comparison A. Mitosis 1. 4 phases 2. Produces 2 diploid cells 3. Daughter cells identical to parent

B. Meiosis 1. 8 phases 2. 4 haploid cells produced 3. Daughter cells not identical to parent 4. Contain tetrads and crossing-over.

• Meiosis differs from mitosis in significant ways. – Meiosis has two cell divisions while mitosis has one. – In mitosis, homologous chromosomes never pair up. – Meiosis results in haploid cells; mitosis results in diploid cells.

Figure 11 -15 Meiosis Section 11 -4 Meiosis I

Figure 11 -17 Meiosis II Section 11 -4 Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Telophase II Meiosis II results in four haploid (N) daughter cells.

That’s All For Now Folks!