ANNOUNCEMENTS• LAB #3 MITOSIS & MEIOSIS has been moved to FRIDAY

because I’m not finished grading lab #1.

• DO THE SAMPLE FREE RESPONSE QUESTIONS FOR HOMEWORK. I’ll post them on facebook and teacherweb.

• Do the lab bench exercise for LAB 3 mitosis & meiosis http://www.phschool.com/science/biology_place/labbench/

• LAB 3 is now on FRIDAY- you will have a lab quiz

• Here are other websites that will help you:

• http://users.nac.net/challoran/apbio.htm

• TEST #2 IS TUESDAY 10/9… YOUR BIG CHANCE TO BRING YOUR GRADE WAY UP! :)

CHAPTER 13

Meiosis & Sexual Life Cycles

Asexual reproduction

produces clones

ex. Hydrasea sponge

ASEXUAL REPRODUCTIONreproduction which does not involve meiosis, reduction, or fertilization.

• Only one parent is involved in asexual reproduction. • A lack of sexual reproduction is relatively rare among multicellular organisms, for reasons that are not completely understood.

• Current hypotheses suggest that asexual reproduction may have short term benefits when rapid population growth is important or in stable environments,

• while sexual reproduction offers a net advantage by allowing more rapid generation of genetic diversity, allowing adaptation to changing environments.

Types of asexual reproduction1.1 Binary fission1.2 Budding1.3 Vegetative reproduction1.4 Spore formation1.5 Fragmentation1.6 Parthenogenesis1.7 Agamogenesis

Figure 13.x1 SEM of sea urchin sperm fertilizing egg

Sexual reproduction= genetic recombination= diversity= better chance of survival

Sexual reproduction offers a net advantage by allowing more rapid generation ofgenetic diversity, allowing adaptation to changingenvironments.

WHY SEX?

Natural selection operates on populations through the phenotypic differences (traits) that individuals display;

meiosis followed by fertilization provides a spectrum of possible phenotypes on which natural selection acts, and variation contributes to the long-term continuation of species.

Figure 13.4 The human life cycle

Meiosis ensures that each gamete (sperm/egg) receives one complete haploid (1n) set of chromosomes.

Fertilization involves the fusion of two gametes, increases genetic variation in populations by providing for new combinations of genetic information in the zygote, and restores the diploid number of chromosomes.

Figure 13.x3 Human female karyotype shown by bright field G-banding of chromosomes

Figure 13.x5 Human male karyotype shown by bright field G-banding of chromosomes

QUIZ:1. What determines whether you

are genetically male or female?

2. What are autosomes?

3. What are gametes?

4. What is a zygote?

5. What is the difference between a diploid cell and haploid cell?

6. What is Meiosis?

1. Sex chromosome combo XX=female XY=male.

2. Non-sex chromosomes (1-22)3. Sex cells- sperm or egg.4. Fertilized egg.5. Diploid=2n (homologous

chromosomes); hapliod=1n (only one of each kind of chromosome)

6. Nuclear division that includes a “reduction” it reduces the chromosome number by 1/2.

The creation of gametes for sexual reproduction (MEIOSIS)Occurs in 2 stages:

MEIOSIS I- REDUCTION1. separates homologous chromosomes.2. 2n ---> 1n 3. ex. 46 ---> 234. split up the “pairs” or TETRAD

Law of Segregation- alleles of a geneSeparate during gamete formation.

MEIOSIS II1. separates sister chromatids2. 1n (2 chromatids) ---> 2 separate x 1n chromosomes*similar to mitosis.

Figure 13.7 The stages of meiotic cell division: Meiosis I

meiosis1 is like separating all the pairs of shoes in your closet… putting one of each kind in one room & the other in another room.

During meiosis, homologous chromosomes are paired, with one homologue originating from the maternal parent and the other from the paternal parent. Orientation of the chromosome pairs is random with respect to the cell poles.

Separation of the homologous chromosomes ensures that each gamete receives a haploid (1n) set of chromosomes composed of both maternal and paternal chromosomes.

Figure 13.7 The stages of meiotic cell division: Meiosis II

Major Differences between Mitosis & Meiosis:(2 divisions- not 1 creates 4 haploid cells- not 2 diploid)

PROPHASE IS SPECIAL…• In Prophase 1 of Meiosis 1

the homologous chromosomesline up together.

2. SYNAPSIS is the process ofpairing homologous chromosomes.

3. TETRAD is 4 chromatids ofa homologous pair.

4. CHIASMATA are the X shapedregions of chromatid overlap.

5. CROSSING OVER producesrecombinant chromosomes

when pieces break off & attach.

CROSSING OVER

• During meiosis, homologous chromatids exchange genetic material via a process called “crossing over,” which increases genetic variation in the resultant gametes.

• Benefit to the organism’s species because it produces genetic variation.

• Recombinant chromosomes are produced.

• New combinations of your parent’s genes in your gametes.

• Diversity = better chances for survival of a species.

Figure 13.7 The stages of meiotic cell division: Meiosis I

INTERPHASE I

• Cell grows by producing proteins (cyclin) and organelles

• Chromosomes replicate

• Centrosomes/centrioles replicate

• Preparation for cell division

PROPHASE I

• Chromatin condenses• Homologous replicated

chromosomes line up together

• “SYNAPSIS”• Crossing over occurs• TETRAD consists of 4

chromatids• CHIASMA(TA)

METAPHASE I• Spindle microtubules from

opposite poles attach to one each of a homologous pair of replicated chromosomes.

• Homologous pairs poised to move to opposite poles of the cell.

• Position of pairs on metaphase plate leads to variation due to independent assortment.

• =Alleles of different genes assort independently during gamete formation.

Figure 13.9 The results of alternative arrangements of two homologous chromosome pairs on the metaphase plate in meiosis I

Independent Assortment means that when you separate

these pairs it doesn’t matter if one side gets the left or right shoe. Each pair is split up independently.

How many ways could you split up these 12 pairs?

2 n (n=#chromosomes) 2 12 =

For humans???? 2 23=

ANAPHASE I

• Homologous pairs of chromosomes are separated.

• Sister chromatids remain attached at their centromere.

• Independent assortment occurs now… the separation of each chromosome pair occurs independently.

Figure 13.9 The results of alternative arrangements of two homologous chromosome pairs on the metaphase plate in meiosis I

TELOPHASE I• Cytokinesis occurs.• 2 haploid daughter

cells are formed.• Each chromosome still

consists of 2 sister chromatids.

• Meiosis II is next.• (INTERKINESIS)

Figure 13.7 The stages of meiotic cell division: Meiosis II

MEIOSIS II

• Essentially mitosis• Begins with haploid cells

(unlike mitosis which starts with diploid cells)

• Sister chromatids pulled apart• Results in 4 haploid cells.• Each with one set of

chromosomes.

Figure 13.8 A comparison of mitosis and meiosis

SPERMATOGENESIS

• Sperm are produced in the seminiferous tubules of the testes of adult males.

• Each ejaculation contains 100-650 million sperm cells. They live 4 days.

• Each diploid stem cell (spermatogonium) produces 4 haploid sperm cells (spermatozoa)

OOGENESIS

DIFFERENCES BETWEEN OOGENSIS & SPERMATOGENESIS:

• Cytokinesis is unequal- almost all the cytoplasm is taken by a single daughter cell SECONDARY OOCYTE. This cell can go on to form the ovum (egg).The other smaller cells are Polar bodies.

• At birth, ovary already contains all the primary oocytes.

• Oogenesis has long resting periods. Starting at puberty, a single primary oocyte completes meiosis I each month. The secondary oocyte completes meiosis II only if a sperm cell enters it.

* Ootid is an undifferentiated ovum.

THE PLANTS • Alternation of Generations

• Sporophytes

• Spores

• Spores

• Haploid

• Gametophytes

• Mitosis

• There aren’t homologous chromosomes to separate by meiosis (already haploid)

• DIPLOID

• HAPLOID

Figure 13.8 A comparison of mitosis and meiosis: summary

Figure 13.5 Three sexual life cycles differing in the timing of meiosis and fertilization (syngamy)