MEIOSIS 11-4 Making gametes…

Warm ups – February 24 th, 2012 Why don’t you look like your brothers and/or sisters? If we have 46 chromosomes in our cells, why don’t our children have 92?

1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis? 2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo? 3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have ? Interest Grabber 46 chromosomes = 92; a developing embryo would not survive if it contained 92 chromosomes. Sperm and egg should each have 23 chromosomes.

Planaria animation: Family Remember from Chapter 1: CHARACTERISTICS OF LIVING THINGS ALL LIVING THINGS __________ REPRODUCE

ASEXUAL REPRODUCTION Bacteria reproduce using __________________________________ Budding & regeneration are used by plants and animals to reproduce asexually (mitosis) Planaria animation: BINARY FISSION

BINARY FISSION & MITOSIS Produces cells that are __________ copies of parent cell identical

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

DISVANTAGES OF ASEXUAL REPRODUCTION ALL ALIKE Species CAN’T change and adapt One disease can wipe out whole population

How about the rest of us? What if a complex multicellular organism (like us) wants to reproduce? –joining of egg + sperm Do we make egg & sperm by mitosis? eggspermzygote What if we did, then…. Doesn’t work! No! 

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

Human female karyotype 46 chromosomes 23 pairs XX diploid = 2 copies 2n

46 chromosomes 23 pairs XY Human male karyotype diploid = 2 copies 2n

EGG + SPERM  If egg and sperm had same number of chromosomes as other body cells... baby would have too many chromosomes! Image by Riedell 23 chromosomes 23 chromosomes 46 chromosomes

gametes How do we make sperm & eggs? Must reduce 46 chromosomes  23 –must half the number of chromosomes –haploid egg sperm 46 meiosis 46 fertilization 23 zygote

MEIOSIS is the way… to make cells with ½ the number of chromosomes for sexual reproduction

DIPLOID & HAPLOID Most cells have 2 copies of each chromosome = ______________ (one from mom; one from dad) All BODY (___________) cells are diploid DIPLOID2n HOMOLOGOUS CHROMOSOMES = SOMATIC

DIPLOID & HAPLOID Some cells have only one copy of each chromosome = _____________ All sperm and egg cells are haploid HAPLOID1n

___________________= MAKING MATURE SPERM Mature & grow flagella SPERMATOGENESIS

Sperm provides DNA All the starting nutrients, organelles, molecule building blocks, etc. have to come from the egg.

POLAR BODIES Produces: 1 “good” egg 3 CYTOPLASM DIVIDES UNEVENLY __________________ = MAKING a MATURE EGG OOGENESIS

Sperm donates mostly DNA WHY MAKE ONLY ONE “GOOD” EGG? Most of the cell parts and nutrients needed for baby come from EGG!

“Self digest” Using ________________ POLAR BODIES DEGENERATE (DIE) LYSOSOMES = __________________ “cell suicide” for good of organism APOPTOSIS

MITOSIS Makes ___ cells genetically _________ to parent cell & to each other Makes ___ cells Makes __________ Used by organisms to: increase size of organism, repair injuries, replace worn out cells 2 identical 2n SOMATIC (body)

MEIOSIS Makes ____ cells genetically different from parent cell & from each other Makes _____ cells Makes ______________ Used for ____________ 4 1n Gametes (sperm & eggs) sexual reproduction

How is MEIOSIS DIFFERENT ? 1.SYNAPSIS & CROSSING OVER mom and dad’s chromosomes do a little dance and actually SWAP DNA! 2.SEGREGATION & INDEPENDENT ASSORTMENT Sperm and egg cells is a RANDOM MIX of mom and dad’s chromsomes, like a lottery drawing. 3. Skip INTERPHASE II (NO S) CELL DIVIDES TWICE, BUT… ONLY COPIES DNA ONCE

Let’s watch a video to see this in action

WHAT happens first? 1.Homologous chromosomes pair up during ________________ = ______________ SYNAPSIS Images modified from: This group of FOUR (4) chromatids is called a _________________ TETRAD PROPHASE I

Mom and dad’s chromosomes do a little dance 1. Exchange of DNA between homologous pairs = _____________ during PROPHASE I CROSSING OVER Allows shuffling of genetic material

HOMOLOGOUS CHROMOSOMES Image modified by Riedell SAME SIZE SAME SHAPE CARRY GENES for the SAME TRAITS BUT ______________! (Don’t have to have the SAME CHOICES) NOT IDENTICAL MomDad

CROSSING OVER Image modified by Riedell Allows for_________________ in different combinations After crossing over, chromatid arms are________________ anymore rearranging of DNA NOT IDENTICAL

How are our sex cells a random mix of mom and dad’s DNA? 2. Separation during ANAPHASE I INDEPENDENT ASSORTMENT Separates gene choices and allows shuffling of genetic material SEGREGATION &

SEGREGATION (Anaphase I)

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!

WHAT MAKES MEIOSIS DIFFERENT ? Crossing over Segregation Independent assortment are ALL ways MEIOSIS results in =______________________________ So daughter cells are ______________ from parents and from each other different GENETIC RECOMBINATION

WHAT MAKES MEIOSIS DIFFERENT ? 3. Skip INTERPHASE II (No S) CELL DIVIDES TWICE, BUT … ONLY COPIES ITS DNA ONCE G1G1 G2G2 S   PM  A T C G1G1    MITOSIS: MEIOSIS:    SG2G2 PM ATC PM A TC ( I ) ( II )

Go to Section: Meiosis I Section 11-4 Figure Meiosis

Go to Section: Meiosis I Section 11-4 Figure Meiosis Meiosis I

Go to Section: Meiosis I Section 11-4 Figure Meiosis Meiosis I

Go to Section: Section 11-4 Figure Meiosis Meiosis I

Go to Section: Section 11-4 Figure Meiosis Meiosis I

Go to Section: Meiosis II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II The 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 Meiosis II

Go to Section: Meiosis II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II The 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 Meiosis II

Go to Section: Meiosis II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II The 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 Meiosis II

Go to Section: Meiosis II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II The 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 Meiosis II

Go to Section: Meiosis II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II The 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 Meiosis II

Ways Meiosis is different? Homologous pairs match up & trade DNA (SYNAPSIS & CROSSING OVER) in PROPHASE I SEGREGATION & INDEPENDENT ASSORTMENT in Anaphase I create genetic recombination Skipping INTERPHASE II- (Dividing TWICE but copying DNA once) produces 1n cells

Activity Draw out the steps of Meiosis using 3 PAIRS of homologous chromosomes This means you should choose 6 COLORS to represent each chromosome Use contrasting colors for homologous chromosomes to show crossing over (Go back to animation for example)

MAKING SPERM & EGGS