MEIOSIS Making gametes…

ASEXUAL REPRODUCTION Produces cells that are IDENTICAL copies of parent cell; can’t adapt/change EX: Binary fission, budding & regeneration Planaria animation: http://www.t3.rim.or.jp/~hylas/planaria/title.htm

SEXUAL REPRODUCTION Family image from: http://babyhearing.org/Parenet2Parent/index.asp Combines genetic material from sperm & egg; offspring are genetically different

ADVANTAGES OF SEXUAL REPRODUCTION Allows for variation in population Allow species adapt to changes in their environment http://naturalsciences.sdsu.edu/classes/lab8/spindex.html

Think-Pair-Share Human body cells contain 46 chromosomes 1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?

Think-Pair-Share 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?

Think-Pair-Share 3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?

DIPLOID VS HAPLOID Body cells (somatic cells) have 2 copies of each chromosome = DIPLOID (2n) (one from mom; one from dad)

DIPLOID & HAPLOID Sex cells have only one copy of each chromosome = All sperm and egg cells are haploid HAPLOID (1n)

MITOSIS CREATES DIPLOID BODY CELLS Makes 2 cells genetically identical to parent cell & to each other Used by organisms to: grow, repair injuries, replace cells http://waynesword.palomar.edu/lmexer2a.htm

MEIOSIS CREATES HAPLOID SEX CELLS Makes 4 cells genetically different from parent cell & from each other Used for sexual reproduction http://waynesword.palomar.edu/lmexer2a.htm

HOMOLOGOUS CHROMOSOMES SAME SIZE & SHAPE CARRY GENES for the SAME TRAITS BUT NOT IDENTICAL! http://sps.k12.ar.us/massengale/genetics%20tutorial.htm

Stages of Meiosis

Meiosis

Meiosis takes place in two series of steps Meiosis I I, P, M, A, T + Meiosis II P, M, A, T Which means…no DNA replication before meiosis II No second “I”

Interphase I DNA replicates creating homologous chromosomes

PROPHASE I Homologous chromosomes pair up = SYNAPSIS TETRAD = group of FOUR (4) chromatids Images modified from: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif

Exchange of DNA between homologous pairs 2. CROSSING OVER Exchange of DNA between homologous pairs After crossing over, chromatid arms are NOT IDENTICAL anymore http://sps.k12.ar.us/massengale/genetics%20tutorial.htm

Metaphase I Tetrads line up in the middle

Anaphase I- Tetrads pull apart to opposite ends of the cell.

Telophase I- Cell separates into two new cells

No Interphase II = chromosomes are NOT copied again. Meiosis II No Interphase II = chromosomes are NOT copied again.

Prophase II ~ TWO cells begin meiosis II

Metaphase II chromosomes line up in the middle of the cell

Anaphase II -chromosomes are pulled to opposite ends of the cell

Telophase II / Cytokinesis ~ The 2 cells divide to form 4 genetically different cells (gametes)

End Result of Meiosis Four new cells Half # chromosomes as parent cell - haploid (n) Humans – 23 chromosomes

MAKING SPERM & EGGS

___________________= MAKING MATURE SPERM SPERMATOGENESIS ___________________= MAKING MATURE SPERM Mature & grow flagella

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

Sperm donates mostly DNA WHY MAKE ONLY ONE “GOOD” EGG? Sperm donates mostly DNA Most of the cell parts and nutrients needed for baby come from EGG! http://bestweekever.blogs.com/photos/uncategorized/imagemain_sperm_egg1_1.gif

What are the major differences between Mitosis and Meiosis?

Mitosis Meiosis Body cells (Somatic) Sex cells (Gamete) 2 daughter cells same as parent cell (diploid – 2n) 4 daughter cells w/half chrom. (haploid – 1n) Asexual reproduction Sexual reproduction