- Slides: 43
MEIOSIS Making gametes…
Recall… CHARACTERISTICS OF LIVING THINGS ALL LIVING THINGS REPRODUCE
ASEXUAL REPRODUCTION Binary fission, budding & regeneration are used by plants and animals to reproduce asexually through mitosis Planaria animation: http: //www. t 3. rim. or. jp/~hylas/planaria/title. htm
ASEXUAL REPRODUCTION & MITOSIS Produces cells that are IDENTICAL copies of parent cell
ADVANTAGES OF ASEXUAL REPRODUCTION Can make offspring faster Don’t need a partner http: //www. mrgrow. com/images/cutting. jpg
DISVANTAGES OF ASEXUAL REPRODUCTION ALL ALIKE Species CAN’T change and adapt One disease can wipe out whole population http: //www. mrgrow. com/images/cutting. jpg
SEXUAL REPRODUCTION Family image from: http: //babyhearing. org/Parenet 2 Parent/index. asp Combines genetic material from 2 parents (sperm & egg) so offspring are genetically different from parents
ADVANTAGES OF SEXUAL REPRODUCTION Allows for variation in population Allow species adapt to changes in their environment http: //naturalsciences. sdsu. edu/classes/lab 8/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 (2 n) (one from mom; one from dad)
DIPLOID & HAPLOID Sex cells have only one copy of each chromosome = HAPLOID 1 n All sperm and egg cells are haploid
Diploid vs Haploid Video
MITOSIS CREATES DIPLOID BODY CELLS Makes 2 cells genetically identical to parent cell & to each other Used by organisms to: increase size of organism, repair injuries, replace worn out cells http: //waynesword. palomar. edu/lmexer 2 a. 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/lmexer 2 a. htm
HOMOLOGOUS CHROMOSOMES SAME SIZE SAME SHAPE CARRY GENES for the SAME TRAITS BUT NOT IDENTICAL! (Don’t have to have the SAME CHOICES) http: //sps. k 12. ar. us/massengale/genetics%20 tutorial. htm
Stages of Meiosis
Meiosis takes place in two series of steps MEIOSIS I + MEIOSIS II I, P, M, A, T d n o P, ec. M, s o N ” I “ A, T WHICH MEANS…NO DNA REPLICATION BEFORE MEIOSIS II
Interphase I DNA replicates creating homologous chromosomes
PROPHASE I 1. Homologous chromosomes pair up = SYNAPSIS This group of FOUR (4) chromatids is called a TETRAD _________ Images modified from: http: //www. emc. maricopa. edu/faculty/farabee/BIOBK/Crossover. gif
2. CROSSING OVER Exchange of DNA between homologous pairs Allows for rearranging of DNA in different combinations After crossing over, chromatid arms are NOT IDENTICAL anymore http: //sps. k 12. ar. us/massengale/genetics%20 tutorial. 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
Meiosis II No Interphase II which means 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 two 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
SPERMATOGENESIS __________= MAKING MATURE SPERM Mature & grow flagella
OOGENESIS _________ = MAKING a MATURE EGG Produces: 1 “good” egg 3 POLAR BODIES CYTOPLASM DIVIDES UNEVENLY; POLAR BODIES DEGENERATE (DIE)
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_egg 1_1. gif
What are the major differences between Mitosis and Meiosis?
Mitosis Meiosis Body cells (Somatic) 2 daughter cells same as parent cell (diploid – 2 n) Sex cells (Gamete) 4 daughter cells w/half chrom. (haploid – 1 n) Asexual reproduction Sexual reproduction
How long does it take a human sex cell to go through meiosis? In the case of eggs, the first division of meiosis occurs before birth of the female. The second division occurs at the time of ovulation somewhere between 12 and 40 years later. Sperm take a couple of days to go through meiosis.
How long does it take a cell to go through mitosis? Human skin cells - entire cell cycle takes about 2024 hours mitosis usually takes about 1 hour Some bacteria cells can complete this cycle in 20 minutes.