Meiosis & Sexual Reproduction 2011-2012
Cell division/asexual reproduction Mitosis produce cells with same information daughter cells: how many? identical? different? What are clones? clones same amount of DNA Aaaargh! I m seeing double!
Cell division/asexual reproduction Mitosis produce cells with same information identical daughter cells exact copies clones same amount of DNA same number of chromosomes same genetic information Aaaargh! I m seeing double!
Asexual reproduction Single-celled eukaryotes yeast (fungi) Protists Paramecium Amoeba Simple multicellular eukaryotes Hydra budding budding What are the disadvantages of asexual reproduction? What are the advantages?
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? No! What if we did, then. 46 + 46 92 egg sperm zygote Doesn t work!
Human female karyotype 46 chromosomes 23 pairs
Human male karyotype 46 chromosomes 23 pairs
Klinefelter s Syndrome Klinefelter s Syndrome: develop as males subtle characteristics that become apparent during puberty. often tall more breast tissue than normal, have a less muscular body usually no secondary sex characteristics (facial hair or underarm and pubic hair) Extra X chromosome primarily affects the testes, which produce sperm and the male hormone testosterone. http://learn.genetics.utah.edu/content/disorders/ whataregd/klinefelter/
http://learn.genetics.utah.edu/content/disorders/whataregd/turner/index.html Turner Syndrome Develop as females Average height of an untreated woman is 4 feet 8 inches. usually sterile stocky appearance, arms that turn out slightly at the elbow, a receding lower jaw, a short webbed neck, and low hairline at the back of the neck. The genes affected are involved in growth and sexual development, which is why girls with the disorder are shorter than normal and have abnormal sexual AP characteristics. Biology
Construct an online karyotype: http://learn.genetics.utah.edu/content/begin/traits/ karyotype/
Homologous chromosomes Paired chromosomes both chromosomes of a pair carry matching genes control same inherited characters homologous = same information diploid 2n 2n = 4 single stranded homologous chromosomes double stranded homologous chromosomes
How do we make sperm & eggs? Must reduce the number of chromosomes from 46 to 23 ( n to n) must reduce the number of chromosomes by 46 46 23 meiosis egg 46 What is this process? 23 23 23 fertilization What is this process? zygote sperm gametes By what process will this cell become many cells?
How do we make sperm & eggs? Must reduce 46 chromosomes 23 must reduce the number of chromosomes by half 46 meiosis 23 egg 23 23 zygote 46 46 23 fertilization sperm gametes
Meiosis: production of gametes Alternating stages chromosome number must be reduced diploid haploid 2n n humans: 46 23 meiosis reduces chromosome number makes gametes fertilization restores chromosome number haploid diploid n 2n haploid diploid
Sexual reproduction lifecycle 1 copy ploidy: 1n Name this process In the next generation We re mixing things up here! A good thing? 2 copies ploidy: 2n Name this process 1 copy ploidy: 1n What are these? What are these? How do these gametes compare to the gametes that generated the organism that produced these gametes?
Sexual reproduction lifecycle 2 copies diploid 2n 1 copy haploid 1n fertilization In the next generation We re mixing things up here! A good thing? meiosis 1 copy haploid 1n gametes gametes
Meiosis Reduction Division special cell division for sexual reproduction reduce 2n 1n diploid haploid two half makes gametes sperm, eggs Warning: meiosis evolved from mitosis, so stages & machinery are similar but the processes are radically different. Do not confuse the two!
Overview of meiosis 2n = 4 IPMATPMAT interphase 1 prophase 1 metaphase 1 anaphase 1 n = 2 n = 2 prophase 2 metaphase 2 anaphase 2 telophase 2 n = 2 telophase 1
http://www.youtube.com/watch?v=kvmb4js99ta Overview of meiosis 2n = 4 IPMATMAT IPMATPMAT interphase 1 prophase 1 metaphase 1 anaphase 1 n = 2 n = 2 prophase 2 metaphase 2 anaphase 2 telophase 2 n = 2 telophase 1
Double division of meiosis DNA replication Blood is thicker than water. 1st division of meiosis separates homologous pairs 2nd division of meiosis separates sister chromatids Meiosis 1 Meiosis 2
Preparing for meiosis 1st step of meiosis Duplication of DNA Why bother? meiosis evolved after mitosis convenient to use machinery of mitosis DNA replicated in S phase of interphase of MEIOSIS (just like in mitosis) 2n = 6 single stranded M1 prophase 2n = 6 double stranded
Meiosis 1 1 st division separates prophase 1 2n = 4 single stranded 2n = 4 double stranded synapsis metaphase 1 2n = 4 double stranded tetrad I Repeat can t after hear you! me! telophase 1 1n = 2 double stranded reduction
Meiosis 1 1st division of meiosis separates homologous pairs prophase 1 2n = 4 single stranded 2n = 4 double stranded synapsis metaphase 1 2n = 4 double stranded tetrad I Repeat can t after hear you! me! telophase 1 1n = 2 double stranded reduction
Meiosis 2 2 nd division separates 1n = 2 double stranded What does this division resemble? 1n = 2 double stranded prophase 2 metaphase 2 1n = 2 single stranded telophase 2
Meiosis 2 2nd division of meiosis separates sister chromatids Blood is thicker than water 1n = 2 double stranded What does this division look like? 1n = 2 double stranded prophase 2 metaphase 2 1n = 2 single stranded 4 telophase 2
Steps of meiosis Meiosis 1 interphase prophase 1 metaphase 1 anaphase 1 telophase 1 Meiosis 2 metaphase 2 anaphase 2 telophase 2 1st division of meiosis separates homologous pairs (2n 1n) reduction division 2nd division of meiosis separates sister chromatids (1n 1n) * just like mitosis *
Meiosis 1 & 2
Trading pieces of DNA synapsis Name this process during, sister chromatids intertwine homologous pairs swap pieces of chromosome DNA breaks & re-attaches prophase 1 tetrad
Trading pieces of DNA Crossing over during Prophase 1, sister chromatids intertwine homologous pairs swap pieces of chromosome DNA breaks & re-attaches prophase 1 synapsis tetrad
Crossing over 3 steps Result: What are the advantages of crossing over in sexual reproduction?
Crossing over 3 steps cross over breakage of DNA re-fusing of DNA New combinations of traits What are the advantages of crossing over in sexual reproduction?
Mitosis vs. Meiosis
Mitosis vs. Meiosis Mitosis Meiosis
Mitosis vs. Meiosis Mitosis 1 division daughter cells genetically identical to parent cell produces 2 cells 2n 2n produces cells for growth & repair no crossing over Meiosis 2 divisions daughter cells genetically different from parent produces 4 cells 2n 1n produces gametes crossing over http://www.pbs.org/wgbh/nova/miracle/divide.html
Putting it all together meiosis fertilization mitosis + development gametes 46 23 46 23 meiosis 46 egg sperm 23 23 46 46 46 46 46 46 46 46 zygote fertilization mitosis development
What?? http://www.youtube.com/watch?v=9mbbr-a2knm So, why aren t we all twins??
The value of sexual reproduction independent assortment of chromosomes random alignment of homologous chromosomes in Metaphase 1 mixing of alleles across homologous chromosomes which sperm fertilizes which egg? Driving evolution providing variation for natural selection metaphase1
The value of sexual reproduction Sexual reproduction introduces genetic variation genetic recombination independent assortment of chromosomes random alignment of homologous chromosomes in Metaphase 1 crossing over mixing of alleles across homologous chromosomes random fertilization which sperm fertilizes which egg? Driving evolution providing variation for natural selection metaphase1
Variation from genetic recombination Independent assortment of chromosomes meiosis introduces genetic variation gametes of offspring do not have same combination of genes as gametes from parents random assortment in humans produces 2 23 (8,388,608) different combinations in gametes from Mom from Dad offspring new gametes made by offspring
Variation from crossing over Crossing over creates completely new combinations of traits on each chromosome creates an infinite variety in gametes
Variation from random fertilization Sperm + Egg =? http://www.morphthing.com/morph any 2 parents will produce a zygote with over 70 trillion (2 23 x 2 23 ) possible diploid combinations http://www.youtube.com/watch?v=vxnatrs83he
Sexual reproduction creates variability Sexual reproduction allows us to maintain both genetic similarity & differences. Jonas Brothers Baldwin brothers Martin & Charlie Sheen, Emilio Estevez
Epididymis Sperm production Vas deferens Testis Coiled seminiferous tubules germ cell (diploid) primary spermatocyte (diploid) secondary spermatocytes (haploid) spermatids (haploid) MEIOSIS I MEIOSIS II Spermatogenesis continuous & prolific process Cross-section of seminiferous tubule each ejaculation = 100-600 million sperm spermatozoa
Egg production Oogenesis eggs in ovaries halted before Anaphase 1 Meiosis 1 completed during maturation Meiosis 2 completed after fertilization 1 egg + 2 polar bodies Meiosis 1 completed during egg maturation What is the advantage of this development system? Meiosis 2 completed triggered by fertilization unequal divisions ovulation
Oogenesis Putting all your egg in one basket! germinal cell (diploid) primary follicles fallopian tube fertilization MEIOSIS I first polar body MEIOSIS II after fertilization second polar body primary oocyte (diploid) secondary oocyte (haploid) ovum (haploid) developing follicle mature follicle with secondary oocyte ruptured follicle (ovulation) corpus luteum
Differences across kingdoms Not all organisms use haploid & diploid stages in same way which one is dominant (2n or n) differs but still alternate between haploid & diploid must for sexual reproduction
Any Questions?? What are the DISadvantages of sexual reproduction? 2007-2008
Meiosis review http://learn.genetics.utah.edu/content/begin/traits/predictdisorder/ http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter28/animation unique_features _of_meiosis.html http://lpscience.fatcow.com/jwanamaker/animati ons/meiosis.html http://www.stolaf.edu/people/giannini/flashanimat/celldivision/meio sis.swf Dance http://www.youtube.com/watch?v=kvmb4js99ta