MEIOSIS ReductionDivision Genetic Recombination 1 Bellringer Agenda Bellringer
MEIOSIS Reduction-Division Genetic Recombination 1
Bellringer Agenda Bellringer What type of cells Meiosis Matching are produced Diploid/Haploid from Meiosis? Mitosis vs. Meiosis How many times does Meiosis occur to complete one cycle? 2
Bellringer What type of cells are produced from Meiosis? Sex cells (egg & sperm) How many times does Meiosis occur to complete one cycle? Agenda Bellringer Meiosis Matching Diploid/Haploid Mitosis vs. Meiosis Twice 3
Bellringer During which stage of Meiosis do homologous chromosomes separate? Agenda Bellringer Meiosis Review Karyotype Video What is synapsis? 4
Bellringer During which stage of Meiosis do homologous chromosomes separate? Anaphase Agenda Bellringer Meiosis Review Karyotype Video I What is synapsis? 2 homologous chromosome pairs join together to make a tetrad 5
Bellringer What is nondisjunction? How many chromosomes should be at each location on a karyotype? Agenda Bellringer Kahoot Review Meiosis Mini Exam Genetics Reading 6
Bellringer What is nondisjunction? When chromosomes fail to separate equally How many chromosomes should be at each location on a karyotype? 2 Agenda Bellringer Kahoot Review Meiosis Mini Exam Genetics Reading 7
Bellringer Agenda In what organ are sperm produced? How many chromosomes are in gamete cells? 8
Bellringer In what organ are sperm produced? Agenda Bellringer Testes How many chromosomes are in gamete cells? 23 (haploid) 9
MEIOSIS The form of cell division by which GAMETES, with HALF the number of CHROMOSOMES, are produced. DIPLOID (2 n) HAPLOID (n) Meiosis is SEXUAL reproduction. TWO divisions (MEIOSIS I and MEIOSIS II). II 10
MEIOSIS Sex cells divide to produce GAMETES (sperm or egg) Gametes have HALF the # of chromosomes. Occurs only in GONADS (testes or ovaries). Male: SPERMATOGENESIS -sperm Female: OOGENESIS - egg or ova 11
SPERMATOGENESIS human sex cell n=23 sperm n=23 2 n=46 diploid (2 n) n=23 haploid (n) n=23 Meiosis II 12
OOGENESIS Haploid (1 n) n=23 human sex cell egg n=23 2 n=46 diploid (2 n) Meiosis I Polar Bodies (die) n=23 Meiosis II 13
INTERPHASE I Similar to mitosis interphase. CHROMOSOMES (DNA) replicate in the S phase Each duplicated chromosome consist of two identical SISTER CHROMATIDS attached at their CENTROMERES CENTRIOLE pairs also replicate. 14
INTERPHASE I Nucleus and nucleolus visible. chromatin Nucleus cell membrane nucleolus 15
MEIOSIS I (FOUR PHASES) Cell division that reduces the chromosome number by onehalf. Four phases: phases a. Prophase I b. Metaphase I c. Anaphase I Prophase I d. Telophase I 16
NON-SISTER CHROMATIDSHOMOLOGS • Homologs contain DNA that codes for the same genes , but different versions of those genes • Genes occur at the same loci 17
PROPHASE I - SYNAPSIS Homologous chromosomes sister chromatids Tetrad sister chromatids 18
HOMOLOGOUS CHROMOSOMES Pair of chromosomes (maternal and paternal) paternal that are similar in shape and size. Homologous pairs (tetrads) carry GENES controlling the SAME inherited traits Each locus (position of a gene) is in LOCI the same position on homologues. Humans have 23 pairs of homologous chromosomes: a. First 22 pairs of autosomes b. Last pair of sex chromosomes 19
HOMOLOGOUS CHROMOSOMES eye color locus hair color locus Paternal Maternal 20
CROSSING OVER Crossing over may occur between non -sister chromatids at sites called chiasmata OCCURS DURING PROPHASE I Crossing over: over segments of nonsister chromatids break and reattach to the other chromatid Chiasmata (chiasma) are where chromosomes touch each other and exchange genes (crossing over. ) over Causes Genetic Recombination 21
GENETIC RECOMBINATION nonsister chromatids chiasmata: site of crossing over Tetrad variation 22
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SEX CHROMOSOMES XX chromosome - female XY chromosome - male 24
MEIOSIS I Meiosis I Homologs separate 25
PROPHASE I • Nucleus & Nucleolus disappear • Spindle forms • Chromosomes coil & Synapsis (pairing) occurs • Tetrads form & Crossing over Occurs spindle fiber centrioles aster fibers TETRAD 26
METAPHASE I Shortest phase Tetrads align on the equator. Independent assortment occurs – chromosomes separate randomly causing GENETIC RECOMBINATION 27
METAPHASE I OR Homologs line up at equator or metaphase plate 28
ANAPHASE I Homologous chromosomes separate and move towards the poles. Sister chromatids remain attached at their centromeres 29
ANAPHASE I Homologs separate 30
TELOPHASE I Each pole now has haploid (1 n) set of chromosomes Cytokinesis occurs and two haploid daughter cells are formed. 31
TELOPHASE I cytokinesis 32
MEIOSIS II Meiosis II Sister Chromatids Separate 33
MEIOSIS II No Interphase II or very short No DNA Replication Remember: Meiosis II is similar to mitosis 34
PROPHASE II Same as Prophase in mitosis Nucleus & nucleolus disappear Chromosomes condense Spindle forms 35
METAPHASE II Same as Metaphase in mitosis Chromosomes (not homologs) line up at equator 36
ANAPHASE II Same as Anaphase in mitosis SISTER CHROMATIDS separate 37
TELOPHASE II Same as Telophase in mitosis. Nuclei and Nucleoli reform, spindle disappears CYTOKINESIS occurs. Remember: FOUR HAPLOID DAUGHTER cells are produced. Called GAMETES (eggs and sperm) 1 n Sperm cell fertilizes 1 n egg to form 2 n zygote 38
TELOPHASE II 39
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VARIATION Also known as GENETIC RECOMBINATION Important to population as the raw material for NATURAL SELECTION. All organisms are NOT alike Strongest “most fit” survive to reproduce & pass on traits 41
KARYOTYPE An organized picture of the chromosomes of a human arranged in pairs by size from largest to smallest. Pairs 1 -22 called AUTOSOMES Last pair are SEX CHROMOSOMES Male - XY 42
KARYOTYPE Female - XX 43
KARYOTYPE Down Syndrome – Trisomy 21 Female - XX 44
FERTILIZATION The fusion of a sperm and egg to form a zygote A zygote is a FERTILIZED EGG n=23 egg sperm n=23 2 n=46 zygote 45
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