MEIOSIS AND THE SEXUAL LIFE CYCLES

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CHAPTER 13

• MEIOSIS AND THE SEXUAL LIFE CYCLES

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• HEREDITY THE CONTINUITY OF TRAITS FROM
  GENERATION TO GENERATION
• GENES HEREDITY UNITS THAT GET TRANSMITTED
• VARIATION INHERITED DIFFERENCES AMONG
  INDIVIDUALS WITHIN THE SAME SPECIES
• GENETICS THE SCIENTIFIC STUDY OF HEREDITY AND
  VARIATION

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• DNA NUCLEIC ACID POLYMER OF 4 NUCLEOTIDES
• CHROMOSOME THREADLIKE GENE CARRYING STRUCTURE
  FOUND IN THE NUCLEUS OF EUKARYOTIC CELLS, WHICH
  CONSISTS OF A VERY LONG DNA MOLECULE AND PROTEINS
• LOCUS A SPECIFIC LOCATION ON A CHROMOSOME THAT
  CONTAINS A GENE

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• LIFE CYCLE SEQUENCE OF STAGES IN AN ORGANISMS
  REPRODUCTIVE HISTORY
• SOMATIC CELL (BODY CELL) A CELL OTHER THAN A
  GAMETE
• GAMETE HAPLOID SPERM OR EGG CELL
• KARYOTYPE PHOTOMICROGRAPH OF AN INDIVIDUALS
  SOMATIC CELLS CHROMOSOMES (DURING METAPHASE)

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• HOMOLOGOUS CHROMOSOMES A PAIR OF CHROMOSOMES
  THAT DEMONSTRATE THE SAME SIZE, CENTROMERE
  POSITION AND STAINING PATTERN
• AUTOSOME NON-SEX CHOMOSOME, IN HUMANS 22 PAIR
• SEX CHROMOSOME X _at_ Y ONE PAIR IN HUMANS
• XY MALE
• XX FEMALE

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• DIPLOID 2n, CONDITION IN WHICH CELLS CONTAIN 2
  FULL SETS OF CHOMOSOMES
• HAPLOID
• n, GAMETE CONTAINS ONE-HALF A FULL SET OF
  CHROMOSOMES
• SPERM MALE
• OVA (EGG) FEMALE

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• FERTILIZATION UNION OF 2 GAMETES (MALE _at_
  FEMALE)
• ZYGOTE (2n, DIPLOID) IS THE RESULT OF
  FERTILIZATION
• GAMETES ARE THE ONLY CELLS IN THE BODY THAT ARE
  NOT PRODUCED BY MITOSIS (MEIOSIS)

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• SYNGAMY THE TIMING OF MEIOSIS AND FERTILIZATION
• THERE ARE THREE BASIC PATTERNS OF SEXUAL LIFE
  CYCLES

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• ANIMALS
• GAMETES ARE ONLY HAPLOID CELLS
• MEIOSIS OCCURS TO PRODUCE GAMETES
• FERTILIZATION PRODUCES DIPLOID ZYGOTE WHICH NOW
  DIVIDES MITOTICALLY TO PRODUCE AN ADULT

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• FUNGI AND SOME PROTISTS
• a. ONLY DIPLOID STAGE IS A ZYGOTE
• b. MEIOSIS OCCURS RIGHT AFTER THE ZYGOTE IS
  FORMED
• c. RESULTING HAPLOID CELLS DIVIDE VIA MITOSIS
  TO PRODUCE A HAPLOID MULTICELLULAR ORGANISM

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• PLANTS AND SOME ALGAE
• a. ALTERATION OF GENERATIONS
• b. MULTICELLULAR DIPLOID STAGE IS CALLED
  SPOROPHYTE- SPORE PRODUCING PLANT, MEIOSIS
  PRODUCES HAPLOID SPORES
• c. SPORES DIVIDE MITOTICALLY TO GENERATE A
  MULTICELLULAR HAPLOID STAGE GAMETOPHYTE- WHICH
  IS A GAMETE PRODUCING PLANT
• d. HAPLOID GAMETOPHYTES PRODUCE GAMETES BY
  MITOSIS
• e. FERTILIZATION PRODUCES A DIPLOID ZYGOTE AND
  DEVELOPS INTO THE NEXT SPOROPHYTE GENTERATION

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• MEIOSIS
• REDUCES THE CHROMOSOME FROM DIPLOID TO HAPLOID
• MEIOSIS SEXUAL REPRODUCTION CREATES GENETIC
  RECOMBINATION, OR VARIATION

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• INTERPHASE 1
• PRECEDES MEIOSIS
• CHROMOSOMES REPLICATE
• CENTRIOLES (PAIRS) REPLICATE (ANIMALS)
• EACH DUPLICATED CHROMOSOME CONSISTS OF 2
  IDENTICAL CHROMATIDS ATTACHED AT THEIR CENTROMERE

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• MEIOSIS SEGREGATION OF THE 2 CHROMOSOMES
  REDUCES THE CHROMOSOME IN HALF

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• PROPHASE 1
• LONGER AND MORE COMPLEX THAN MITOSIS
• CHROMOSOMES CONDENSE
• SYNAPSIS OCCURS HOMOLOGOUS PAIRS COME TOGETHER
  AND FORM TETRADS
• TETRAD COMPLEX OF 4 CHROMATIDS
• CHIASMATA X SHAPED REGION OF NON-SISTER
  CHROMATIDS THAT OVERLAP, WHERE CROSSING OVER
  MAY OCCUR
• CHROMOSOMES THICKEN AND DETACH FROM THE NUCLEAR
  ENVELOPE
• CENTRIOLE PAIRS MOVED APART AND SPINDLE
  MICROTUBULES FORM (ANIMALS)
• NUCLEAR ENVELOPE DISAPEARS
• CHROMOSOMES BEGIN TO MOVE TOWARD CENTER
• 90 OF MEIOSIS IS IN PROPHASE

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• METAPHASE 1
• TETRADS ALIGN ON THE METAPHASE PLATE (EQUATOR)
• EACH HOMOLOGUE IS ATTACHED TO THE KINETOCHORE
  MICROTUBULES, AND SEPARATION IS DESTINED TOWARDS
  OPPOSITE POLE

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• ANAPHASE 1
• HOMOLOGUES SEPARATE AND MOVE TOWARD OPPOSITE
  POLES
• SISTER CHROMATIDS MOVE AS A UNIT TO THE SAME POLE
  AND REMAIN ATTACHED AT THE CENTROMERE (UNLIKE
  MITOSIS)

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• TELOPHASE 1 _at_ CYTOKINESIS
• EACH POLE HAS A HAPLOID SET OF CHROMOSOMES,
  SISTER CHROMATIDS ARE STILL ATTACHED AT THE
  CENTROMERE
• ANIMAL CELL CLEAVAGE FURROW
• PLANT CELL PLATE
• FORMS 2 HAPLOID DAUGHTER CELLS
• SOME CELLS WILL ENTER INTERKINESIS, SOME WILL GO
  DIRECTLY TO MEIOSIS II
• REGARDLESS NO DNA REPLICATION OCCURS PRIOR TO
  MEIOSIS II

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• MEIOSIS II- SEPARATION OF SISTER CHROMATIDS
• PROPHASE II
• SPINDLE APPARATUS FORMS AND CHROMOSOMES MOVE
  TOWARD METAPHASE PLATE

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• METAPHASE II
• KINETOCHORES OF SISTER CHROMATIDS POINT TOWARDS
  OPPOSITE POLES
• CHROMOSOMES ALIGN ON THE METAPHASE PLATE

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• ANAPHASE II
• CENTROMERES SEPARATE
• SISTER CHROMATIDS OF EACH NEW PAIR (NOW
  INDIVIDUAL CHROMOSOMES) MOVE TO THE OPPOSITE POLES

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• TELEPHASE II _at_ CYTOKINESIS
• NUCLEI FORM AT OPPOSITE ENDS OF THE CELL
• CYTOKINESIS WILL PRODUCE 4 HAPLOID DAUGHTER
  CELLS

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• MEIOSIS
• REDUCTION DIVISION
• GENETIC VARIATION
• SERIES OF TWO SUCCESSIVE NUCLEAR DIVISIONS

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• THREE REASONS FOR GENETIC VARIATION

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• INDEPENDENT ASSORTMENT
• THE RANDOM DISTRIBUTION OF MATERNAL _at_ PATERNAL
  CHROMOSOMES TO GAMETES
• PROCESS WILL PRODUCE 2n POSSIBLE COMBINATIONS
  (nHAPLOID ) HUMANS 2-23 OR ABOUT 8 MILLION
  POSSIBILITIES
• 50-50 CHANCE A DAUGHTER CELL WILL RECEIVE
  MATERNAL OR PATERNAL GENES
• EACH HOMOLOGOUS PAIR ORIENTS INDEPENDENTLY OF THE
  OTHER PAIRS AT METAPHASE1
• A GAMETE CONTAINS JUST ONE OF ALL POSSIBLE
  COMBINATIONS OF MATERNAL AND PATERNAL
  COMBINATIONS OF CHROMOSOMES

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• CROSSING OVER
• a. THE EXCHANGE OF MATERIAL BETWEEN HOMOLOGOUS
  PAIRS
• b. OCCURS DURING LATE PROPHASE DUE TO CHIASMATA
  FORMATION
• c. THE RESULT IS THAT THE CHROMOSOME NOW HAS
  GENES FROM BOTH PARENTS
• d. AVG. 2-3 CROSSOVERS PER CHROMOSOME PAIR IN
  HUMANS
• e. SYNAPSIS IS SO PRECISE THAT HOMOLOGUES ALIGN
  GENE BY GENE

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• 3. RANDOM FERTILIZATION
• a. EGG CELL 8 MILLION
• b. SPERM CELL 8 MILLION (POSSIBLE COMBOS FOR
  BOTH)
• c. RESULTING ZYGOTE HAS A 1 IN 64 TRILLION
  POSSIBLE COMBOS

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• DARWINS THEORY ON NATURAL SELECTION IS BASED ON
  EVOLUTIONARY CHANGE
• INCREASED FREQUENCY OF INHERITABLE VARIATION TO
  FAVOR REPRODUCTIVE SUCCESS
• RESULT IS ADAPTATION
• INCREASES THE ABILITY FOR THE SPECIES TO ADAPT
  FAVORABLY TO ENVIRONMENTAL CHANGES

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• EVOLUTIONARY ADAPTATION DEPENDS ON A POPULATIONS
  GENETIC VARIATION, WHICH COMES FROM 2 SOURCES
• SEXUAL REPRODUCTION
• MUTATION