meiosis and sexual life changes. you must know… the differences between asexual and sexual...
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MEIOSIS AND SEXUAL LIFE CHANGES
YOU MUST KNOW…• THE DIFFERENCES BETWEEN
ASEXUAL AND SEXUAL REPRODUCTION
• THE ROLE OF MEIOSIS AND FERTILIZATION IN SEXUALLY REPRODUCING ORGANISMS
• THE IMPORTANCE OF HOMOLOGOUS CHROMOSOMES TO MEIOSIS
YOU MUST KNOW…• HOW THE CHROMOSOME NUMBER IS
REDUCED FROM DIPLOID TO HAPLOID THROUGH THE STAGES OF MEIOSIS
• THREE IMPORTANT DIFFERENCES BETWEEN MITOSIS AND MEIOSIS
• THE IMPORTANCE OF CROSSING OVER, INDEPENDENT ASSORTMENT, AND RANDOM FERTILIZATION TO INCREASING GENETIC VARIABILITY
CONCEPT 13.1• OFFSPRING ACQUIRE GENES
FROM PARENT BY INHERITING CHROMOSOMES
• GENES ARE SEGMENTS OF DNA • A LOCUS IS THE LOCATION OF A
GENE OF A CHROMOSOME• ASEXUAL REPRODUCTION – SINGLE
PARENT, ARISE BY MITOSIS, CLONE• SEXUAL REPRODUCTION – TWO
PARENTS, RESULTS IN GREATER GENETIC VARIATION
BACTERIA• REPRODUCE
ASEXUALLY
BY BINARY
FISSION OR
SEXUALLY BY
CONJUGATION• ONE COILED
CHROMOSOME
CONCEPT 13.2• FERTILIZATION AND MEIOSIS
ALTERNATE IN SEXUAL LIFE CYCLES
LIFE CYCLE• THE GENERATION-TO-GENERATION
SEQUENCE OF STAGES IN THE REPRODUCTIVE HISTORY OF AN ORGANISM FROM CONCEPTION TO PRODUCTION OF ITS OWN OFFSPRING
KARYOTYPE• A PICTURE OF ITS COMPLETE SET OF
CHROMOSOMES, ARRANGED IN PAIRS OF HOMOLOGOUS CHROMOSOMES FROM THE LARGEST PAIR TO THE
SMALLEST PAIR• MADE FROM A
HUMAN SOMATIC
CELL
HOMOLOGOUS CHROMOSOMES
• CONTROL THE SAME INHERITED CHARACTERISTICS
• EACH PAIR IS INHERITED FROM EACH PARENT
• NONSEX CHROMOSOMES - AUTOSOMES
• EXCEPTION- SEX CHROMOSOMES
MEIOSIS• GAMETES – EGG AND SPERM,
HAPLOID CELLS – n• ZYGOTE – FERTILIZED EGG, DIPLOID
– 2n• MEIOSIS REDUCES THE NUMBERS OF
SETS OF CHROMOSOMES FROM TWO TO ONE
• FERTILIZATION RESTORES THE DIPLOID NUMBER
CONCEPT 13.3• MEIOSIS REDUCES THE NUMBER
OF CHROMOSOME SETS FROM DIPLOID TO HAPLOID
MEIOSIS• PRECEDED BY THE REPLICATION OF
THE CELL’S DNA (INTERPHASE)• FOLLOWED BY TWO STAGES OF CELL
DIVISION, MEIOSIS I AND II• RESULTS IN FOUR DAUGHTER CELLS
WITH THE HAPLOID NUMBER
PROPHASE I• SYNAPSIS OCCURS (JOINING OF
HOMOLOGOUS CHROMOSOMES ALONG THEIR LENGTH) FORMING TETRADS
• TETRADS UNDERGO CROSSING OVER WHICH INCREASES GENETIC VARIATION
• AREAS OF CROSSING OVER FORM CHIASMATA (HOLDS THE HOMOLOGUES TOGETHER UNTIL ANAPHASE I)
• CENTRIOLES MOVE AWAY FROM EACH OTHER, THE NUCLEAR ENVELOPE DISINTEGRATES, AND SPINDLE MICROTUBULES ATTACH TO THE KINETOCHORES OF THE HOMOLOGUES
METAPHASE I• HOMOLOGOUS PAIRS OF
CHROMOSOMES ARE LINED UP AT THE METAPHASE PLATE
• MICROTUBULES FROM EACH POLE ATTACH TO EACH MEMBER OF THE PAIR
ANAPHASE I• SPINDLES HELP MOVE THE
CHROMOSOMES TOWARD OPPOSITE ENDS OF THE CELL
• SISTER CHROMATIDS STAY CONNECTED AND MOVE TOGETHER TOWARD THE POLES
TELOPHASE I • HOMOLOGOUS CHROMOSOMES
MOVE UNTIL THEY REACH OPPOSITE POLES
• EACH POLE CONTAINS A HAPLOID SETS OF CHROMOSOMES, WITH EACH CHROMOSOME STILL CONSISTING OF TWO SISTER CHROMATIDS
CYTOKINESIS• DIVISION OF THE CYTOPLASM • CLEAVAGE FURROW OCCURS IN
ANIMAL CELLS• CELL PLATE OCCURS
IN PLANT CELLS• RESULTS IN TWO
HAPLOID CELLS
MEIOSIS II• NO DUPLICATION OF CHROMOSOMES• PROPHASE II – SPINDLES FORM AND
SISTER CHROMATIDS MOVE TOWARD THE METAPHASE PLATE
• METAPHASE II – CHROMOSOMES ARE LINED UP ON THE METAPHASE PLATE
• ANAPHASE II – CENTROMERES OF THE SISTER CHROMATIDS SEPARATE AND INDIVIDUAL CHROMOSOMES MOVE TO OPPOSITE ENDS OF THE CELL
MEIOSIS II• TELOPHASE II – CHROMATIDS HAVE
MOVED ALL THE WAY TO OPPOSITE ENDS OF THE CELL
• NUCLEI REAPPEAR• CYTOKINESIS – EACH OF THE 4
DAUGHTER CELLS HAS THE HAPLOID NUMBER OF CHROMOSOMES AND IS GENETICALLY DIFFERENT FROM THE PARENT CELL AND THE OTHER DAUGHTER CELLS
• 3 EVENTS OCCUR DURING MEIOSIS I THAT DO NOT OCCUR DURING MITOSIS
• SYNAPSIS AND CROSSING OVER DO NOT NORMALLY OCCUR DURING MITOSIS
• AT METAPHASE I, TETRADS ARE POSITIONED ON THE METAPHASES PLATE RATHER THAN INDIVIDUAL REPLICATED CHROMOSOMES AS IN MITOSIS
• AT ANAPHASE I, DUPLICATED CHROMOSOMES OF EACH HOMOLOGOUS PAIR MOVE TOWARD OPPOSITE POLES, BUT THE SISTER CHROMATIDS OF EACH DUPLICATED CHROMOSOME STAY ATTACHED. THE CHROMATIDS SEPARATE IN MITOSIS.
CONCEPT 13.4• GENETIC VARIATION PRODUCED
IN SEXUAL LIFE CYCLES CONTRIBUTES TO EVOLUTION
IMPORTANT PROCESSES• CROSSING OVER• INDEPENDENT ASSORTMENT OF
CHROMOSOMES – IN METAPHASE I, WHEN THE HOMOLOGOUS CHROMOSOMES ARE LINED UP ON THE METAPHASE PLATE, THEY CAN PAIR UP IN ANY COMBINATION
• RANDOM FERTILIZATION
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