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