2. INTRODUCTION TO HEREDITY HEREDITY = CONTINUITY OF BIOLOGICAL TRAITS FROM ONE GENERATION TO THE NEXT VARIATION = INHERITED DIFFERENCES AMONG INDIVIDUALS OF THE SAME SPECIES GENETICS = THE STUDY OF HEREDITY AND VARIATION

3. HEREDITY OFFPRING ACQUIRE GENES FROM PARENTS BY INHERITING CHROMOSOMES DNA = TYPE OF NUCLEIC ACID GENES = UNITS OF HEREDITARY INFO THAT ARE MADE OF DNA AND ARE LOCATED ON CHROMOSOMES

4. HEREDITY THE ACTUAL TRANSMISSION OF GENES FROM PARENTS TO OFFSPRING DEPENDS ON THE BEHAVIOR OF CHROMOSOMES CHROMOSOMES = ORGANIZATIONAL UNIT OF HEREDITY MATERIAL IN THE NUCLEUS OF EUKARYOTIC ORGANISMS LOCUS = SPECIFIC LOCATION ON A CHROMOSOME THAT CONTAINS A GENE

5. THE ROLE OF MEIOSIS IN SEXUAL LIFE CYCLES FERTILIZATION AND MEIOSIS ALTERNATE IN SEXUAL LIFE CYCLES ALTERNATION BETWEEN HAPLOID (n) AND DIPLOID (2n) CONDITION SOMATIC CELLS - CONTAIN 46 CHROMOSOMES KARYOTYPE = A DISPLAY OF AN INDIVIDUAL’S SOMATIC-CELL METAPHASE CHROMOSOMES

6. SEXUAL LIFE CYCLES HOMOLOGOUS CHROMOSOMES = A PAIR OF CHROMOSOMES THAT HAVE THE SAME SIZE, CENTROMERE POSITION AND STAINING PATTERN AUTOSOME - A CHROMOSOME THAT IS NOT A SEX CHROMOSOME (22 PAIRS IN HUMANS) SEX CHROMOSOMES = IT IS THE 23RD CHROMOSOME PAIR IN HUMANS FEMALES (XX) MALES (XY)

7. ALTERNATION OF GENERATIONS DIPLOID = CELLS CONTAIN TWO SETS OF CHROMOSOMES (2n);ALL AUTOSOMES HAPLOID = CELLS CONTAIN ONE SET OF CHROMOSOMES(n); GAMETES GAMETE = SEX CELLS; SPERM AND OVA

8. FERTILIZATION THE DIPLOID NUMBER IS RESTORED DURING FERTILIZATION, THE UNION OF TWO GAMETES ZYGOTE = A DIPLOID CELL FORMED FROM THE UNION OF TWO HAPLOID GAMETES

9. SEXUAL LIFE CYCLE VIDEO

10. ASEXUAL LIFE CYCLE VIDEO

11. MEIOSIS: A CLOSER LOOK MEIOSIS AND SEXUAL REPRODUCTION GREATLY CONTRIBUTE TO GENETIC VARIATION AMONG OFFSPRING MEIOSIS INCLUDES STEPS THAT CLOSELY RESEMBLE MITOSIS, SO YOU ALREADY KNOW A LOT OF THIS!

12. MEIOSIS V. MITOSIS LIKE MITOSIS, MEIOSIS IS PRECEDED BY REPLICATION OF CHROMOSOMES MEIOSIS DIFFERS IN THAT THIS SINGLE REPLICATION IS FOLLOWED BY TWO CONSECUTIVE CELL DIVISIONS FOUR DAUGHTER CELLS ARE FORMED DURING MEIOSIS THE DAUGHTER CELLS ARE HAPLOID, THEY ONLY HAVE HALF THE NUMBER OF CHROMOSOMES AS THE ORIGINAL CELL

13. MEIOSIS-INTERPHASE I CHROMOSOMES REPLICATE EACH DUPLICATED CHROMOSOME CONSISTS OF TWO IDENTICAL SISTER CHROMATIDS ATTACHED AT THEIR CENTROMERES CENTRIOLE PAIRS IN ANIMAL CELLS ALSO REPLICATE INTO TWO PAIRS

14. MEIOSIS I THIS CELL DIVISION SEGREGATES THE TWO CHROMOSOMES OF EACH HOMOLOGOUS PAIR AND REDUCES THE CHROMOSOME NUMBER BY ONE-HALF. IT INCLUDES THE FOLLOWING FOUR PHASES: –PROPHASE I, METAPHASE I, ANAPHASE I, TELOPHASE I

15. PROPHASE I THIS PHASE TAKES UP 90% OF THE TIME REQUIRED FOR MEIOSIS CHROMOSOMES CONDENSE SYNAPSIS OCCURS: HOMOLOGOUS CHROMOSOMES COME TOGETHER AS PAIRS SINCE EACH CHROMOSOME HAS TWO CHROMATIDS, EACH HOMOLOGOUS PAIR IN SYNAPSIS APPEARS AS A COMPLEX OF FOUR CHROMATIDS, OR A TETRAD

16. PROPHASE I (CON’T) IN EACH TETRAD, SISTER CHROMATIDS OF THE SAME CHROMOSOME ARE ATTACHED AT THEIR CENTROMERES. NONSISTER CHROMATIDS ARE LINKED BY X-SHAPED CHAISMATA, SITES WHERE HOMOLOGOUS STRAND EXCHANGE OR CROSSING OVER OCCURS. CROSSING OVER IS VERY IMPORTANT. THIS EXCHANGE OF GENETIC MATERIALS ALLOWS FOR GENETIC VARIATION AMONG OFFSPRING

17. PROPHASE I VIDEO

18. METAPHASE I TETRADS ARE ALIGNED ON THE METAPHASE PLATE EACH SYNAPTIC PAIR IS ALIGNED SO THAT CENTROMERES OF HOMOLOGUES POINT TOWARD OPPOSITE POLES EACH HOMOLOGUE IS ATTACHED TO KINETOCHORE MICROTUBULES EMERGING FROM THE POLE IT FACES, SO THAT THE TWO HOMOLOGUES SEPARATE IN ANAPHASE AND MOVE TOWARD OPPOSITE POLES

19. METAPHASE I VIDEO

20. ANAPHASE I HOMOLOGUES SEPARATE AND ARE MOVED TOWARD THE POLES BY THE SPINDLE SISTER CHROMATIDS REMAIN ATTACHED AT THEIR CENTROMERES AND MOVE AS A UNIT TOWARD THE SAME POLE, WHILE THE HOMOLOGUE MOVES TO OTHER POLE THIS DIFFERS FROM MITOSIS DURING WHICH CHROMOSOMES LINE UP INDIVIDUALLY ON METAPHASE PLATE, AND SISTER CHROMATIDS ARE SPLIT APART

21. ANAPHASE I VIDEO

22. TELOPHASE I AND CYTOKINESIS EACH POLE NOW HAS A HAPLOID SET OF CHROMOSOMES THAT ARE STILL MADE OF TWO SISTER CHROMATIDS ATTACHED AT THE CENTROMERE CYTOKINESIS OCCURS, FORMING TWO HAPLOID DAUGHTER CELLS. CLEAVAGE FURROWS FORM IN ANIMAL CELLS

23. TELOPHASE I VIDEO

24. MEIOSIS II THERE IS NO INTERPHASE II. THE REASON IS THAT THE DNA WILL NOT BE DUPLICATED AGAIN BEFORE THE SECOND CELL DIVISION THIS SECOND MEIOTIC DIVISION SEPARATES SISTER CHROMATIDS OF EACH CHROMOSOME

25. PROPHASE II SPINDLE APPARATUS FORMS AND CHROMOSOMES MOVE TOWARD THE METAPHASE II PLATE

26. METAPHASE II CHROMOSOMES ALIGN SINGLY ON THE METAPHASE PLATE KINETOCHORES OF SISTER CHROMATIDS POINT TOWARD OPPOSITE POLES

27. ANAPHASE II CENTROMERES OF SISTER CHROMATIDS SEPARATE SISTER CHROMATIDS OF EACH PAIR (NOW INDIVIDUAL CHROMOSOMES) MOVE TOWARD OPPOSITE POLES OF THE CELL

28. TELOPHASE II NUCLEI FORM AT OPPOSITE POLES OF THE CELL CYTOKINESIS OCCURS PRODUCING FOUR HAPLOID DAUGHTER CELLS

29. MEIOSIS II VIDEO

30. KEY DIFFERENCES: MEIOSIS AND MITOSIS MEIOSIS IS A REDUCTION DIVISION. CELLS PRODUCED BY MITOSIS HAVE THE SAME # AS THE ORIGINAL CELL, WHEREAS CELLS MADE BY MEIOSIS HAVE HALF THE # OF CHROMOSOMES MEIOSIS CREATES GENETIC VARIATION DUE TO CROSSING OVER, WHICH IS ABSENT IN MITOSIS MEIOSIS IS TWO SUCCESSIVE NUCLEAR DIVISIONS, WHEREAS MITOSIS IS JUST ONE DIVISION

31. COMPARISON: MEIOSIS I AND MITOSIS PROPHASE: SYNAPSIS OCCURS TO FORM TETRADS METAPHASE: HOMOLOGOUS PAIRS (TETRADS) ALIGN ANAPHASE: PAIRS OF CHROMOSOMES SEPARATED. CENTROMERE DO NOT DIVIDE, SISTER CHROMATIDS STAY TOGETHER, MOVE TO SAME POLE PROPHASE: NO SYNAPSIS OR CROSSING OVER METAPHASE: INDIVIDUAL CHROMOSOMES ALIGN ANAPHASE: SISTER CHROMATIDS OF INDIVIDUAL CHROMOSOMES SEPARATE AND MOVE TO OPPOSITE POLES MEIOSIS IMITOSIS

32. ORIGINS OF GENETIC VARIATION SEXUAL REPRODUCTION CONTRIBUTES TO GENETIC VARIATION BY: –INDEPENDENT ASSORTMENT OF CHROMOSOMES –CROSSING OVER IN MEIOSIS I –RANDOM FUSION OF GAMETES DURING FERTILIZATION

33. INDEPENDENT ASSORTMENT DURING METAPHASE I, EACH HOMOLOGOUS PAIR OF CHROMOSOMES ALIGNS. EACH PAIR CONSISTS OF ONE MATERNAL AND ONE PATERNAL CHROMOSOME THERE IS A 50-50 CHANCE THAT A DAUGHTER CELL WILL RECEIVE EITHER MATERNAL OR PATERNAL CHROMOSOME EACH HOMOLOGOUS PAIR ORIENTS INDEPENDENTLY

34. INDEPENDENT ASSORT (CON’T) SINCE EACH PAIR ASSORTS INDEPENDENTLY, THE PROCESS PRODUCES 2 n POSSIBLE COMBINATIONS OF MATERNAL AND PATERNAL CHROMOSOMES IN GAMETES, WHERE n IS THE HAPLOID # IN HUMANS, THE POSSIBLE COMBINATIONS WOULD BE 2 23, OR ABOUT 8 MILLION THUS, EACH HUMAN GAMETE CONTAINS ONE OF EIGHT MILLION POSSIBLE ASSORTMENTS OF CHROMOSOMES INHERITED FROM BOTH PARENTS

35. INDEPENDENT ASSORTMENT

36. CROSSING OVER OCCURS DURING PROPHASE I, CHAISMATA BECOME VISIBLE AT PLACES WHERE THE EXCHANGE OCCURS PRODUCES CHROMOSOMES THAT CONTAIN GENES FROM BOTH PARENTS IN HUMANS, THERE IS AN AVERAGE OF TWO OR THREE CROSSOVER PER CHROMOSOME PAIR SYNAPSIS IS PRECISE, HOMOLOGUES ALIGN GENE BY GENE

37. CROSSING OVER

38. RANDOM FERTILIZATION IN HUMANS, WHEN INDIVIDUAL OVUM REPRESENTATIVE OF ONE OF EIGHT MILLION POSSIBLE COMBINATIONS IS FERTILIZED BY A SPERM CELL WITH THE SAME POSSIBILITIES, THE RESULTING ZYGOTE CAN HAVE ONE OF 64 TRILLION POSSIBLE DIPLOID COMBINATIONS