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THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• “LIKE BEGETS LIKE…MORE OR LESS”• ASEXUAL REPRODUCTION VS. SEXUAL
REPRODUCTION– ASEXUAL DEFINITION?– SEXUAL DEFINITION?
• HOW DO OFFSPRING OF PARENTS FROM SEXUAL REPRODUCTION COMPARE TO THEIR PARENTS? EACH OTHER? NON-RELATED ORGANISMS?
• CHROMOSOMES– DEFINITION??
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CELLS ARISE ONLY FROM PRE-EXISTING CELLS• THE PERPETUATION (CONTINUATION) OF LIFE,
IN ALL ITS ASPECTS RELIES ON THE PRINCIPLES OF CELLULAR REPRODUCTION
• CELL DIVISION = CELLULAR REPRODUCTION
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CELL DIVISION PLAYS THREE MAJOR ROLES– 1) ??– 2) ??– 3) ??
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• PROKARYOTES REPRODUCE BY BINARY FISSION– MOST PROKARYOTES
HAVE A SINGLE, CIRCULARCHROMOSOME
– EVEN COPYING A SINGLECIRCULAR CHROMOSOMECAN BE EXTREMELYDIFFICULT
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• THE LARGE, COMPLEX CHROMOSOMES OF EUKARYOTES DUPLICATE WITH EACH CELL DIVISION
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CHROMOSOMES ARE ONLY VISIBLE DURING ACTIVE CELL DIVISION
• CHROMOSOME ??• CHROMATIN ??• SISTER CHROMATIDS ??• CENTROMERE ??
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• THE CELL CYCLE MULTIPLIES CELLS– CELLS DIVIDE TO (OTHER THAN REPRODUCE)• GROWTH AND DEVELOPMENT• REPLACE LOST/DEAD CELLS
– CELL CYCLE• AN ORDERLY SEQUENCE OF EVENTS THAT EXTENDS
FROM THE TIME A CELL DIVIDES TO FORM 2 DAUGHTER CELLS TO THE TIME THESE DAUGHTER CELLS DIVIDE AGAIN
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• INTERPHASE ??– G1– S– G2
• MITOTIC PHASE (CELL DIVISION) ??– MITOSIS– CYTOKINESIS
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CELL DIVISION IS A CONTINUUM OF DYNAMIC CHANGES
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• MITOSIS IS BROKEN UP INTO 4 MAIN STAGES– PROPHASE– METAPHASE– ANAPHASE– TELOPHASE
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• SPECIAL STRUCTURES THAT ASSIST MITOSIS– MITOTIC SPINDLE– CENTROSOMES (2 CENTRIOLES)• ONLY IN ANIMAL CELLS!!!
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CYTOKINESIS– DIVISION OF THE CELL MEMBRANE TO FORM TWO
DISTINCT CELLS– DIFFERS
BETWEENPLANT ANDANIMAL CELLS
– WHY??
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CLEAVAGE VS CELL PLATE FORMATION
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• DO YOU THINK IT IS GOOD FOR CELLS TO CONSTANTLY BE DIVIDING?– ANCHORAGE, CELL DENSITY,
AND CHEMICAL GROWTH FACTORS IMPACT CELL DIVISION• ANCHORAGE ??• DENSITY-DEPENDENCE ??
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• GROWTH FACTORS– PROTEIN SECRETED BY
A CELL THATSTIMULATES CELL DIVISION IN NEARBYCELLS
– IMPACT THE CELL CYCLECONTROL SYSTEM
– THIS PARTICULAR ASPECT OF BIOLOGY IS BEING CLOSELY STUDIED TO BETTER UNDERSTAND CANCER!!
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CANCER– DEFINITION ??– TUMOR ??– BENIGN VS MALIGNANT– METASTASIS
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• FOUR CATEGORIES OF CANCER– CARCINOMA– SARCOMA– LEUKEMIA– LYMPHOMA
• TWO MAJOR TYPES OF TREATMENT– CHEMOTHERAPY– RADIATION THERAPY
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• REVIEW– ROLE OF MITOTIC CELL DIVISION• 1)• 2)• 3)
– REMEMBER, MITOTIC CELL DIVISION RESULTS IN THE SAME NUMBER AND TYPES OF CHROMOSOMES IN THE DAUGHTER CELLS!!!
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• BEFORE WE CAN DISCUSS SEXUAL REPRODUCTION, WE NEED TO UNDERSTAND A BIT MORE ABOUT CHROMOSOMES…
• ORGANISMS TYPICALLY HAVE TWO GENERIC TYPES OF CELLS– SOMATIC CELLS– SEX CELLS (GAMETES)
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• SOMATIC CELLS CONTAIN HOMOLOGOUS PAIRS OF CHROMOSOMES– HOMOLOGOUS CHROMOSOMES ??
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• TWO GENERAL TYPES OF CHROMOSOMES– AUTOSOMES– SEX CHROMOSOMES
• WHAT IS A “LOCUS”?
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• SEX CELLS (GAMETES) TYPICALLY ONLY HAVE A SINGLE SET OF CHROMOSOMES (LACK HOMOLOGOUS PAIRS)– WHY IS THIS IMPORTANT?? (WHAT HAPPENS IN
SEXUAL REPRODUCTION??)• TERMS RELATED TO CHROMOSOMES NUMBER– DIPLOID– HAPLOID
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• WHAT IS FERTILIZATION?– DEFINITION
• WHAT IS A ZYGOTE?– DEFINITION
• IF YOU ARE FROM THE FUSION OF TWO HAPLOID CELLS, HOW DO YOU CREATE A HAPLOID CELL? CAN YOU USE MITOTIC CELL DIVISION FOR THIS?
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• MEIOSIS– OCCURS ONLY IN REPRODUCTIVE
ORGANS; A SPECIAL TYPE OF CELL DIVISION TO GIVE RISE TO SEX CELLS (GAMETES) WITH THE HAPLOID NUMBER OF CHROMOSOMES
– REDUCES THE CHROMOSOMENUMBER FROM DIPLOID TO HAPLOID
– RESEMBLES MITOSIS, BUT THERE AREKEY DIFFERENCES
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• MEIOSIS– CELLS UNDERGO TWO
CONSECUTIVE DIVISIONS(MEIOSIS I AND MEIOSIS II)
– THE DIVISIONS ARE PRECEDED BYONLY ONE DUPLICATION OFDNA(S PHASE)
– FOUR DAUGHTER CELLS RESULT– EACH DAUGHTER CELL IS HAPLOID
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• MEIOSIS I– THE ACTUAL HALVING OF CHROMOSOME
NUMBER OCCURS IN THIS STAGE– ALL THE “STUFF” THAT IS DIFFERENT TAKES PLACE
IN THIS STAGE– THE GOAL OF MEIOSIS I IS TO SEPARATE THE
HOMOLOGOUS CHROMOSOMES
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• STAGES OF MEIOSIS I– PROPHASE I– METAPHASE I– ANAPHASE I– TELOPHASE I
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• MEIOSIS II– CLOSELY RESEMBLES MITOSIS (BUT IS OCCURING
WITH A HAPLOID NUMBER OF CHROMOSOMES)– THE GOAL OF MEIOSIS II IS TO SEPARATE THE
SISTER CHROMATIDS
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• STAGES OF MEIOSIS II– PROPHASE II– METAPHASE II– ANAPHASE II– TELOPHASE II
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• A COMPARISON OF MITOSIS AND MEIOSISMITOSIS MEIOSIS
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• WHAT ADVANTAGE IS THEIR TO UTILIZING SEXUAL REPRODUCTION INSTEAD OF ASEXUAL REPRODUCTION?– POSSIBLE ANSWERS…
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• SEXUAL REPRODUCTION OFFERS AN OPPORTUNITY FOR VARIATION IN GENETIC MAKEUP (TRAITS POSSESSED BY AN ORGANISM)
• INDEPENDENT ORIENTATION OF CHROMOSOMES, CROSSING OVER, RANDOM FERTILIZATION, AND MUTATION ALL ALLOW FOR VARIATION
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• INDEPENDENT ORIENTATION OF CHROMOSOMES
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• INDEPENDENT ORIENTATION– THE ORIENTATION OF THE HOMOLOGOUS PAIRS
OF CHROMOSOMES (TETRADS) IN METAPHASE I OF MEIOSIS IS BY RANDOM CHANCE
– THE TOTAL NUMBER OF POSSIBLE COMBINATIONS FOR CHROMOSOMES PACKAGED IN INDIVIDUAL GAMETES WILL ALWAYS BE 2N WHERE N = THE HAPLOID NUMBER OF CHROMOSOMES
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• HOW DOES THIS INDEPENDENT ORIENTATION LEAD TO VARIATION?– HOMOLOGOUS CHROMOSOMES CARRY
DIFFERENT VERSIONS OF A TRAIT (GENE) AT THE SAME LOCI; SO…
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CROSSING-OVER FURTHER ENHANCES GENETIC VARIATION– CROSSING-OVER• THE EXCHANGE OF
CORRESPONDING SEGMENTSBETWEEN TWO HOMOLOGOUSCHROMOSOMES
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CROSSING-OVER– CHIASMA A PLACE WHERE TWO HOMOLOGOUS
(NON-SISTER) CHROMATIDS ARE ATTACHED TO EACH OTHER
– CROSSING OVER TAKES PLACE DURING SYNAPSIS AND ADDS TO GENETIC VARIABILITY
• GENETIC RECOMBINATION– THE PRODUCTION OF GENE COMBINATIONS
DIFFERENT FROM THOSE CARRIED BY THE ORIGINAL CHROMOSOMES
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CROSSING-OVER– STEPS IN CROSSING OVER
1. SYNAPSIS OF TETRAD2. BREAKAGE OF HOMOLOGOUS CHROMATIDS3. JOINING OF HOMOLOGOUS CHROMATIDS4. SEPARATATION OF HOMOLOGOUS CHROMOSOMES
AT ANAPHASE I5. SEPARATION OF CHROMATIDS AT ANAPHASE II AND
COMPLETION OF MEIOSIS
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• ACCIDENTS DURING MEIOSIS CAN ALTER CHROMOSOME NUMBER
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• ACCIDENTS DURING MEIOSIS CAN ALTER CHROMOSOME NUMBER– NONDISJUNCTION –
THE FAILURE OF CHROMOSOMAL PAIRS TO SEPARATE
– CAN HAPPEN IN EITHERMEIOSIS I OR MEIOSIS II
– MORE SERIOUS INMEIOSIS I; WHY??
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CHROMOSOMAL ABNORMALITIES– TRISOMY 21 (MOST COMMON – 1 OUT OF 700)• COMMON NAME = DOWN’S SYNDROME
– MOST INCORRECTCHROMOSOME NUMBERS WILLABORT
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CHROMOSOMAL ABNORMALITIESSex chromosomes Syndrome Origin of
NondisjunctionFrequency in Population
XXY Klinefelter syndrome (male)
Meiosis in egg or sperm formation
1 / 2,000
XYY None (normal male) Meiosis in sperm formation
1 / 2,000
XXX Metafemale Meiosis in egg or sperm formation
1 / 1,000
XO Turner syndrome (female) Meiosis in egg or sperm formation
1 / 5,000
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• HOW CAN WE DIAGNOSE CHROMOSOMAL ABNORMAILITES?
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• WE USE KARYOTYPES– KARYOTYPE AN ORDERLY DISPLAY OF
MAGNIFIED IMAGES OF AN INDIVIDUALS CHROMOSOMES
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CHROMOSOMAL ABNORMALITIES– THESE ARE NOT JUST LIMITED TO CHROMOSOME
NUMBER– EVEN WHEN THE TOTAL NUMBER OF
CHROMOSOMES IS CORRECT, ALTERATIONS IN THE STRUCTURE OF CHROMOSOMES CAN STILL OCCUR/EXIST
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• CHROMOSOMAL ABNORMALITIES– THERE ARE FOUR MAJOR TYPES OF CHANGES
THAT CAN OCCUR• DELETION• DUPLICATION• INVERSION• TRANSLOCATION
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT
• WE HAVE EXPLAINED HOW CELLS DIVIDE, BUT WE HAVEN’T ADDRESSED WHY CERTAIN TRAITS APPEAR IN OFFSPRING OF SUCCESSIVE GENERATIONS
• COME BACK TO FIND OUT THEFULL STORY!!!
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