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??

• 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

• CELL DIVISION PLAYS THREE MAJOR ROLES– 1) ??– 2) ??– 3) ??

• PROKARYOTES REPRODUCE BY BINARY FISSION– MOST PROKARYOTES

HAVE A SINGLE, CIRCULARCHROMOSOME

– EVEN COPYING A SINGLECIRCULAR CHROMOSOMECAN BE EXTREMELYDIFFICULT

• THE LARGE, COMPLEX CHROMOSOMES OF EUKARYOTES DUPLICATE WITH EACH CELL DIVISION

• CHROMOSOMES ARE ONLY VISIBLE DURING ACTIVE CELL DIVISION

• CHROMOSOME ??• CHROMATIN ??• SISTER CHROMATIDS ??• CENTROMERE ??

• 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

• INTERPHASE ??– G1– S– G2

• MITOTIC PHASE (CELL DIVISION) ??– MITOSIS– CYTOKINESIS

• CELL DIVISION IS A CONTINUUM OF DYNAMIC CHANGES

• MITOSIS IS BROKEN UP INTO 4 MAIN STAGES– PROPHASE– METAPHASE– ANAPHASE– TELOPHASE

• SPECIAL STRUCTURES THAT ASSIST MITOSIS– MITOTIC SPINDLE– CENTROSOMES (2 CENTRIOLES)• ONLY IN ANIMAL CELLS!!!

• CYTOKINESIS– DIVISION OF THE CELL MEMBRANE TO FORM TWO

DISTINCT CELLS– DIFFERS

BETWEENPLANT ANDANIMAL CELLS

– WHY??

• CLEAVAGE VS CELL PLATE FORMATION

• 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 ??

• 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!!

• CANCER– DEFINITION ??– TUMOR ??– BENIGN VS MALIGNANT– METASTASIS

• FOUR CATEGORIES OF CANCER– CARCINOMA– SARCOMA– LEUKEMIA– LYMPHOMA

• TWO MAJOR TYPES OF TREATMENT– CHEMOTHERAPY– RADIATION THERAPY

• 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!!!

• 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)

• SOMATIC CELLS CONTAIN HOMOLOGOUS PAIRS OF CHROMOSOMES– HOMOLOGOUS CHROMOSOMES ??

• TWO GENERAL TYPES OF CHROMOSOMES– AUTOSOMES– SEX CHROMOSOMES

• WHAT IS A “LOCUS”?

• 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

• 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?

• 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

• 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

• 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

• STAGES OF MEIOSIS I– PROPHASE I– METAPHASE I– ANAPHASE I– TELOPHASE I

• 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

• STAGES OF MEIOSIS II– PROPHASE II– METAPHASE II– ANAPHASE II– TELOPHASE II

• A COMPARISON OF MITOSIS AND MEIOSISMITOSIS MEIOSIS

• WHAT ADVANTAGE IS THEIR TO UTILIZING SEXUAL REPRODUCTION INSTEAD OF ASEXUAL REPRODUCTION?– POSSIBLE ANSWERS…

• 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

• INDEPENDENT ORIENTATION OF CHROMOSOMES

• 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

• HOW DOES THIS INDEPENDENT ORIENTATION LEAD TO VARIATION?– HOMOLOGOUS CHROMOSOMES CARRY

DIFFERENT VERSIONS OF A TRAIT (GENE) AT THE SAME LOCI; SO…

• CROSSING-OVER FURTHER ENHANCES GENETIC VARIATION– CROSSING-OVER• THE EXCHANGE OF

CORRESPONDING SEGMENTSBETWEEN TWO HOMOLOGOUSCHROMOSOMES

• 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

• 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

• ACCIDENTS DURING MEIOSIS CAN ALTER CHROMOSOME NUMBER

• 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??

• CHROMOSOMAL ABNORMALITIES– TRISOMY 21 (MOST COMMON – 1 OUT OF 700)• COMMON NAME = DOWN’S SYNDROME

– MOST INCORRECTCHROMOSOME NUMBERS WILLABORT

• 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

• HOW CAN WE DIAGNOSE CHROMOSOMAL ABNORMAILITES?

• WE USE KARYOTYPES– KARYOTYPE AN ORDERLY DISPLAY OF

MAGNIFIED IMAGES OF AN INDIVIDUALS CHROMOSOMES

• 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

• CHROMOSOMAL ABNORMALITIES– THERE ARE FOUR MAJOR TYPES OF CHANGES

THAT CAN OCCUR• DELETION• DUPLICATION• INVERSION• TRANSLOCATION

• 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!!!

THE CELLULAR BASIS OF REPRODUCTION AND DEVELOPMENT.

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