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, CIRCULAR
CHROMOSOME
– EVEN COPYING A SINGLE
CIRCULAR CHROMOSOME
CAN BE EXTREMELY
DIFFICULT
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
BETWEEN
PLANT AND
ANIMAL 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 THAT
STIMULATES CELL
DIVISION IN NEARBY
CELLS
– IMPACT THE CELL CYCLE
CONTROL 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 CHROMOSOME
NUMBER FROM DIPLOID TO
HAPLOID
– RESEMBLES MITOSIS, BUT THERE ARE
KEY DIFFERENCES
THE CELLULAR BASIS OF
REPRODUCTION AND DEVELOPMENT
• MEIOSIS
– CELLS UNDERGO TWO
CONSECUTIVE DIVISIONS
(MEIOSIS I AND MEIOSIS II)
– THE DIVISIONS ARE PRECEDED BY
ONLY ONE DUPLICATION OF
DNA(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 MEIOSIS
MITOSIS
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 SEGMENTS
BETWEEN TWO HOMOLOGOUS
CHROMOSOMES
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.
2.
3.
4.
SYNAPSIS OF TETRAD
BREAKAGE OF HOMOLOGOUS CHROMATIDS
JOINING OF HOMOLOGOUS CHROMATIDS
SEPARATATION OF HOMOLOGOUS CHROMOSOMES
AT ANAPHASE I
5. 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 EITHER
MEIOSIS I OR MEIOSIS II
– MORE SERIOUS IN
MEIOSIS 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 INCORRECT
CHROMOSOME NUMBERS WILL
ABORT
THE CELLULAR BASIS OF
REPRODUCTION AND DEVELOPMENT
• CHROMOSOMAL ABNORMALITIES
Sex chromosomes
Syndrome
Origin of
Nondisjunction
Frequency 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 THE
FULL STORY!!!