Chapter 8 Cellular Basis of Reproduction and Inheritance
Cell – smallest unit of life that can independently reproduce
itself
How do living cells reproduce themselves?
Chromosomes
Bacteria – nucleoid -> 1 chromosome (circular)
Eukaryotes – nucleus (double-membraned) which contains
chromatin
Chromosomes -> Genes -> traits
Bacteria and Archeae versus Eukarya
Binary Fission
Asexual Reproduction v. Sexual reproduction
Asexual reproduction – simply mitosis; no exchange of
genetic material
Sexual reproduction – DOES INVOLVE exchange of genetic
material between the parent cells; allows for genetic variation
between parents and the offspring
Cell Cycle
Role of the Nucleus
Parent Cell -> Daughter Cell
Mitosis in Eukaryotic Organisms
Somatic Cells – cells of the tissue/body/organism
Gametic Cells – undergo meiosis
Primary oocyte (female)
Primary spermatocyte (male)
Reproduction: cells arise only from preexisting cells
(Dr. Rudolf Virchow in 1858)
Unicellular organism - > unicellular organism
Multicellular organisms
Sexual reproduction: Once Male sperm cell penetrates
female egg cell, a zygote (fertilized egg) is formed. Zygote
starts to divide and divide and divide and … to form the
embryo
Cell differentiation
3 basic cell types of the embryo
Mesoderm: muscles; circulatory system
Endoderm: digestive system + repro sys
Ectoderm: skin and nervous system
Prokaryotes
Binary fission
1 chromosome -> 2 chromosomes
Synthesize more cell wall, more cell membrane
Chromosomes
of eukaryotic
organisms
1 chromosome –> will duplicate into two sister chromatids
(held together by the centromere)
Cell Cycle
Interphase – 90%/ metabolic activity
G1 phase: first gap -> cell growth
S phase: DNA synthesis
e.g., humans have 46 chromosomes in their somatic
cells
liver cell in S phase 46->92 chromosomes
G2 phase: second gap -> cell growth
M phase: Mitosis -> cell division
Don’t want mistakes when replicating chromosomes
MITOSIS IS AN ACCURATE PROCESS
Checkpoints
G1 checkpoint
G2 checkpoint
M checkpoint
Interphase – cell growth; period of synthesis;
Chromatids have replicated; organelles have replicated;
“getting ready”
Prophase – 1st stage in mitosis
Nuclear envelope starts to disappear
Chromatin starts to condense
Nucleolei disappear
Start to see the formation of mitotic spindle
Start to see centrosomes separate
Prometaphase – 2nd stage in mitosis
Chromatin becomes coiled /folded/visible
Chromosomes visible
Centrosomes are now polarized (1 at each end of the
cell)
Spindles are starting to connect the centrosome with
the chromosomes via the kinetochore
Microtubules are going to aid in pulling the
chromosomes across the cell
Metaphase – 3rd stage in mitosis
All the chromosomes are lined up at the metaphase
plate (center of the cell)
Anaphase – 4th stage in mitosis
Daughter chromosomes -are split and move across
the cell to the opposite pole
Cell becomes elongated
Motor proteins- aid in motion of daughter
chromosomes across the cell
Telophase – 5th stage in mitosis
See separation of nuclear material
See formation of “two” cells
See formation of nucleoli
See formation of nuclear envelope
In animal cells – formation of a cleavage
furrow
Cytokinesis
Cleavage furrow – will start to pinch off the daughter
cells so that they become “new, independent cells”
Cytokinesis: plant versus animal
Cytokinesis – when parent cell finally splits into two
“genetically” identical daughter cells
Animal cell: form a cleavage furrow – contracting ring of
microfilaments
Plant cell: vesicles start to form in the center of cell which will
form the cell plate -> divide the parent cell into two daughter
cells -> cell membrane AND cell wall are formed
Anchorage, cell density and chemical growth factors
Surface area
How many cells per unit volume
Chemical growth factors (e.g., growth stimulating hormone)
Growth Factors signal the cell cycle control system
Checkpoints
G1 – most important
Growth factor (outside the cell) -> combines receptor
protein -> relaying of “cell receiving growth factor” through
relay proteins – cell continues to grow
G0 – non-dividing state
G2 checkpoint: occurs just before mitosis begins
M checkpoint
Were the number of chromosomes properly doubled?
Normal cell division
Abnormal cell division
Hyperplasia – greater cell division for a particular tissue
that could be due to stress, environment
Neoplasia – leads to carcinoma
Cysts
Tumors
Benign
Malignant
Metastatis – spreading of cancerous cells throughout the body
Radiation therapy –
Cobalt treatments
Chemotherapy
Series of drugs, drug cocktails (mixtures)
Surgury
Leukemia – white blood cells
Lymphoma – cancer of lymph nodes
Lupus
Humans
46 chromosomes (23 pairs)
44 autosomal chromosomes
(22 homologous pairs)
2 sex chromosomes
XX -> female
XY -> male
2 sets of chromosomes – diploid
1 set of chromosomes – haploid
ploidy -> chromosomal sets
SOMATIC CELLS
Mitosis: diploid parent cell to two diploid daughter cells
Meiosis – cell division that is ONLY SEEN WITH GAMETIC
CELLS
-sexual reproduction
- diploid parent cell to haploid daughter cells
46 -> 23
-genetic diversity
Homologous
chromosomes
Tetrad
Human Female
1 primary oocyte ->
Meiosis I
2 secondary oocytes
1 secondary
oocyte 23 chromosomes and most of the cytoplasm of
the parent cell
Other secondary oocyte 23 chromosomes ->
hardly any cytoplasm
1 secondary oocyte -> Meiosis II
2 daughter cells
1 mature ovum (has all the cytoplasm of the
original gamete)
Other is another polar body
Human Male
1 Primary spermatocyte -> 2
secondary spermatocytes (haploid, 23
chromosomes)
-> 4 spermatids (haploid, 23
chromosomes) ->develop and mature
into sperm cells
Sperm cell -> delivery of the “goods”
= chromosomes
Meiosis – Sexual reproduction
Separation of Homologous
chromosomes
Diploid to haploid state
Interphase
Meiosis I
Prophase I – most complex phase of MI; 90% of the
time required for meiosis
Chromatin is coiling/condensing
Synapsis occurs
Homologous chromosomes come together
and “pair off”: 2 homologous chromosomes, each with 2 sister
chromatids -> tetrad
Because of synapse process and closeness of
these homologous pairs – possibility of “crossing over” ->
source of genetic variability
Metaphase I – chromosome tetrads aligning on the
metaphase plate; spindles form and combine with the
centromere (kinetochore)
Anaphase I – migration of chromosomes toward poles
Telophase I – chromosomes now at poles; cleavage
furrow forming
Cytokinesis – cells separate; chromosomes uncoil –
might have nuclear envelope re-form
Meiosis II
Separation of sister chromatids
Haploid to Haploid
Prophase II – spindle forming; chromosomes moving
toward the center of the cell
Metaphase II – lining up of chromatids across the
metaphase plate
Anaphase II – migration of the chromatids toward the
poles of the cell
Telophase II – cleavage furrow starts to form
Cytokinesis – cells split, each with haploid number of
chromatids
Differences between
MITOSIS
Asexual Reprod
Somatic Cells
Diploid to Diploid
Daughter cells
Genetically same
As parent cell
Stages
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
Mitosis and Meiosis
MEIOSIS
Sexual Reprod
Gamete Cells
Diploid to Haploid
Daughter cells are not
genetically same
1 set of chrom
Recombination
Stages
Meiosis I (Diploid to Haploid)
Prophase I
Tetrads form through synapse
Metaphase I
Anaphase I
Telophase I
Cytokinesis
Meiosis II (like MITOSIS)
Prophase II
Metaphase II
Anaphase II
Telophase II
Cytokinesis
Daughter cells are haploid
Locus – place on chromosome that contains the gene
responsible for trait
Versions of genes: Alleles
Homologous chromosomes can carry different versions of
genes: carrying
Allow for genetic variability – through crossing over
Crossing over involves: tetrad (2 homologous
chromosomes), chiasma
Not two types of chromatids, but ….. four types of
chromatids
Two parental types of chromosomes
1 from mom
1 from dad
Two recombinant chromosomes
Karyotype
Accidents – Non-disjunction
Non-disjunction in Meiosis I
n + 1 n+ 1
n–1 n-1
Non-disjunction in Meiosis II
n + 1 n+ 1
n n
Fertilization
Egg: n+1
Sperm: n
Zygote: 2n + 1
Abnormal Sex Chromosomes
XY
XX th
normal male
normal female
XXY
Klinefelter syndrome 1 out 2000
Female genetalia
XYY
meiosis in sperm formation
XXX
normal female
XO
Turner syndrome
1 out 2000
1 out of 1000
XXYY
XXXY
XXXXY
Lethality
Alterations of Chromosome Structure
Deletion: part of chromosomes is deleted
Lost fragment of chromosome
Chromosome becomes shorter
Duplication: part of chromosomes is replicated
Fragment is replicated
Chromosome becomes longer
Inversion: two (adjacent) fragments of chromosome exchange
places
2 fragments exchanging places
Chromosome length remains the same
Translocation: fragment from 1 chromosome breaks off and
“travels” to another chromosome and binds with it
Fragments break off and bind with another chromosome
Chromosome length can be longer or shorter