PCZO100 — FOUNDATIONS OF ZOOLOGY (LECTURE)
MODULE 3 – Cell Division and Inheritance
Cell Cycle
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cyclical process of growth and mitosis
Consists of interphase and mitosis
Terminologies/notes
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Heterologous - chromatins are contributed
from 2 different parents.
Homologous -chromatins that contain the
same genetic materials.
Gametes - sex cells
Humans contain 23 pairs of chromosomes
with a total of 46 individual chromosomes.
Female chromosome – XX
Male chromosome – XY
Genetic disorders that result from
uncontrolled division – down syndrome
Checkpoints before mitosis
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G1 phase – 1st checkpoint
o Checking
the
materials
are
complete and if there are any errors
in the cell.
o Apoptosis – programmed cell death
or G0 phase also known as resting
phase.
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G2 phase – 2nd checkpoint.
o Checking for replication error
o Checking if there are enough
organelles before cell division.
o If there are mitotic spindles
available.
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Metaphase – 3rd checkpoint
o Check whether the spindle fibers
are properly attached to the
centromeres.
Interphase
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Stage between cell division
Occupies about 90% of the total cell cycle.
The process wherein the cells duplicate
themselves.
The chromosomes appear in irregular –
granular form and it maintained as
chromatin fibers
Normal activities of the cell during
interphase:
o Metabolism
o Cellular respiration
o Protein synthesis
o Lipid synthesis
Divided into subphases.
o G1 phase
▪ early growth phase
▪ Cell continues to grow in
volume.
o S phase
▪ Synthesis phase
▪ Involved DNA replication.
G2 period
▪ Prepares for cell division.
▪ Replication of mitochondria
▪ Synthesis of microtubules
▪ Chromosome condensation
Mitosis
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Only applies to somatic cells.
The goal is to produce 2 identical daughter
cells.
Also called duplication division
For growth and development and
replacements for old cells.
Refers to the division of the nucleus
(karyokinesis)
Division of the cytoplasm (cytokinesis)
Consists of 4 phases
PCZO100 — FOUNDATIONS OF ZOOLOGY (LECTURE)
MODULE 3 – Cell Division and Inheritance
Prophase
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Each chromosome consists of 2 chromatins
that are joined at the centromere.
Centrioles move to the opposite ends of the
cell.
Nucleus and nuclear envelope start to
dissolve.
Mitotic apparatus is nearly formed. (Asters
and spindle fibers)
Metaphase
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Mitotic spindles are now fully formed.
The chromosomes align at the metaphase
plate.
Anaphase
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The phase of migration
Chromatids separate to form two sets of
identical chromosomes.
Cytokinesis begins.
o Plant cells – cell plate
o Animal cell – cleavage furrow
Telophase
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the phase of reconstruction
chromosome uncoils.
o Chromatins recondenses.
Nucleus develops.
Spindles disappear.
formation of 2 new daughter cells with 23
pairs of chromosomes each.
Ploidy level – diploid
o Formula: 2n = 23
Meiosis
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Produces 4 daughter cells with the haploid
number of chromosomes as parent cells.
Also called reduction division
o Reducing ploidy level from 2n -> n
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Involves meiosis I and II
Formula = n = 23
Meiosis I
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Results in reducing the
chromosomes.
Accompanied by cytokinesis.
number
of
Prophase I
● Crossing-over – process wherein the
chromatids exchange segments and
transfer genes.
● Chiasma – site of crossing over.
● Chiasmata – overlapping region during
crossing over.
Metaphase I
● Separates chromosomes (tetrads) and
places them in the metaphase plate.
● Produces diversity in the 2 gametes.
Anaphase I
● The chromosomes are separate pulling to
either region of the cell
Telophase I
● The chromosomes arrive at the pole of the
cell
● Each pole has a haploid chromosome cell
Meiosis II
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Prophase II – spindle fibers form
Metaphase II – Line up at the metaphase
plate
Anaphase II – Separate the chromosomes.
Telophase II – nuclei form at the poles
Cytokinesis occurs.
23 individual chromosomes from the sperm
23 individual chromosomes from the egg
2 haploids = diploid
PCZO100 — FOUNDATIONS OF ZOOLOGY (LECTURE)
MODULE 3 – Cell Division and Inheritance
Eukaryotic Chromosomes
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Eukaryotic chromosomes are composed of
chromatin.
Chromatin is the aggregate mass of DNA
and histone proteins.
The association of DNA with histones
efficiently
packs
the
DNA
into
chromosomes.
DNA: The Genetic Material
DNA (deoxyribonucleic acid) as the candidate:
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Organization of a Chromosome
1.
Supercoil of chromatin within the
chromosome.
2. Folding within the supercoil
3. An individual fiber in the supercoil consists
of a nucleosome: DNA strand coiled around
histones like beads on a string.
4. Linker proteins anchor DNA to the core and
wind the chain into a cylinder.
The Structure of DNA
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Sex Chromosomes and Autosomes
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Sex chromosomes (XY ♂ and XX ♀) differ in
males and females, and function in sex
determination.
Autosomes are not involved in sex
determination.
Number of Chromosomes
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Number of chromosomes is constant within
species.
But chromosome number varies among
different species.
N identifies the number of different kinds
of chromosomes.
– 2 sets of
○ Diploid (2N)
chromosomes
○ Haploid – 1 set of chromosomes
○ Polyploid – more than 2 sets of
chromosomes
Able to code for the sequence of amino
acids in proteins and control protein
synthesis
Able to replicate itself prior to cell division
Contained in the nuclei of eukaryotic cells
Able to change over time to account for
evolutionary change
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Double helix
With major and minor grooves
Complete spiral every 10 base pairs
Antiparallel: 3’ – 5’ and 5’ – 3’
Nucleotide
=
nitrogenous
base +
deoxyribose sugar + phosphate group
Base-pairing
○ Adenine – Thymine
○ Cytosine – Guanine
Bases
○ Purine (2 rings): A, G
○ Pyrimidine (1 ring): C, T
Hydrogen bonding of bases
GC bonding - allow us to thrive in different
environment
DNA Replication
Replication: DNA-DNA
Semiconservative
PCZO100 — FOUNDATIONS OF ZOOLOGY (LECTURE)
MODULE 3 – Cell Division and Inheritance
1. Helicases unwind the parental double helix.
2. Single-strand binding proteins stabilize the
unwound parental DNA.
3. The leading strand is synthesized
continuously in the 5 -> 3 directions by DNA
polymerase
4. The lagging strand is synthesized
discontinuously.
5. Primase synthesizes a short RNA primer,
which is extended by DNA polymerase to
form an Okazaki fragment.
6. After the RNA primer is replaced by DNA,
DNA ligase joins the Okazaki fragment to
the growing strand.
From Gene to Protein
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Translation: mRNA – protein
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The process by which messenger
RNA(mRNA) is translated into proteins.
Synthesis of a protein
tRNA converts codon information into
amino acid sequence.
catalyzed by rRNA.
mRNAs are single-stranded RNA molecules.
They are copied from the TEMPLATE
strand of the gene, to give the SENSE
strand in RNA
They are transcribed from the 5’ to the 3’
end
They are translated from the 5’ to the 3’ end
The Genetic Code
Gene – a DNA sequence that codes for one
polypeptide or a trait
Genetic information is transmitted from
the nucleus to the cytoplasm where protein
synthesis occurs.
Transcription
Terms: DNA Methylation – methyl group is added
to nucleotides. Modifies DNA
The process by which DNA is copied to RNA
involves an enzyme called RNA Polymerase
Steps to Transcribe DNA:
1. RNA Polymerase attaches to DNA at a
sequence called the promoter.
2. DNA strand separates temporarily.
3. RNA polymerase adds RNA nucleotides to
the DNA template.
4. RNA polymerase travels along the template
strand.
Inheritance Patters In Animals
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A gene or a DNA sequence coding for a trait
is located at a specific locus or site in the
chromosome.
Different alleles of the gene occupy the
same locus.
Terminologies
Trait – a characteristic brought by the expression
of a gene
PCZO100 — FOUNDATIONS OF ZOOLOGY (LECTURE)
MODULE 3 – Cell Division and Inheritance
5 - 3 orientation antiparallel
Alleles – alternative forms of a gene
Multiple Alleles – when more than a pair of alleles
control a trait
Codominant – different alleles are both expressed
in a heterozygote.
Incomplete dominance – when one allele is not
completely dominant over another.
Genotype – genetic composition
Phenotype – visual expression of the genotype
Dominant Allele – Hides the expression of another
allele.
Recessive allele – expression is masked another
allele.
Heterozygous – two different alleles of the gene
occupy the loci of homologous chromosome.
Homozygous – two identical alleles of the gene
occupy the loci homologous chromosome.
Principle of Segregation
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Pairs of genes are distributed between
gametes during gamete formation when
homologous chromosomes are distributed
to different gametes during meiosis.
Law of segregation:
Principle of Independent Assortment
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During Meiosis, pairs of genes segregate
independently of one another.
The distribution of genes for one trait is not
influenced by the genes for another trait.
Punnett Square
dna replication
1. helicase unwinds the parental double helix
2. single strand binding protein stabilize the
unwound parental DNA
3. DNA polymerase
okazaki fragment
DNA methylation- process methyl group is added
in nucleotide
20 amino acids
mutation increase
wild type hemoglobin glutamic acid- Glu
heat tolerant
drought tolerant
aneuploidy
locus
allele