A 39 page summary of all Genetics covered in the lectures of Biology 124 in Semester One. This summary contains definitions, explanations and diagrams. The information covered includes: mitosis, meiosis, Mendel's experiment, DNA replication and so on.
Reasons for cell division ● Growth & development
● Repair and replacement
● Reproduction
Eukaryotic Cell Cycle ● Growth: Synthesis of proteins, lipid and
carbohydrates
DNA REPLICATION
- Mitosis: produces cells that are genetically identical
to parent cell
- This is essential for normal development
DNA is packaged in chromosomes with associated proteins.
See diagram below.
Chromosome Numbers in ● Diploid Organism: An organism that contains two
Diploid Organism copies of each type of chromosome in its nucleus.
● Diploid: 2n
● Human: 46 chromosomes
● Gorilla: 48 Chromosomes
NB: The two chromosomes of each pair are called
homologous chromosomes
Homologous Chromosomes
https://slideplayer.com/slide/11759716/
, ● Homologous chromosome: Same genes in the same
order in each chromosome.
Chromosome Numbers in ● Human somatic cells are diploid (2n).
Human Cells 46 chromosomes, 23 pairs of homologous
chromosomes. One maternal and one paternal
chromosome.
● Human gametes are haploid (n).
23 chromosomes = a single copy of each
chromosome.
Mitotic Cycle (Mitosis)
Anagram: PMATC
P - Prophase
M - Metaphase
A - Anaphase
T- Telophase
C- Cytokinesis
INTERPHASE
G1: Growth before DNA replicates (Multicellular organisms
stop dividing here)
S: Replication of chromosomes occurs, 10-12 hours
G2: Cell continues to grow, 4-6 hours
Then undergoes mitosis: 1 hour or less
PROPHASE
Doubled chromosomes condense - centrosomes generate
the spindle as they separate.
(Prometaphase) Nuclear envelope disappears and spindle
enters the former nuclear area - microtubules from opposite
spindle poles attach to kinetochores of each chromosome.
METAPHASE
Chromosomes align at the spindle midpoint.
ANAPHASE
Spindle separates the two sister chromatids and moves
them to opposite spindle poles.
TELOPHASE
Chromosomes return to interphase state.
New nuclear envelopes form around daughter nuclei.
CYTOKINESIS
Cytoplasm divides.
How Cytokinesis Occurs:
1. A contractile ring of microfilaments forms a groove in
the plasma of the membrane.
2. Continued constriction causes grooves to deepen.
3. Constriction continues while cytoplasmic division
distributes organelles and other structures.
Importance of Mitotic Spindles The mitotic spindle is a structure composed of
microtubules which segregates chromosomes into the
daughter cells during mitosis.
A microtubule is a rope-like component of the
cytoskeleton. The centrosome is an organelle that
serves as a microtubule organizing center during cell
division.
, KINETOCHORES
Kinetochore is a protein structure that forms on a
chromatid during cell division and allows it to attach to
a spindle fiber on a chromosome. A chromatid is one of
two strands that form when a chromosome replicates
Abnormalities Three Checkpoints:
G1/S Transition:
The cell will not pass through if..
● Cell size is incorrect
● Not enough nutrients in environment
● Parent DNA is damaged
● Not enough resources in the cell to replicate
DNA
G2/M Transition:
The cell will not pass through if..
● DNA replication is incomplete
● DNA is “faulty” or damaged
Checkpoint M:
● Can only occur if all previous issues did not
occur
(Image: lecture slides, source unknown)
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