Genetics and Cell Cycle
Chapter 18
Objectives
• Explain how the structure and replication of DNA are essential to
heredity and protein synthesis, that changes in DNA may alter genetic
expression.
• Understand the steps in mitosis and meiosis
• Predict and interpret patterns of inheritance.
• Understand that genetic information coded in DNA is passed from
parents to offspring by sexual reproduction.
Chromosomes
• In each of your cells is found a nucleus.
• Inside the nucleus is found chromatin, or
spaghetti looking DNA.
• During times of cell division, chromatin
bunches together into 46 chromosomes,
or colored stained x shaped structures.
Autosomes and Sex chromosomes
• 22 pairs are autosomes, Homologous- same shape
•
1 pair is the gender or sex chromosome.
• Males have an X and y shaped pair.
• Females have two X shaped chromosomes.
Karyotype
• White Blood Cells separate from blood using centrifuge.
• Cells are placed in a petri dish.
• Cells are stimulated to divide.
• Chromatin condenses to a chromosome.
• Nucleus dissolves.
• A chemical stops division and a picture is taken.
• The similar size chromosomes are placed together.
Diploid
• Having two sets of chromosomes
• 46 chromosomes
• Each pair has genes that code for a trait in the
body, one on each side.
• Each side is called a sister chromatid.
• They are joined at a centromere.
Cell Cycle and Mitosis
• The process to divide cells to grow and heal.
• Interphase
• Cell division or Mitosis
Interphase
• Most of the life of the cell is spent making proteins, carbs, etc.
• Three stages
• G1 phase- Growth phase or Gap 1
• Organelles are doubled, makes proteins needed for DNA replication.
• S phase- DNA replication or synthesis.
• DNA is copied or doubled.
• Chromosomes will have two sister chromatids.
• G2 phase- Gap 2 or Growth phase.
• Makes proteins in microtubules which pull apart chromatids.
https://www.youtube.com/watch?v=NR0mdDJMHIQ
Mitosis and Cytokinesis
• Division of the nuclear material or sister chromatids.
• Each new cell will have the same number of chromatin or DNA
strands. 46 chromosomes.
• Two daughter cells will result after cytokinesis or cell division.
• Takes about 4 hours in humans.
• In RBCs, WBCs, skin, etc.
Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Interphasecell growth
Prophase
Spindle fibers are made of microtubules made of tubulin proteins
Metaphase
Anaphase
Telophase and Cytokinesis and Interphase
Actin filaments form a ring that contracts.
https://www.youtube.com/watch?v=pOsAbTi9tHw
Single cells only do Binary Fission
• Bacteria only have one chromosome so don’t do Mitosis. They just
split one circular chromosome.
Control of Cell Cycle
• Apoptosis: programmed cell death. Destroys cells that divide when
they shouldn’t
• Controlled by hormones in checkpoints in G1, G2, and Mitosis
• Human growth hormone.
• G1 checkpoint is when the cell will divide.
• If the cell is checked before this the cell will grow but not divide.
DNA integrity is checked. If damaged then protein P53 stops the cycle and starts repair.
If DNA can’t be repaired then cell will go through apoptosis.
• G2 checkpoint verifies DNA has duplicated.
• Allows damage from UV or X rays to be repaired
Control of Cell cycle
• Mitosis check
• 2 places to ensure chromosomes are properly attached and separated
Hormones control cell cycle
• Hormones attach to receptors on the cell membrane, signal genes
inside the cell to make proteins to start division.
• Epidermal growth factors- cause skin to repair around an injury.
• Progesterone- helps cells to line uterus
Meiosis
• Increases variety in offspring.
• Called Reduction division. Parent makes 4 different sex cells.
• Makes sex cells which have half the number of chromosomes as other
body cells.
• 46 chromosomes reduce to 23 chromosomes
• Diploid is reduced to Haploid gametes
• 2n becomes n
• Gametes are Sperm in males, Eggs in females
Homologous chromosomes
• Similar shaped chromosomes pair up. 4 chromatids together in
synapsis in Prophase I
• Spindle appears
• Crossing over may happen between similar shaped chromosomes
• Allows exchange of traits
Crossing over can increase variety
• During Meiosis I, homologous chromosomes may exchange genes.
• Brown and blonde genes may switch
•
Meiosis
• Meiosis has two phases of mitosis called Meiosis I & II which reduces
number of chromosomes in half from 46 to 23
• Interkinesis: time between Meiosis I and II
Meiosis
Meiosis
Result of meiosis
4 gametes are formed, with different combinations of genes
Humans have 23 chromatids so that is 2*23 possibilities of genes or
8,388,608 possible combinations of traits.
Sperm joins with egg to form a diploid cell that grows into a new baby.
Compare Mitosis & Meiosis
• Mitosis has same number of chromosomes as parent cell. Mitosis
makes two daughter cells
• Meosis begins with 4 sets of chromosomes, ends with half the
number of chromosomes as parent cell, chromosomes can cross over
in metaphase I. Meiosis makes four daughter cells
https://www.youtube.com/watch?v=toWK0fIyFlY