Introduction to Genetics
• Meiosis produces specialized cells (gametes) that contain half the
normal number of chromosomes.
• Every living organism inherits a blueprint for life from its parents,
which is the result of the combination of these specialized cells.
• During this unit we will understand how DNA is organized in
chromosomes and the importance of this organization in the
process of meiosis and gamete production that will lead to the
inheritance of characteristics.
What is genetics?
• Branch of biology concerned with the storage of information in
living organisms and how this information can be passed from
parents to progeny.
• Comes from the word “genesis” = origin
Chromosomes: how is DNA organized?
Crossing over
What is a gene?
• A gene is a heritable factor that consists of a length of DNA and
influences a specific characteristic.
• Heritable
• Passed from parent to offspring
• Characteristic
• Genetic traits such as hair color or blood type.
• About 30.000 genes that you possess are organized in
chromosomes. The complete set of genes of a living thing is its
genome.
• Each gene is a sequences of DNA that codes for a protein
Alleles
• Alleles: different forms of
a gene
• Differs from other alleles
by one or a few bases
• Alleles occupy the same
place (locus) on each
chromosome pair
Mutations
• Random rare changes in genetic material
Base substitution mutations:
Sickle cell anemia
Activity
1. Explain the consequences of a base substitution mutation in
relation to the processes of transcription and translation, with
regards to sickle cell anemia (8).
2. Answer the questions on Pearson pg 93 about sickle cell anemia
• Mutation is a change in the genetic make-up;
• Base substitution mutation occurs when one (nitrogenous) base in DNA chain is
replaced by another;
• This is a gene mutation / change in the base sequence of a gene;
• Effect of mutation ranges from no effect / no change in amino acid sequence to
drastic changes;
• Sickle-cell anemia involves change in gene for one of polypeptides in hemoglobin /
Hb / HBA;
• GAG has mutated to GTG (on DNA); adenine replaced by thymine in DNA;
• Transcription of DNA produces the triplet GUG instead of GAG on mRNA; one codon
is different in mRNA; new codon is for valine rather than glutamic acid;
• tRNA brings amino acid to ribosome during translation; different amino acid placed
in polypeptide chain being formed by translation;
• The two amino acids differ in solubility / have different properties / valine causes
HBS to be less soluble;
• Causes red blood cells to become sickle shaped / carry oxygen less efficiently;
• HBS allele causes sickle-cell anemia but gives resistance to malaria;
Bacterial chromosomes
• Prokaryotes have one chromosome
consisting of a circular DNA molecule.
• There is no association with proteins
(naked)
• Some prokaryotes also have plasmids:
small extra DNA molecules.
• They contain genes for antibiotic resistance
• Copies of plasmids can be transferred from
one cell to another allowing the spread
through a population (variability)
• Plasmids are also used by biologists to
transfer genes between species artificially.
Genome
• Genome: the complete set of
characteristics of a living
organism (all your DNA).
• Homework: Investigate about
the human genome project.
Comment in wikispaces.
Genome sizes
Organism
Genome size (million base
pairs)
Description
T2 phage
0.18
Virus that attacks Echerichia
coli
Echerichia coli
5
Gut bacterium
Drosophila melanogaster
140
Fruit fly
Homo sapiens
3,000
Humans
Paris japonica
150,000
Woodland plant
Haploid vs Diploid
• Haploid nuclei have one chromosome of each pair
• Gametes
• In humans: 23 chromosomes
• Diploid nuclei have pairs of homologous chromosomes
• Two copies of every gene
• Except in sex chromosomes
• In humans: 46 chromosomes (23 pairs)
Meiosis I
Meiosis II
Compare Mitosis
and Meiosis
Compare mitosis and meiosis
Meiosis
End result (number of
cells produced)
Normally there are four cells, each cell has half
the
number of chromosomes as the parent cell.
Function
Sexual reproduction , production of gametes (sex
cells).
Where it occurs?
Animals, fungi, plants, and some protists.
Stages
Genetical composition
Crossing over process
Pairing of homologous
chromosomes
Steps in the process Prophase I, Metaphse I,
Anaphase I,
Telophase I, Prophase II, Metaphase II, Anaphase II,
Telophase II.
Not similar to parents
Occurs in Prophase I
Mitosis
Two cells, each cells has the same
number of
chromosomes as that of the parent.
Cellular reproduction, growth, repair
wear and tear of cells,
sexual reproduction.
Occurs in all eukaryotic organisms.
Prophase, Metaphase, Anaphase,
Telophase.
Usually similar to parents.
Sometimes
Yes
No
Cytokinesis
Occurs in Telophase I and Telophase II
Occurs in Telophase
Splitting of chromosomes
Does not occur in Anaphase I; occurs in
Anaphase II
Occurs in Anaphase
Karyotyping and karyograms
Karyotyping is arranging cromosomes by their
size
RAT
Amniocentesis and chorionic villus sampling
Non-disjunction
Sources
•
TutorVista.com (2014) Meiosis. NCS Pearson http://biology.tutorvista.com/cell/meiosis.html
•
TutorVista.com (2014) Structure of Chromosomes. NCS Pearson http://www.tutorvista.com/content/biology/biologyiii/chromosomes/chromosomes-structure.php
•
Scooter Blood smears from patients with sickle cell http://www.sicklecellanaemia.org/OER/article.php?id=138
•
Coriell institude for medical research (2014) Karyotyping http://www.coriell.org/researchservices/cytogenetics/karyotyping
•
Understanding evolution http://evolution.berkeley.edu/evolibrary/article/mutations_06
•
http://t24.com.tr/haber/amniyosentez-tarihe-karisiyor,215516
•
http://www.dnalabcenter.com/Chorionic-Villus-Prenatal.html
•
National health museum (2014) Mutation of chromosomes http://www.accessexcellence.org/RC/VL/GG/mutation.php
•
http://www.clt.astate.edu/mhuss/toppage6.htm
•
http://quizlet.com/11580914/chapter-25-slides-flash-cards/
•
http://www.museumboerhaave.nl/onderwijs/museumjeugduniversiteit-geweest/museum-jeugduniversiteit-2010/kouweblauwe-oren-en-andere-genen/
•
Imarcade (Online Image Arcade) http://imgarcade.com/1/anaphase-2-meiosis/