Approaches to the Study of Genetics (genetics and Evolution)

Genetics

1. Lec-01: Introductory Lecture
1.20103 – Introduction to Genetics & Evolution

2. •Genetics is a fundamental biological science
for without genes there is no life
•It is the study of how hereditary traits are
transmitted from one generation to another
and variation in organisms.
•Historically, geneticists have worked in three
different areas
:

I.Classical Genetics
II.Molecular Genetics
III.Population & Evolutionary Genetics

3. •Concerned with genes, mutations, genotypes &
phenotypes
•It discusses:
i.Arrangement of genes on the chromosomes
ii.Transmission of genes to the next generation
through meiosis
iii.Process of mitosis that allows for growth
iv.Methods that generate mutations and identify
mutants
v.Various patterns of inheritance to produce a
specific trait or phenotype

4. •Dominated by Gregor Mendel’s carefully
controlled breeding experiments with the
garden pea, Pisum sativum
•Mendel published his work - the rules of
inheritance in 1866
•Mendel correctly hypothesized that traits
such as pod colour were controlled by
genetic elements (we now call genes)
•He also hypothesized that adult organisms
have two copies of each gene(diploid
state); and gametes receive just one of
these copies(haploid state)

5. •Mendel’s work has been distilled into 2 rules:

1)Law of Segregation – two alleles separate
from each other during gamete formation
2)Law of Independent Assortment – alleles
of different genes sort independently of each
other into gametes
•This were hypothesized way before the role
of chromosomes and genes in inheritance
was established
•Eventually the Chromosomal Theory of
Inheritance was born

6. •Is the study of the structure, replication
and expression of the genetic material
and the expressed protein

•It includes methods involved in
manipulating the expression and analysis
of genetic material (recombinant DNA
technology & genomics)

7. •Genetic material for all living things is the
double-stranded DNA
 repeating units of sugars(deoxyribose)
 phosphate groups &
 puridines and pyrimidines (A, T, C, G)
•DNA undergoes replication(semi- conservative)
with aid of DNA polymerase
•Groups of 3 nucleotides form a codon that
specifies one of 20 naturally occurring amino
acids used in protein synthesis
•Sequences of bases forms the ‘genetic code’

8. •In gene expression, information is transcribed
from DNA into RNA
•RNA gets translated into amino acid
sequences


•CENTRAL DOGMA in this field describes the
flow of genetic information – it states that
DNA is transcribed into mRNA, which is
then translated into a protein

9. •Study of mechanisms that results in
changes in allele frequencies in a
population over time and the
consequences of those changes.
•Darwin’s Concept of Evolution by
Natural Selection finds a firm genetic
footing in this area of study of inheritance
•Merging of Darwinian theory and
population genetics is termed neo -
Darwinism

10. •Hardy- Weinberg Equilibrium was
developed to show a simple genetic
equilibrium occurs in populations if they
are large, have random mating, has
negligible effects of mutation, migration
and natural selection.
•This equilibrium gives scientists a
baseline for comparing populations
to see whether any evolutionary
processes are occurring.

11. •One area of evolutionary biology that has
generated much controversy is the Theory of
Sociobiology – study of how biology
affects human social behaviour.
Founded on Darwin's Theory of Evolution
Theory suggests that many cultural traits
are rooted in our genetic makeup
...suggesting we are all genetically programmed
to act in certain ways!!

12. COMMON EXPERIMENTAL
MODELS IN GENETIC STUDIES

13. •Certain organisms are used repeatedly
in genetic experiments in the laboratory
•These organisms possess attributes,
both practical and genetic, that makes
them desirable model organisms for
research
•They should have the following five (5)
traits:

14. 1)Short generation time to reach
sexual maturity – allows researchers
analysis of multiple generations of
specific crosses in a short space of time

2)Produce large number of offspring –
greater chance of exhibiting expected
phenotypic and genotypic ratios

3)Can easily and inexpensively be
reared in small space in lab

15. 4)Exhibit interesting features that is
common and correspond to a variety of
living things - & relating it to humans in
some way

5)Has genomic DNA that has been
largely or entirely sequenced. Knowing
genomic DNA increases chances of
identifying genes in both normal and
mutant individuals as well as its uses in
recombinant DNA technology

16. E.coli (bacteria)
Saccharomyces cerevisiae (bakers
yeast)
Drosophila melanogaster (fruit fly)
Caenorhabditis elegans (worm)
Arabidopsis thaliana (flowering plant)
Mus musculus (mouse)
Danio rerio (Zebra fish)

19. DNA &
C
HROMOSOMES

20. DNA & CHROMOSOMES

21. •All organisms contain massive amount of
information in form of DNA
•DNA organized into informational units
called genes – controls all aspects of life!!
•All cells are formed from pre- existing cells
 thus at cell division, information in DNA
must be precisely duplicated and copies
transmitted to daughter cells
•This occurs by MITOSIS in eukaryotic
cells

22. •Major carriers of genetic information in
eukaryotes are the chromosomes
contained within the nucleus
•Discovered by botanist Karl von Nageli
in 1842
•Heinrich Waldeyer coined the term
‘chromosome’ in 1888 meaning
‘coloured body’ but are virtually
colourless (name refers to ability to be
stained)

24. •Chromosomes are made of chromatin –
complex material consisting of fibres of
proteins & deoxyribonucleic acid(DNA)
•When cell not dividing, chromosome
appear as thin threads of chromatin
•When dividing chromatin fibres
condense and become visible distinct
structures

25. •Associated with chromosomal
activity are these structures, largely
non-membrane bound
proteinaceous structures
•Centrosomes consist of two
cylindrical structures called
centrioles. These serve as
organizing structures for the
microtubules/spindle fibres.
•ALL critical for meiosis and mitosis

26. • Eukaryotic chromosomes are made of:
−Linear, double stranded DNA &
−Proteins collectively referred to as
chromatin (euchromatin (loosely
packed) or heterochromatin
(condensed & visible)

•Prokaryotic chromosome are made of:
−a circular, double stranded DNA &
other accessories
−Some have extra chromosomal
material (plasmids)

27. •Most eukaryotes are diploid (have 2
sets of chromosomes – homologous
chromosomes or homologs)
Humans have 23 homologous
chromosome pairs often expressed
as 2n=46
•Few eukaryotes and reproductive
cells(gametes) have only one set of
chromosome - haploid
Expressed as n=23

28. •Each chromosome contains hundreds of
genes
e.g. Humans have ≈ 70- 100,000 genes
•
Chromosomes of different species generally differ in number & genetic
information
e.g. Human have 46 chromosomes
•Some species can share same number but never the same genetic information

29. •Most animal & plants usually have
between 10- 50 chromosomes

•
The number of chromosomes is NOT
what makes each species unique but rather the information specified by genes on the chromosome that makes species unique.

30. •Total chromosomal complement of a cell can be
photographed during mitosis and rearranged in
pairs to make a picture called karyotype.