INVESTIGATION APPROACH TO GENETICS

Classical Investigative
Cytogenetics
Molecular Genetic Analysis &
Population Genetics

BIO511
Brooker, CHAPTER 1 PG. 10-13 Mus musculus

INTRODUCTION
• Genetics is a broad discipline encompassing C. elegans

molecular, cellular, organism, and population

biology

•Investigation approach involves viruses,

bacteria and wide variety of plants and
animals. Experimentally, geneticists often
focus their efforts on MODEL ORGANISM

•What? Organism studied by many different

researchers . Why? so they can compare
their results and determine scientific
principles that apply more broadly to other A. thaliana
species.
E. coli S. cerevisiae

Danio rerio D. melanogaster

 (1) Classical Investigation
 The most classic investigative approach is the
study of TRANSMISSION GENETICS
 Patterns of inheritance of traits are examined in
transmission genetics
 Experiments are design so that the transmission
of traits from parents to offspring can be
analyzed through several generation
 The first significant experimentation of this kind
to have a major impact on the understanding of
heredity was performed by Gregor Mendel in
the middle of the 19th century (Principle of
segregation & Principle of independent
assortment)
 The information derived from his work serves
today as the foundation of transmission
genetics
 Pedigree is another way to analyze inheritance (Humans present a special
problem to geneticist because CONTROLLED CROSSES are NOT POSSIBLE (or
desirable) – Small number of offspring, can’t work with ratios as well.
 PEDIGREE CHART are diagrams that show the relationships among the
members of the family
 It is customary to represents males as squares and females as circles
 A horizontal line connecting a circle and a square represents a mating
 The offspring of the mating are shown beneath the mates, starting with the first
born at the left and proceeding through the birth order to the right
 Individuals that have a genetic condition are indicated by coloring or shading
 Q : Practice Problem

A man marries and has two sons and a daughter.

Then his wife dies and he marries again, having
one daughter by the second marriage. Draw a
pedigree that illustrates this scenario .
(Hint: connect the man to both of his wives)
 A: Solved Problem
Q:
A man marries and has two sons and a daughter. Then his wife
dies and he marries again, having one daughter by the second
marriage. Draw a pedigree that illustrates this scenario .
(Hint: connect the man to both of his wives)

First Second
Wife Wife
Autosomal recessive
inheritance: Two copies
of abnormal allele are
needed to express an
autosomal recessive
trait.
Heterozygotes - Rr
Homozygotes - rr/RR

Propositus
The first identified case
of an inherited disease
in a family. Def: an elderly
man who passed on the
disorder to three of his
four children and 9 of 14
grandchildren

Consanguineous
marriage is the union of
individuals having a
common ancestor
•Human genetics are studied using
pedigree diagram how a trait is
inherited in a family

•A pedigree helps us determine

genotypes of the family members

•For example, the GENETIC

TRANSMISSION for the recessive
allele that cause albinism can be
shown through HUMAN PEDIGREE
CHART.

• Albinos are humans that have no

pigment, their skin is very pale and
all their hair is white, including
eyebrows and eyelashes.

Albinism is one of the example of

autosomal recessive disorder
AUTOSOMAL RECESSIVE INHERITANCE

1. Two copies of abnormal allele are needed to

express ALBINSM ( autosomal recessive
trait).
2. The appearance of the disorder frequently
observed in only ONE generation of a family
as isolated cases.
3. If normal parents have an affected child, both
parents must be heterozygous. ¼ of their
children are affected, ½ are heterozygote
and ¼ are normal.
4. Heterozygote are phenotypically normal
(carrier)
5. Example: Albinsm
AUTOSOMAL DOMINANT INHERITANCE
1. Only one abnormal allele
of gene is needed to
express an autosomal
dominant trait.
2. An affected person has an
affected parent
3. A heterozygous affected
parent and an unaffected
parent have, on average,
an equal number of
affected and unaffected
children. (50%)
4. Males and females are
equally likely to be
affected.
5. Example: Huntington
disease – a brain disorder
that affects a person
ability to think, talk and
move.
 (2) CYTOGENETICS
Cytogenetics is the study of CHROMOSOMES and their ROLE
in HEREDITY.
The earliest such studies used light microscope
Figure 1: Explanation of Cytogenetics
The initial discovery of chromosome behaviour during
mitosis,
mitosis meiosis and fertilization,
fertilization late in the 19th century was a
critical event in the history of genetics
The important role of this observation played in the
rediscovery and acceptance of Mendelian principles
The light microscope continues to be useful in the
investigation of chromosome structure and abnormalities
and is instrumental in preparing karyotypes, which include all
of the chromosome characteristics of any species arranged in a
standard sequences
With the advent of electron microscope, the repertoire of
investigative approaches in genetic has grown
In high resolution microscope, genetic molecules and their
behaviour during gene expression can be visualized directly
(2) CYTOGENETICS
•This research blossomed during the twentieth century, as microscopes improved and
better procedures for preparing and staining chromosomes were developed

•The demonstration that genes reside on chromosomes boosted interest in this research
and led to important studies on chromosome number and structure

•Today cytogenetics has significant applied aspects, especially in medicine where it is

used to determine whether disease condition are associated with chromosome
abnormalities
 (3) MOLECULAR GENETIC ANALYSIS
Molecular genetics
field of biology and genetics that studies the structure
and function of genes at a molecular level.
level The field
studies how the genes are transferred from generation
to generation. Molecular genetics employs the
methods of genetics and molecular biology. General questions within the field of
molecular genetics are the following:
 This approach had the greatest impact on the
recent growth of genetic knowledge. 1.What are the molecular structures of
DNA & RNA?
2.How is the genetic material copied?
Molecular studies, initiated in the early 1940’s
3.How are genes expressed at the
Have consistently expanded our knowledge of the molecular level?
Role of genetics in life process. 4.How is gene expression regulated so
Examples ?  3 Experiments that gives the evidence that it occurs under the appropriate
that DNA is the genetic material ?? conditions and in the appropriate cell
type?
 Although experiments relied on bacteria & viruses 5.What is the underlying relationship
between genes and genetic disease?
that infect them, extensive information provide the
nature, expression, replication & regulation of genetic
information in eukaryotes as well.
 Techniques in molecular genetics

There are three general techniques used for molecular genetics:

amplification, separation and detection, and expression.
 RECOMBINANT DNA TECHNOLOGY
Recombinant DNA (rDNA) has various definitions, ranging from
very simple to strangely complex. The following are three
examples of how recombinant DNA is defined :

1.A DNA molecule containing DNA originating from two or

more sources.

1.DNA that has been artificially created. It is DNA from two or

more sources that is incorporated into a single recombinant
molecule.

1.According to the NIH guidelines, recombinant DNA are

molecules constructed outside of living cells by joining natural
or synthetic DNA segments to DNA molecules (VECTOR) that
can replicate in a living cell, or molecules that result from their
replication.
Recombinant DNA Technology
 Recombinant DNA
Vector technology includes DNA
(plasmid backbone) cloning, gene cloning and
+ molecular cloning.
DNA fragment
to be cloned
 DNA from one organism is
transferred to a bacterial
DNA fragment ligated (inserted) plasmid for replication.
into vector creating recombinant
DNA molecule.  Although viruses,
bacterial artificial
To make many copies of the
recombinant DNA molecule, the
chromosomes, and yeast
vector (including the DNA fragment) artificial chromosomes
is introduced into bacteria. may be used for
replicating DNA, bacterial
plasmids are most
Bacterial
commonly used in this
cell technology and are called
Chromosomal DNA
VECTORS.
 Recombinant DNA
Construction
1. The chromosomal DNA is
isolated and digested with a
restriction enzyme (EcoR1) to
get the desired fragment.
2. The plasmid DNA is also cut at
one side with the same
restriction enzyme - (EcoR1),
so the vector will have the
same sticky ends as the
chromosomal DNA fragments.
3. DNA ligase is then added to
catalyze the covalent linkage
between DNA fragments.
4. The vector containing a piece
of chromosomal DNA is
referred to as a
RECOMBINANT VECTOR /
rDNA

Brooker, CHAPTER 18 PG. 486

 GENE CLONING
 The gene cloning procedure involves two
essential steps:
1. The incorporation of the gene of interest into
a small self replicating chromosome
(PLASMID vector)
2. The amplification of the recombinant
minichromosome by its replication in an
appropriate host cell (Bacterial HOST- E. coli)
 Step 1 involves the joining of two or more
different DNA molecules in vitro to produce
recombinant DNA molecules.
 Step 2 is really the gene cloning event in
which the recombinant DNA molecule is
replicated or cloned to produced many
identical copies for subsequent biochemical
analysis
 Thus, although the entire procedure is often
referred to as the recombinant DNA or gene
cloning technique, these terms actually refer
to two separate in the overall process.
 Building on this approach, the new fields of
genomics and bioinformatics now exists whereby
the entire genetic make up of an organism may be
cloned, sequenced and the function of the genes
explored
 Using this new technology, it is now possible to
explore gene function in extreme detail
 Such molecular and biochemical analysis has created
the potential for gene therapy and has profound
implications in medicine,
medicine agriculture and bioethics
 One of the most striking achievements in the
history of DNA biotechnology occurred in 1996 at
the Roslin Institute in Scotland, when the world’s
most famous lamb, Dolly was born
 Representing the first animal ever to be cloned from
an adult somatic cell, Dolly was the result of the
research of Ian Wilmut, who fused genetic material
from the nucleus of an udder cell taken from a six
year old sheep with an enucleated oocyte of
another sheep
DOLLY
THE CLONING
PROCESS

 The cloning of Dolly the sheep by the Roslin Institute in Edinburgh was a genetic
milestone.
 It was the first successful clone produced using genetic material from an adult
(udder) cell rather than from a gamete (egg or sperm).
 The DNA from the udder cell was fused with an ovum stripped of its own DNA.
 The fused cells divided in vitro to form an embryo that was then implanted into a
surrogate mother.
 The resulting lamb was a clone of the ewe that had provided the udder cell.
Dolly, a Finn Dorset sheep cloned from the genetic material of an
adult mammary cell, shown next to her surrogate mother at Roslin
Institute
 (3) Molecular Genetic Analysis

Resource Issue: Cloning

• Statement of the Problem: Cloning is a new found technology which may

change the way life on Earth works

PRO CON
- Saves lives - Human cloning abuse
- Cures disease - Unethical
- May decrease deforestation - Scientific complications
- May save endangered species - Destroys Embryo
Brooker, CHAPTER 24 PG. 667

(4) POPULATION GENETICS

 In this investigation, scientist attempt to define how and why certain genetic variation
is maintained in populations, while other variation diminishes or is lost with time
 Such information is critical to the understanding of evolutionary processes
 Population genetic also allows us to predict gene frequencies in future generations

Polymorphism in the
Hawaiian happy-face spider

These spiders are members of the

same species and carry the same
genes. However, several genes that
affect pigmentation patterns are
polymorphic (there is more than one
allele for each gene within the
population).
 SUMMARY

 Together this varied approaches used in investigating genetic have

transformed a subject that was only poorly understood in 1900 into one of the
most advanced scientists disciplines today
 As a result, the impact of genetics on society has been, and will continue to
be immense!