2. GENETICS
Branch of biology that deals
with genes, variations and
heredity in organisms.
It examines how the trait passes
from one generation to another.
Genetics is generally divided
into four major subdivisions:
Classical genetics: Describes how traits
(physical characteristics) are passed along
from one generation to another.
Molecular genetics: The study of the
chemical and physical structures of DNA,
its cousin RNA, and proteins.
Population genetics: deals with genetic
differences within and between populations
Quantitative genetics: A highly
mathematical field that examines the
statistical relationships between genes and
the traits they encode.
3. Common Terminologies used in genetics…
• Chromosomes
• Genes
• Alleles
• Single Nucleotide Polymorphism (SNP)
• Recombination
• Linkage analysis
• Linkage disequilibrium
4. CHROMOSOMES
• A threadlike structure of nucleic acids
and protein found in the nucleus of most
living cells.
• Carrying genetic information in the
form of gene.
• 23 pairs of chromosomes are present,
which include 22 autosomal
chromosomes and 1 pair of sex
chromosome.
https://en.wikipedia.org/wiki/Chromosome
5. GENES A basic physical and
functional unit of life.
Made up of DNA.
It holds the information
to build and maintain
their cells and pass
genetic traits to
offspring.
According to human
genome project,
humans have genes in
between 20000 and
25000.
Every person has two
copies of each gene,
one inherited from each
parent.
6. ALLELES
• Is a variant form of a given gene.
• Humans are called diploid organisms because they have
two alleles at each genetic locus.
• Each pair of alleles represents the genotype of a specific
gene.
• Genotypes are described as:
- homozygous = if two alleles are same at a locus.
- heterozygous = if two alleles are different at a locus.
• Alleles are dominant as well as recessive.
7. SINGLE NUCLEOTIDE POLYMORPHISM
(SNP)
• It is a common type of genetic variation in people.
• It is a substitution of a single nucleotide that occurs at a specific
position in the genome.
• SNP are found in both coding and non-coding regions.
• Occur with a high frequency.
• SNP close to gene act as a marker for that gene.
• The genetic differences between human populations make one
population more susceptible to disease.
8. RECOMBINATION
• It is a process in which pieces of DNA are
broken and recombine to produce new
combination of alleles.
• Recombination typically occurs during the
first stage of meiosis (Prophase).
• During the alignment the arms of
chromosomes can overlap and temporarily
fuse, causing a crossing over.
• It is the exchange of genetic material
between paternal and maternal
chromosomes.
9. LINKAGE ANALYSIS
• The tendency of DNA sequences that are close
together on chromosome to be inherited together
during the meiosis.
• The genes on same chromosome are said to be
exhibit linkage and are called linked genes.
• The nearer two genes are on a chromosome, the
lower the chance of recombination between them,
and the more likely they are to be inherited together.
• Types of linkage based on crossing over:
• Complete linkage - genes located on the same
chromosome do not separate and are inherited
together over the generations due to the absence of
crossing over
• Incomplete linkage - genes present in the same
chromosome tend to separate due to crossing over
and hence produce recombinant progeny.
10. LINKAGE DISEQUILIBRIUM
▪ A non-random association of alleles at different loci in a given population.
▪ It aims to identify and/or localize genes related to disease susceptibility.
▪ Recombination breaks down non-random genetic associations.
▪ LD = Difference between Observed and expected frequencies of alleles on a loci.
If LD = 1, then two loci are co-inherited or in linkage disequilibrium
LD = 0, then two loci are non co-inherited or no linkage disequilibrium
i.e., the situation is called as linkage equilibrium.
