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GENETICSWhat is Genetics?
It is the science that deals with the study of heredity and variation.
GENETICS came from the word gen, genetikos meaning
generative and genesis meaning beginning.
Heredity is a biological process where a parent passes certain
genes onto their children or offspring.GENE
◉ Biological unit of heredity.
◉ Gene hold the information to build and
maintain their cells and pass genetic
traits to off springs.
◉ In cells, a gene is portion of DNA.Continued...
Cell Structure Cell Enzymes
◉ Is one member of a pair or series
of different forms of a gene.
◉ Homozygous-an organism in
which 2 copies of genes are
identical i.e. have same alleles
◉ Heterozygous-an organism which
has different alleles of the geneChromosomes
◉ Chromatin: DNA, RNA & proteins that
make up chromosome
◉ Chromatids: One of the two identical parts
of the chromosome.
◉ Centromere: The point where two
◉ 46 chromosomes, 22 pairs Autosomes and
1 pair Sex chromosomes.NUCLEOTIDE: group of molecules that when linked together, form
the building blocks of DNA and RNA; composed of phosphate
group, the bases: adenosine, cytosine, guanine and thymine and a
pentose sugar. In case of RNA, thymine base is replaced by uracil.
CODON: series of three adjacent bases in one polynucleotide
chain of a DNA or RNA molecule which codes for a specific amino
GENETIC CODE: the sequence of nucleotides in a DNA or RNA
molecule that determines the amino acid sequence in the
synthesis of proteinsCauses of diseases
• Genetic diseases
• Complex traitsGenetic diseases
◉ Inherited diseases
◉ Diseases due to mutations in somatic cells- cancerMutationsDefinition:
Permanent changes in the DNA. Those that affect
germ cells are transmitted to the progeny.
Mutations in the somatic cells are not transferred
to the progeny but are important in the causation
of cancer and some congenital diseases.CAUSES OF MUTATIONS
Antiviral drug iododeoxy uridine
Benzpyrene in tobacco smoke
◉ X – rays & ultraviolet light
◉ Certain viruses such as bacterial virusTypes of MutationsPoint Mutation
These affect a single amino acid or short sequence. These
are also called single-base substitutions.
• Missense mutations may change the code for a particular
• Nonsense mutations may make a change so that the whole
chain stops. This mutation codes for a Stop codon.Frame shift Mutations
Insertion or deletion of one or two base pairs
alters the reading frame of the DNA strand.Snips or SNPs (Single nucleotide
These are the most common type of genetic variation
among people. Each SNP represents a difference in a single
DNA base for example nucleotide cytosine (C) replaced with
the nucleotide thymine (T) in a certain stretch of DNA.Trinucleotide Repeat Mutations
Set of genetic disorder caused by trinucleotide repeat in certain
genes exceeding normal, stable threshold e.g. Fragile X
Syndrome.Classification Of Genetic Diseases
◉ Single Gene Defects/Mendelian Disorders.
◉ Disorders with Multifactorial or Polygenic inheritance.
◉ Cytogenetic Disorders.
◉ Disorders showing atypical patterns of inheritance.Mendelian Disorders
A genetic disease caused by a single mutation in the
structure of DNA, which causes a single basic defect
with pathologic consequencesPatterns Of Inheritance
◉ Autosomal Dominant.
◉ Autosomal Recessive.