GENETICSDr. Kaustubh

GENETICS• A branch of science

concerned with genes, heredity & variation in living organisms.

• Heredity is a biological process where parents pass certain genes onto their children or offsprings.

• Mutation: A permanent alteration of the nucleotide sequence of the genome of an organism.

Inheritance

Genes

DisordersTraits

GENES• Genes are the working parts

of DNA.

• It is a sequence of DNA that

codes for a known cellular

function or process.

• Genome: An organism’s

complete set of nuclear DNA.

Gene

Sequence of nucleotides

Genetic code

‘Translation’

Amino acids

Proteins

FUNCTIONS OF GENES

• For information storage

• Determination of Phenotype

• Processes in functioning

• Inheritance of traits (& disorders)

CHROMOSOMES• These are thread-like structures

located inside the nucleus of animal and plant cells.

• Each chromosome is made up of protein & a single molecule of DNA.

• Cell structures strongly stained by some colourful dyes used in research. (name)

• Function- Package DNA into histones

TELOMERES• Structures found at the ends

of our chromosomes.

• Consists of same sequence of bases repeated over & over again

• In humans, the telomere sequence is TTAGGG

• Nearly 3000 repetitions of the same sequence

Functions of Telomeres

Organise chromosomes in nucleus

Protect the ends of chromosomes

Protect DNA during cell replication

Telomere shortening

End replication problem Oxidative stress

When telomeres become too short, the chromosome reaches ‘Critical length’ and can no longer be replicated. It triggers the

process of ‘Apoptosis’ or Programmed Cell Death.

TELOMERASE• It is an enzyme that adds the TTAGGG telomere

sequence to the ends of chromosomes.

• Found in very low concentrations in the Somatic cells. Ageing cells —> ageing body.

• Found in high levels in Germ-line cells & Stem cells. Telomere length maintained after DNA division —> no signs of ageing.

• Found in high-levels in Cancer cells.

• It allows cells to keep multiplying & avoid ageing.

Eukaryotic Cell Prokaryotic Cell

Nucleus Present Absent

Chromosomes More than one One- Plasmids (not true)

Cell type Usually multicellular Unicellular

Nuclear membrane Present Absent

Examples Animals & Plants Bacteria & Archaea

Cytoskeleton Present May be absent

Mitochondria Present Absent

Cell organelles Present Absent

Chloroplasts(plants) Present Absent (chlorophyll scattered)

Cell size Relatively large Smaller in size

CELL DIVISION• It a process by which a parent cell

divides into two or more daughter cells.

• Eukaryotes divide by either Vegetative cell division or a Reproductive cell division.

• Prokaryotes undergo vegetative cell division called binary fission.

• All cell divisions are preceded by a single round of DNA replication.

• Consists of interphase, prophase, metaphase, anaphase and telophase.

DIFFERENCES

Meiosis Mitosis

2 successive cell divisions One cell division

Forms four daughter cells Forms two daughter cells

Daughter cells are haploid Daughter cells are diploid

Daughter cells- genetically different Daughter cells- genetically identical

Occurs in animals, plants & fungi Occurs in all organisms except viruses

Creates germ cells (egg & sperm) only Creates somatic cells (no germ cells)

Involves recombination/crossing over No recombination (prophase)

Sexual reproduction Asexual reproduction

INHERITANCE• It is the process by which characters or traits are

transferred from one generation to next.

• Variation is the degree by which progeny differs from each other & with their parents.

• Gregor Johann Mendel, for the first time conducted experiments to understand the pattern of inheritance in living beings.

• He conducted experiments on garden pea plant (Pisum sativum) & proposed the laws of inheritance.

WHY PEA PLANT?

Easy availability

Many varieties

Distinct characteristics

Self-pollinated Cross-pollinated

CONCEPTS• Genotype: Genes present in DNA of organism. Genes

are unit of inheritance.

• Phenotype: Physical expression of traits of the organism

• Alleles or allelomorphs: Alternative forms of the same gene. These are genes that code for pair of contrasting traits.

• Punnett square: It is the graphical representation to calculate the probability of all possible genotypes of offsprings in a genetic cross.

• Co-dominance: The 2 alleles are able to express themselves independently when present together. Offsprings show resemblance to both parents. Example- ABO blood groups in humans.

• Pleiotropy: The phenomenon in which a single gene exhibits multiple phenotypic expressions. A single pleiotropic gene may produce more than one effect. Eg:Phenylketoneuria disease

• Polygenic inheritance: The traits are controlled by 3 or more genes. Called quantitative inheritance.

MENDEL’S LAWS1. Law of Dominance (dominant, recessive, ratio

of 3:1 in F2 generation)

2. Law of Segregation (pair of alleles, gamete formation, no blending)

3. Law of Independent assortment (punnett square, segregation of one pair of characters is independent of the other pair of characters)

THE GENETIC MATERIAL

• DNA & RNA are two types of nucleic acids found in living systems.

• Nucleic acids are polymers of nucleotides.

• DNA acts as genetic material in most organisms, whereas RNA acts as genetic material in some viruses.

DE-OXYRIBO NUCLEIC ACID

• An organic chemical of complex molecular structure found in prokaryotic & eukaryotic cells, and in many viruses.

• It contains each person’s unique genetic code.

• Holds instructions for building proteins that are essential for our bodies to function.

• Found in the nucleus & mitochondria (maternal).

STRUCTURE OF DNA

• It is a right-handed double helical structure, with alternating sugar and phosphate groups.

• The two strands are complementary.

• It is made-up of chemical building blocks called nucleotides.

THE POLY-NUCLEOTIDE CHAIN

• The nitrogenous bases are Purines (adenine, guanine) & Pyrimidines (cytosine, uracil & thymine). Thymine in DNA & Uracil is specific to RNA.

• The bases are paired through H-bonds.

• Nitrogenous base & Pentose sugar form a nucleoside.

• Backbone of chain if formed by sugar & phosphates.

• The base pairs are complementary to each other. Structure of Nucleotide

SIGNIFICANCE

• The DNA double-helix is packaged in cells by proteins called histones.

• Humans have 3b bases & 20000 genes on 23 pairs of chromosomes.

• DNA functions: information storage, development, survival & reproduction.

RIBOSE NUCLEIC ACID• RNA typically is a single-

stranded bi-polymer.

• Three most well-known types are mRNA, tRNA & rRNA, which are present in all organisms.

• Plays important role in both- the normal cellular processes & diseases.

DIFFERENCES FROM DNA• A ribose sugar

• Single-stranded, made up of nucleotides

• Less stable than DNA

• Length of the strand is less than DNA

• Uracil is present instead of Thymine

• Formed in nucleolus, & then moves to specialised regions of cytoplasm depending on type of RNA

• Codes for amino acids & acts as a messenger for the information

• More resistant to damage from UV light than DNA

HOW DOES DNA CREATE PROTEINS?

Transcription is the process of producing a strand of RNA from a strand of DNA.Translation is the process where the information carried in mRNA molecules is used to create proteins.

In Detail..• The specific sequence of nucleotides in the mRNA

molecule provide the code for the production of a protein with a specific sequence of amino acids.

• Much like how RNA is built from many nucleotides, a protein is formed from many amino acids. A chain of amino acids is called a ‘polypeptide chain’ and a polypeptide chain bends and folds on itself to form a protein.

• During translation, the information of the strand of RNA is ‘translated’ from RNA language into polypeptide language i.e. the sequence of nucleotides is translated into a sequence of amino acids.

RETROVIRUSES• A retrovirus is a virus whose genes are encoded

in RNA instead of DNA.

• Like other viruses, retroviruses need to use the cellular machinery of the organisms they infect to make copies of themselves.

• The retrovirus genome needs to be reverse-transcribed into DNA  before it can be copied in the usual way. The enzyme that does this backwards transcription is known as reverse transcriptase.

• Retroviruses are "retro" because they reverse the direction of the normal gene copying process. Usually, cells convert DNA into RNA so that it can be made into proteins. But with retroviruses, the process has to start by going backwards.

• Examples are HIV & HTLV-1

“Thank You”