GENETICS. Dr. Kaustubh

GENETICS

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

Disorders Traits

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

Gene Sequence of nucleotides Genetic code ‘Translation’ Amino acids Proteins

FUNCTIONS OF GENES

• Determination of Phenotype • Processes in functioning

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

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

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

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.

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,

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

WHY PEA PLANT?

Easy availability

Many varieties

Distinct characteristics

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 LAWS

1.

Law of Dominance

(dominant, recessive, ratio

of 3:1 in F

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.

STRUCTURE OF DNA

• It is a right-handed double helical structure, with alternating sugar

and phosphate groups.

• The two strands are complementary.

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}

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,

RIBOSE NUCLEIC ACID

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

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

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.