Life Science

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Louis Pasteur:

principles of vaccination

microbial fermentation

pasteurization

Germ Theory of Diseases

August Weismann:

Germ Plasm Theory:

Inheritance only takes place by means of the germ cells—the gametes such as egg cells and sperm cells.

Other cells of the body—somatic cells—do not function as agents of heredity.

VAPOUR AND FLUID THEORIES: (PYTHAGORAS)

Every organ of animal body gives out some type of vapours . These vapours unite and form a new individual.

Preformation Theory: (Marcello Malphigi)

organisms develop from miniature versions of themselves.

INHERITANCE OF ACQUIRED CHARACTERS: (LAMARCK)

physiological changes acquired over the life of an organism may be transmitted to offspring.

Theory of Pangenesis: (CHARLES DARWIN)

each part of the animal body produces many minute particles known as gemmules ,which are first collected in the blood and then concentrated in the reproductive organs. When the animal reproduces into new individual ,these gemmules pass on to it and it has blending of both parents.

Blending Inheritance:

Individuals inherit a smooth blend of traits from their parents.

Limitations:

the potential for variation would tend to narrow, quite dramatically, with each generation

It failed to explain how traits that seemingly disappeared for several generations often reasserted themselves down the line, unaltered.

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Genetics: Genetics is a discipline of biology, that deals with science of genes, heredity, and variation in living organisms.

It deals with the following aspect of genes

Molecular structure & function

Behavior (Dominant or recessive)

Pattern of Inheritance

Variation in the population

Genotype + Environment ---- Phenotype

e.g.-- Arctic Fox, Hydrangea plant

Industrial Melanism:

(The occurrence of an increased amount of dark pigmentation (melanin) (skin, feathers, eyes or hair) in an organism)

e.g.-- Moth Evolution

DNA finger printing:

On some human chromosomes, a short sequence of DNA has been repeated a number of times like (GATA)n or (CACATTA)n

Exploits the difference in the number of tandem repeats between individuals.

Locus – location of a gene/marker on the chromosome.

Allele –variants of a gene/marker at a particular locus.

Wild type- For a given pair of alternate trait that is more frequent in a population (+/+)

Mutant- Alternate form of trait rare in natural population.

i) Dominant Allele: Upper case letter (A)

ii) Recessive Allele: Lower case letter (a)

Genome – the collection of genetic information.

Chromosomes – storage units of genes.

Gene – basic unit of genetic information. Genes determine the inherited characters.

DNA - is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life

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ABO system:

ABO gene encodes an enzyme glycosyl transferase.

Modifies the oligosaccharide on cell surface glycoprotein

A allele adds N-acetyl galactosamine

B allele adds galactose

o allele is deletion which lacks the glycosyl transferase activity.

Differences between Gene & Allele:

Genes are something we inherit from our parents. While Alleles determine how they are expressed in an individual.

Alleles occur in pairs but there is no such pairing for genes.

Alleles determine the traits we inherit.

The genes we inherit are the same for all humans. However, how these manifest themselves is actually determined by alleles.

At each locus (except for sex chromosomes) there are 2 alleles of a gene. These constitute the individual’s genotype at the locus (like Aa or Tt).

Law of Segregation states that when any individual produces gametes, the alleles separate, so that each gamete receives only one allele. A gamete will receive one allele or the other.

Back Cross: crossing of a hybrid with one of its parents or an individual genetically similar to its parent, in order to achieve offspring with a genetic identity which is closer to that of the parent.

Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele.

This is because the semidominant allele produces the gene product in a lesser amount.

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Codominance – Both the alleles of a pair are fully expressed in a heterozygote. Heterozygotes are phenotypically distinct from homozygotes.

HETEROZYGOUS- having two different alleles for a given trait (the allele inherited from the mother is different from the allele inherited from the father). Like Aa.

HOMOZYGOUS- having identical alleles for a trait (the allele inherited from the mother is identical to the allele inherited from the father). Like AA, aa.

A monohybrid cross is one where only one trait is crossed.

e.g. A tall pea plant TT is crosses with a short pea plant tt.

A dihybrid cross is one where two traits are crossed.

e.g. a tall, purple flowered plant TtGg is crossed with a short, white flowered plant ttgg.

The Law of Independent Assortment:

also known as "Inheritance Law", states that alleles of different genes assort independently of one another during gamete formation.

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The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment.

Epistasis is phenomenon where the effect of one gene (hypostatic) is modified by other gene (epistatic).

It is interaction between different genes (non alleles) While, dominance is interaction between different alleles of the same gene

Complementary gene action:

A gene or genotype at one locus may produce a phenotype virtually identical to gene or genotype in another locus.

Recessive Epistasis:

In rodents, coat colour is determined by a pair of alleles at different genetic loci.

At one locus, the dominant allele C allows pigment formation ie. development of colour; the recessive allele c when homozygous prevents pigment formation regardless of the genotype of other coat colour genes. Black mice are C/- ; albinos are c/c.

At the other locus, the dominant allele A determines agouti pattern (ie. yellow

Banding of hairs) and the recessive allele a when homozygous produces non agouti

mice. Thus, A/- mice are agouti; a/a mice are non agouti.

Pleiotropy:

A gene that affects more than one trait.

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Amorphic allele: A mutation that causes complete loss of gene function. Amorph is sometimes used interchangeably with "genetic null".

Hypomorph allele : A mutation that causes a partial loss of gene function

Hypermorph allele: A mutation that causes an increase in normal gene function. Hypermorphic alleles are dominant gain of function alleles.

Antimorph allele: A dominant mutation that acts in opposition to normal gene activity.

Antimorphs: are also called dominant negative mutations

Neomorphic allele: A mutation that causes dominant gain of gene function that is different from the normal function

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A pedigree is a diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships.

Pedigrees are often used to determine the mode of inheritance (dominant, recessive, etc.) of genetic diseases.

The Law of Independent Assortment states that alleles of different genes assort independently of one another during gamete formation. (F2 ratio- 9:3:3:1)

However, in early 1900, Bateson and Punnet, were studying the inheritance pattern of 2 genes in sweet potatoes found that certain combination of alleles showed more often than expected , as though 2 genes were physically attached.

When two genes are close together on the same chromosome that don’t assort independently but produce a recombinant frequency of less than 50% are said to be linked.

Crossing over: Physical exchange of chromosomal segments of homologous chromosomes during meiosis.

Mapping: Identification of the locus of gene in a chromosome.

1 genetic map unit (m.u) = recombinant frequency of 1%

Recombinant frequency NOT additive FOR DISTANCE LARGER THAN 15mu -20mu

If the distance is large, double cross can reduce the recombination frequency.