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Friday, October 2, 2009

Colour Blind Woman (Short Note)

Friday, October 2, 2009 - 0 Comments

Persons suffering from colour blindness have difficulty in distinguishing red from green. It is common trait and more common in males than females. It is because Y chromosome is inert for this trait in males. Only one gene of this trait will render a colour blind man. In case of woman it must have two genes for this trait to become colour blind. There are rare cases of colour blindness in women.

This trait of colour blindness can easily be detected by using special charts made up of a number of coloured dots so arranged that colour blind persons see different pattern than other persons do.

Polygenic Inheritance (Short Note)

The traits that are controlled by two or more than two separate pairs of genes, which manifest themselves in an additive fashion to yield continuously varying traits. This is known as Polygenic inheritance. The simplest polygenic situation occurs when there are at least two gene pairs that affect the same trait in additive fashion. In certain type of what with coloured kernels for example, there are two genes pairs for the kernel colour, each with alleles A and a. to distinguish two pairs subscripts 1 and 2 are used for each gene allele. Thus the dominant alleles are written as A1 and A2 while the recessive as a1 and a2. with all the dominant alleles A1A1, A2A2 four doses of pigments are produced,
thus the colour of kernel will be deep dark red. With all the recessive alleles a1a1, a2a2, no pigment is produced and colour remain white. The intermediate number of dominant alleles yields intermediate intensities of red colour.

Albinism (Short Note)

Albinism is complete or partial absence of pigments from skin, hair and eyes in many species of Mammals including man. It behaves as simple Mendelian trait an albinism is recessive to normal pigmented individuals (non albinos). Albino individuals are found in almost all human races but the trait occurs with rarity for example in English population one about 20,000 babies born in an albino. In albino the skin colour is pale reddish white, the iris is reddish and hair is pale straw colour. The reddish tinge depends upon the colour of blood which shows through the superficial layer of skin. This tinge is hidden by dark pigment present in the skin layer in case of non albinos. Albinos are sensitive to bright light and their skin is easily sun burned.

Genetic Code (Short Note)

The word code is used several times to refer to the information stored in DNA and ultimately translated into amino acid sequence of Proteins.

The genetic code is conceptually similar to Morse code. One set of symbols (bases in nucleic acids, dots and dashes in Morse Code) can be translated into another set of symbols (amino acids in Proteins).

Genetic code was three bases to specify each amino acid. There are four different bases in DNA: adenine (A), Cytosine (C), guanine (G) and thymine T. there are also four bases in RNA: adenine, cytosine, guanine and uracil (u). But there are 20 different amino acids in Proteins, so the bases cannot serve as one to one code for amino acid.

Genetic code might use short sequence of bases to encode each amino acid, just as Morse Code uses a short sequence of dots and dashes to encode the letters of alphabet.

If a sequence of two bases codes for an amino acid, then there will be 16 (4 × 4) possible combination of bases.

Gene Mutation (Short Note)

A change in the genetic message of a cell is referred to as mutation. Mutational changes that affect the message itself, producing alternations in the sequence are called point mutations, since they usually involve only one or a few nucleotide. In both bacteria and eukaryote individual genes may move form one place on the chromosome to another by a process called transposition. When a particular gene moves to different location, there is often alternation in its expression or in that of the neighbouring genes. In eukaryote large segments of chromosomes may change their relative location or undergo duplication. Such chromosomal rearrangement often has drastic effects on the expression of the genetic message.

Sex Linked Inheritance (Short Note)

A form of inheritance in which the transmission of the genetic material is correlated with the sex of the parents is called sex linked inheritance, or may genetic trait which is transmitted through sex chromosomes is called sex linked inheritance e.g. : Drosophila melanogaster, a common fruit fly. T. H. Morgan in 1910 performed various breeding experiments with wild type red eyed drosophila flies. He noticed white eyes mutant. This was male and turned out to be true breeding strain of white eyes flies. He crossed this white eyed male with true red eyes female.
F1 and F2 population followed the simple Mendelian ratio. When white eyed female was crossed with red eyed male, the results were not similar. When red eyed female XX is crossed with white eyes male XY, F1 shows all red flies, females as well as male. F2 shows red eyed and white eyed flies in ration 3:1 (all female are red but 1\2 male red and 1\2 male white eyed). Again female flies were two types one producing only red type offspring and another producing half red eyed and other half white eyed offsprings.

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