Heredity and Environment, Biology tutorial


The phenotypic reaction or response of gene action is an outcome of the coordinated effect of the whole set of gene or a single gene which might influence numerous characteristics, each expressed characteristic might be affected by numerous genes. Each and every gene perhaps governs one fundamental reaction; however the characteristics are stated as the phenotype outcome from many such reactions. Thus to state that each and every feature of an organism is governed by one gene is wrong. In certain cases we are fortunate adequate to determine that one gene consists of an obvious effect on the mature organism and therefore is studied readily. This is not, though, the condition that for all time exists.

The genes of an organism find out its potentialities; however the realization of such potentialities based on the environment in which the genes carry out their function. The genotype might state itself differently in various environments giving rise to transformation of the phenotype. The genetic material gives the messages and directions for phenotypic development; however growth as well based on different environmental factors (example: temperature, light, moisture and supply of minerals). For illustration, with most plants, when the seed are germinated in the dark, chlorophyll will not be build up in the seedling. When such seedlings are exposed to light before they die, chlorophyll grows rapidly. The genes for chlorophyll production are present, however light is as well necessary for such manifesting. As well when magnesium is deficient in the soil, chlorophyll formation will not take place as the chlorophyll molecule consists, as one of its component pans, an atom of magnesium the potentiality for the formation of chlorophyll is present in the genes, however necessary atom is missing and the molecule can't be synthesized.

The time of flowering in most of the plants is affected by the duration of light and in others by temperature. Water supply is the other factor which significantly affects plant growth, harsh stunting being a simply recognizable effect of water scarcity. It is significant to comprehend that it is the genotype which is inherited and that the atmosphere affects the manner in which this genotype is stated as the phenotype.

Probability in Genetics:

Probability is a stream of mathematics that can be applied to such events which completely depends on chance.


Probability = No of times an event takes place/Total number of trials

Probability is as a rule stated in units ranging from 0 to 1. Mendel's works are mainly based on probability. Two principles are essential to comprehend the significance of probability in genetics. These are:

a) The outcome of one trial of a chanced event does not influence the outcome of later trials of the similar event.

b) The chance which two independent events will take place altogether concurrently is the product of their chances of occurring one by one.

Application of Probability to the Formation of Gametes:

Assume that a plant consists of the genotype Aa, what type of gamete will it generate and in what ratio? As only one of pair of chromosomes got segregated at the time of meiosis, the probable gamete generated from AA parent plant is 1/2 A and 1/2 A. When the parent plant is heterozygous (A) (a), the probable gamete will be 1/2 A x 1/2 a.

Application of Probability to the Formation of Offspring in Plants:

a) When a plant consists of genotype Aa, the probability of forming a gamete having gene A is 1/2 or 50% and that of forming a gamete having gene a is as well 1/2 or 50%.

b) When a plant consists of genotype aa, the probability of developing a gamete having gene a is 1.

c) When a plant of genotype Aa is crossed with the other plant of genotype aa, then the probability of generating different genotypes in offspring are probability of Aa = probability of A x probability of a = 1/2 x 1 = 1/2

Application of Probability to the Formation of Offspring in Humans:

Assume that a male carrier of albino gene get married a female albino, what type of albino will be estimated? The male is heterozygous (Aa) and the female is homozygous recessive (aa). As the male is heterozygous, the probability that 1/2   of the gamete will obtain (A) or (a) gene is 1/2   whereas that of the female is 1/1.

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