BIOLOGY M.C.Q (1 Marks)

Experimental Evidences of Chemical Evolution

Experi ik mentally chemical theory of evolution performed by SL Miller and HC Uray in $1953 .$

He created electric discharge in a closed flask containing $CH _{4}, H _{2}, N H _{3}$ and water vapour at $800\, C .$ He observed formation of amino acids. In similar experiments other the observed, formation of sugar, nitrogen bases, pigments and fats

The first non-cellular forms of life could have originated-$3$ billion years back. The first cellular form of life did not possibly originated till about $2$ billion years ago because the conditions were non-biogenic at that time. This version of biogenesis, $i.e.,$ the first form of life arose slowly through evolutionary forces from non-living molecule was accepted by majority

$(i)$ No Mutation Sudden appearance of variations are called mutations. There should not be either gene or chromosomal mutation. Mutation causes changes in gene frequency

$(ii)$ No Gene flow (Gene Migration) Within the gene pool of a given breeding population there is a continuous interchange of alleles between organisms. Gene flow refers to the movement of alleles from one population to another as a result of interbreeding between the members of two population. There must not be gene flow between the population

$(iii)$ No Genetic Drift Genetic drift is also known as 'Sewall Wright Effect' (named after its discoverer). It is random in gene (allele) frequency. It occurs only by chance. It is non directional. Genetic drift can cause elimination of certain alleles or fixation of the other alleles in the population. Genetic drift refers to a change in the population of alleles in the gene pool. So genetic drift must not occur

$(iv)$ No Genetic Recombination The alleles of the parental linkage groups separates and new associations of alleles are formed in the gamate cells, this process is known as genetic recombination. Thus, crossing over during meiosis is a major source of genetic variation within population.

Offspring formed from these gametes showing 'new' combination of the characteristics are called recombinants. There is no genetic recombination

$(v)$ No Natural Selection Pressure There must be no natural selection pressure with respect to the alleles in question.

According to Hardy-Weinberg Principle, gene frequencies will remain constant if all above five conditions are met

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$(i)$ Stabilizing Selection (Balancing selections) This type of selection favours average sized individuals, while eliminates small sized individuals. It reduces variation and hence, do not promote evolutionary changes. It maintains the mean value from generation to generation. If we draw a graphical curve of population, it is bell-shaped

$(ii)$ Directional Selection (Progressive Selection) In this selection, the population changes towards one particular direction. It means this type of selection favours small or large-sized individuals and more individuals of that type will be present in new generation. The mean size of the population changes

$(iii)$ Disruptive Selection (Diversifying selection) This type of selection favours both small-sized and large-sized individuals. It eliminates most of the members with mean expression, so as to produce two peaks in the distribution of the trait that may lead to the development of two different populations. This kind of selection is opposite of stabilizing selection and is rare nature but is very important in bringing about evolutionary changes

$p^{2}+2 p q+q^{2}=1$

Here, $p=A$ and $q$ is $=B$

Allele frequency of $B=1-0.4=0.6$

Allele frequency of heterozygous is $=2 \times 0.6 \times 0.4$

$\therefore 0.48$