Question

The factor that leads to Founder effect in a population is [NEET 2021]

(a) natural selection

(b) genetic recombination

(c) mutation

(d) genetic drift

Answer/Explanation

Ans. (d)

The factor that leads to Founder effect. in a population is genetic drift. It is the change in the frequency of an existing gene variant (allele) in a population due to random sampling of organisms. Genetic drift can cause big losses of genetic variation for small population. The Founder effect is when a few individuals in a population colonize a new location that is separated from the old population. This also greatly reduces the population size, as well as reduces the genetic variability of the population.
Other options can be explained as Natural selection is the process through which populations of living organisms adapt and change.
Genetic recombination, in genetics, primary mechanism through which variation is introduced into populations. Mutation is sudden heritable change.

Question

 A population of a species invades a new area. Which of the following conditions will lead to adaptive radiation? [NEET (Odisha) 2019]

(a) Area with large number of habitats having very low food supply

(b) Area with a single type of vacant habitat

(c) Area with many types of vacant habitats

(d) Area with many habitats occupied by a large number of species

Answer/Explanation

Ans. (c)

Option (c) is correct.

The adaptive radiation occurs when a population of a species invades a new area. It is because it provides organisms of a population a new habitat with plenty of niche spaces. Darwiris finches represent one of the best examples of this phenomenon.

Question

 Which of the following represents order of “Horse”? [NEET 2017]

(a) Equidae

(b) Perissodactyla

(c) Caballus

(d) Ferus

Answer/Explanation

Ans. (b)

Order being the higher taxon of classification exhibit the few similar characters of families. The order of horse is perissodactyla.

Concept Enhancer The order perissodactyla includes odd toed mammals. For example, Equus asinus (donkey), Rhinoceros indicus(the great one horned rhinoceros).

Question

 In Hardy-Weinberg equation, the frequency of heterozygous individual is represented by [NEET 2016, Phase II]

(a) $p^2$

(b) $2 p q$

(c) $p q$

(d) $q^2$

Answer/Explanation

Ans. (b)

Hardy-Weinberg principle states that the allele frequencies in a population are stable and remain constant from generation to generation. This can be expressed by the equation:
or $\begin{aligned} p^2+2 p q+q^2 & =1 \\ (p+q)^2 & =1\end{aligned}$
where, $p^2$ represents frequency of homozygous dominant genotype, $2 p q$ represents the frequency of heterozygous genotype and $q^2$ represents the frequency of homazygous recessive genotype. Hence, option (b) is correct.

Question

 The tendency of population to remain in genetic equilibrium may be disturbed by [NEET 2013]

(a) random mating

(b) lack of migration

(c) lack of mutations

(d) lack of random mating

Answer/Explanation

Ans. (d)

According to Hardy-Weinberg principle, allele frequencies in a population are stable and is constant from generation to generation only if the following conditions are met.
(i) There is no mutation, no gene flow and all mating is random.
(ii) All genotypes reproduce equally well (i.e., no natural selection). But all there conditions are rarely met in nature.

Question

According to Darwin, the organic evolution is due to [NEET 2013]

(a) intraspecific competition

(b) interspecific competition

(c) competition within closely related species

(d) reduced feeding efficiency in one species due to the presence of interfering species

Answer/Explanation

Ans. (b)
Darwin stated that the organic evolution is due to the interspecific competition. It is the competition between members of different species. Intraspecific competition occurs amongst members of the same species for obtaining optimum amounts of their food, shelter, mate, water, light, etc. Closely related species if compete cannot cause evolution. Reduced feeding efficiency in one species due to the presence of interfering species is due to the struggle for existence.

Question

 Adaptive radiation refers to [CBSE AIPMT 2007]

(a) adaptations due to geographical isolation

(b) evolution of different species froma common ancestor

(c) migration of members of a species to different geographical areas

(d) power of adaptation in an individual to a variety of environments

Answer/Explanation

Ans. (b)

Adaptive radiation is the development of different functional structures from a common ancestral form.

Question

 Industrial melanism as observed in peppered moth proves that [CBSE AIPMT 2007]

(a) the true black melanic forms arise by a recurring random mutation

(b) the melanic form of the moth has no selective advantage over lighter form. in industrial area

(c) the lighter form moth has no selective advantage either in polluted industrial area or non-polluted area

(d) melanism is a pollution generated feature

Answer/Explanation

Ans. (a)

Industrial melanism is a term used to describe the evolutionary process in which darker individuals come to predominate over lighter individuals since the industrial revolution as a result of natural selection. In 1848 a black form of the moth was recorded in Manchester and by $1895,98 \%$ of the peppered moth population in Manchester was black. This black ‘melanic’ form arose by a recurring random mutation, but its phenotypic appearance had a strong selective advantage in industrial areas.

Question

One of the important consequences of geographical isolation is [CBSE AIPMT 2007]

(a) no change in the isolated fauna

(b) preventing speciation

(c) speciation through reproductive isolation

(d) random creation of new species

Answer/Explanation

Ans. (c)

Speciation is the formation of new species and the development of species diversity occurs when gene flow within the common pool is interrupted by an isolating mechanism. The isolation can
occur through geographical separation of population, known as allopatric speciation

Question

 Which one of the following is not a living fossil? [CBSE AIPMT 2006]

(a) King crab

(b) Sphenodon

(c) Archaeopteryx

(d) Peripatus

Answer/Explanation

Ans. (c)

Archaeopteryx lithographica is not a living fossil. It is a fossil bird that lived in Jurassis period about 180 million years ago. Its fossil displays the characters of both reptiles (e.g. long tail, bones non pneumatic, claw, presence of weak sternum, free caudal vertebra, etc) and birds (e.g. presence of feathers, modified jaws, etc).

Question

 Jurassic period of the Mesozoic era is characterised by [CBSE AIPMT 2006]

(a) radiation of reptiles and origin of mammal-like reptiles

(b) dinosaurs become extinct and angiosperms appear

(c) flowering plants and first dinosaurs appear

(d) gymnosperms are dominant plants and first birds appear

Answer/Explanation

Ans. (d)

Jurassic period is the second geological period of Mesozoic era. In this period, the gymnosperms were dominant and the plants included ferns, cycads, Ginkgo, bushes and conifers. Among animals, important invertebrates included ammonites, corals, brachiopods, bivalves and echinoids. Reptiles dominated the vertebrates and the first flying reptiles the pterosaurs appeared.
The first primitive bird, Archaeopteryx, also made its appearance.

Question

 Industrial melanism is an example of [CBSE AIPMT 2003]

(a) defensive adaptation of skin against. ultraviolet radiations

(b) drug resistance

(c) darkening of skin due to smoke from industries

(d) protective resemblance with the surroundings

Answer/Explanation

Ans. (c)
Industrial melanism is an example of directional selection. Changing environment leading to changes in the phenotypic/genotypic constitution of a population.

Question

 In which condition the gene ratio remains constant for any species? [CBSE AIPMT 2002]

(a) Sexual selection

(b) Random mating

(c) Mutation

(d) Gene flow

Answer/Explanation

Ans. (b)

According to Hardy-Weinberg theorem, the mixing of alleles at meiosis and their subsequent recombination will not alter the frequencies of alleles in the future generations provided the mating within the population is random.

Question

 In which era reptiles were dominant? [CBSE AIPMT 2002]

(a) Coenozoic era

(b) Mesozoic era

(c) Palaeozoic era

(d) Archaeozoic era

Answer/Explanation

Ans. (b)

Mesozoic era began about $24.8$ crore year ago and lasted for about $18.3$ crore year. It is also known as the ‘Age of reptiles’. Main events in of this era are as follows:
(i) Gymnosperms dominate landscape, first dinosaurs and mammals.
(ii) Gymnosperms continue as dominant plants, dinosaures dominant, first birds.
(iii) Flowering plants (angiosperms) appear, dinosaurs and many groups of organisms become extinct at end of period.

Question

 Occurrence of endemic species in South-America and Australia is due to [CBSE AIPMT 2001]

(a) these species have been extinct from other regions

(b) continental separation

(c) there is no terrestrial route to these places

(d) retrogressive evolution

Answer/Explanation

Ans. (b)

Seas separating the continents form barriers to free intercontinental movement causing evolution of organisms independently in these continents leading to endemism. Endemic species are those species which are found in a rest ricted area of the world.

Question

Genetic drift operates only in [CBSE AIPMT 1998]

(a) smaller populations

(b) larger populations

(c) Mendelian populations

(d) island populations

Answer/Explanation

Ans. (a)

Genetic drift may be of significance in small populations only, where alleles may easily get extinct by chance alone.

Question

In general, in the developmental history of a mammalian heart, it is observed that it passes through a two-chambered fish-like heart, three-chambered frog-like heart and finally to four-chambered stage. To which hypothesis can this above cited statement be approximated? [CBSE AIPMT 1998]

(a) Hardy-Weinberg law

(b) Lamarck’s principle

(c)Biogenetic law

(d) Mendelian

Answer/Explanation

Ans. (c)

Biogenetic law was propounded by Ernst Haeckel in 1866. According to this, during its development an animal passes through ancestral adult stages.

Question

Golden age of dinosaurs’/Age of reptiles was [CBSE AIPMT 1994]

(a) Mesozoic

(b) Coenozoic

(c) Palaeozoic

(d) Psychozoic

Answer/Explanation

Ans. (a)

Mesozoic era is the age of reptiles. During this era, the dinosaurs achieved an enormous size and were most abundant, Mesozoic era is also known as golden age of dinosaurs.

Question

 The earliest fossil form in the phylogeny of horse is [CBSE AIPMT 1994]

(a) Merychippus

(b) Mesohippus

(c) Eohippus

(d) Equus principles

Answer/Explanation

Ans. (c)

Hooted animals like-horse originated in Ecoene epoch in North America. First horse-like animals from which the modern horse Equus evolved was Hyracotherium(old) name Eohippus). The fossil record is most complete in horse.

Question

 Two geographical regions separated by high mountains are [CBSE AIPMT 1994]

(a)Oriental and Australian

(b) Palaearctic and Oriental

(c) Nearctic and Palaearctic

(d) Neotropical and Ethiopian

Answer/Explanation

Ans. (b)
Dr. PL Scalater (1858) proposed first time the division of the world into six realms or biogeographic regions according to the distribution of birds. In $1876 \mathrm{AR}$ Wallace, adopted it for all the animals, these regions include i.e. Palaearctic, Ethiopian, Oriental, Australian, Nearctic and Neotropical. Palaearctic and Oriental realms are separated by high mountain ranges, i.e. Himalayas.

Question

 Genetic drift is change of [CBSE AIPMT 1993]

(a) gene frequency in same generation

(b) appearance of recessive genes

(c) gene frequency from one generation to next

(d) None of the above

Answer/Explanation

Ans. (c)

Genetic drift is defined as any random change, either directed or undirected in gene frequency in a population.

Question

 Correct order is [CBSE AIPMT 1991]

(a) Palaeozoic $\rightarrow$ Archaeozoic $\rightarrow$ Coenozoic

(b) Archaeozoic $\rightarrow$ Palaeozoic $\rightarrow$ Proterozoic

(c) Palaeozoic $\rightarrow$ Mesozoic $\rightarrow$ Coenozoic

(d) Mesozoic $\rightarrow$ Archaeozoic $\rightarrow$ Proterozoic

Answer/Explanation

Ans. (c)

Era is a division of geological time that includes one or more periods. It follows the order-Palaeozoic, Mesozoic and Coenozoic. Palaeozoic and Mesozoic eras are sub-divided into periods but Coenozoic is divided into periods and epochs. Mesozoic era is the Age of reptiles, and Coenozoic era is called as ‘Age of mammals and birds.

Question

 Parallelism is [CBSE AIPMT 1990]

(a) adaptive divergence

(b) adaptive divergence of widely separated species

(c) adaptive convergence of widely different species

(d)adaptive convergence of closely related groups

Answer/Explanation

Ans. (d)

When convergent evolution is found in closely related species, it is called ‘Parallel evolution’ (or parallelism), e.g. development of running habit in deer [2 toed)and horse ( 1 toed) with two vestigial splint bones.

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