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If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
In asexual reproduction, the resulting offspring are identical to the parents (have a near exact copy of their parents DNA). However, sometimes this copying of DNA is not accurate, so the newly formed DNA has some variations giving rise to a new trait. This trait is then inherited by future generations and successive generations keep accumulating variations. Therefore, if a trait A exists in 10% of the population and a trait B exists in 60% of the same population, we can conclude that traint B has arisen earlier because the trait has been replicating and existing in a higher percentage of the population.
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How does the creation of variations in a species promote survival?
Species are adapted to survive in a particular habitat. Drastic changes in the environment can disturb the habitat and prove fatal for certain species. For example, there are many microorganisms that inhabit freshwater ponds. If there is a sudden increase in the temperature of water, it will kill the bacteria living in it. However, some species of bacteria that are resistant to heat shall survive in the heat. These species will survive and reproduce in the changed environment. If there were no heat-resistant variants, the entire species of bacteria would be extinct. Thus, creation of variations in a species promotes its survival.
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Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not
Geographical isolation prevents transfer of genes between two species. In self-pollinating plant, pollen is transferred from the anther of one flower to the stigma of the same flower or of another flower of the same plant. It does not require any external agent for pollination, neither is it dependant on another plant for pollination. So, geographical isolation cannot affect the speciation of a self-pollinating plant.
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In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
In evolutionary terms, we cannot say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design. Evolutionary process takes into account the development of most efficient and suitable features in a body design for survival and adaptation favoring a particular niche. For example, organisms with a complex body design may not survive in particular situation whereas, bacteria with the simplest body design is able to survive in extreme habitats. Evolution only leads to development of complex body designs and cannot be equated with progress.
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A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as (a) TTWW (b) TTww (c) TtWW (d) TtWw
(c) There are two flower colours violet and white but F1 showed only violet flowers. This means violet flower colour (V) is the dominant trait that masks the recessive trait (v) (white flower colour). The F1 had half tall and half short plants. This indicates both dominant and recessive traits expressed in the F1 progeny. So, we can infer that the tall plants were not true breeding and must be genetically heterozygous for the character height (Tt). So, the genetic make-up of the tall parent can be depicted as TtVV. Therefore, the cross involved in the given question. Therefore, half the progeny is tall, but all of them have violet flowers.
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An example of homologous organs is (a) our arm and a dog’s fore-leg. (b) our teeth and an elephant’s tusks. (c) potato and runners of grass. (d) all of the above.
(d) All of the Above. As in all cases the basic internal structure and origin of the organs are the same though they differ functionally. For example, elephant's tusk is a modified incisor. So, origin is the same but the function is different. Tubers of potato and grass runners are both stem modifications but functions are different, hence these are homologous organs.
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In evolutionary terms, we have more in common with (a) a Chinese school-boy. (b) a chimpanzee. (c) a spider. (d) A bacterium
(a) In evolutionary terms, we have more in common with a Chinese school boy. Because both belong to the same species Homo sapiens. Chimpanzees and humans both have a common ancestor but are two different species.
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A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Children with light-coloured eyes can either have LL or Ll or ll genotypes. Let us assume that the children have LL (both dominant alleles) genotype. This is possible only when both parents are also of the LL genotype. If the children with light-coloured eyes have ll genotype, then their parents will also have ll genotype. Therefore, it cannot be concluded whether light eye colour is dominant or recessive.
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Explain the terms analogous and homologous organs with examples.
Homologous organs are similar in origin (or are embryologically similar) but perform different functions. Forelimbs of frog, lizard, pigeon, bats, whales, horses and humans have the same basic structural plan but different functions. For example, the wings help in flight whereas human forearm helps in various activities. Homologous organs The organs which have similar functions but are different in their structural details and origin are called analogous organs. For example, the wings of a bird and a bat are similar in function, but this similarity does not mean that these animals are more closely related. The basic structure of the wings of insects is different from that of a bird and a bat but similar in function. Also, on careful observation we will find that the wings of a bat are just the folds of skin that are stretched between its fingers whereas the wings of birds are present all along the arm. Similarly, fins of fishes and flippers of whales are also examples of analogous organs. Therefore, these organs are analogous organs.
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Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
In sexual reproduction, two parents are involved. Both parents contribute their genes to the offspring. The child obtains half number of chromosomes from the father and half from the mother i.e. he inherits one copy of genes from father and another copy from the mother. So, two individuals having different variations combine their DNA to give rise to a new individual. Therefore, sexual reproduction leads to variations. In asexual reproduction, chance variations can only occur when the copying of DNA is not accurate. Also, during asexual reproduction, the offspring inherits the entire cellular apparatus from the parent. If there are major variations then the resultant DNA will not be able to survive inside the inherited cellular apparatus. However, in sexual reproduction, more variations are allowed and the resultant DNA is also able to survive, thus making the variations viable. Sexual reproduction helps the organism to adapt better to the environment. Variations help the species to survive in all the conditions. Environmental conditions such as a disease, pests, and food availability can change suddenly affect a place. In this situation, only those variants resistant to these conditions would be able to survive. This will slowly lead to the evolution of a better adapted species. Thus, variation helps in the evolution of sexually reproducing organisms. However, in case of a sudden change in the environment of asexually reproducing species can cause their extinction.
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