Does geographical isolation of individuals of a species lead to formation of a new species? Provide a suitable explanation.
Yes, geographical isolation can lead to the formation of a new species. When a population of a species becomes geographically separated by barriers such as mountains, rivers, oceans or deserts, individuals of the isolated group can no longer interbreed with the original population.
Over time, the separated individuals reproduce among themselves and accumulate genetic variations due to mutation, genetic drift and natural selection. Continuous accumulation of such variations through several generations may ultimately lead to reproductive isolation. Once reproductive isolation is established, the isolated population becomes incapable of interbreeding with the original population and thus forms a new species.
Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria? Provide a suitable explanation.
This is a debatable issue. If increasing complexity of body structure is used as a measure of evolution, then human beings appear to be more evolved than bacteria. However, bacteria are highly successful organisms, having survived on Earth for billions of years.
When we consider the totality of life characteristics such as adaptability, survival ability, reproductive efficiency and ecological success, it becomes difficult to label one organism as more evolved than the other. Bacteria perform essential biological roles and thrive in extreme environments. Hence, despite their simpler body plan, they cannot be considered less evolved. Evolution does not imply superiority, only adaptation to the environment.
All the human races like Africans, Asians, Europeans, Americans and others might have evolved from a common ancestor. Provide a few evidences in support of this view.
Several evidences support the view that all human races evolved from a common ancestor:
• Common body plan: All human races possess a similar structural organisation.
• Similar physiology and metabolism: The basic biochemical processes and metabolic pathways are identical in all humans.
• Constant chromosome number: All humans have 46 chromosomes arranged in the same pattern.
• Common genetic blueprint: DNA structure, gene sequences and hereditary mechanisms are remarkably similar among all races.
• Freely interbreeding populations: Individuals of different races can interbreed freely, producing fertile offspring. This indicates they belong to the same species and share a common ancestry.
Differentiate between inherited and acquired characters. Give one example for each type.
Inherited characters: These are characteristics passed on from parents to offspring through genes. They are present in the DNA of germ cells and can be transmitted to the next generation. Examples include colour of eyes, colour of seeds, blood group, etc.
Acquired characters: These are characteristics that appear in an individual during its lifetime due to environmental influence, habits or experiences. They are not associated with changes in germ cell DNA and cannot be inherited. Examples include an obese body due to overeating, muscle development in athletes, or loss of a finger in an accident.
Give reasons why acquired characters are not inherited.
Acquired characters do not bring about changes in the DNA of germ cells. Only those traits that cause hereditary changes in germ cells can be passed on to the next generation.
Acquired traits such as loss of limbs, change in body size, or development of muscles occur in somatic (body) cells, and these changes are not reflected in reproductive cells. Since they do not alter the genetic material of gametes, they cannot be transmitted to offspring.
Evolution has exhibited a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion.
At the molecular level, living organisms exhibit remarkable similarity despite their vast differences in external morphology. Basic biomolecules such as DNA, RNA, proteins and carbohydrates have highly conserved structures across species.
This suggests that molecular structures change very slowly through evolutionary time, indicating stability. Morphological structures, however, can differ widely due to environmental pressures, natural selection and adaptations that lead to diversification in form and function.
The molecular similarities point to a shared ancestry of all organisms, while morphological changes reflect adaptations for survival. Thus, evolution shows greater stability at the molecular level compared to the morphological level.
In the following crosses write the characteristics of the progeny:
(a) RRYY × RRYY – Round, yellow × Round, yellow
(b) RrYy × RrYy – Round, yellow × Round, yellow
(c) rryy × rryy – wrinkled, green × wrinkled, green
(d) RRYY × rryy – Round, yellow × wrinkled, green
(a) All progeny will be Round, yellow.
(b) Progeny will show a phenotypic ratio of 9 Round yellow : 3 Round green : 3 Wrinkled yellow : 1 Wrinkled green.
(c) All progeny will be wrinkled and green.
(d) All progeny will be Round, yellow.
Study the following cross and showing self-pollination in F1, fill in the blank and answer the question that follows:
Parents: RRYY × rryy
F1: RrYy × ?
The missing genotype is RrYy. The F1 generation will be heterozygous Round, yellow.
In question 44, what are the combinations of characters in the F2 progeny? What are their ratios?
The F2 phenotypic ratio for a dihybrid cross (RrYy × RrYy) is:
(i) Round yellow — 9
(ii) Round green — 3
(iii) Wrinkled yellow — 3
(iv) Wrinkled green — 1
Thus, the ratio is 9 : 3 : 3 : 1.
Give the basic features of the mechanism of inheritance.
The basic features of inheritance are as follows:
(i) Characters are controlled by genes.
(ii) Each gene controls one character.
(iii) A gene may exist in two or more forms called alleles.
(iv) One form of the gene may be dominant over the other.
(v) Genes are located on chromosomes.
(vi) An individual has two alleles for each gene, whether similar or dissimilar.
(vii) The two alleles separate at the time of gamete formation due to segregation.
(viii) The alleles come together during fertilisation in the zygote.
Give reasons for the appearance of new combinations of characters in the F2 progeny.
The appearance of new combinations of characters in the F2 progeny occurs because the tall/short trait and round/wrinkled seed trait are inherited independently. This follows Mendel’s law of independent assortment.
During gamete formation, different pairs of alleles assort independently, leading to new combinations when fertilisation occurs. As a result, offspring in the F2 generation display recombinant traits not seen in the parents.