Exchange of genetic material takes place in
vegetative reproduction
asexual reproduction
sexual reproduction
budding
Two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny. The nature of the cross will be
double fertilisation
self pollination
cross fertilisation
no fertilisation
A cross between a tall plant (TT) and short pea plant (tt) resulted in progeny that were all tall plants because
tallness is the dominant trait
shortness is the dominant trait
tallness is the recessive trait
height of pea plant is not governed by gene T or t
Which of the following statement is incorrect?
For every hormone there is a gene.
For every protein there is a gene.
For production of every enzyme there is a gene.
For every molecule of fat there is a gene
If a round, green seeded pea plant (RR yy) is crossed with wrinkled, yellow seeded pea plant (rr YY) the seeds produced in F₁ generation are
round and yellow
round and green
wrinkled and green
wrinkled and yellow
In human males all the chromosomes are paired perfectly except one. This/these unpaired chromosome is/are
(i) large chromosome
(ii) small chromosome
(iii) Y-chromosome
(iv) X-chromosome
(i) and (ii)
(ii) only
(iii) and (iv)
(ii) and (iv)
The maleness of a child is determined by
the X chromosome in the zygote
the Y chromosome in zygote
the cytoplasm of germ cell which determines the sex
sex is determined by chance
A zygote which has an X-chromosome inherited from the father will develop into a
boy
girl
X-chromosome does not determine the sex of a child
either boy or girl
Select the incorrect statement
Frequency of certain genes in a population change over several generations resulting in evolution
Reduction in weight of the organism due to starvation is genetically controlled
Low weight parents can have heavy weight progeny
Traits which are not inherited over generations do not cause evolution
New species may be formed if
(i) DNA undergoes significant changes in germ cells
(ii) chromosome number changes in the gamete
(iii) there is no change in the genetic material
(iv) mating does not take place
(i) and (ii)
(i) and (iii)
(ii), (iii) and (iv)
(i), (ii) and (iii)
Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds produce F₁ progeny that have round, yellow (RrYy) seeds. When F₁ plants are selfed, the F₂ progeny will have new combinations of characters. Choose the new combination from the following
round, yellow
round, green
wrinkled, yellow
wrinkled, green
A basket of vegetables contains carrot, potato, radish and tomato. Which of them represent the correct homologous structures?
Carrot and potato
Carrot and tomato
Radish and carrot
Radish and potato
Select the correct statement
Tendril of a pea plant and phylloclade of Opuntia are homologous
Tendril of a pea plant and phylloclade of Opuntia are analogous
Wings of birds and limbs of lizards are analogous
Wings of birds and wings of bat are homologous
If the fossil of an organism is found in the deeper layers of earth, then we can predict that
the extinction of organism has occurred recently
the extinction of organism has occurred thousands of years ago
the fossil position in the layers of earth is not related to its time of extinction
time of extinction cannot be determined
Which of the following statements is not true with respect to variation?
All variations in a species have equal chance of survival
Change in genetic composition results in variation
Selection of variants by environmental factors forms the basis of evolutionary processes
Variation is minimum in asexual reproduction
A trait in an organism is influenced by
paternal DNA only
maternal DNA only
both maternal and paternal DNA
neither by paternal nor by maternal DNA
Select the group which shares maximum number of common characters
two individuals of a species
two species of a genus
two genera of a family
two genera of two families
According to the evolutionary theory, formation of a new species is generally due to
sudden creation by nature
accumulation of variations over several generations
clones formed during asexual reproduction
movement of individuals from one habitat to another
From the list given below, select the character which can be acquired but not inherited
colour of eye
colour of skin
size of body
nature of hair
The two versions of a trait (character) which are brought in by the male and female gametes are situated on
copies of the same chromosome
two different chromosomes
sex chromosomes
any chromosome
Select the statements that describe characteristics of genes
(i) genes are specific sequence of bases in a DNA molecule
(ii) a gene does not code for proteins
(iii) in individuals of a given species, a specific gene is located on a particular chromosome
(iv) each chromosome has only one gene
(i) and (ii)
(i) and (iii)
(i) and (iv)
(ii) and (iv)
In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F2 is
1 : 3
3 : 1
1 : 1
2 : 1
The number of pair(s) of sex chromosomes in the zygote of humans is
one
two
three
four
The theory of evolution of species by natural selection was given by
Mendel
Darwin
Morgan
Lamarck
Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution this means that
reptiles have evolved from birds
there is no evolutionary connection between reptiles and birds
feathers are homologous structures in both the organisms
birds have evolved from reptiles
How is the sex of a newborn determined in humans?
The sex of the individual is genetically determined. Genes inherited from parents decide whether the newborn will be a boy or a girl. A newborn who inherits an 'X' chromosome from the father will be a girl, and one who inherits a 'Y' chromosome from the father will be a boy.
Do genetic combination of mothers play a significant role in determining the sex of a newborn?
No. Mothers have a pair of X chromosomes, so all children inherit an 'X' chromosome from their mother regardless of whether they are boys or girls. The sex of the child is determined by the type of sex chromosome contributed by the father (X or Y).
Mention three important features of fossils which help in the study of evolution.
Fossils represent modes of preservation of ancient species.
Fossils help in establishing evolutionary traits among organisms and their ancestors.
Fossils help in establishing the time period in which organisms lived.
Why do all the gametes formed in human females have an X chromosome?
Human females have two X chromosomes (XX). During meiosis at the time of gamete formation, one X chromosome enters each gamete. Hence all the gametes produced by a female contain an X chromosome.
In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.
The sex of an infant is determined by the type of sex chromosome contributed by the male gamete. Male gametes are of two types — those containing an X chromosome and those containing a Y chromosome. Since the ratio of X-bearing to Y-bearing sperm is approximately 1:1, the statistical probability of having a male or female child is 50 : 50.
A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Smaller populations often undergo extensive inbreeding which reduces genetic variation. Limited variation reduces the ability of the population to adapt to environmental changes, putting the species at greater risk of extinction if conditions change.
What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?
Homologous structures are structures that have a common basic plan but perform different functions in different organisms. For example, the forelimbs of reptiles, amphibians and mammals are homologous — they share a common basic structure modified for different activities.
Yes, homologous structures usually indicate a common ancestor from which the structures were modified, though the modifications suit different functions.
Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Although animals show vast diversity, this does not necessarily imply completely diverse ancestry for each group. A common ancestry in all cases may limit the extent of diversity. Many diverse animals inhabit similar habitats and their evolution by geographical isolation and speciation may not be likely in every case. Thus a single common ancestor for all animals is not the most likely theory; diversity can arise from branching evolution and varied selective pressures.
Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive:
(i) yellow seed
(ii) round seed
(i) Yellow — dominant; green — recessive.
(ii) Round — dominant; wrinkled — recessive.
Why did Mendel choose pea plant for his experiments?
Mendel chose the pea plant because it was easy to grow, had a short life span, showed easily distinguishable characters, had sufficiently large flowers for manipulation, and was capable of self-pollination which allowed controlled crosses.
A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
(a) The woman produces ova that carry only the X chromosome.
(b) The man produces sperms carrying either X or Y chromosomes; it is the chromosome contributed by the sperm that actually determines the sex of the baby. If, in a series of children, the fertilizing sperms happened to carry X chromosomes each time, all children will be daughters.
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.