Lesson: Heredity and Evolution
Exchange of genetic material takes place in:
(a) Vegetative Reproduction
(b) Asexual Reproduction
(c) Sexual Reproduction
Two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny. The nature of the cross will be:
(a) Double Fertilisation
(b) Self Pollination
(c) Cross Fertilisation
(d) No Fertilisation
A cross between a tall plant (TT) and short pea plant (tt) resulted in progeny that were all tall plants because:
(a) Tallness is the dominant trait
(b) Shortness is the dominant trait
(c) Tallness is the recessive trait
(d) Height of pea plant is not governed by gene ‘T’ or ‘t’
Which of the following statement is incorrect?
(a) For every hormone there is a gene.
(b) For every protein there is a gene.
(c) For production of every enzyme there is a gene.
(d) For every molecule of fat there is a gene
If a round, green seeded pea plant (RRyy) is crossed with wrinkled, yellow seeded pea plant, (rrYY) the seeds produced in F1 generation are:
(a) Round and yellow
(b) Round and green
(c) Wrinkled and green
(d) Wrinkled and yellow
In human males, all the chromosomes are paired perfectly except one. This/this unpaired chromosome is/ are:
(i) Large chromosome
(ii) Small chromosome
(iii) Y- chromosome
(iv) X- chromosome
(a) (i) and (ii)
(b) (iii) only
(c) (iii) and (iv)
(d) (ii) and (iv)
The maleness of a child is determined by:
(a) The X chromosome in the zygote
(b) The Y chromosome in the zygote
(c) The cytoplasm of germ cell, determines the sex
(d) Sex is determined by chance
A zygote which has an X-chromosome inherited from the father will develop into a:
(c) X- chromosome does not determine the sex of a child
(d) Either boy or girl
Select the incorrect statement:
(a) Frequency of certain genes in a population, change over several generations resulting in evolution.
(b) Reduction in weight of an organism, due to starvation is genetically controlled.
(c) Loss-weight parents can have heavy weight progeny.
(d) 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
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii), (iii) and (iv)
(d) (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 combination of characters. Choose the new combination from the following:
(i) Round, yellow
(ii) Round, green
(iii) Wrinkled, yellow
(iv) Wrinkled, green
(a) (i) and (ii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (i) and (iii)
A basket of vegetables contains carrot, potato, radish and tomato. Which of them represent the correct homologous structures?
(a) Carrot and potato
(b) Carrot and tomato
(c) Radish and carrot
(d) Radish and potato
Select the correct statement:
(a) Tendril of a pea plant and phylloclade of Opuntia are homologous
(b) Tendril of a pea plant and phylloclade of Opuntia are analogous
(c) Wings of birds and limbs of lizards are analogous
(d) Wings of birds and wings of bat are homologous
If the fossil of an organism is found in deeper layers of earth, then we can predict that:
(a) The extinction of organism has occurred recently.
(b) The extinction of organism has occurred thousands of years ago.
(c) The fossil position in the layers of earth is not related to its time of extinction.
(d) Time of extinction cannot be determined.
Which of the following statements is not true with respect to variation?
(a) All variations in a species have equal chance of survival.
(b) Change in genetic composition results in variation.
(c) Selection of variants by environmental factors, forms the basis of evolutionary processes.
(d) Variation is minimum in asexual reproduction.
A trait in an organism is influenced by:
(a) Paternal DNA only
(b) Maternal DNA only
(c) Both maternal and paternal DNA
(d) Neither by paternal nor by maternal DNA
Select the group which shares maximum number of common characters
(a) Two individuals of a species
(b) Two species of a genus
(c) Two genera of a family
(d) Two genera of two families
According to the evolutionary theory, formation of a new species is generally due to:
(a) Sudden creation by nature
(b) Accumulation of variations over several generations
(c) Clones formed during asexual reproduction
(d) Movement of individuals from one habitat to another
From the list given below, select the character that can be acquired, but not inherited:
(a) Colour of eye
(b) Colour of skin
(c) Size of body
(d) Nature of hair
The two versions of a trait (character) that are brought in by the male and female gametes are situated on:
(a) Copies of the same chromosome
(b) Two different chromosomes
(c) Sex chromosomes
(d) 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.
(a) (i) and (ii)
(b) (i) and (iii)
(c) (i) and (iv)
(d) (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:
a) 1: 3
b) 3: 1
c) 1: 1
d) 2: 1
The number of pair (s) of sex chromosomes in the zygote of humans is:
The theory of evolution of species by natural selection, was given by:
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:
(a) Reptiles have evolved from birds.
(b) There is no evolutionary connection between reptiles and birds.
(c) Feathers are homologous structures in both the organisms.
(d) Birds have evolved from reptiles.
How sex of a new-born is determined in humans?
Sex of a new born human is genetically determined i.e., genes inherited from parents decide whether the new born will be a boy or a girl. If a father’s sperm with X chromosome fertilizes the mother’s egg, it results in development of a girl child. Whereas, if a sperm with Y chromosome fertilizes the egg, it results in the development of a male child.
Do genetic combinations of a mother play a significant role in determining the sex of a new born?
No, it does not. Mothers have a pair of X-chromosomes. Sex of a new-born is determined by the 23rd chromosome in the sperm. All children inherit an ‘X’ chromosome from their mothers regardless of whether they are boys or girls. So, the genetic combination of a mother has no role in determining the sex of a new born.
Mention three important features of fossils that help in study of evolution.
Fossils preserved traces of living organisms. The three important features of fossils are given below.
(a) It helps in determining the sequence of appearance of a particular character in a particular group of species.
(b) It helps in establishing evolutionary traits among organisms and their ancestors.
(c) It helps in establishing the time period in which a particular species lived.
Why do all the gametes formed in human females have an X chromosome?
Human females have two X chromosomes called sex chromosomes. During gametogenesis, one X chromosome enters each gamete. Hence all the gametes formed in human female possess an X chromosome.
In human beings, the statistical probability of getting either a male or a female child is 50:50. Give a suitable explanation.
A somatic cell in human male has XY chromosomes. If one gametocyte undergoes meiosis, it produces two sperms. In which one sperm gets X chromosome and another gets Y chromosome. Since the ratio of male gametes containing X chromosome and those containing Y chromosome is 50:50, the statistical probability of male or a female infant is also 50:50.
A smaller population of a species faces greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Limited number of individuals in a species imposes extensive inbreeding, resulting in negligible variations through successive generations. Since the number of individuals is small, the population is always exposed to the dangers of sudden changes in environment. In many such cases, individuals fail to cope up with the environmental changes, therefore they become extinct.
What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?
Homologous structures have a common basic design but perform different functions.
Example: The fore limbs of reptiles, amphibians and mammals have common ancestor, but are variously modified to carry out different activities.
Yes, it is necessary that homologous structures always have a common ancestor.
Does the occurrence diverse animals on Earth, also suggest their diverse ancestry? Discuss this point in light of evolution.
No, diversity of animals on Earth does not suggest their diverse ancestry. Animals have a vast diversity in structures on Earth that is based on certain common characters. We can group these animals into different groups and subgroups. For example, all animals without notochord are grouped under invertebrates.
Given 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
Green seed is the contrasting trait of yellow seed.
Wrinkled seed is the contrasting trait of round seed.
i. Yellow dominant
ii. Round dominant
Why did Mendel choose pea plant for his experiments?
Mendel chose pea plants for the following reasons.
(a) It is easy to grow
(b) It has short life span. This helps in conducting many experiments in a short period.
(c) It has easily distinguishable characteristics.
(d) It has large size flowers.
(e) It undergoes self-pollination.
A woman has only daughters. Analyse the genetic situation and provide a suitable explanation.
Birth of a male or female child depends on the presence of X or Y chromosome in the sperm that fertilizes the egg. Therefore, the father genetically contributes towards the birth of a girl child or a male child.
Does geographical isolation of individuals of a species lead to formation of a new species? Provide a suitable explanation.
Yes, geographical isolation of individuals of a species leads to the formation of a new species. Geographical isolation, initially imposes limitations for sexual reproduction of the separated population, thereby leading to a gradual genetic drift.
Slowly, the separated individuals start reproducing among themselves and generate new variations. Continuous accumulation of those variations for a few generations may ultimately lead to the formation of 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.
Evolution cannot always be equated with progress or better body designs. So, it does not mean that simple body designs are inefficient. When we take complexity of a body design as a criterion for evolution, then human beings are more evolved than bacteria.
On the other hand, if we take the ability to survive in almost all kinds of habitat as a criterion; bacteria, having a simple body design, are still the most evolved organisms found on earth. From this perspective, bacteria appear to be more evolved than human beings.
All 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.
All human beings on this earth have the capability to interbreed. This shows that all of them belong to the same species, and they all show maximum number of common characters. Some of the common characters in human beings are as follows:
· Similar size of the brain
· Same body design
· Bipedal locomotion
· Hair on body
· Ability to communicate using language
· Social behaviour
Similarity in traits indicates common ancestry for all human beings.
Differentiate between inherited and acquired characters. Give one example for each type.
Traits that are passed on from parents to offspring.
Traits that appear in an individual’s lifetime, but cannot be transmitted to the next generation.
Traits alter the genotype and phenotype.
Traits that alter only the phenotype.
Traits are the result of genetic recombination.
Traits that are the result of individual’s response to environmental challenges.
Hair colour, eye colour, skin colour, seed colour, etc.
Muscular body, loss of a body part in an accident, hair loss, etc.
Give reasons why acquired characters are not inherited.
Acquired characters appear in an individual because of his/her response to external stimuli. These characters do not produce any change in the DNA of the germ cells. Only those characters that have a gene for them can be inherited. Since there is no gene for the acquired characters, they cannot be inherited.
Evolution exhibits a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion.
Morphological structures can be easily seen by us. Life began as a simple form of unicellular organisms. Gradually, it evolved into many complex organisms. Whatever diversity we see around us, is because of the diversity in the morphological structure such as size, form and other morphological features. Thus, it can be said that morphological structures show least stability.
On the other hand, molecular structures are found at the molecular level. All the organisms are made up of same biomolecules such as DNA, RNA, protein, lipid, carbohydrates, etc. Even though, the number of biomolecules varies from organism to organism, their structures remain the same in every organism. Hence, it can be said that molecular structures show greater stability when compared to the morphological structures.
In the following crosses write the characteristics of the progeny.
(a) RRYY Round, yellow
(b) RRYY Round, yellow
RrYy Round, yellow
RRyy Round, green
Rryy Round, green
rrYY Wrinkled, yellow
rrYy Wrinkled, yellow
rryy Wrinkled, green
(c) rryy Wrinkled, green
(d) RrYy Round, yellow
Study the following cross showing self-pollination in F1, and fill in the blank and answer the question that follows:
Parents RRYY x rryy
Round, yellow wrinkled, green
F1 RrYy x ?
RrYy Round, yellow
In question 44, what are the combinations of character in the F2 progeny? What are their ratios?
I. Round yellow (RRYY) and (RrYy) 9
II. Round green (RRyy) and (Rryy) 3
III. Wrinkled yellow (rrYY) and (rrYy) 3
IV. Wrinkled green (rryy) 1
This can be shown by the following Punette Square:
The ratio is 9: 3: 3: 1
Give the basic features of the mechanism of inheritance.
Characters are controlled by genes. Each gene controls one character. There may be two or more forms of genes. One form may be dominant over the other. These genes are present in DNA. DNAs; in turn are present in the form of chromosomes. Every trait is present in pairs, i.e. alleles. Out of a pair of contrasting traits, one is present in a particular chromosome and the other in another chromosome. This ensures that, when gametes are formed, one trait goes to one gamete and another goes to the other one. This forms the basis of the law of segregation as proposed by Mendel.
In his monohybrid, cross experiment, Mendel crossed a pure-bred tall plant with a pure-bred short plant. In F1 generation, the gene governing the tallness dominated. So, the all the plants in F1 generation were tall. However, in F2 generation, some plants were tall while others were short. This could be possible because of recombination of gametes during fertilization.
Give reasons for the appearance of new combinations of characters in the F2 progeny.
Appearance of a new combination of characters in F2 progeny can be explained by illustrating dihybrid cross as was carried out by Mendel.
During the dihybrid cross, Mendel crossed the pure bred of tall plants having round seeds with pure bred of short plants having wrinkled seeds. It was observed that all the F1 generation plants were tall with round seeds. This indicated that the traits of tallness and round seeds were dominant. However, genes for recessive traits were present in all the plants.
Later, the self-breeding of F1 generation seeds yielded F2 generation. The F2 generation plants had the characters of tall with round seeds (9 plants), tall with wrinkled seeds (3 plants), short with round seeds (3plants) and short with wrinkled seeds (1 plant). The tall-wrinkled seeds and short-round seeds were the new combination, which developed only when the traits were inherited independently.