Heredity and Evolution
Multiple Choice Questions
- Mendel did his experiments on which plant ?
- The chromosome responsible for sex determination in a male is
- A trait in an offspring is influenced by
(a) DNA of mother gamete
(b) DNA of father gamete
(c) both DNAs of father and mother
(d) neither of mother or father gamete DNA.
- Gamete cells are
(c) Either diploid or haploid
(d) None of these.
- Human baby will be a female if its 23rd chromosome pair is
- A Mendelian experiment consisted of breeding tall pea plants bearing vinder 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 dipicted as
- The number of chromosomes found in human beings is
(a) 23 pairs
(b) 24 pairs
(c) 20 pairs
(d) 22 pairs.
- The number of pair(s) of sex chromosomes in the zygote of human is
- In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F, is
- From the list given below, select the character which can be acquired but not inherited
(a) Colour of eye
(b) Colour of skin
(c) Size of body
(d) Nature of hairs
- A zygot which has an X-chromosome inherited from the father will develop into a
(c) either boy or girl
(d) it does not determine the sex.
- Exchange of genetic material takes place in
(a) vegetative reproduction
(b) asexual reproduction
(c) sexual reproduction
- Two pink coloured flowers on crossing results in 1 red, 2 pink and I white Bower progeny. The nature of the cross will be
(a) double fertilisation
(b) self pollination
(c) cross fertilisation
(d) no fertilisation.
Ans. 1. (a), 2. (c), 3. (c), 4. (b), 5. (a). 6. (c). 7. (a), 8. (a), 9. (c), 10. (c)
- (b), 12. (c), 13. (b).
Fill in the Blanks
- In snails, individuals can change…………….
- The more…………….. two species will have in common, the more closely they are related.
- The full form of DNA is…………
- A section of DNA that provides information for one protein is called …………for that protein.
- Mendel proposed the law of……….
Ans. 1. Sex, 2. Characteristics, 3. Deoxyribo Nucleic Acid, 4. Gene, 5. Inheritance.
- Characteristics are details of appearance and behaviour.
- Johann Mendel proposed the rules of development of flowers.
Ans. 1. True, 2. False.
Match the Columns
Column ‘A’ Column B
- Mendel. (a) Inheritance of traits
- Sex determination. (b) Control characteristics
- Genes. (c) 23rd pair of chromosomes
- Sex chromosome (d) sex determination
Ans. 1. (a), 2. → (c), 3. (b), 4. → (d).
Answer in one Word/Sentences
- What is the name of father of genetics?
Ans. Gregor Johann Mendel.
- What will be the 23rd chromosome pair for a female
- On crossing tall plants with dwarf plants what percentage of dwarf plants in F₂ generation was found by mendel.
Ans. 25% dwarf plants.
- What is the information source in a cell ?
Ans. Cellular DNA.
- What are characteristics?
Ans. Characteristics are details of appearance or behaviour.
Very Short Answer Type Questions
- 1. Define Variation.
Ans. Offspring of same parents do not exactly resemble each other as well as their parents.
- 2. Define Genetic Drift.
Ans. The elimination of the genes of certain traits when a section of a population of a species migrates or dies of natural calamity. This process is called genetic drift.
Q.3. Why are the traits acquired during the lifetime of an individual not inherited?
Ans. An acquired trait involves change in non-reproductive tissues which cannot be passed on to germ cells or the progeny. Therefore, these traits cannot be
- 4. What factors could lead to the rise of a new species? inherited.
Ans. Natural selection, genetic drift and acquisition of traits during the lifetime of an individual can give rise to new species.
- 5. What is heredity? What are heredity characters Or
Ans. Heredity and Heredity Characters “The transfer of characters in living organisms from one generation to another generation is called heredity and the characters so transfered are called heredity characters.
- 6. How do Mendel’s experiments show that traits may be dominant recessive?
Ans. Mendel observed during his experiments that on crossing two plants of different characters, some characters disappear and some characters come out. Those characters which appear are dominant and those characters which disappear are recessive characters.
Short Answer Type Questions
- 1. Explain how sexual reproduction rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually ?
Ans. Sexual reproduction gives rise to more viable variations due to the following reasons
- Error in DNA copying, which are not highly significant.
- Random seggregation of paternal and maternal chromosomes at the time of gamete
- Exchange of genetic material between homologous chromosomes during formation of gametes.
- Accumulation of variations occurred due to sexual reproduction over generation after generation and selection by nature created wide diversity. In case of asexual reproduction, only the very small changes due to inaccuracies in DNA copying pass on to the progeny. Thus, offsprings of asexual reproduction are more or less genetically similar to their parents. So, it can be concluded that evolution in sexually reproducting organisms proceeds at a faster pace then in asexually reproducing organisms.
- 2. With the help of one example for each, distinguish between the acquired traits and the inherited traits. Why are the traits/experiences acquired during the entire lifetime of an individual not inherited in the next generation ? Explain the reason of this fact with an example.
A trait or characteristics which develops in response to the environment and cannot be inherited. Example-A person learns to swim.
A characteristics feature inherited from the previous generation. Example-A girl has blue eyes just like her mother.
Only those traits are inherited which are developed because of change in genes. An acquired trait or experience is developed as a response to the environment, it is not inherited. These are not developed due to changes in genes.
Example: Human beings experiencing weight loss due to starvation. There will be reduction in weight as a response to starvation. This will result in the reduction in the number of body cells or overall body mass ratio of the individual. It will not have any effect on the genetic constitution of the individual because there is no change in the genes of the individual. It is not an inherited trait.
Long Answer Type / Analytical Questions
- 1. Why did Mendel choose the pea plant for his experiments?
Ans. Mendel selected pea for his experiments due to following reasons:
(1) It can be easily grown in garden.
(2) Its plants are herbaceous and annul and can be grown twice a year. Hence, the results of experiments are obtained quickly.
(3) The plant has clearly contrasting characters, whereby characters may easily be divide into separate classes,
(4) In pea mostly self-pollination occurs but the structure of flower is such that pollination can also be done.
(5) Fruits and flowers are abundantly available in pea plants, whereby seeds can be cross
- 2. How did Mendel explain that it is possible that a trait is inherited but not expressed in an organism?
Ans. Mendel explained that it is possible that a trait is inherited but not expressed in an organism with the help of a monohybrid cross.
(1) He crossed pea plants with different characteristics-a tall plant (TT) and a short plant (tt).
(2) The progeny he received in the first generation (F₁) was tall. The dwarfness did not show up in the F, generation.
(3) He then crossed the tall plants of the F₁ generation and found that one quarter of dwarf plants are obtained in second generation (F₂). Out of four, one pea plant was dwarf.
This indicates that both the tallness and shortness traits were inherited in F₁ plants, but only tallness trait was expressed.
- 3. How is the sex of a child determined in
human beings ?
Ans. In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY.
The gametes, as we know, receive half of the chromosomes.
Most human chromosomes have a maternal andpaternal copy and we have 22 such pairs. But one pair, (23rd pair) called the sex chromosome, is odd in not always being a perfect pair. The male gametes have a mismatched MALE a short one called Y. Therefore, type of male gametes: Fig. 9.2. Sex determination in human beings pair in which one is normal sized X while the other is 22 X or 22+ Y.
However, since the females have XX sex chromoscimes, their gametes can only have X sex chromosome. Type of female gamete: 22 + X. Thus, all children will inherit an X chromosome from their mother, regardless of whether they are boys or girls. Thus, the sex of the children will be determined by what they inherit from their father (See Fig). A child who inherits an X chromosome from her father will be a girl and one who inherits a Y chromosome from him, will be a boy
- 4. How is the equal genetic contribution of male and female parents ensured
in the progeny?
Ans. In human beings, equal genetic contribution of male and female parents in ensured in the progeny through inheritance of equal number of chromsomes from both parents. There are 23 pairs of chromosomes. All human chromosomes are not paired Out of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair is known as sex chromosome represented as X and Y. Females have a perfect pair of two X sex chromosomes and males have a mismatched pair of one X and one Y sex chromosome. During the course of reproduction, as fertilisation takes place, the male gamete (haploid) fuses with the female gamete (haploid) resulting in the formation of the diploid zygote. The zygote in the progeny receives an equal contribution of genetic material from the parents. Out of 23 pairs of chromosomes in progeny, male parent contributes 22 autosomes and one X or Y chromosome and female parent contributes 22 autosomes and one X chromosome.