Ans: He selected pea plant for his experiment due to the following reasons:
1. Pea plants can be cultivated easily and have a short life cycle.
2. They produce a large number of offsprings.
2. Write down the significance of Mendel's law.
Ans: The significances of Mendel's law are:
1. Hybrids with desired characteristics can be produced.
2. The genotypes and phenotypes likely to be produced in successive generations can be predicted before the cross is made.
3. Define genotype.
Ans: Genotype is the gene composition of an individual, which determines the individual’s form, size, colour, behavior, etc.
4. Define monohybrid cross.
Ans: When only one unit character is involved in a cross, it is called monohybrid cross.
5. Define recessive character.
Ans: The suppressed character which does not express itself in the successive generation is known as recessive character.
6. Define dominant characters.
Ans: The characters which appear in successive generations are called dominant characters.
7. Define homozygotes.
Ans: The organisms having two similar genes for a particular character in a homozygous pair of chromosomes are known as homozygotes.
8. Define heterozygotes.
Ans: The organisms containing both dominant and recessive characters of an allelic pair are called heterozygotes.
9. Define alleles.
Ans: Two or more alternating forms of a gene are called alleles.
10. Define pure organisms.
Ans: Those organisms which have same phenotype and genotype are called pure organisms.
11. State law of dominance.
Ans: Law of dominance states that when a cross is made between a pair of pure contrasting characters, only one of them is able to express itself phenotypically while the other remains hidden in the F1 generation.
12. What is law of segregation?
Ans: Law of segregation states that the two members of a pair of factors separate during the formation of gametes.
13. Blue eyed offspring may be produced from brown eyed parents, why?
Ans: Blue-eyed offspring may be produced from brain eyed parents, if the brain eyed parents are (not pure) hybrid. In a hybrid, both the blue-eyed as well as brain eyed characters are present. The blue-eyed character is recessive which if expressed in the next generation, results in offsprings with blue eyes.
14. Define acquired characters.
Ans: The characters developed by the organisms themselves through their own effort are called acquired characters.
15. Define RNA.
Ans: RNA represents ribose nucleic acid, which acts as a genetic material in some lower organisms like viruses.
16. Define DNA.
Ans: DNA represents deoxyribose nucleic acid which is a small segment of the gene that carries the hereditary material.
17. Mendel selected pea plant for his experiment, why?
Ans: He selected pea plant for his experiment due to the following reasons:
1. Pea plants can be cultivated easily and have a short life cycle.
2. They produce a large number of offsprings.
18. Write down the significance of Mendel's law.
Ans: The significances of Mendel's law are:
1. Hybrids with desired characteristics can be produced.
2. The genotypes and phenotypes likely to be produced in successive generations can be predicted before the cross is made.
19. Mendel could not succeed in his experiment, if he used frogs instead of pea plants?
Ans: It is because a frog reproduces by crossing only. Thus, purity of characters cannot be checked in them. Similarly, they lack a large number of contrasting pairs of characteristics that can be observed from outside.
20. Write any two applications of Mendel's law of inheritance?
Ans: The two applications of Mendel's law of inheritance are:
i. It gives a new idea about the new combination of hybrids.
ii. New types of plant with new combinations can be formed.
21. Can we apply Mendel's law in human beings too? State difficulties Mendel would have faced if he had carried his experiment on a human instead of plants.
Ans: Yes, Mendel's law can also be applied in human beings. The difficulties that he would have faced, if he had carried it on human are:
i. Human beings produce only one offspring at a time. So, it would be difficult to compare the characteristics in the same generations.
ii. If it had been in human, he would wait for many years.
22. Study the given diagram and answer the following questions.
| Rr | Rr |
| Rr | rr |
b. Which law of Mendel does it support?
c. Write phenotype and genotype of the generation?
d. Write the characteristics of the parents.
a. F2 generation is shown in the given diagram.
b. It supports the law of purity of gametes.
c. Phenotypic ratio = 3:1
Genotypic ratio = 1:2:1
d. This shows the cross between pure red (RR) and pure white (rr). That is parents are pure red and pure white.
23. Describe Mendel's law of dominance with one example.
Ans: Mendel's law of dominance states that when a cross is made between a pair of pure contrasting characters, only one of them is able to express itself phenotypically while the other remains hidden in F1 generation. The character which is expressed is called dominant while the other which is not expressed or remains hidden is called recessive.
Example:
When a pure tall pea plant (TT) and pure dwarf pea plant (tt) is cross-pollinated, all the offspring are toy bird tall in the first filial generation. In this case, tallness appears by suppressing the dwarfness.
24. Define dihybrid cross.
Ans: When two unit characters are involved in a cross, it is called dihybrid cross.
25. Define hybrids.
Ans: Hybrids are those organisms which have different phenotype and genotype.
26. Define mutation.
Ans: The sudden and unexpected change from one generation to another generation is called mutation.
27. What is the law of independent assortment?
Ans: Law of independent assortment states that when two pairs of independent alleles are brought together in the hybrid (F1), they, at the time of gamete formation, segregate or assort independently at random and freely.
28. Define polyhybrid cross.
Ans: When more than two unit characters are involved in a cross, it is called a polyhybrid cross.
29. Differentiate between dominant character and recessive character.
Ans:
Dominant character | Recessive character |
1. Dominant character is expressed by hybrid. | 1. The recessive character is not expressed by hybrid. |
| 2. It is not suppressed by the other character. | 2. It is suppressed by the other character. |
30. Define mutants and mutagens.
Ans: The organisms in which mutation occur, are called mutants. The cause of mutation is called mutagen. Example: X -rays, gamma rays, chemicals, etc.
31. What will be the results of crossing black hybrid masses and pure white mouse if black colour is dominant character? Insert in table.
Ans: The genotype for black hybrid mouse is Bb. The genotype for pure white mouse is bb.
The cross between them is shown as:
Gametes | B | b |
b | Bb | bb |
b | Bb | bb |
It results two hybrid black and two pure white coloured mouse.
32. How is hybrid produced? Explain with an example.
Ans: When cross is made between two parents having pure contrasting pair of characteristics then, hybrid is produced. For example, when a pure tall plant is crossed with pure dwarf plant then in it generation, hybrid tall is produced. i e.
33. Draw the result of crossing between tall and dwarf pea plant up to second filial generations.
Ans: Here,
TT represents tallness and it represents dwarfness.
TT = Pure tall
Tt = Hybrid tall
tt = Pure dwarf
Phenotypic ratio = 3:1
Genotypic ratio = 1:2:1
34. Show the genotype and phenotype of the offspring produced by crossing drosophila with long wings and short wings up to second filial generations.
Ans: The genotype for long-winged drosophila is LL.
The genotype for short-winged drosophila is ll.
Genotypic ratio = 1:2:1
Phenotypic ratio = 3:1
35. Every living beings reproduces its own kind of offspring, why?
A hybrid tall pea (Tt) is crossed with dwarf (tt) plant to get F1 generation, what will be the genotypic and phenotypic ratio in this case.
Ans: It is due to the presence of hereditary information in the chromosome of the gametes, which then passes into the zygote and finally to the offspring.Hybrid tall pea plant = Tt
Dwarf pea plant = tt
Genotypic ratio = 1:1
Phenotypic ratio = 1:1
36. Write a name of sex linked disease seen only in male. Draw a chart to show first and second generation offspring obtained by crossing between black coloured mother (BB) and white coloured father bb. Also write phenotypic and genotypic ratio of second generation offspring.
Ans: Haemophilia is the sex-linked (X-linked) diseases that are seen only in the male.
BB = Pure black.
Bb = Hybrid black
bb = pure white
Genotypic ratio = 1:2:1
Phenotypic = 3:1
37.
a. In humans, the gene for black skin colour (B) is dominant over the gene for white colour (b). Study the given chart and answer the following questions.
i. Write down the genotype and phenotype of the mother.
ii. What is the phenotypic and genotypic ratio of black and white complexion in the F2 generation?
b. State law of Segregation with an example.
Ans: a.i. Write down the genotype and phenotype of the mother.
ii. What is the phenotypic and genotypic ratio of black and white complexion in the F2 generation?
b. State law of Segregation with an example.
i. Write down the genotype and phenotype of the mother.
The genotype of the mother = bb
The phenotype of the father = white coloured skin
ii. What is the phenotypic and genotypic ratio of black and white complexion in F2 generation?
Phenotypic ratio and white complexion is 1:1
The genotypic ratio of black and white complexion is also 1:1.
b. State law of Segregation with an example.
Mendel's law of segregation states that the hybrid obtained in F1 generation contain two contrasting characteristics i.e. dominant and recessive. Those characteristics remain together for a long period of time in hybrids but do not mix with each other and separate or segregate at the time of gamete formation so that each gamete gets only one characteristic, either dominant or recessive characteristics. Example: When a cross is made between pure red-flowered and pure white has red parents which are shown in the chart below.
38. Define continuous variation.Ans: The gradual change from one generation to another generation is called continuous generation.
39. Differentiate between monohybrid and dihybrid cross.
Ans:
Monohybrid cross | Dihybrid cross |
1. Only one unit character is involved in a cross. | 1. Two unit character is involved in a cross. |
| 2. A cross between pure tall and pure dwarf pea plant. | 2. A cross between a tall pea plant with red flower and dwarf plant with a white flower. |
40. Write any two differences between phonotype and genotype.
Ans:
Phenotype | Genotype |
1. It is the external appearance of an organism.
| 1. It is the genetic makeup of an organism. |
| 2. It can be known/identified through direct observation. | 2. It cannot be known through direct observation. |
41. Write any two differences between variation and mutation?
Ans:
Variation | Mutation |
1. The structural differences that provide individuality to eachmember of a species are calledvariation. | 1. A sudden inheritable change in the genetic materials of an organism is called mutation. |
| 2. It is also called continuous variation | 2. It is also called discontinuous variation |
42. Differentiate between environmental variation and genetic variation.
Ans:
Genetic variation | Environmental variation |
1. This is acquired by the organism due to changes in the chromosomes or genes.
|
|
| 2. It is inheritable. | 2. It is non-inheritable. |
43. When black and brown dogs are crossed, all the dogs at F1 generation are found to black. Give reasons of not forming brain dogs. Also, give a chart to show the cross.
Ans: In this particular cross, black colour is dominated and the brown is the recessive character. According to Mendel's first law that is the law of dominance only one character is expressed in the offspring while the other remains in expressed or recessive. Here, also the black colour being dominant, it is expressed in the F1 generation. So, all the dogs of F1 generation are found to be black.
Showing the above information in the chart,
Black= BB
Brown= bb
All of the offspring of F1 generation are (hybrid) black. (Bb)
.