The life on this planet earth is from hundreds of generations ago and will continue for hundreds of generations. This continuity of generations is due to the biological process called reproduction. Reproduction is defined as the process in which an organism gives birth to its young ones. Show This chapter gives us complete information on how organisms reproduce and their development. The types of reproduction sexual and asexual taking place in various organisms are explained in a precise manner. This chapter also highlights how the unicellular organisms reproduce and compare it with multicellular organisms. Access Lakhmir Singh Solutions For Class 10 Biology Chapter 4Very Short Answer Type Questions1. Which of the processes, sexual reproduction or asexual reproduction, bring about maximum variations in the offsprings? Answer In the process of sexual reproduction maximum variations in the offsprings occur. 2. Name one variation in humans connected with ears. Answer Free earlobes and attached earlobes are an example of variation in human ears. 3. What constitutes the link between one generation and the next? Answer The link between one generation and the next is constituted by Gametes. These help in passing on the paternal and maternal characteristics. 4. If the trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier? Answer Trait B is likely to have arisen earlier, due to the greater rate in population. 5. Mendel said that the characteristics or traits of organisms are carried from one generation to the next by internal factors which occur in pairs. What is the modern name for these factors? Answer Genes is the modern name of these factors is genes. 6. Some plants occur in one of the two sizes: tall or dwarf. This characteristic is controlled by one pair of genes. Tallness is dominant to dwarfness. Choose suitable letters for this gene pair. Answer Let us assume that ‘T’ stands for tall, and ’t’ stands for dwarf. Hence, the gene pair will be Tt. 7. What are the chromosomes XY and XX known as? Answer Chromosomes XY and XX are known as sex chromosomes. 8. Which of the two, sperm or ovum, decides the sex of the child? Answer The sperm decides the sex of a child. 9. State whether the following statement is true or false: Answer False 10. A new born child has an XY pair of chromosomes. Will it be a baby boy or a baby girl? Answer The child will be a boy. 11. Which of the following combinations of sex chromosomes produce a male child: XX or XY? Answer Combination XY of sex chromosomes produces a male child. 12. Name the first scientist who studied the inheritance of traits from one generation to the next. Answer The first scientist, who studied the inheritance of traits from one generation to the next was Gregor Mendel. 13. What type of plants were used by Mendel for conducting his experiments on inheritance? Answer Mendel used different varieties of pea plants for conducting his experiments on inheritance. 14. The gene for red hair is recessive to the gene for black hair. What will be the hair colour of a person if he inherits a gene for red hair from his mother and a gene for black hair from his father? Answer The hair colour of the person will be black because the gene for red hair is recessive compared to black. 15. What are the four blood groups in humans? Answer The four blood groups in humans are A, B, AB and O. 16. Name one reptile in each case where higher incubation temperature leads to the development of: (a) male progeny, (b) female progeny. Answer (a) Lizard (b) Turtle 17. Fill in the following blanks with suitable words: Answer (a) Genes always work in pairs. (b) In pea plants, the gene for dwarfness is recessive, whereas that for tallness is dominant. (c) Most people have free earlobes but some have attached earlobes. (d) A human gamete contains 23 chromosomes, whereas a normal body cell has 46 chromosomes in it. (e) All races of man have different blood groups. (f) The sex chromosomes for a female are XX, whereas that for a male are XY. Short Answer Type Questions 18. Which of the following represent tall plants and which represent short plants (or dwarf plants)? Answer (a) Tt represents tall plants, as T (tall) is dominant gene over recessive gene t (dwarf). (b) tt represents dwarf plants, as t (dwarf) due to the presence of recessive gene. (c) TT represents tall plants, as T (tall) due to the presence of dominant gene. 19. A man having blood group O marries a woman having blood group B and they have a daughter. What will be the blood group of the daughter? Answer The daughter will have equal chance of having blood group O and blood group B, 20. (a) Name the scientist
who gave the laws of inheritance. Answer (a) Gregor Mendel (b) Snail is an example of an animal that can change sex. This indicates that sex not determined genetically in some organisms. 21. Explain with an example, how genes control the characteristics (or traits). Answer Genes are the section of DNA that carry the chromosome and determine the characteristics of an organism. Suppose, a plant species possesses a gene for the characteristic called ‘tallness’. The gene for tallness will give instructions to the plant cells to generate many plant-growth hormones due to which the plant will grow tall. On the other hand, if the plant has the gene for shortness, less plant-growth hormones will be produced, due to which the plant will not grow much and remain a dwarf plant. 22. (a) State one advantage of variation to a
species. (a) The increase in the chances of the species’ survival in a changing environment is the advantage of variation to a species. (b) The chromosomes that determine the sex of a person are called sex chromosomes. There are two types of sex chromosomes, the X chromosome and the Y chromosome. XX determines the male and XY determines the female in human beings. 23. Explain how, sex is determined in human babies. Answer There are two types of sex chromosomes, the X chromosome and the Y chromosome. XX determines the male and XY determines the female. The sex of a person is determined at the time of fertilization. If the father contributes X chromosome during fertilization through his sperm, then the baby born will be a girl. On the other hand, if chromosome Y is contributed through his sperm, then the new born will be a boy. 24. What do the following symbols used in the topic on heredity represent? Answer (a) TT represents a tall plant. (b) tt represents a dwarf plant. (c) XX represents a female. (d) XY represents a male. 25. (a) What
will you get in the F1 and F2 generations in the following cross? Answer (a) In the F1 generation, we will get all tall plants. In the F2 generation, we will get tall and dwarf plants in the ratio 3:1. (b) It is an example of monohybrid cross, as only one character (i.e., plant height) is considered for crossing. 26. In the F2 generation of a cross, progeny having different traits are produced in the ratio 3:1. State whether it is a monohybrid cross or a dihybrid cross? Give one example of such a cross. Answer The given condition is a monohybrid cross. In the F1 generation, when a tall pea plant (TT) is crossed with a dwarf pea plant (tt), all tall pea plants (with genotype Tt) are obtained. In the F2 generation, If these tall plants (Tt) are self-crossed, then the tall and dwarf plants will be in the ratio 3:1. 27. (a) What is the genotype of dwarf plants which always produced dwarf offspring? Answer (a) The genotype of dwarf plants which always produces a dwarf offspring is tt. (b) The genotype of tall plants which always produces a tall offspring is TT. (c) (i) The genotype of dwarf plants is tt (ii) The genotype of tall plants is TT. The parental cross of (ii) always produces a tall offspring. 28. (a) If a normal human cell has 46 chromosomes, how many chromosomes will be there in a human (i) sperm cell, and (ii) zygote? Answer (a) (i) The number of chromosomes present in it will be 23 as the sperm cell will have half the number of chromosomes than present in a normal cell. (ii) The number of chromosomes present in it will be 46 as the number of chromosomes in a zygote will be same as present in a normal cell. (b) Tall and dwarf plants will be produced in the ratio 3:1. 29. In a human, how many chromosomes are present in : Answer (a) 46 chromosomes (b) 23 chromosomes (c) 23 chromosomes (d) 46 chromosomes (e) 46 chromosomes 30. Gregor Mendel’s first law of genetics states “Of a pair of contrasted characters, only one can be represented in a gamete by its internal ‘factor’. (a) Genes is the modern name for this factor. (b) These factors or genes are present on chromosomes in gametes. 31. Does genetic combination of mother play a significant role in determining the sex of a new born baby? Answer Genetic combination of father decides the sex of the baby which the mother will give birth to hence, genetic combination of mother does not play a significant role in determining the sex of a new born baby. 32. Give the contrasting traits of the following characters in pea plant and mention which is dominant and which is recessive: Answer (a) Green seed. Yellow seed is the dominant trait and green seed is the recessive trait. (b) Wrinkled seed. Round seed is the dominant trait and wrinkled seed is the recessive trait. Long Answer Type Questions33. (a) What is meant by
‘heredity’? What are the units of heredity? Answer (a) The transmission of characters from the parents to their offsprings is called heredity. Genes are the units of heredity which transfer characteristics from parents to their offsprings during reproduction. (b) Mendel’s first law of inheritance states that the characteristics of an organism are determined by internal factors which occur in pairs. Only one of a pair of such factors can be present in a single gamete. 34. (a) Why did Mendel choose pea plants for conducting his experiments on inheritance? Answer (a) Mendel chose pea plants for studying inheritance because of the following reasons:
(b) Mendel’s second law of inheritance states that in the inheritance of more than one pair of traits in a cross simultaneously, the factors responsible for each pair of traits are distributed independently to the gametes. 35. (a) What do you understand by the term ‘variation’? (a) The differences in the characters (or traits) among the individuals of a species is called variation. (b) Human height and skin colour are two traits which show variation. (c) The great advantage of variation to a species is that it increases their chances of survival in a changing environment. Variants help the species to survive in all the conditions. Environmental conditions such as heat, light, pests, and food availability can change suddenly at only one place. If variants were not there, the entire species would have been destroyed. 36. (a) What are genes? Where are they located in our body? (b) What is meant by dominant genes and recessive genes? Give one example of each. (c) Explain how, characteristics (or traits) are inherited through genes. Answer (a) Genes are units of heredity which transfer characteristics (or traits) from parents to their offsprings during reproduction. Genes are located in chromosomes. (b) The gene which decides the appearance of an organism even in the presence of an alternative gene is known as dominant gene. The gene which can decide the appearance of an organism only in the presence of another identical gene is called a recessive gene. For example, in pea plants, the dominant gene for tallness is T and the recessive gene for dwarfism is t. (c) Genes are responsible for the characteristic features of an organism. The characteristics or traits of parents are transmitted to their progeny through genes present on their chromosomes during the process of sexual recombination. There is a pair of genes for each characteristic of an organism. Each parent passes only one of the two genes of the pair for each characteristic to its progeny through gametes. Thus, the male gamete and female gamete carry one gene for each characteristic form the gene pairs of parents. But when a male gamete fuses with a female gamete during fertilisation, they make a new cell called zygote with a full set of genes. This zygote grows and develops to form a new organism having characteristics from both the parents. 37. (a) How do Mendel’s experiments show that traits may be dominant or recessive? Answer (a) Mendel conducted the experiments using or pea plant. He selected homozygous tall (TT) and dwarf (tt) pea plants. He crossed the tall pea plant with the dwarf pea plant. It was observed that the F1 generation are all tall plants. Thus, it was concluded that the gene causing tallness is dominant while the gene causing dwarfness is recessive. The trait expressing itself in the hybrid is the dominant one. This experiment proves Mendel’s first law of inheritance. It states that when a pair of contrasting factors is brought in a hybrid, one factor inhibits the appearance of the other, one which inhibits is the dominant one and which is inhibited is recessive. (b) Mendel performed an experiments in which he took a tall plant with round seeds and a short plant with wrinkled-seeds. In F1, They were all tall and had round seeds. Tallness and round seeds were thus dominant traits. When he used these F1 progeny to generate F2 progeny by self-pollination, he found that some F2 progeny were tall plants with round seeds, and some were short plants with wrinkled seeds. At the same time there were tall plants, but had wrinkled seeds, while others were short, but had round seeds. Thus, Mendel’s experiments show that the tall/short trait and the round seed/wrinkled seed trait are independently inherited. Multiple choice questions:38. When two parents are crossed, the offspring are referred to as: Answer (c) F1 generation 39. A cross between two individuals results in a ratio of 9 : 3 : 3 : 1 for four possible phenotypes of progeny. This is an example of a : Answer (a) dihybrid cross Answer (c) pea plants Answer (a) male 42. The science of heredity is known as: Answer (c) genetics 43. A gene is a : Answer (d) part of a chromosome that transmits a trait 44. A normal cell of human body contains 23 pairs of chromosomes. The number of chromosomes in a sex cell (sperm or ovum) of a human being is most likely to be : Answer (b) 23 45. In order to ensure that he had pure-breeding plants for his experiments, Mendel : Answer (b) let each variety self fertilize for several generations 46. In the human blood grouping, the four basic blood types are type A, type B, type AB, and type O. The blood proteins A and B are: Answer (c) codominant traits 47. A plant with two ‘small’ genes breeds with a plant with two ‘tall’ genes to produce : Answer (c) all tall plants 48. A pregnant woman has an equal chance of
her baby being blood group A or blood group AB. Which one of the following shows the possible genotypes of the woman and the father of her child? Answer (a) IA IA and IB IO 49. The palisade cells of a species of plant contain 28 chromosomes. How many chromosomes will there be in each gamete produced by the plant? Answer (c) 14 50. Which of the following may be used to obtain an F2 generation? Answer (a) allowing flowers on a parent plant to be self-pollinated
From these results, it can be concluded that the actual number of round seeds he obtained was: Answer (d) 5643 52. The visible characteristic in an organism is known as: Answer (c) phenotype 53. The exchange of genetic material takes place in: Answer (c) sexual reproduction 54. A cross between a tall plant (TT) and short plant (tt) resulted in progeny that were all tall plants because : Answer (a) tallness is the dominant
trait Answer (b) two 56. In peas, a pure tall plant (TT) is crossed with a pure short plant (tt). The ratio of pure tall plants to pure short plants in F2 generation will be: Answer (c) 1 : 1 Answer (a) copies of the same chromosome 58. Select the statements that describe characteristics of genes : (a) (i) and (ii) Answer (b) (i) and (iii) 59. Select the group which shares the maximum number of common characters: Answer (a) two individuals
of a species Answer (c) both maternal and paternal DNA (a) (i) and (ii) Answer (c) (iii) and (iv) 62. The sex of a child is determined by which of the following? Answer (d) the presence of a Y chromosome in a
sperm Answer (b) baby girl Answer (d)
for every type of fat there is a gene Answer (c) dihybrid ratio What is gene class 10th?A gene is defined as the fundamental unit of heredity. It is a segment of DNA that has information coded in it in the form of a nucleotide sequence. It has the ability to undergo mutation and crossing over.
What is gene PPT? The gene is the unit of genetic information that controls a specific aspect of the phenotype. The gene is the unit of genetic information that specifies the synthesis of one polypeptide. 6. genes are the fractions or part of DNA molecule which regarded as the genetic material.
What is a gene Class 9?Gene is unit of DNA that is usually located on a chromosome and that controls the development of one or more traits and is the basic unit by which genetic information is passed from parent to offspring. A gene is the basic physical and functional unit of heredity. Suggest Corrections.
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