Solutions of Heredity and Evolution Lakhmir Singh Manjit Kaur LAQ, and MCQ Pg No. 192 Class 10 Biology
33A. What is meant by 'heredity' ? What are the units of heredity?
Answer
→ (A) Heredity refers to passing on of traits/characters genetically from parents to offspring.
The units of heredity are genes which are found on chromosomes. Chromosomes are organized structures of DNA and protein and are found in the nucleus.
33B. State Mendel's first law of inheritance.
Answer
→ (B) Mendel’s first law of inheritance is Law of Segregation which states that gene determines the characteristics/traits of an organism which always occur in pairs. One member of the gene pair segregates into a gamete.
34A. Why did Mendel choose pea plants for conducting his experiments on inheritance?
Answer
→ (A) Mendel choose pea plant for conducting his experiments on inheritance because they are easy to raise and are self-pollinating too. Also many generations can be produced in a lesser time.
34B. State Mendel's second law of inheritance.
Answer
→ (B) Mendel’s second law of inheritance is also known as law of independent assortment which states that in 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.
35A. What do you understand by the term 'variation'?
Answer
→ (A) The difference between groups of organism of any specie that is brought about by genetic differences is known as variation.
35B. Name two human traits which show variation.
Answer
→ (B) Human height (Tall or dwarf) and Ear lobe (free or attached) show variations in human.
35C. How does the creation of variation in a species ensure its survival?
Answer
→ (C) Nature always selects the fittest organism so if no variation occurred in genes there would not have been so many species of the organism. Variation always increases the chances of survival of a species in a changing environment. For example- bacteria having heat resistant trait will survive when temperature rises too much, and bacteria that do not have this heat resistant trait will die when temperature in their surrounding rises too much.
36A. (a) What are genes? Where are they located in our body?
Answer
→ (A) Genes are the units of heredity that transfer characteristics/traits from parent to offspring. They are found on chromosomes in our body and chromosomes are found in nucleus of the cell.
36B. (b) What is meant by dominant genes and recessive genes? Give one example of each.
Answer
→ (B) A dominant gene is a gene that is expressed or appears in an organism in the presence of any another gene. Whereas, a recessive gene is a gene that is suppressed in an organism (doesn’t appears) in the presence of a dominant gene. A recessive gene is expressed or appears in an organism only if the other gene present is recessive.
Example- Height in Pea plant. Tall Plants may have gene combination of TT or Tt. (where T is a dominant gene). Dwarf plants will only have gene combination of tt(where t is a recessive gene)
36C. (c) Explain how, characteristics (or traits) are inherited through genes.
Answer
→ (C) Genes are unit of heredity transmitted from parents to offspring. Each parent has a gene pair in each cell for each characteristic studied. One member of the gene pair segregates into a gamete, thus each gamete only carries one member of the gene pair from each parent and hence only one out of a pair of contrasted characters is represented in a gamete by its gene. When sperm fertilizes the egg, they form a zygote which develops to an organism having characteristics from both the parents which it would have inherited in the gametes through segregation.
37A. How do Mendel's experiments show that traits may be dominant or recessive?
Answer
→ (A) In his experiment with Pea Plant, Mendel crossed pure tall plants (TT) with pure dwarf plants (tt) and he obtained all tall plants in the F1 generation (Tt) which suggested that only one of the traits of parental plant showed in the F1 generation i.e. tall.
He crossed these tall plants of F1 generation amongst each other and obtained tall and dwarf plants in the ratio of 3:1 as the second generation (F2 generation). So he observed that the dwarf trait that had disappeared in the F1 generation reappear in the Second generation (F2 generation). Thus this shows that the traits may be dominant or recessive.
37B. How do Mendel's experiments show that traits are inherited independently?
Answer
→ (B) Mendel performed another experiment with Pea plants, this time taking two traits into consideration, yellow round seeds and green wrinkled seeds. He crossed these two plants and in the F1 generation and obtained all yellow round seeds. Yellow and round were dominant so they were expressed and Green and wrinkled were recessive so they remain suppressed. He self-pollinated these F1 generation plants to produce F2 generation and found yellow round seeds, green wrinkled seeds. Also he found yellow wrinkled seeds and green round seeds. Thus this experiment showed that the traits are inherited independently.
Multiple Choice Questions (MCQs)-Pg-193
38. When two parents are crossed, the offspring are referred to as :
A. Recessive
B. Test cross
C. F1 generation
D. F2 generation
Answer
→ F1 generation
Filial Generation of the offspring of parental (mother and father) type. Filial means offspring of a cross.
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;
A. Dihybrid cross
B. Monohybrid cross
C. Test cross
D. None of these
Answer
→ Dihybrid Cross.
Cross between two individual involves two pairs of heterozygous genes giving a ratio of 9:3:3:3 (theoretical).
40. For his experiments on heredity, Mendel used:
A. Papaya plants
B. Potato plants
C. Pea plants
D. Pear plants
Answer
→ Pea Plants
Mendel selected pea plants because they are easy to raise, they give many offspring per mating; they fertilize on their own and have varieties in genotype and phenotype
41. The human animal which has an XY pair of chromosomes is called:
A. Male
B. hybrid
C. Female
D. doomed
Answer
→ Male
Sperm with Y chromosome fertilizes with egg (having one X chromosome) thus producing a male with XY pair of chromosome.
42. The science of heredity is known as:
A. Biology
B. Embryology
C. Genetics
D. Biochemistry
Answer
→ Genetics
Heredity is passed on through genes.
43. A gene is a:
A. Hybrid
B. Heritable trait
C. Pure breed
D. Part of a chromosome that transmits a trait.
Answer
→ Part of a chromosome that transmits a trait
Gene is present in pairs on chromosome and they transmit characteristics to offspring from parent.
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:
A. 46
B. 23
C. 21
D. 42
Answer
→ 23
Somatic cells have 46 chromosomes (23 pairs of chromosome) i.e., they are diploid. The chromosome number is haploid in sex cells so they have 23 chromosomes.
45. In order to ensure that he had pure-breeding plants for his experiments, Mendel:
A. Cross-fertilized each variety with each other
B. Let each variety self-fertilize for several generations
C. Removed the female parts of the plants
D. Removed the male parts of the plants.
Answer
→ Let each variety self-fertilize for several generation
46. In the human blood grouping, the four basic blood types are type A, type B, type AB, and type 0. The blood proteins A and B are:
A. Simple dominant recessive traits
B. Incomplete dominant traits
C. Co-dominant traits
D. Sex-linked traits
Answer
→ Co-dominant traits
47. A plant with two 'small' genes breeds with a plant with two 'tall' genes to produce:
A. Small plants and tall plants in the ratio 1:3
B. All small plants
C. All tall plants
D. Tall plants and small plants in the ratio 3:1
Answer
→ All tall plants; When two small genes plant ‘tt’ breeds with two tall genes plant ‘TT’ they result in four combinations of all ‘Tt’ genes, where T is dominant and it suppresses the recessive gene t ; so al plants will be tall .
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?
A. IAIA and IB IO
B. IA IB and IB IO
C. IA IO and IB IO
D. IA IB and IA IO
Answer
→ IAIA and IBIO. IAIA will express Blood Type A. IBIO will either express blood type B or O. Since O are always recessive then the resulting combinations from where they are inherited are blood type AB or blood type O.
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?
A. 56
B. 28
C. 14
D. 4
Answer
→ 14
Palisade cells are somatic cells and gamete cell contain half the number of chromosome has in its somatic cells. So 28/2=14.
50. Which of the following may be used to obtain an F2 generation?
A. Allowing flowers a parent plant to be self-pollinated
B. Allowing flowers on an F1plant to be self-pollinated
C. Cross-pollinating an F1 plant with a parent plant
D. Cross-pollinating two parent plants
Answer
→ Allowing flowers a parent plant to be self-pollinated.
Self-pollination of F1 progeny will lead to F2 progeny as it happens in monohybrid and Dihybrid crosses.
51. The following results were obtained by a scientist who crossed the F1 generation of pure-breeding parents for round and wrinkled seeds.
Dominant trait -Round seeds
Recessive trait -Wrinkled seeds
No. of F2 offspring -7524
From these results, it can be concluded that the actual number of round seeds he obtained was:
A. 1881
B. 22572
C. 2508
D. 5643
Answer
→ 5643; When Round ‘RR’ and wrinkled ‘rr’ seed bearing plants are crossed, all heterozygous round seed bearing plants are obtained in the F1 generation. When the plants of these F1 generations are cross bred, the F2 generation had round and wrinkled seed bearing plant in the ratio 3:1. (total=4)
Hence, (3/4) * 7524= 5643
52. The visible characteristic in an organism is known as:
A. Prototype
B. stereotype
C. Phenotype
D. genotype
Answer
→ Phenotype
It is defined as visible characteristics of an individual which occur from the interaction of its genotype with the environment.
53. The exchange of genetic material takes place in:
A. Vegetative reproduction
B. Asexual reproduction
C. Sexual reproduction
D. Budding
Answer
→ Sexual reproduction
Sexual reproduction involves fusion of gametes which results in exchange of genetic material.
54. A cross between a tall plant (TT) and short 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 plant is not governed by gene T or t
Answer
→ Tallness is the dominant trait.
When a cross between tall plant TT and a short plant tt occurs , the resulting offspring are all ‘Tt’ where T is the dominant trait so all plants are tall due to that dominant trait which does not lets the recessive trait i.e. shortness express itself.
55. The number of pair(s) of sex chromosomes in the zygote of humans is:
A. One
B. Two
C. Three
D. Four
Answer
→ One. XX chromosome in female; XY chromosome in male.
56. In peas, a pure tall plant (IT) is crossed with a pure short plant (tt). The ratio of pure tall plants to pure short plants in F2 generation will be:
A. 1 : 3
B. 3 : 1
C. 1 : 1
D. 2 : 1
Answer
→ 1:1
When pure tall plant TT is crossed with pure short plant tt, all ‘Tt’ offspring are obtained in the F1 generation. When selfing of these F1 generation plants is done, the offspring obtained are ‘TT’ ‘Tt’ ‘Tt’ ‘tt’- in the ratio 3:1 (Tall : short), where pure tall plant and pure short plant are in the ratio 1:1(TT and tt).
57. The two versions of a trait (character) which are brought in by the male and female gametes are situated on:
A. Copies of the same chromosome
B. Sex chromosomes
C. Two different chromosomes
D. Any chromosomes
Answer
→ Copies of the same chromosome
These versions of traits are known as genes which when brought in by the male and female gametes are found on copies of same chromosome so that they do not assort independently and are said to be linked.
58. 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)
Answer
→ (i) and (iii)
Genes are specific sequences of bases that are present on chromosomes found in nucleus of DNA.
59. Select the group which shares the 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
Answer
→ Two individuals of a species
Species is the lowest taxanomic category and share common features, thus two individuals of a species share maximum no. of characters (share common gene pool).
60. A trait in an organism is influenced by:
A. Paternal ONA only
B. Maternal DNA only
C. Both maternal and paternal DNA
D. Neither paternal, nor maternal DNA
Answer
→ Both maternal and paternal DNA
This is because the gametes coming from the mother and father have genes that carry different traits. When these gametes fuse, the traits are mixed and expressed accordingly.
61. 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
A. (i) and (ii)
B. (iii) only
C. (iii) and (iv)
D. (ii) and (iv)
Answer
→ (iii) and (iv) Y chromosome and X chromosome
Males have all 22 pairs of chromosomes paired perfectly. The 23rd pair of chromosome that is the pair of sex chromosomes are not paired perfectly because in the pair one chromosome is X and the other is Chromosome Y , so they are not paired perfectly.
62. The sex of a child is determined by which of the following?
A. The length of the mother's pregnancy
B. The length of time between ovulation and copulation
C. The presence of an X chromosome in an ovum
D. The presence of a Y chromosome in a sperm
Answer
→ The presence of Y chromosome in sperm.
If sperm carries a Y chromosome and fertilizes with egg (having an X chromosome) the sex of the child will be male. But if the sperm carries a X chromosome and fertilizes with egg the sex of the child will be female.
63. A zygote which has inherited an X chromosome from the father will develop into :
A. Baby boy
B. Baby girl
C. Adult
D. Either boy or girl
Answer
→ Baby Girl
The mother already has X chromosome in the unfertilized egg. When a sperm, carrying X from the father will fertilize the egg, the combination would be XX and thus a baby girl will develop.
64. 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 type of fat there is a gene
Answer
→ For every type of fat there is a gene
For every hormone production, every protein formation and for production of every enzyme, genes exist but no such genes exist for fat. So the statement (d) is incorrect. Fat is a kind of Acquired characteristic.
65. If the ratio of each phenotype of the seeds of pea plants in the F2 generation is 9 : 3 : 3 : 1, it is known as :
A. Tetra hybrid ratio
B. Monohybrid ratio
C. Dihybrid ratio
D. Tri hybrid ratio
Answer
→ Dihybrid cross
Ratio in F2 generation of a Dihybrid cross is always 9:3:3:1