Class 10 SELINA Solutions Biology Chapter 3 - Genetics - Some Basic Fundamentals
Genetics - Some Basic Fundamentals Exercise Ex. 1
Solution A.1
a) 3 : 1
Solution A.2
(a) all tall
Solution A.3
(c) independent assortment
Solution A.4
(c) Gs and gs
Solution B.1
(a) - (iii) Study of laws of inheritance of characters
(b) - (v) Chromosomes other than the pair of sex chromosomes
(c) - (iv) A gene that can express when only in a similar pair
(d) - (ii) The alternative forms of a gene
(e) - (i) Chromosomes similar in size and shape
Solution B.2
Solution B.3
Homozygous dominant - RR
Homozygous recessive - rr
Solution C.1
(a)
Phenotype |
Genotype |
The observable characteristic which is genetically controlled is called phenotype. |
The set of genes present in the cells of an organism is called its genotype. |
(b)
Character |
Trait |
Any heritable feature is called a character. |
The alternative form of a character is called trait. |
(b)
Monohybrid cross |
Dihybrid cross |
Phenotypic ratio - 3:1 |
Phenotypic ratio- 9:3:3:1 |
Solution C.2
Solution C.3
Character |
Dominant trait |
Recessive trait |
Flower Colour |
Purple |
White |
Seed Colour |
Yellow |
Green |
Seed Shape |
Round |
Wrinkled |
Pod Shape |
Inflated |
Constricted |
Flower Position |
Axial |
Terminal |
(Any 3)
Solution C.4
Males have only one X chromosome. If there is recessive gene present on X chromosome, then the male will suffer from colour-blindness.
Females have two X chromosomes. It is highly impossible that both the X chromosomes carry abnormal gene. Hence, if one gene is abnormal and since it is recessive, its expression will be masked by the normal gene present on the other X chromosome. Females are unlikely to suffer from colour-blindness.
Solution D.1
(a) Pedigree chart: A pedigree chart is a diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next. In the pedigree chart, males are shown by squares and females by circles.
(b) Variations: The small differences among the individuals of the same species are called variations.
(c) Mutation: Mutation is a sudden change in one or more genes, or in the number or in the structure of chromosomes.
Solution D.2
(i) Law of Dominance Out of a pair of contrasting characters present together, only one is able to express itself while the other remains suppressed. The one that expresses is the dominant character and the one that is unexpressed is the recessive one.
(ii) Law of Segregation : The two members of a pair of factors separate during the formation of gametes. The gametes combine together by random fusion at the time of zygote formation. This law is also known as 'law of purity of gametes'.
(iii) Law of Independent Assortment: When there are two pairs of contrasting characters, the distribution of the members of one pair into the gametes is independent of the distribution of the other pair.
Solution D.3
If the egg fuses with X-bearing sperm, the resulting combination is XX and the resulting child is female.
If the egg fuses with Y-bearing sperm, the resulting combination is XY and the resulting child is male.
Solution D.4
(a) Differences between karyotype and karyokinesis:
Karyotype |
Karyokinesis |
The complete set of chromosomes in the cells of an organism is its karyotype. |
The division of the nucleus during mitosis is called karyokinesis. |
(b) Differences between autosomes and sex chromosomes:
Autosomes |
Sex chromosomes |
1. They determine the somatic traits. |
1. They determine the sex of an organism. |
2. They are numbered as 1 to 22. |
2. They are recognized by the letters XO, XY, ZO, ZW. |
3. They show Mendelian inheritance. |
3. They do not show Mendelian inheritance. |
4. Human show 22 pairs of autosomes. |
4. Humans show only 1 pair of sex chromosome. |
(c) Differences between homozygous and heterozygous chromosomes:
Homozygous chromosomes |
Heterozygous chromosomes |
It has two same copies of the same allele coding for a particular trait. |
It contains two different copies of alleles coding for a particular trait. |
Solution E.1
|
B |
b |
B |
BB |
Bb |
b |
Bb |
bb |
Genotype - 1(Homozygous Black Fur) :2 (Heterozygous Black Fur):1 (Homozygous Brown Fur)
Phenotype - 3 (Black Fur) :1(Brown Fur)
Solution E.2
(a) Black
(b) No
Solution E.3
(a)
F2 generation -
Gametes |
T |
t |
T |
TT |
Tt |
t |
Tt |
Tt |
Genotype - 1(Homozygous tall) :2 (Heterozygous tall):1 (Homozygous dwarf)
Phenotype - 3 (Tall) :1(Dwarf)
(b)
F2 generation -
Gametes |
R |
r |
R |
RR |
Rr |
r |
Rr |
rr |
Genotype - 1(Homozygous red) :2 (Heterozygous red):1 (Homozygous white)
Phenotype - 3 (Red) :1(White)
Solution E.4
(a) Father
(b) Two sons and three daughters
(c) The child 1 (daughter) is colour blind
(d) X chromosome
(e) Haemophilia