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Chapter 3

Genetics — Some Basic Fundamentals

Class 10 - Selina Concise Biology Solutions


Multiple Choice Type

(Select the most appropriate option)

Question 1

Which one of the following is the phenotypic monohybrid ratio in F2 generation?

a) 3 : 1 ✓
b) 1 : 2 : 1
c) 2 : 2
d) 1 : 3

Question 2

If a pure tall plant is crossed with a pure dwarf plant, then offspring will be

(a) all tall ✓
(b) all dwarf
(c) 3 tall 1 dwarf
(d) 50% tall 50% dwarf

Question 3

The 9 : 3 : 3 : 1 dihybrid ratio is due to

(a) segregation
(b) crossing over
(c) independent assortment ✓
(d) homologous pairing

Question 4

A plant with green pods and smooth seeds with genotype Ggss will give rise to the following gametes:

(a) Gg and Ss
(b) Gs and ss
(c) Gs and gs ✓
(d) Gg and gs

Very Short Answer Type

Question 1

Match the terms in column I with their the explanations in column II.

Column I
(Term)
Column II
(Explanation)
a. Genetics(i) Chromosomes similar in size and shape
b. Autosomes(ii) The alternative forms of a gene
c. Recessive gene(iii) Study of laws of inheritance of characters
d. Allele(iv) A gene that can express only when in a similar pair
e. Homologous chromosomes(v) Chromosomes other than the pair of sex chromosomes

Answer

Column I
(Term)
Column II
(Explanation)
a. Genetics(iii) Study of laws of inheritance of characters
b. Autosomes(v) Chromosomes other than the pair of sex chromosomes
c. Recessive gene(iv) A gene that can express only when in a similar pair
d. Allele(ii) The alternative forms of a gene
e. Homologous chromosomes(i) Chromosomes similar in size and shape

Question 2

Name any two genetic diseases in humans.

Answer

Colour blindness and Haemophilia are two genetic diseases in humans.

Question 3

Which one of the following genotypes is homozygous dominant and which one homozygous recessive in regard to tongue rolling:
Rr, rr, RR?

Answer

Homozygous recessive – rr
Homozygous dominant - RR

Short Answer Type

Question 1

Differentiate between:

(a) Genotype and Phenotype

(b) Character and Trait

(c) monohybrid and dihybrid cross (phenotypic ratio in F2 generation).

Answer

(a) Difference between Genotype and Phenotype

GenotypePhenotype
The set of genes present in the cells of an organism.The observable characteristics which are genetically controlled.

(b) Difference between Character and Trait

CharacterTrait
Any inheritable feature of an organism is a character.The alternative forms of a character are called traits.

(c) Difference between Monohybrid and Dihybrid cross (phenotypic ratio in F2 generation).

Monohybrid CrossDihybrid Cross
Phenotypic ratio in F2 generation is 3 : 1Phenotypic ratio in F2 generation is 9 : 3 : 3 : 1

Question 2

Among lion, tiger and domestic cat, all the three have the same number of 38 chromosomes, yet they have different appearances. How do you account for such differences?

Answer

All species have a fixed number of chromosomes. However, the characteristics of species including physical appearance, body functions, behavior, etc. are not simply the outcome of chromosome number, but these are the result of the units called genes which the chromosomes carry. The lion and the cat have the same number of chromosomes (38). Yet one is distinct from the other in body size, appearance, colour, behavior, etc. All such characteristics of an organism are the result of the genes located on the chromosomes.

Question 3

List any three features of garden pea with their dominant and recessive traits.

Answer

CharacterDominant traitRecessive trait
Flower ColourPurpleWhite
Seed ColourYellowGreen
Seed ShapeRoundWrinkled
Pod ShapeInflatedConstricted
Flower PositionAxialTerminal

Question 4

Explain why generally only the male child suffers from colour blindness and not the female?

Answer

Colour blindness is caused due to recessive genes, which occur on the ‘x’ chromosomes.
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. Due to this reason, females are unlikely to suffer from colour-blindness.

Descriptive Type

Question 1

Define the following terms:
(a) Pedigree chart
(b) Variations
(c) Mutation

Answer

(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. Mutation alters the hereditary material of an organism's cells and results in a change in certain characters or traits for example :

  1. Sickle cell anaemia
  2. Radioactive radiations

Question 2

State the three Mendel's laws of inheritance.

Answer

Mendel's law of inheritance are as follows —

  1. 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.

  2. Law of Segregation (also called the law of purity of gametes) — The two members of a pair of factors separate during the formation of gametes. They do not blend but segregate or separate into different gametes. The gametes combine together by random fusion at the time of zygote formation.

  3. 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.

Question 3

Does the sex of the child depend on the father or is it just a matter of chance? Discuss.

Answer

The sex of the child depends upon the kind of sperm that fertilises the egg. The egg contains only one X chromosome, but half of the sperms released into the genital tract of the female during coitus are X-bearing and the remaining half are Y-bearing. It is simply a matter of chance as to which category of sperm fuses with the ovum:

  • If the egg (X) is fused by X-bearing sperm, the resulting combination is XX i.e. female constitution and the child produced is a female (Daughter).
  • If the egg (X) is fused by Y-bearing sperm, the resulting combination is XY i.e. male constitution and the child produced is a male (Son).
Does the sex of the child depend on the father or is it just a matter of chance? Discuss. Genetics, Concise Biology Solutions ICSE Class 10.

Question 4

Distinguish between the following pairs:

(a) Karyotype and Karyokinesis

(b) Autosomes and Sex chromosomes

(c) Homozygous and Heterozygous chromosomes

Answer

(a) Difference between karyotype and karyokinesis —

KaryotypeKaryokinesis
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) Difference between autosomes and sex chromosomes

AutosomesSex chromosomes
They determine the somatic traits.They determine the sex of an organism.
They are numbered as 1 to 22.They are recognized by the letters XO, XY, ZO, ZW.
They show Mendelian inheritance.They do not show Mendelian inheritance.
Human show 22 pairs of autosomes.Humans show only 1 pair of sex chromosome.

(c) Difference between homozygous and heterozygous chromosomes

Homozygous chromosomesHeterozygous 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.

Structured / Application / Skill Type

Question 1

In a certain species of animals, black fur (B) is dominant over brown fur (b). Predict the genotype and phenotype of the offspring, when both parents are 'Bb' or have heterozygous black fur.

Answer

In a certain species of animals, black fur (B) is dominant over brown fur (b). Predict the genotype and phenotype of the offspring, when both parents are 'Bb' or have heterozygous black fur. Genetics, Concise Biology Solutions ICSE Class 10.
Bb
BBBBb
bBbbb

In the question it is given that B refers to black fur and b refers to brown fur. So the genotype and phenotype of the offspring will be:

Genotype — 1 (Homozygous Black Fur) : 2 (Heterozygous Black Fur) : 1 (Homozygous Brown Fur)

Phenotype — 3 (Black Fur): 1 (Brown Fur)

Question 2

Two pairs (A and B) of rabbits were crossed as given below:

Two pairs (A and B) of rabbits were crossed as given below. Can you tell which coat colour (black or white) is dominant? Is the coat colour sex-linked? Genetics, Concise Biology Solutions ICSE Class 10.

(a) Can you tell which coat colour (black or white) is dominant?

(b) Is the coat colour sex-linked?

Answer

(a) Black

(b) No

Question 3

Make a Punnett square and find out the genotypic and phenotypic ratios of F1 and F2 generations in the progeny of a genetic cross between:

(a) A pure tall (TT) pea plant with a pure dwarf (tt) pea plant.

(b) Red flower variety of pea (RR) with white flower variety of pea (rr).

Answer

(a) A pure tall (TT) pea plant with a pure dwarf (tt) pea plant:

Make a Punnett square and find out the genotypic and phenotypic ratios of F1 and F2 generations in the progeny of a genetic cross between A pure tall (TT) pea plant with a pure dwarf (tt) pea plant. Genetics, Concise Biology Solutions ICSE Class 10.

F2 Generation:

GametesTt
TTTTt
tTttt

Genotype - 1 (Homozygous tall) : 2 (Heterozygous tall) : 1 (Homozygous dwarf)

Phenotype - 3 (Tall) : 1 (Dwarf)

(b) Red flower variety of pea (RR) with white flower variety of pea (rr):

Make a Punnett square and find out the genotypic and phenotypic ratios of F1 and F2 generations in the progeny of a genetic cross between Red flower variety of pea (RR) with white flower variety of pea (rr). Genetics, Concise Biology Solutions ICSE Class 10.

F2 Generation:

GametesRr
RRRRr
rRrrr

Genotype — 1 (Homozygous red) : 2 (Heterozygous red) : 1 (Homozygous white)

Phenotype — 3 (Red) : 1 (White)

Question 4

A family consists of two parents and their five children and the pedigree chart shown below shows the inheritance of the trait colour blindness in them.

A family consists of two parents and their five children and the pedigree chart shown below shows the inheritance of the trait colour blindness in them. Who is colour blind in the parents - the Father or the Mother? What does the child 1 indicate about this trait? On which chromosome is the gene of this trait located? Name one other trait in humans which follows a similar pattern of inheritance. Genetics, Concise Biology Solutions ICSE Class 10.

(a) Who is colour blind in the parents - the Father or the Mother?

(b) How many daughters and how many sons have been born in the family?

(c) What does the child 1 indicate about this trait?

(d) On which chromosome is the gene of this trait located?

(e) Name one other trait in humans which follows a similar pattern of inheritance.

Answer

(a) Father

(b) Two sons and three daughters

(c) The child 1 (daughter) is colour blind

(d) X chromosome

(e) Haemophilia

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