Science & Technology · Chapter 04

71 solved questions

Chapter 4: Heredity

Every question in this chapter, answered and explained — step-by-step solutions drawn live from the chapter library across 7 question sections.

Very Short Answer Questions22 Short Answer Questions9 Give Reason Questions14 Differentiate Between9 Long Answer Questions3 Diagram-Based Questions5 Application / Conceptual Questions9

Very Short Answer Questions

1SEE Boardqb-q0

What is heredity?

Ans.The phenomenon in which parental characters are transferred to offspring is called heredity.

2SEE Boardqb-q1

What is a gene?

Ans.The smallest fragment of DNA in a chromosome that codes for a specific character of an organism.

3SEE Boardqb-q2

What is a chromosome made up of?

Ans.A chromosome is made up of DNA and histone protein.

4SEE Boardqb-q3

How many pairs of chromosomes are found in a human cell?

Ans.23 pairs (46 chromosomes in total).

5SEE Boardqb-q4

How many pairs of sex chromosomes are found in a human cell?

Ans.1 pair.

6SEE Boardqb-q5

What are the sex chromosomes of a male and a female called?

Ans.A male has XY sex chromosomes; a female has XX sex chromosomes.

7SEE Boardqb-q6

What is the main function of sex chromosomes?

Ans.To determine the sex of an individual.

8SEE Boardqb-q7

Name the four nitrogen bases found in DNA.

Ans.Adenine, guanine, cytosine and thymine.

9SEE Boardqb-q8

Name the four nitrogen bases found in RNA.

Ans.Adenine, guanine, cytosine and uracil.

10SEE Boardqb-q9

What is the main function of RNA?

Ans.To help synthesize protein.

11SEE Boardqb-q10

How many daughter cells are formed at the end of mitosis?

Ans.Two daughter cells.

12SEE Boardqb-q11

How many daughter cells are formed at the end of meiosis?

Ans.Four daughter cells.

13SEE Boardqb-q12

Which cell division is also called equational division?

Ans.Mitosis.

14SEE Boardqb-q13

Which cell division is also called reductional division?

Ans.Meiosis.

15SEE Boardqb-q14

Who is called the father of genetics?

Ans.Gregor Johann Mendel.

16SEE Boardqb-q15

Which plant did Mendel use for his experiments?

Ans.The pea plant.

17SEE Boardqb-q16

What is the phenotypic ratio obtained in Mendel's monohybrid cross F2 generation?

Ans.3:1 (dominant:recessive).

18SEE Boardqb-q17

What is the genotypic ratio obtained in Mendel's monohybrid cross F2 generation?

Ans.1:2:1 (pure dominant : hybrid : pure recessive).

19SEE Boardqb-q18

What is the hybrid animal produced by crossing a male lion and a female tiger called?

Ans.Liger.

20SEE Boardqb-q19

What is the hybrid animal produced by crossing a donkey and a horse called?

Ans.Mule.

21SEE Boardqb-q20

Who was the first child in the world born through IVF, and when?

Ans.Louise Joy Brown, born on 25 July 1978.

22SEE Boardqb-q21

Who was Nepal's first IVF (test-tube) baby?

Ans.Om Mani Tamang, born on 3 March 2005.

Short Answer Questions

1SEE Boardqb-q22

What is a chromosome? Clarify the role of chromosomes in the body of living beings.

Ans.A chromosome is a condensed, thickened thread of chromatin made of DNA and histone protein, seen during cell division. Chromosomes carry the genes of an organism and determine its characteristics; during cell division, they replicate and divide so that hereditary information is passed from mother cell to daughter cells, and from parents to offspring.

2SEE Boardqb-q23

Explain the importance of mitotic cell division in the growth and development of the body.

Ans.Mitosis increases the number of cells with the same genetic makeup, which is essential for physical growth. It also helps regenerate cells in injured areas, helps in the asexual reproduction of some plants and invertebrates, and maintains genetic stability by producing genetically identical daughter cells.

3SEE Boardqb-q24

Explain the role of mitosis and meiosis in the reproduction of organisms.

Ans.Meiosis occurs in the testes and ovaries to form haploid gametes (sperm and ovum) needed for sexual reproduction; the fusion of these gametes during fertilization forms a diploid zygote. Mitosis then repeatedly divides this single-celled zygote to form the complete multicellular body of the offspring. Thus, meiosis provides the gametes for sexual reproduction, while mitosis drives the growth and development of the resulting individual.

4SEE Boardqb-q25

What will happen if meiotic cell division does not occur in the reproductive cells of an organism? Explain.

Ans.If meiosis does not occur, the reproductive cells cannot reduce their chromosome number to half, so gametes with the normal (diploid) chromosome number would be produced instead of haploid gametes. If two such gametes fused, the resulting zygote would have double the normal chromosome number, leading to serious genetic and developmental disorders; also, no genetic variation would be introduced through crossing over, reducing the raw material for evolution.

5SEE Boardqb-q26

Clearly explain the role of genes in the transmission of hereditary characteristics in organisms.

Ans.Genes are segments of DNA found in chromosomes, and each gene codes for a specific character of an organism. During cell division, chromosomes carrying genes are copied and passed from mother cell to daughter cells; during sexual reproduction, one set of genes comes from the father and one from the mother. This is how genes carry and transmit hereditary characteristics from parents to offspring across generations.

6SEE Boardqb-q27

How is sex determined in humans? Explain with a chart.

Ans.In humans, males have XY sex chromosomes and females have XX. The male's testis mother cell (44+XY) undergoes meiosis to form sperm with either 22+X or 22+Y chromosomes, while the female's ovary mother cell (44+XX) forms ova with only 22+X chromosomes. If a 22+X sperm fertilizes the 22+X ovum, the child is female (44+XX); if a 22+Y sperm fertilizes it, the child is male (44+XY). [See the sex determination chart: father 44+XY and mother 44+XX -> gametes 22+X/22+Y and 22+X -> fertilization -> 44+XX (daughter) or 44+XY (son)].

7SEE Boardqb-q28

A woman is pregnant. What is her probability of giving birth to a daughter? Write in percent.

Ans.50%, since half of the father's sperm carry an X chromosome (which combines with the mother's X-bearing ovum to give a daughter, 44+XX) and half carry a Y chromosome (giving a son, 44+XY).

8SEE Boardqb-q29

Explain Mendel's law of dominance and law of purity of gametes.

Ans.Law of dominance: when a cross is made between two pure individuals with a pair of contrasting characters, only one character (the dominant character) is expressed in the F1 generation, while the other (recessive) character remains hidden. Law of purity of gametes (segregation): although a hybrid carries two different alleles for a character, these alleles remain distinct and separate cleanly during gamete formation in meiosis, so each gamete carries only one pure allele - this is why self-pollinating F1 hybrids produces a 3:1 ratio of dominant to recessive characters in F2.

9SEE Boardqb-q30

Explain the importance of genetic engineering.

Ans.Genetic engineering allows scientists to alter the DNA of an organism directly - by changing a base pair, or adding/deleting a gene - to develop new, desired traits quickly and precisely. It is widely used in agriculture to improve crop yield and quality and resistance to biotic/abiotic stress, in medicine and biotechnology for producing useful proteins, and its techniques underlie modern DNA-based technologies such as DNA testing for forensic and paternity investigations.

Give Reason Questions

1SEE Boardqb-q31

Offspring have the same characteristics as their parents.

Ans.Parental characters are carried by genes present in the chromosomes of the parents' cells. During sexual reproduction, gametes containing these genes combine to form the zygote, so the offspring inherits a combination of genes from both parents, making the offspring resemble them.

2SEE Boardqb-q32

The male has a main role in the determination of sex.

Ans.A woman's ova always carry an X chromosome, but a man's sperm can carry either an X or a Y chromosome. Since the sex of the child depends on whether the fertilizing sperm carries an X or a Y chromosome, the male's sperm determines whether the child will be male or female.

3SEE Boardqb-q33

Though males have both X and Y sex chromosomes, some of them have only male or only female kids.

Ans.The sex chromosome carried by an individual sperm cell is determined randomly during meiosis and fertilization, so which type of sperm (X-bearing or Y-bearing) happens to fertilize the egg in each pregnancy is a matter of chance; it is statistically possible, though not very likely over many pregnancies, for a couple to have only sons or only daughters purely by chance.

4SEE Boardqb-q34

Meiotic cell division is also called reductional cell division.

Ans.In meiosis, one diploid (2n) mother cell divides to form four haploid (n) daughter cells, in which the chromosome number is reduced to exactly half that of the mother cell; because of this reduction, meiosis is called reductional cell division.

5SEE Boardqb-q35

Mitotic cell division is also called equational cell division.

Ans.In mitosis, the DNA is replicated before division, and the two daughter cells formed have the same (diploid) chromosome number as the mother cell, with no change or reduction in chromosome number; because the chromosome number remains equal, mitosis is called equational cell division.

6SEE Boardqb-q36

Sexual reproduction is impossible without meiotic cell division.

Ans.Sexual reproduction requires the fusion of a male and a female gamete to form a zygote with the normal diploid chromosome number. Only meiosis can produce haploid gametes with half the chromosome number; without meiosis, gametes would remain diploid, and their fusion would double the chromosome number in every generation, making normal sexual reproduction impossible.

7SEE Boardqb-q37

Meiotic cell division brings variation.

Ans.During the first phase of meiosis, crossing over occurs between non-sister chromosomes, exchanging segments of genetic material between them. This reshuffling of genes, along with the random combination of chromosomes into gametes, produces genetic variation in the daughter cells (gametes), so offspring are genetically different from their parents and from each other.

8SEE Boardqb-q38

Mendel selected pea plants for his experiment.

Ans.Pea plants are bisexual with naturally closed, self-pollinating flowers, but can also be cross-pollinated when needed; they have a short life cycle, produce many seeds and offspring quickly, show many pairs of clearly contrasting characters, and are easy to cultivate - all of which made them ideal for Mendel's breeding experiments.

9SEE Boardqb-q39

When tall pea plants and dwarf pea plants are cross-pollinated, tall plants are produced in the first filial generation.

Ans.Tallness is the dominant character and dwarfness is the recessive character in pea plants. According to the law of dominance, when a cross is made between two pure individuals with contrasting characters, only the dominant character is expressed in the F1 generation, so all F1 plants appear tall even though they carry one gene for tallness and one for dwarfness.

10SEE Boardqb-q40

When self-breeding is done between hybrids, different types of offspring are produced.

Ans.A hybrid (e.g., Tt) carries two different alleles for a character. During meiosis, according to the law of segregation, these alleles separate so that gametes carry either the dominant (T) or the recessive (t) allele in equal proportion. When two such hybrids self-pollinate, the random combination of these gametes at fertilization produces different genotype combinations (TT, Tt, Tt, tt), resulting in different types of offspring in the ratio 1:2:1 genotypically and 3:1 phenotypically.

11SEE Boardqb-q41

DNA testing is a reliable technique for criminal investigation.

Ans.DNA is unique to each individual (except identical twins), and DNA sequences are inherited in predictable patterns from parents. By comparing DNA from a crime scene sample with that of a suspect, or comparing a child's DNA with that of a potential parent, DNA testing can establish identity or biological relationship with very high scientific accuracy, making it a reliable tool for criminal investigation and paternity testing.

12SEE Boardqb-q42

Genetic engineering involves the detailed study of DNA.

Ans.Genetic engineering requires scientists to identify specific genes, understand their function and the coded instructions they carry, and know exactly where and how to make changes (adding, deleting or substituting nitrogen bases or genes) in the DNA sequence to achieve a desired trait; all of this requires a detailed, precise study of DNA structure and function.

13SEE Boardqb-q43

Offspring produced by cross-breeding may be sterile.

Ans.Cross-breeding often combines two different species (e.g., donkey and horse to form a mule, or zebra and horse to form a zebroid). Because the parent species have different numbers or structures of chromosomes, the chromosomes of the hybrid offspring may not pair up properly during meiosis, preventing the formation of normal, functional gametes and making the hybrid sterile.

14SEE Boardqb-q44

Special attention should be given while collecting samples for DNA testing.

Ans.DNA testing is a complex and highly sensitive procedure, and even a simple error, mix-up, or contamination of the sample during collection or transportation can lead to significant inaccuracies in the result. Since DNA test results can have serious legal or personal consequences (e.g., in criminal or paternity cases), special care is needed to keep the process reliable, fair and effective.

Differentiate Between

1SEE Boardqb-q45

Differentiate: Autosome and Sex Chromosome

Autosome	Sex Chromosome
Determines the physical characteristics of an individual.	Determines the sex of an individual.
Both members of a pair have the same shape/size.	The two members of a pair may differ in shape/size (X and Y).
22 pairs found in humans.	1 pair found in humans.

2SEE Boardqb-q46

Differentiate: Mitosis and Meiosis

Mitosis	Meiosis
Occurs in somatic cells.	Occurs in mother cells of testis and ovary only.
Forms 2 diploid daughter cells.	Forms 4 haploid daughter cells.
No crossing over; genetically identical daughter cells.	Crossing over occurs; brings variation.
Also called equational division.	Also called reductional division.

3SEE Boardqb-q47

Differentiate: DNA and RNA

DNA	RNA
Double-stranded.	Single-stranded.
Deoxyribose sugar; bases A, G, C, T.	Ribose sugar; bases A, G, C, U.
Stores and transmits hereditary information.	Helps in protein synthesis.

4SEE Boardqb-q48

Differentiate: Haploid and Diploid

Haploid	Diploid
One set of chromosomes (n).	Two sets of chromosomes (2n).
Found in gametes.	Found in somatic cells.
Human gamete: 23 chromosomes.	Human somatic cell: 46 chromosomes.

5SEE Boardqb-q49

Differentiate: Dominant and Recessive Characters

Dominant Character	Recessive Character
Expressed in F1 generation.	Hidden in F1 generation, may reappear in F2.
Represented by a capital letter.	Represented by a small letter.

6SEE Boardqb-q50

Differentiate: Phenotype and Genotype

Phenotype	Genotype
Externally visible character.	Genetic constitution (allele combination).
E.g., tall plant.	E.g., TT or Tt.

7SEE Boardqb-q51

Differentiate: Inbreeding and Cross-breeding

Inbreeding	Cross-breeding
Breeding between closely related individuals.	Breeding between two unrelated individuals/species.
Produces purebred offspring.	Produces hybrid offspring.

8SEE Boardqb-q52

Differentiate: Artificial Insemination and In Vitro Fertilization

Artificial Insemination	In Vitro Fertilization
Semen is placed into the female reproductive tract using equipment.	Egg and sperm are fused outside the body in a laboratory dish.
Fertilization occurs inside the female's body.	Fertilization occurs in the laboratory; the embryo is then transferred to the uterus.
Simpler and less expensive.	More complex and expensive; used for more severe fertility problems.

9SEE Boardqb-q53

Differentiate: Tigon and Liger

Tigon	Liger
Offspring of a male tiger and a female lion.	Offspring of a male lion and a female tiger.
Smaller than both parents.	Larger than both parents.
Resembles a tiger in appearance, but behaves mostly like a lion.	Generally behaves like a lion.

Long Answer Questions

1SEE Boardqb-q54

What is monohybrid cross? Show in a filial chart the result obtained by cross-pollinating and then self-pollinating a red-flowering pea plant and a white-flowering pea plant.

Ans.A monohybrid cross is a cross made between two pure organisms considering only one pair of contrasting characters. Taking red flower colour (R) as dominant and white (r) as recessive: Parent generation - pure red (RR) x pure white (rr). Gametes: R and r. F1 generation: all Rr (red, since red is dominant). Self-pollinating F1 (Rr x Rr) gives gametes R and r from each parent, combining to give F2 genotypes RR : Rr : Rr : rr, i.e. a genotypic ratio of 1 RR : 2 Rr : 1 rr, and a phenotypic ratio of 3 red : 1 white.

2SEE Boardqb-q55

Explain with an example that Mendel's experiment can be done not only in plants but also in animals.

Ans.Mendel's laws apply generally to sexually reproducing organisms, not just pea plants. For example, when a pure black guinea pig (BB) is crossed with a pure white guinea pig (bb), all F1 offspring are hybrid black (Bb), showing black is dominant - exactly as tallness was dominant over dwarfness in pea plants. When these F1 hybrid black guinea pigs (Bb) are crossed with each other, the F2 generation shows 75% black and 25% white guinea pigs, giving a phenotypic ratio of 3:1 and a genotypic ratio of 1:2:1 (pure black : hybrid black : pure white) - the same pattern of dominance and segregation seen in Mendel's pea plant experiments, confirming that his laws of inheritance apply to animals as well as plants.

3SEE Boardqb-q56

Is genetic engineering a boon or a bane for the present era? Give your arguments.

Ans.Genetic engineering can be seen as both a boon and a bane, depending on how it is used. As a boon: it allows the development of crop varieties with higher yield, better quality, and resistance to pests, diseases and environmental stress; it enables production of useful proteins and medicines through biotechnology; and it supports forensic science and paternity testing through DNA-based technologies, and helps understand and potentially correct certain genetic disorders. As a possible bane: uncontrolled or careless genetic modification could introduce unpredictable changes into ecosystems, reduce natural genetic diversity, raise ethical concerns about modifying living organisms (including potential future use in humans), and could be misused if not properly regulated. On balance, genetic engineering offers great potential benefits for agriculture, medicine and science, but careful regulation, testing and ethical oversight are needed to prevent its misuse.

Diagram-Based Questions

1SEE Boardqb-q57

A technician working in a radiotherapy laboratory was tested after a long time of marriage when there was no childbirth. It was found that his child-production capacity was reduced because he worked in high-intensity radiation for a long time. Which part of the cell is affected in this case?

Ans.DNA. High-intensity radiation damages the DNA in the reproductive cells (during meiosis in the testis), which can impair normal sperm formation and reduce fertility.

2SEE Boardqb-q58

If there is no DNA transcription in a cell, which process is affected?

Ans.Protein synthesis. Transcription copies genetic information from DNA into RNA, and this RNA (especially mRNA) is required to synthesize proteins; without transcription, protein synthesis cannot occur.

3SEE Boardqb-q59

If a nucleotide is destroyed during DNA replication, what happens to the organism?

Ans.A genetic disorder can occur. Loss or alteration of a nucleotide changes the DNA sequence (a mutation), which can alter the gene's coded instructions and lead to abnormal proteins being made, potentially causing a genetic disorder in the organism.

4SEE Boardqb-q60

Complete the concept maps: (A) Reproductive cell -> cell division -> gamete; (B) Somatic cell -> cell division -> ?. Write the differences between these processes.

Ans.(A) The cell division shown is meiosis (Reproductive cell -> meiosis -> gamete). (B) Somatic cell -> mitosis -> somatic (daughter) cell. Differences: meiosis occurs in reproductive cells (testis/ovary) and produces four haploid gametes with genetic variation from crossing over; mitosis occurs in somatic cells and produces two diploid daughter cells genetically identical to the mother cell, mainly for growth and repair.

5SEE Boardqb-q61

Round-seeded pea plants and wrinkle-seeded pea plants are cross-pollinated first, and then the F1 offspring are self-pollinated. The Punnett square below shows the F2 result: R/r x R/r giving RR, Rr, Rr, rr. Answer: (i) the ratio of plants showing dominant and recessive characters, (ii) the genotypic and phenotypic ratio of this generation, (iii) which plant is purely round-seeded and why.

Ans.

(i) Dominant (round) to recessive (wrinkled) ratio is 3:1.
(ii) Genotypic ratio is RR:Rr:rr = 1:2:1; phenotypic ratio is round:wrinkled = 3:1.
(iii) The plant with genotype RR is purely round-seeded, because it carries two copies of the dominant round-seed allele (R) and no recessive allele, so it will always breed true for the round-seed character.

Application / Conceptual Questions

1SEE Boardqb-q62

A white-skinned child was born to dark-skinned parents. What is the likely genetic reason for this?

Ans.This can happen if both parents are hybrids (heterozygous) carrying one dominant gene for dark skin and one recessive gene for light/white skin, even though they themselves appear dark-skinned because dark skin colour is dominant. When two such hybrid parents have children, according to Mendel's law of segregation, there is a chance (about 1 in 4, similar to the recessive class in a monohybrid cross) that a child inherits the recessive (white-skin) allele from both parents, resulting in a white-skinned child despite both parents being dark-skinned.

2SEE Boardqb-q63

In order to produce good meat, farmers look for Boer goats and cross them with local goats. What kind of breeding method is this?

Ans.This is selective breeding, specifically cross breeding - farmers are deliberately crossing an improved/exotic breed (Boer goat, known for good meat quality) with local goats to combine the desirable meat-producing traits of the Boer goat with the hardiness or adaptability of the local breed in their offspring (hybrids).

3SEE Boardqb-q64

Ramit produced a new plant by crossing an orange plant and a lemon plant. What type of plant is this?

Ans.This is a hybrid plant, produced by cross breeding two different but related species (both citrus) to combine desired characteristics from each parent plant.

4SEE Boardqb-q65

Roshani's family keeps a mule for transporting goods in the Himalayan region. She asked her father how a mule gives birth to a child. What is the correct explanation?

Ans.Mules cannot produce offspring naturally - they are generally sterile. A mule is a hybrid produced by cross-breeding a donkey and a horse; because donkeys and horses have different numbers of chromosomes, the mule's chromosomes cannot pair up properly during meiosis, so it cannot produce functional gametes. Therefore, when the family needs a new mule, they must breed a horse and a donkey again rather than expecting the mule itself to reproduce.

5SEE Boardqb-q66

When a cross is made between a black guinea pig and a white guinea pig, the offspring of the first filial generation were all black. Explain why white guinea pigs did not appear in this generation.

Ans.This happens if the parent guinea pigs were pure black (BB) and pure white (bb). Black is the dominant character and white is the recessive character. According to Mendel's law of dominance, when two pure individuals with contrasting characters are crossed, only the dominant character is expressed in the F1 generation. Since all F1 offspring are hybrid (Bb), carrying one dominant black allele, they all appear black; the recessive white character remains hidden (masked) in this generation and would only reappear in later generations if the F1 hybrids are bred further.

6SEE Boardqb-q67

In a case where a person's paternity of a child needs to be established (for example, following a serious crime or dispute over parentage), how can the father of the child be identified?

Ans.The father of a child can be scientifically identified using DNA testing (paternity testing). Since a child inherits half of their DNA/genetic material from the biological father and half from the mother, a sample of the child's DNA (and, where relevant, the mother's DNA) can be compared with a DNA sample from the alleged father, collected under proper legal and medical procedure. If the child's DNA pattern matches the expected combination from the mother and the alleged father, paternity can be confirmed with very high scientific accuracy; careful sample collection and handling by trained professionals is essential for the result to be reliable and legally valid.

7SEE Boardqb-q68

The district animal development centre conducted a camp to fertilize many cows at once. Which technique did that organization adopt at that time? Explain this technique in brief.

Ans.The organization most likely used artificial insemination (AI). In this technique, semen is collected from a male of an advanced/improved breed, tested for fertility, and then, using special equipment, introduced into the reproductive tract of each female (cow) at the appropriate time in her reproductive cycle. This allows many cows to be fertilized using semen from a single high-quality bull without needing to keep or transport that bull to each farm, improving the genetic quality of the herd efficiently and economically.

8SEE Boardqb-q69

How has artificial insemination (AI) technology helped bring benefits to farmers? Explain.

Ans.AI allows farmers to use semen from genetically superior, high-quality male animals without the expense and difficulty of keeping such males themselves, saving on rearing costs. It reduces the risk of disease transmission during mating, allows semen to be tested for fertility and transported over long distances, and can even be used after the death of a valuable male using previously stored semen. This improves the genetic quality, productivity (e.g., milk yield, meat quality) and overall value of farm animals, helping strengthen farmers' economic status.

9SEE Boardqb-q70

IVF is proved to be a boon for childless couples. Justify this statement.

Ans.IVF offers a scientific method of conception for couples who are otherwise unable to conceive due to infertility or genetic problems, even when standard tests do not reveal an obvious cause, as in cases similar to the textbook's case study. It allows use of the couple's own egg and sperm, or donor gametes if needed, and is generally more successful than other assisted reproductive techniques. IVF can help avoid the transmission of certain chromosomal disorders, increases the chance of a healthy pregnancy, and has enabled many couples worldwide - and in Nepal, since Om Mani Tamang's birth in 2005 - to have biological or genetically related children when natural conception was not possible, justifying its description as a boon for childless couples, despite its cost and possible side effects.

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