Heredity (Part I) - Class 10 Science Guide [New Syllabus]
Unit - 4
Heredity (Part - I)
Exercise
1. Choose the correct option for the given questions.
a. How many pairs of sex chromosomes are found in the human cell?
i. 1 pair
ii. 22 pairs
iii. 23 pairs
iv. 46 pairs
b. What is a chromosome made up of?
i. DNA and RNA
ii. DNA and carbohydrate
iii. DNA and protein
iv. RNA and protein
C. What is the main function of sex chromosomes?
i. To determine physical characteristics
ii. To determine sex
iii. To increase immunity
iv. To determine the structure of the eye
d. What is the smallest unit of the chromosome that helps in the transmission of hereditary characteristics?
i. DNA
iii. Centromere
ii. Chromatid
iv. Gene
e. Which of the following statements is correct for mitotic cell division?
i. Four cells are formed at the time of cell division.
ii. Haploid cells are formed at the end of cell division. (Note that: Haploid cells are formed at the end of meiosis II)
iii. It has the main role to form gametes.
iv. This cell division helps to repair tissue.
f. A technician working in a radiotherapy laboratory was tested after a long time of marriage when there was no childbirth. After the test, 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?
i. DNA
iii. Cytoplasm
ii. RNA
iv. Nucleus
g. If there is no DNA transcription in a cell. which process is affected?
i. Photosynthesis
ii. Sexual reproduction
iii. Protein synthesis
iv. Cell division
h. If a nucleotide is destructed during DNA replication, what happens to the organism?
i. Genetic disorder occurs
ii. It brings a problem in cell division
iii. It brings a problem in reproduction.
iv. The chromosome does not function.
i. Which of the following indicates the set of chromosomes in a cell of a woman?
i. 44+XY
ii. 44+XX
iii. 22+XY
iv. 22+XX
j. Which of the following statements is true?
i. Ovum contains only a Y chromosome and sperm contains an X chromosome.
ii. Ovum contains only an X chromosome and sperm contains a Y chromosome.
iii. Ovum contains only an X chromosome and sperm contains either an X or Y chromosome.
iv. Ovum and sperm both contain X and Y-chromosomes.
2. Write differences:
a. Autosome and sex chromosome
Autosome vs Sex Chromosome
Autosome
Sex Chromosome
1. Autosomes are non-sex chromosomes that determine most of an organism's traits.
1. Sex chromosomes determine the biological sex of an organism.
2. Humans have 22 pairs of autosomes.
2. Humans have 1 pair of sex chromosomes (XX for females, XY for males).
3. Autosomes are present in both males and females.
3. Sex chromosomes differ between males and females.
4. Autosomes carry genetic information related to traits such as eye color, height, etc.
4. Sex chromosomes carry genetic information related to gender determination and reproductive system development.
5. Example: Chromosome 1, Chromosome 2, etc.
5. Example: X chromosome, Y chromosome.
b. Mitosis and meiosis
Mitosis vs Meiosis
Mitosis
Meiosis
1. Mitosis is the process of cell division that results in two identical daughter cells.
1. Meiosis is the process of cell division that reduces the chromosome number by half, producing four genetically diverse gametes.
2. It occurs in somatic (body) cells.
2. It occurs in germ (sex) cells to produce sperm and eggs.
3. The chromosome number remains the same in the daughter cells (2n → 2n).
3. The chromosome number is halved in the daughter cells (2n → n).
4. Mitosis involves one division (prophase, metaphase, anaphase, telophase).
4. Meiosis involves two divisions (Meiosis I and Meiosis II), each with prophase, metaphase, anaphase, and telophase.
5. The result is two diploid (2n) daughter cells that are genetically identical.
5. The result is four haploid (n) daughter cells that are genetically different from each other and the parent cell.
6. Example: Cell division for growth, repair, and asexual reproduction.
6. Example: Cell division for sexual reproduction, forming gametes (sperm and eggs).
C. DNA and RNA
DNA vs RNA
DNA
RNA
1. DNA stands for Deoxyribonucleic Acid.
1. RNA stands for Ribonucleic Acid.
2. DNA is double-stranded in a double helix structure.
2. RNA is single-stranded.
3. DNA contains the sugar deoxyribose.
3. RNA contains the sugar ribose.
4. DNA has the base Thymine (T).
4. RNA has the base Uracil (U) instead of Thymine (T).
5. DNA is primarily located in the nucleus of the cell.
5. RNA is synthesized in the nucleus but is found in both the nucleus and the cytoplasm.
6. DNA stores genetic information and is responsible for heredity.
6. RNA plays a role in protein synthesis and gene expression.
7. DNA is more stable due to its double-stranded structure.
7. RNA is more prone to degradation due to its single-stranded nature.
8. Example: The human genome is made of DNA.
8. Example: mRNA, tRNA, and rRNA are types of RNA.
d. Haploid and Diploid
Haploid vs Diploid
Haploid
Diploid
1. Haploid cells have one set of chromosomes (n).
1. Diploid cells have two sets of chromosomes (2n).
2. Haploid cells are found in gametes (sperm and egg cells).
2. Diploid cells are found in somatic (body) cells.
3. Haploid cells are produced by meiosis.
3. Diploid cells are produced by mitosis.
4. Haploid cells have half the chromosome number of diploid cells.
4. Diploid cells have a full set of chromosomes, which are inherited from both parents.
5. Example: Human gametes (sperm and egg).
5. Example: Human somatic cells (skin cells, muscle cells, etc.).
6. Haploid number in humans is 23.
6. Diploid number in humans is 46 (23 pairs of chromosomes).
7. Haploid cells are not genetically identical; they have different combinations of chromosomes due to recombination.
7. Diploid cells are genetically identical to each other (except in the case of mutations).
3. Give reason:
a. Offspring have the same characteristics as their parents.
→ Offspring have the same characteristics as their parents because chromosomes in the nucleus replicate and divide during cell division, passing identical genetic information to daughter cells.
b. The male has a main role in the determination of sex.
→ The male has a main role in the determination of sex because he can contribute either an X or a Y chromosome, while the female only contributes an X chromosome. If the male contributes an X chromosome, the offspring will be female (XX), and if the male contributes a Y chromosome, the offspring will be male (XY).
C. Though males have both X and Y sex chromosomes, some of them have only male or only female kids.
→ The sperm cells of men hold approximately 50 percent of Y chromosome and other 50 percent of X chromosome. Therefore, despite having both X and Y chromosomes, there is possibility that some of them have kids of only one gender.
d. Meiotic cell division is also called reductional cell division.
→ Meiotic cell division is called reductional cell division because it reduces chromosome number half in the daughter cells if compared to their mother cell.
e. Mitotic cell division is also called equational cell division.
→ It’s because the daughter cells have same no. of chromosome as in mother cell.
f. Sexual reproduction is impossible without meiotic cell division.
→ Meiotic cell division maintains a definite and constant number of chromosomes in the sexual reproduction as it avoids the multiplication of chromosomes in offspring by reduction division. But in mitosis cell division no. of chromosomes is equal in daughter cell and reproduction is impossible. Thus, sexual reproduction is impossible without meiotic cell division.
g. Meiotic cell division brings variation.
→ During meiotic cell division, homologous chromosomes (one from each parent) align along their lengths. At specific points called chiasmata, the chromosomes cross over, breaking and rejoining to exchange genetic material. This recombination results in variation.
4. Answer the following question.
a. What is a gene?
→ The smallest fragment of DNA in a chromosome which codes or represents a specific character of an organism is called gene.
b. What is a chromosome? Clarify the role of chromosomes in the body of living beings.
→ The chromatin fibers inside nucleus of cell which becomes short, thickened and prominent during cell division are called chromosomes.
→ The role of chromosomes in the body of living beings are as follows:
- Somatic chromosomes determine the physical characteristics of an individual.
- Sex chromosomes determine the sex of an individual.
C. Explain the importance of mitotic cell division in the growth and development of the body.
→ Mitotic cell division plays a key role in physical growth, as the number of cells with same genetic makeup increases during cell division. It helps regenerate cells in injured area, returning them to original state. It maintains genetic stability.
d. Explain the role of mitosis and meiosis in the reproduction of organisms.
→ Mitosis and meiosis both play key roles in reproduction:
- Mitosis is responsible for the growth, repair, and asexual reproduction of cells. It produces two genetically identical daughter cells, maintaining the chromosome number of the original cell.
- Meiosis is involved in sexual reproduction, reducing the chromosome number by half to produce gametes. So, when fertilization occurs, the resulting offspring have the correct number of chromosomes. Meiosis also promotes genetic variation through recombination.
e. What will happen if meiotic cell division does not occur in the reproductive cell of an organism? Explain.
→ Without meiotic cell division, sexual reproduction would not be possible, and the organism would be unable to produce viable, genetically diverse offspring.
f. Clearly explain the role of genes in the transmission of hereditary characteristics in organisms.
→ The role of genes in transmission of hereditary characteristics in organisms are as follows:
· Genes are segments of DNA that carry the genetic information from parents to offspring.
· They determine inherited traits like eye color, height, and blood type based on the alleles inherited.
· Genes control the synthesis of proteins, which influence the physical and functional characteristics of an organism.
· Genetic variation arises through recombination during meiosis, leading to diversity in offspring.
g. How is sex determined in humans? Explain with a chart.
→
 |
| Figure: Sex determination Chart |
h. A woman is pregnant. What is her probability of giving birth to a daughter? Write in percent.
→ Her probability of giving birth to a daughter is 50%.
i. A couple gave birth to only a son. Does it mean that the testes of those male-produced sperms have Y-chromosomes only?
→ No, it doesn’t necessarily mean that. If a couple has a son, it means that the father’s sperm that fertilized the egg carried a Y chromosome, resulting in the combination XY, which is male. However, the father’s testes still produce both X and Y bearing sperm.
j. Complete the concept maps 'a' and 'b'. Write the differences between these processes.
Reproductive cell → cell division → Gamete [A]
Somatic Cell → cell division → Mitosis [B]
→ Differences between process A and B are as follows:
Process A:
-Reproductive cells divide by meiosis, producing four genetically different cells with half the chromosome number.
-Meiosis reduces the chromosome number by half (haploid) to ensure proper fertilization.
Process B:
-Somatic cells divide by mitosis, producing two identical cells.
-Mitosis maintains the same chromosome number in daughter cells (diploid).
Review of Chapter:
Ø The branch of biology that deals with the study of genes is called genetics.
Ø Cell division is the process by which a cell splits into two or more new cells, called daughter cells.
Ø There are 3 types of cell division- Amitosis, Mitosis and Meiosis cell division.
Ø Amitosis Cell division: it is simple and primitive type of cell division. The amitosis cell division is means of asexual reproduction which commonly occurs in some protozoa, bacteria, yeast etc.
Ø Mitosis cell division: mitosis is a type of cell division in which a single cell divides to form two daughter cells, having same no of chromosomes as in parent cell. It occurs in somatic and vegetative cells and hence called somatic cell division. This cell division completes in two phases (It actually completes in 3 phases but you don’t need to study the first phase called interphase where no visible changes occurs in nucleus): Karyokinesis and Cytokinesis. The significance of mitosis cell division are as follows:
- It maintains fixed no. of chromosomes in somatic cells.
- It helps in growth and development of new organs in multicellular organisms.
- It repairs old cells and regenerates the damaged tissues and organs.
- It helps in asexual reproduction.
Ø Meiosis Cell division: Meiosis is a type of cell division in which one mother cell produces four daughter cells; each daughter cell bears half the number of chromosome as compared to mother cell. This cell division completes in two phases namely Meiosis I and Meiosis II.
a. Meiosis I: The key processes involved in it are:
1. Crossing over occurs, leading to the exchange of genetic material between non sister chromatids, creating genetic variation.
2. Karyokinesis divides the nucleus into two haploid nuclei.
3. Cytokinesis forms two haploid cells.
Chromosome number is reduced to half, making it a reduction division.
b. Meiosis II: It is second phase. The key processes involved here are:
1. Each haploid cells undergoes a mitotic like division.
2. Karyokinesis divides nucleus again.
3. Cytokinesis forms a total of four haploid cells.
Chromosomes number remains unchanged in this phase, maintaining the haploid state.
Ø DNA:
Location: Found in prokaryotic cytoplasm, eukaryotic chromosomes, and virus capsids.
Structure: Made of two antiparallel strands; Basic unit is Nucleotide (nitrogen base + sugar + phosphate); Nitrogen bases are Adenine (A) which pairs with Thymine (T), and Guanine (G) which pairs with Cytosine (C)
Function: Carries hereditary information and codes traits through genes; also passes traits during cell division.
Significance: Variations in nucleotide sequences create diversity. Transcription of DNA forms RNA, aiding in protein synthesis.
Ø RNA:
Location: Found in the cytoplasm and nucleus of cells.
Structure: Single-stranded molecule; Basic unit is Nucleotide (nitrogen base + ribose sugar + phosphate); Nitrogen bases are Adenine (A) which pairs with Uracil (U), and Guanine (G) which pairs with Cytosine (C)
Function: Helps in protein synthesis by translating genetic instructions from DNA. Acts as a messenger (mRNA), transfer molecule (tRNA) or part of ribosomes (rRNA).
Significance: Essential for gene expression and protein formation. Temporary carrier of genetic information.
Ø CHROMOSOMES: The condensed form of chromatin fibres found within nucleus are called chromosomes. The no of chromosome for particular species is usually fixed but it varies considerably among species.
Human beings: 46 chromosomes
Gorillas: 48 chromosomes
Rat: 42 chromosomes
Ophioglossum: 1266 chromosomes
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