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Q5:
How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Solution :
Core Biological Principle & Setup
The biological distinction between progeny formed via asexual reproduction and those formed via sexual reproduction lies in their genetic constitution, the mechanism of cell division utilized, and their evolutionary potential. Asexual reproduction fundamentally involves uniparental inheritance without the fusion of gametes, whereas sexual reproduction relies on biparental inheritance, the formation of haploid gametes via meiosis, and syngamy (fertilization) to restore the diploid state.
Step 1: Analyzing the Genetic Constitution of Asexual Progeny
In asexual reproduction, the progeny are produced through continuous mitotic cell divisions (or mechanisms akin to mitosis, such as binary fission in prokaryotes). Because mitosis is an equational division, the genome is duplicated and segregated equally.
- Clonal Nature: The offspring are exact morphological and genetic replicas of the single parent. The term clone is scientifically applied to such individuals.
- Genetic Variance: Variation is strictly absent, except in the highly statistically improbable event of a spontaneous somatic mutation during DNA replication. [Per the principles of Mitotic Equational Segregation].
Step 2: Analyzing the Genetic Constitution of Sexual Progeny
Sexual reproduction mandates the fusion of male and female gametes ($n$ + $n \rightarrow 2n$). Gametogenesis involves meiosis, a reductional division.
- Recombination and Variation: During the Pachytene stage of Prophase I in meiosis, non-sister chromatids of homologous chromosomes exchange genetic material. [Driven by the mechanism of Crossing Over facilitated by the recombinase enzyme complex].
- Independent Assortment: Chromosomes align randomly at the metaphase plate, generating myriad combinations of maternal and paternal genes. [Per Mendel’s Law of Independent Assortment].
- Unique Identity: As a result, the progeny are genetically distinct from both parents and from one another (with the exception of monozygotic twins).
Step 3: Evolutionary and Ecological Significance
The genetic homogeneity of asexual progeny renders the entire population highly susceptible to environmental fluctuations or novel pathogens; if an ecological shift is lethal to the parent, it is equally lethal to the clones. Conversely, the high degree of heterozygosity and genetic recombination in sexual progeny creates phenotypic diversity. [According to Darwinian Evolutionary Theory, this variation serves as the primary substrate for Natural Selection, thereby significantly enhancing the adaptability and survival probability of the species in dynamic environments].
Step 4: Comprehensive Analytical Comparison
| Biological Parameter | Progeny from Asexual Reproduction | Progeny from Sexual Reproduction |
|---|---|---|
| Genetic Identity | 100% genetically identical to the parent (Clones). | Genetically unique; an admixture of maternal and paternal genes. |
| Cellular Mechanism | Formed exclusively via Mitosis (equational division). | Requires Meiosis (reductional division) followed by syngamy, then Mitosis. |
| Ploidy Conservation | Ploidy ($n$ or $2n$) is directly inherited and maintained without gametic fusion. | Haploid ($n$) gametes fuse to restore the diploid ($2n$) state in the zygote. |
| Adaptability / Vigor | Low adaptive capacity; evolutionary stagnation. | High adaptive capacity; exhibits hybrid vigor (heterosis) and continuous evolution. |
Step 5: Visualizing Genetic Inheritance Models
The following vector diagram rigorously illustrates the transmission of genetic material, distinguishing the clonal expansion of asexual reproduction from the genetic recombination inherent to sexual reproduction.
Final Solution: The fundamental difference is that progeny from asexual reproduction are precise genetic and morphological clones of a single parent generated via mitosis, lacking variation. Conversely, progeny from sexual reproduction are genetically unique hybrids, generated through the meiotic formation and subsequent fusion (syngamy) of male and female gametes, which introduces high genetic variation crucial for evolutionary adaptation.
More Questions from Class 12 Biology Reproduction in Organisms EXERCISES
- Q1: Why is reproduction essential for organisms?
- Q1: Why is reproduction essential for organisms?
- Q2: Which is a better mode of reproduction: sexual or asexual? Why?
- Q2: Which is a better mode of reproduction: sexual or asexual? Why?
- Q3: Why is the offspring formed by asexual reproduction referred to as clone?
- Q3: Why is the offspring formed by asexual reproduction referred to as clone?
- Q4: Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
- Q4: Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
- Q5: How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
- Q6: Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
- Q6: Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
- Q7: What is vegetative propagation? Give two suitable examples.
- Q7: What is vegetative propagation? Give two suitable examples.
- Q8(a): Define (a) Juvenile phase,
- Q8(a): Define (a) Juvenile phase,
- Q8(b): Define (b) Reproductive phase,
- Q8(b): Define (b) Reproductive phase,
- Q8(c): Define (c) Senescent phase.
- Q8(c): Define (c) Senescent phase.
- Q9: Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
- Q9: Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
- Q10: Explain why meiosis and gametogenesis are always interlinked?
- Q10: Explain why meiosis and gametogenesis are always interlinked?
- Q11(a): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (a) Ovary ———————————
- Q11(a): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (a) Ovary ———————————
- Q11(b): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (b) Anther ———————————
- Q11(b): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (b) Anther ———————————
- Q11(c): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (c) Egg ———————————
- Q11(c): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (c) Egg ———————————
- Q11(d): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (d) Pollen ———————————
- Q11(d): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (d) Pollen ———————————
- Q11(e): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (e) Male gamete ———————————
- Q11(e): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (e) Male gamete ———————————
- Q11(f): Identify each part in a flowering plant and write whether it is haploid (\(n\)) or diploid (\(2n\)). (f) Zygote ———————————
- Q11(f): Identify each part in a flowering plant and write whether it is haploid ((n)) or diploid ((2n)). (f ) Zygote ———————————
- Q12: Define external fertilisation. Mention its disadvantages.
- Q12: Define external fertilisation. Mention its disadvantages.
- Q13: Differentiate between a zoospore and a zygote.
- Q13: Differentiate between a zoospore and a zygote.
- Q14: Differentiate between gametogenesis from embryogenesis.
- Q14: Differentiate between gametogenesis from embryogenesis.
- Q15: Describe the post-fertilisation changes in a flower.
- Q15: Describe the post-fertilisation changes in a flower.
- Q16: What is a bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
- Q16: What is a bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
- Q17: Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers?
- Q17: Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers?
- Q18: Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
- Q18: Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
CBSE Solutions for Class 12 Biology Reproduction in Organisms
Chapters in CBSE - Class 12 Biology
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Evolution
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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