🧬 Heredity | Speciation
Class 10 Science | CBSE + Foundation + Competitive Level
Variation • Isolation • Natural Selection • Formation of New Species
🧬 Heredity | Speciation
1. Speciation – Introduction | प्रजाति निर्माण
Speciation is the evolutionary process through which one existing population becomes separated into two or more populations that eventually become distinct species.
Speciation = Formation of new species
हिन्दी: Speciation वह विकासवादी प्रक्रिया है जिसमें एक जनसंख्या समय के साथ अलग-अलग समूहों में विभाजित होकर नई और अलग प्रजातियों का निर्माण कर सकती है।
Speciation = Formation of new species
हिन्दी: Speciation वह विकासवादी प्रक्रिया है जिसमें एक जनसंख्या समय के साथ अलग-अलग समूहों में विभाजित होकर नई और अलग प्रजातियों का निर्माण कर सकती है।
CBSE Key Point: Speciation is associated with the accumulation of heritable variations and the development of reproductive isolation between populations.
2. What is a Species? | प्रजाति क्या है?
A species is generally a group of organisms that can interbreed under natural conditions and produce fertile offspring.
प्रजाति: सामान्यतः ऐसे जीवों का समूह जो प्राकृतिक परिस्थितियों में आपस में प्रजनन करके उर्वर संतति उत्पन्न कर सकते हैं।
प्रजाति: सामान्यतः ऐसे जीवों का समूह जो प्राकृतिक परिस्थितियों में आपस में प्रजनन करके उर्वर संतति उत्पन्न कर सकते हैं।
Important: The biological species concept works best for sexually reproducing organisms. It is not directly applicable to organisms that reproduce only asexually and has exceptions in some biological situations.
3. How Does Speciation Occur? | Speciation कैसे होती है?
Variation
विविधता
विविधता
→
Isolation
पृथक्करण
पृथक्करण
→
Different Selection Pressures
अलग चयन
अलग चयन
→
Genetic Divergence
आनुवंशिक विचलन
आनुवंशिक विचलन
→
Reproductive Isolation
प्रजनन पृथक्करण
प्रजनन पृथक्करण
→
New Species
नई प्रजाति
नई प्रजाति
4. Role of Variation | विविधता की भूमिका
Variation means differences in characteristics among individuals of the same population.
Variations arise through processes such as:
Variations arise through processes such as:
- DNA copying errors
- Mutation
- Recombination during sexual reproduction
- Gene flow between populations
- Other genetic processes
Some variations may provide an advantage in a particular environment. If such heritable variations increase survival and reproduction, they may become more common over generations.
Remember: Not every variation causes speciation. Speciation usually requires populations to become sufficiently genetically different and reproductively isolated over generations.
5. Geographical Isolation | भौगोलिक पृथक्करण
Geographical isolation occurs when a population is physically separated by barriers such as:
- Mountains
- Rivers
- Deserts
- Oceans
- Islands
- Large distances
When gene flow between separated populations becomes very limited, the populations can accumulate different genetic changes.
Hindi: भौगोलिक बाधा के कारण दो समूहों के बीच जीन का आदान-प्रदान कम या बंद हो सकता है।
Hindi: भौगोलिक बाधा के कारण दो समूहों के बीच जीन का आदान-प्रदान कम या बंद हो सकता है।
🗺️ Animated Concept Diagram – Geographical Isolation
Concept: Physical separation can reduce gene flow and allow populations to diverge.
6. Genetic Drift | आनुवंशिक बहाव
Genetic drift is a random change in the frequency of alleles in a population, especially noticeable in small populations.
Because the change is random, some alleles may become more common while others may disappear from a population.
Example: If a small population becomes isolated and only a few individuals contribute most of the offspring to future generations, allele frequencies may change considerably by chance.
7. Natural Selection and Speciation | प्राकृतिक चयन
Natural selection favours heritable variations that provide an advantage in a particular environment. Over many generations, advantageous variants may become more frequent.
If isolated populations experience different environmental conditions, natural selection may favour different traits in each population. This can contribute to genetic divergence and eventually reproductive isolation.
Heritable Variation + Different Selection Pressures + Isolation → Genetic Divergence
8. Reproductive Isolation | प्रजनन पृथक्करण
Reproductive isolation means that two populations can no longer successfully exchange genes through reproduction.
| Type | Meaning | Example / Idea |
|---|---|---|
| Pre-zygotic isolation | Prevents fertilisation from occurring. | Different mating behaviour, timing or reproductive structures. |
| Post-zygotic isolation | Occurs after fertilisation and reduces successful reproduction of offspring. | Hybrid may have reduced fertility. |
For Class 10 CBSE, the key idea is that reproductive isolation prevents gene flow and helps populations become distinct.
9. Differences in Mating Behaviour | संभोग व्यवहार में अंतर
Different populations may develop differences in:
- Mating calls
- Courtship behaviour
- Mating season
- Choice of mate
- Recognition signals
If individuals from two populations no longer recognise each other as suitable mates, gene flow between them may decrease.
10. Temporal Isolation | समय संबंधी पृथक्करण
Two populations may reproduce at different times.
For example, one population may breed in one season while another population breeds in a different season.
For example, one population may breed in one season while another population breeds in a different season.
Since their reproductive periods do not overlap sufficiently, mating and gene exchange become less likely.
11. Structural / Functional Differences | संरचनात्मक एवं कार्यात्मक अंतर
Differences in reproductive structures or reproductive mechanisms can prevent successful mating or fertilisation between populations.
12. Gene Flow and Speciation | जीन प्रवाह
Gene flow is the movement of genes/alleles between populations through migration and reproduction.
High Gene Flow → Populations remain genetically similar
Reduced Gene Flow → Genetic differences can accumulate
Reduced gene flow alone does not automatically create a new species. Long-term genetic divergence and reproductive isolation are important.
13. Adaptive Radiation | अनुकूली विकिरण
Adaptive radiation is the diversification of an ancestral group into several forms adapted to different ecological niches.
A classic example is Darwin's finches of the Galápagos Islands. Different populations evolved differences in beak characteristics associated with different food sources and ecological conditions.
🐦 Adaptive Radiation – Concept Diagram
14. Island Speciation | द्वीपों पर Speciation
Geographical isolation is especially important on islands. A small population reaching a new island may become isolated from the original population.
Over generations, mutation, recombination, genetic drift and natural selection can produce differences between island and mainland populations.
15. Complete Speciation Pathway | Speciation की पूरी प्रक्रिया
Original Population
→
Variation
→
Geographical Isolation
→
Reduced Gene Flow
→
Different Selection / Drift
→
Genetic Divergence
→
Reproductive Isolation
→
New Species
16. Example of Speciation | Speciation का उदाहरण
Consider a population of organisms living in one geographical region. A mountain range separates a part of the population.
The two groups now experience different environmental conditions and have limited gene flow.
Over many generations, natural selection, mutation, recombination and genetic drift can cause genetic differences to accumulate.
If the two groups eventually become reproductively isolated, they can be considered separate species.
The two groups now experience different environmental conditions and have limited gene flow.
Over many generations, natural selection, mutation, recombination and genetic drift can cause genetic differences to accumulate.
If the two groups eventually become reproductively isolated, they can be considered separate species.
17. Why Human Speciation is Different? | मानव में Speciation
Humans have large amounts of migration and gene flow among populations. Therefore, geographical differences between human populations should not be interpreted as evidence of separate biological species.
Exam Point: Modern humans belong to a single species, Homo sapiens.
18. Speciation vs Evolution | अंतर
| Speciation | Evolution |
|---|---|
| Formation of new species. | Change in heritable characteristics of populations over generations. |
| A major outcome of evolutionary divergence. | Broader process including changes within and between populations. |
| Usually involves reproductive isolation. | May occur without immediate formation of a new species. |
19. Natural Selection and Artificial Selection
| Natural Selection | Artificial Selection |
|---|---|
| Environment determines which heritable variations are favoured. | Humans select organisms with desired traits for breeding. |
| Occurs naturally. | Human-directed. |
| Can contribute to adaptation and speciation. | Used in agriculture and animal breeding. |
20. Mutation and Speciation | उत्परिवर्तन
A mutation is a change in DNA sequence. Mutations can create new genetic variants.
Most mutations may be neutral or harmful, while some can be advantageous under particular environmental conditions.
Only variations that are heritable and can contribute to differences in reproductive success can play a direct role in evolutionary change across generations.
21. Role of Sexual Reproduction
Sexual reproduction generates variation through:
- Independent assortment of chromosomes
- Crossing over during meiosis
- Recombination
- Random fusion of gametes
These variations provide raw material on which natural selection can act.
22. Important Terms | महत्वपूर्ण शब्दावली
| Term | Meaning |
|---|---|
| Variation | Differences among individuals of a population. |
| Population | Group of organisms of the same species living in a particular area. |
| Gene Flow | Movement of genes between populations. |
| Genetic Drift | Random change in allele frequencies, especially important in small populations. |
| Isolation | Separation that restricts gene flow. |
| Natural Selection | Preferential survival and reproduction of organisms with advantageous heritable variations. |
| Reproductive Isolation | Prevention of successful gene exchange between populations through reproduction. |
| Speciation | Formation of new species. |
| Adaptive Radiation | Diversification of an ancestral group into different ecological niches. |
23. 30 MCQs | बहुविकल्पीय प्रश्न
Q1. Speciation refers to:
A. Formation of new species
B. Formation of new organs
C. Growth of an individual
D. Repair of tissues
Answer: A
Speciation is the evolutionary process leading to the formation of distinct new species.
Q2. Which factor is most directly associated with the formation of new species?
A. Digestion
B. Reproductive isolation
C. Respiration
D. Growth
Answer: B
Reproductive isolation prevents gene exchange and allows populations to diverge.
Q3. Geographical isolation can be caused by:
A. Mountains
B. Rivers
C. Oceans
D. All of these
Answer: D
Physical barriers such as mountains, rivers and oceans can separate populations.
Q4. Genetic drift is particularly significant in:
A. Very large populations only
B. Small populations
C. Only plants
D. Only bacteria
Answer: B
Random changes in allele frequencies can have a large effect in small populations.
Q5. Which process introduces new genetic variants?
A. Mutation
B. Digestion
C. Excretion
D. Respiration
Answer: A
Mutation changes DNA and can produce new genetic variants.
Q6. Gene flow means:
A. Movement of water
B. Movement of genes between populations
C. Movement of food
D. Movement of hormones only
Answer: B
Migration followed by reproduction can transfer alleles between populations.
Q7. Which condition generally favours genetic divergence between populations?
A. High gene flow
B. Complete mixing
C. Reduced gene flow
D. Identical selection pressures forever
Answer: C
Reduced gene flow allows genetic differences to accumulate independently.
Q8. Darwin's finches are commonly associated with:
A. Artificial insemination
B. Adaptive radiation
C. Binary fission
D. Budding
Answer: B
Darwin's finches are a classic example of diversification into different ecological niches.
Q9. Which of the following is a physical barrier?
A. Mountain range
B. Mating behaviour
C. Courtship call
D. Breeding season
Answer: A
A mountain range can physically separate populations.
Q10. Natural selection acts directly on:
A. Heritable variations expressed as traits
B. Future generations only
C. Rocks
D. Non-living matter
Answer: A
Selection favours individuals with advantageous heritable characteristics in a given environment.
Q11. Which is NOT normally a cause of geographical isolation?
A. River
B. Mountain
C. Ocean
D. Similar diet
Answer: D
Similar diet is not a physical geographical barrier.
Q12. A difference in breeding season between populations may cause:
A. Temporal reproductive isolation
B. Digestion
C. Mutation repair
D. Photosynthesis
Answer: A
Different reproductive timing can prevent mating between populations.
Q13. The main significance of reproductive isolation is that it:
A. Increases gene flow
B. Prevents gene exchange
C. Stops mutation
D. Prevents all variation
Answer: B
Reproductive isolation prevents successful gene exchange between populations.
Q14. Which process can randomly alter allele frequencies?
A. Genetic drift
B. Photosynthesis
C. Respiration
D. Transpiration
Answer: A
Genetic drift causes random changes in allele frequencies.
Q15. Which statement is correct?
A. All variations cause speciation
B. Speciation can occur without any genetic differences
C. Isolation can contribute to speciation
D. Gene flow always causes speciation
Answer: C
Isolation can reduce gene flow and allow populations to diverge.
Q16. Adaptive radiation means:
A. Formation of one identical population
B. Diversification into different ecological niches
C. Loss of all variations
D. No evolutionary change
Answer: B
Adaptive radiation involves diversification of an ancestral group into different ecological niches.
Q17. Humans belong to:
A. Homo sapiens
B. Homo erectus only
C. Australopithecus
D. Pan sapiens
Answer: A
Modern humans are classified as Homo sapiens.
Q18. Which can produce variation during sexual reproduction?
A. Recombination
B. Only digestion
C. Only respiration
D. Excretion
Answer: A
Recombination creates new combinations of genetic material.
Q19. A mutation is:
A. A change in DNA sequence
B. A type of tissue
C. A hormone
D. A digestive enzyme
Answer: A
Mutation refers to a change in DNA sequence.
Q20. High gene flow generally:
A. Makes populations more genetically similar
B. Always produces new species
C. Stops reproduction
D. Stops DNA replication
Answer: A
Gene flow transfers alleles between populations and tends to reduce genetic differences.
Q21. Which is an example of reproductive isolation?
A. Two populations breeding in different seasons
B. Two populations sharing the same habitat
C. Similar DNA sequences
D. Same food source
Answer: A
Different breeding seasons can prevent mating and gene exchange.
Q22. Speciation usually occurs over:
A. Several generations
B. A few minutes
C. One heartbeat
D. One meal
Answer: A
Evolutionary divergence generally accumulates over many generations.
Q23. Which combination best supports speciation?
A. Isolation + genetic divergence + reproductive isolation
B. Digestion + respiration
C. Growth + nutrition
D. Photosynthesis + transpiration
Answer: A
Isolation can reduce gene flow, allowing genetic divergence and eventual reproductive isolation.
Q24. A population separated by an ocean may experience:
A. Geographical isolation
B. No evolutionary change ever
C. Instant speciation
D. Guaranteed extinction
Answer: A
An ocean can act as a physical barrier to gene flow.
Q25. Natural selection is:
A. Random production of all traits
B. Differential survival and reproduction associated with heritable variation
C. Deliberate breeding by humans
D. DNA destruction
Answer: B
Natural selection changes the frequency of heritable variants because some variants lead to greater reproductive success.
Q26. Which is most important for maintaining separate species?
A. Reproductive isolation
B. Common food
C. Identical environment
D. High gene flow
Answer: A
Reproductive isolation prevents the populations from merging genetically.
Q27. Genetic drift is:
A. Always beneficial
B. Random
C. Always harmful
D. Controlled by humans
Answer: B
Genetic drift involves random changes in allele frequencies.
Q28. Which statement about speciation is correct?
A. It happens within one individual
B. It is an evolutionary population-level process
C. It stops all variation
D. It happens instantly
Answer: B
Speciation is a population-level evolutionary process occurring over generations.
Q29. Darwin's finches diversified partly because of:
A. Different ecological niches and food resources
B. Absence of variation
C. Identical selection pressures
D. Lack of reproduction
Answer: A
Different ecological conditions and food resources favoured different adaptations.
Q30. The correct sequence is:
A. Isolation → divergence → reproductive isolation → speciation
B. Speciation → no variation → isolation
C. Respiration → digestion → speciation
D. Excretion → growth → speciation
Answer: A
Isolation can reduce gene flow, allowing divergence and eventual reproductive isolation.
24. 30 Subjective Questions with Answers
2 Marks
Q1. What is speciation?
Speciation is the evolutionary process by which new species arise from existing populations. It generally involves genetic divergence and reproductive isolation.
2 Marks
Q2. Define geographical isolation.
Geographical isolation is the physical separation of populations by barriers such as mountains, rivers, oceans or large distances, reducing gene flow between them.
2 Marks
Q3. What is reproductive isolation?
It is a condition in which populations cannot successfully exchange genes through reproduction.
2 Marks
Q4. What is genetic drift?
Genetic drift is a random change in allele frequencies in a population. Its effects are often stronger in small populations.
2 Marks
Q5. What is gene flow?
Gene flow is the transfer of genes or alleles between populations, usually through migration followed by reproduction.
3 Marks
Q6. Explain the role of variation in speciation.
Variation provides differences among individuals. If populations become isolated, different variations may be favoured in different environments. Over generations these differences may accumulate and contribute to reproductive isolation and speciation.
3 Marks
Q7. How can geographical isolation lead to speciation?
A physical barrier separates a population. Gene flow between the groups decreases. Different mutations, genetic drift and natural selection act in the separated populations. Over many generations they may become genetically and reproductively isolated.
3 Marks
Q8. Why is genetic drift important in small populations?
In a small population, chance events can greatly change allele frequencies. Some alleles may become common while others may disappear. This can increase genetic differences between isolated populations.
3 Marks
Q9. What is adaptive radiation? Give an example.
Adaptive radiation is diversification of an ancestral group into different forms adapted to different ecological niches. Darwin's finches are a classic example.
3 Marks
Q10. Different breeding seasons can cause speciation. Explain.
If two populations reproduce at different times, their reproductive periods may not overlap. This reduces mating and gene flow. Long-term reproductive isolation can contribute to speciation.
4 Marks
Q11. Explain four factors that can contribute to speciation.
- Geographical isolation
- Mutation and genetic variation
- Natural selection
- Genetic drift
4 Marks
Q12. Differentiate between geographical isolation and reproductive isolation.
Geographical isolation is physical separation by barriers such as mountains or oceans. Reproductive isolation means populations cannot successfully exchange genes through reproduction. Geographical isolation can contribute to reproductive isolation over time.
4 Marks
Q13. Explain the relationship between gene flow and speciation.
Gene flow tends to make populations genetically similar. When gene flow is reduced, populations can accumulate different genetic changes. Continued divergence may eventually result in reproductive isolation and speciation.
4 Marks
Q14. Why does sexual reproduction contribute to speciation?
Sexual reproduction produces variation through recombination, independent assortment and random fertilisation. These variations provide raw material for natural selection and can contribute to genetic divergence between isolated populations.
4 Marks
Q15. Explain how natural selection can contribute to speciation.
When populations are isolated, they may experience different environmental pressures. Different heritable variations may be favoured in each population. Over generations, the populations become genetically different. If reproductive isolation develops, new species may arise.
5 Marks
Q16. Describe the complete process of speciation.
- A population contains heritable variations.
- A physical or reproductive barrier reduces gene flow.
- Separated populations experience different selection pressures and random genetic changes.
- Genetic differences accumulate over generations.
- Reproductive isolation develops.
- The separated populations may eventually become distinct species.
5 Marks
Q17. Explain adaptive radiation with reference to Darwin's finches.
An ancestral finch population reached different islands. Different environmental conditions and food resources favoured different beak characteristics. Over generations, populations became adapted to different ecological niches. This diversification from a common ancestor is called adaptive radiation.
5 Marks
Q18. Explain the role of mutation, genetic drift and natural selection in speciation.
Mutation can generate new genetic variants. Genetic drift can randomly alter allele frequencies, especially in small populations. Natural selection favours advantageous heritable variations under particular environmental conditions. Together, especially when populations are isolated, these processes can contribute to genetic divergence.
5 Marks
Q19. Explain why reduced gene flow is important in speciation.
Gene flow keeps populations genetically connected. If gene flow decreases because of geographical or reproductive isolation, each population evolves more independently. Genetic differences can accumulate until reproductive isolation becomes established.
5 Marks
Q20. Explain why speciation is a population-level process.
Evolutionary changes occur in allele frequencies within populations across generations. Individuals do not become new species during their lifetime. Speciation occurs when populations diverge sufficiently and become reproductively isolated.
6 Marks
Q21. Explain the importance of isolation in speciation.
Isolation reduces gene flow between populations. Geographical isolation may occur due to mountains, rivers, oceans or distance. Reproductive isolation may develop due to differences in mating behaviour, reproductive timing or compatibility. Once gene flow is reduced, mutation, recombination, genetic drift and natural selection can cause populations to diverge. Continued divergence may lead to formation of new species.
6 Marks
Q22. Describe different reproductive isolating mechanisms.
Reproductive isolation may occur before or after fertilisation.
Pre-zygotic mechanisms: differences in mating behaviour, reproductive structures or breeding time can prevent mating or fertilisation.
Post-zygotic mechanisms: fertilisation may occur, but hybrid offspring may have low viability or reduced fertility.
These mechanisms reduce successful gene exchange.
Pre-zygotic mechanisms: differences in mating behaviour, reproductive structures or breeding time can prevent mating or fertilisation.
Post-zygotic mechanisms: fertilisation may occur, but hybrid offspring may have low viability or reduced fertility.
These mechanisms reduce successful gene exchange.
6 Marks
Q23. Explain how a mountain can contribute to speciation.
A mountain range may divide a population into two geographically isolated groups. The groups have limited gene flow. Different environmental conditions can favour different variations. Mutation, recombination and genetic drift can also cause genetic differences. Over generations, these differences may become large enough for reproductive isolation to develop, resulting in speciation.
6 Marks
Q24. Explain the relationship between variation, natural selection and speciation.
Variation creates differences among individuals. Some variations are heritable and can affect survival and reproductive success. Natural selection may favour advantageous variations. If different populations experience different selection pressures and have reduced gene flow, their genetic composition can diverge. Continued divergence and reproductive isolation can eventually lead to speciation.
6 Marks
Q25. Explain genetic drift with a suitable situation.
Genetic drift is random alteration of allele frequencies. It is particularly important in small populations. Suppose a small isolated population contains two alleles in unequal proportions. By chance, individuals carrying one allele may leave more offspring. The frequency of that allele can increase even if it provides no selective advantage. Repeated random changes can contribute to divergence between isolated populations.
6 Marks
Q26. Explain why humans are not considered separate species based on geographical differences.
Modern humans belong to Homo sapiens. Human populations have historically experienced migration and gene flow. Geographical differences in traits do not by themselves indicate separate species. There is no clear reproductive isolation separating modern human populations into different biological species.
6 Marks
Q27. Compare natural selection, genetic drift and gene flow.
| Process | Main feature |
|---|---|
| Natural selection | Non-random change associated with differences in survival and reproduction of heritable variants. |
| Genetic drift | Random changes in allele frequencies, especially in small populations. |
| Gene flow | Movement of alleles between populations through migration and reproduction. |
6 Marks
Q28. Explain adaptive radiation and its significance in evolution.
Adaptive radiation occurs when organisms from a common ancestral population diversify into forms adapted to different ecological niches. Different environments and food resources favour different characteristics. Darwin's finches demonstrate this process. Adaptive radiation explains how one ancestral group can give rise to several specialised forms.
6 Marks
Q29. Draw and explain the pathway of speciation.
Variation
→
Isolation
→
Reduced Gene Flow
→
Divergence
→
Reproductive Isolation
→
New Species
6 Marks
Q30. "Speciation is an outcome of evolution." Justify the statement.
Evolution involves changes in heritable characteristics of populations over generations. When populations become isolated, genetic differences can accumulate through mutation, recombination, natural selection and genetic drift. If the differences become large enough to produce reproductive isolation, the populations can form separate species. Therefore, speciation is an important outcome of evolutionary divergence.
25. Assertion–Reason Questions
Q1. Assertion: Geographical isolation can contribute to speciation.
Reason: Geographical isolation can reduce gene flow between populations.
Reason: Geographical isolation can reduce gene flow between populations.
Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.
Q2. Assertion: Genetic drift can be important in small populations.
Reason: Chance events can cause large changes in allele frequencies in small populations.
Reason: Chance events can cause large changes in allele frequencies in small populations.
Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.
Q3. Assertion: High gene flow generally promotes genetic similarity between populations.
Reason: Gene flow transfers alleles between populations.
Reason: Gene flow transfers alleles between populations.
Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.
Q4. Assertion: Every variation causes formation of a new species.
Reason: Speciation usually requires genetic divergence and reproductive isolation.
Reason: Speciation usually requires genetic divergence and reproductive isolation.
Answer: Assertion is false, but Reason is true.
Q5. Assertion: Darwin's finches are an example associated with adaptive radiation.
Reason: Different ecological conditions favoured different adaptations in different finch populations.
Reason: Different ecological conditions favoured different adaptations in different finch populations.
Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.
26. HOTS / Competency-Based Questions
HOTS 1. A population of beetles is divided by a newly formed mountain range. After thousands of generations, the two populations can no longer successfully reproduce with each other. Explain how this could happen.
The mountain reduced gene flow. Different environmental pressures, mutation, recombination and genetic drift caused genetic divergence. Over generations, reproductive differences developed. Eventually reproductive isolation could result in two distinct species.
HOTS 2. Population A and Population B have frequent migration between them. Would speciation be easy? Give reason.
No. Frequent migration increases gene flow, which tends to keep the populations genetically similar and reduces divergence.
HOTS 3. Two small populations are isolated from each other. One population loses a rare allele by chance. Which evolutionary mechanism can explain this?
Genetic drift can cause random loss of alleles, particularly in small populations.
HOTS 4. Two populations live in different environments. The same trait is advantageous in one population but disadvantageous in the other. What can happen over many generations?
Different selection pressures can favour different heritable variants. If gene flow is low, the populations may genetically diverge and eventually develop reproductive isolation.
HOTS 5. Why is isolation alone not always sufficient to create a new species?
Isolation reduces gene flow, but populations must accumulate sufficient genetic differences and eventually become reproductively isolated. If the populations remain genetically compatible, they may still be members of the same species.
27. Diagram Labelling Practice
Label the following terms in the speciation diagram:
| Label | Expected Term |
|---|---|
| A | Separated population |
| B | Separated population |
| Barrier | Geographical isolation |
| Final outcome | Reproductive isolation / New species |
28. CBSE Golden Points ⭐
- Speciation means formation of new species.
- Variation is the raw material for evolutionary change.
- Geographical isolation can reduce gene flow.
- Reduced gene flow allows populations to diverge genetically.
- Natural selection can favour different variations in different environments.
- Genetic drift is random and especially important in small populations.
- Reproductive isolation is central to the maintenance of separate species.
- Different breeding seasons can contribute to reproductive isolation.
- Darwin's finches are a classic example of adaptive radiation.
- Evolution occurs in populations over generations.
- Individuals do not evolve into new species during their lifetime.
- High gene flow generally reduces genetic differences between populations.
- Mutation can generate new genetic variants.
- Sexual reproduction generates variation through recombination and other processes.
- Modern humans are Homo sapiens and constitute one species.
29. Memory Trick 🧠
SPECIATION = V-I-D-R-N
V = Variation
I = Isolation
D = Divergence
R = Reproductive Isolation
N = New Species
👉 याद रखें: Variation → Isolation → Divergence → Reproductive Isolation → New Species
V = Variation
I = Isolation
D = Divergence
R = Reproductive Isolation
N = New Species
👉 याद रखें: Variation → Isolation → Divergence → Reproductive Isolation → New Species
G-D-N-R Trick
G = Geographical Isolation
D = Genetic Divergence
N = Natural Selection
R = Reproductive Isolation
G = Geographical Isolation
D = Genetic Divergence
N = Natural Selection
R = Reproductive Isolation
30. One-Line Revision | एक पंक्ति में पूरा Chapter
Variation + Isolation + Genetic Divergence + Reproductive Isolation → Speciation
Hindi:
विविधता + पृथक्करण + आनुवंशिक विचलन + प्रजनन पृथक्करण → नई प्रजाति का निर्माण
31. Final Summary | अंतिम सारांश
Speciation is a long-term evolutionary process. A population contains genetic variation. When populations become geographically or reproductively isolated, gene flow decreases. Mutation, recombination, genetic drift and natural selection can then cause the isolated populations to become increasingly different. If reproductive isolation becomes established, the populations may form separate species.
Exam Formula:
Isolation reduces gene flow → populations diverge → reproductive isolation develops → new species may form.
Isolation reduces gene flow → populations diverge → reproductive isolation develops → new species may form.
🧬 Heredity | Speciation
Class 10 Science | CBSE + Foundation + Competitive
© Educational Study Material
Class 10 Science | CBSE + Foundation + Competitive
© Educational Study Material
