Heredity & Evolution - Practice Test, Class 10 Science - Class 10 MCQ

Type of Variation
There are two main types of variations that can occur in individuals: somatic variation and germinal variation. However, only one type of variation is inherited.
Somatic Variation
- Somatic variation refers to genetic changes that occur in somatic cells, which are any cells in the body other than the reproductive cells (sperm and egg).
- These variations are not inherited because they do not affect the genetic makeup of the individual's offspring.
Germinal Variation
- Germinal variation, also known as germline variation, refers to genetic changes that occur in the germ cells (sperm and egg) and are passed down to offspring.
- These variations are inherited because they are present in the reproductive cells and can be transmitted to the next generation.
Both Somatic and Germinal Variation
- While somatic variation may occur throughout an individual's lifetime, it does not affect the genetic information passed on to offspring.
- Germinal variation, on the other hand, is the only type of variation that can be inherited.
Conclusion
- In summary, germline or germinal variation is the type of variation that is inherited because it occurs in the reproductive cells and can be passed down to offspring.
- Somatic variation, although it may occur in an individual's somatic cells, does not affect the genetic makeup of future generations.

Homologous Organs:
Homologous organs are the organs that have the same basic structure but perform different functions. These organs are found in different organisms and are evidence of a common ancestry.
Examples of Homologous Organs:
- The forelimbs of vertebrates, such as humans, bats, cats, and whales, are homologous organs. They have a similar bone structure, despite their different functions in each organism.
- The wings of birds and the arms of humans are also homologous organs. They have a similar structure and are derived from the same embryonic tissues.
- The flippers of seals and the legs of horses are homologous organs. Although they have different functions, they share a similar structure.
Importance of Homologous Organs:
- Homologous organs provide evidence for the theory of evolution, as they suggest that different organisms share a common ancestor.
- The study of homologous organs helps in understanding the evolutionary relationships between different species.
- It allows scientists to trace the evolutionary history of organisms and determine their common traits.
Differences from Vestigial and Analogous Organs:
- Vestigial organs are remnants of organs that were functional in ancestral species but have lost their original function in the present organism. They may have reduced in size or become functionless.
- Analogous organs have a similar function but different structure. They are not evidence of a common ancestry but are the result of convergent evolution.
In conclusion, homologous organs play a crucial role in understanding evolutionary relationships between species and provide evidence for the theory of evolution. They have the same basic structure but perform different functions in different organisms.

Explanation:

When fossils are found at deeper layers of the earth, it can be concluded that they are very old. This is because the deeper layers of the earth represent older geological time periods. Here is a detailed explanation:
1. Fossils and Layers of the Earth:
- Fossils are the preserved remains or traces of plants, animals, and other organisms from the past.
- The earth's crust is made up of different layers, and each layer represents a specific time period in history.
- The deeper layers of the earth are formed earlier than the upper layers, so they contain older rocks and fossils.
2. Law of Superposition:
- The Law of Superposition states that in any undisturbed sequence of rock layers, the youngest rocks are on top, and the oldest rocks are at the bottom.
- This principle allows scientists to determine the relative age of fossils based on their position in the rock layers.
3. Conclusion:
- When fossils are found at deeper layers of the earth, it indicates that they are located in older rock layers.
- Therefore, we can conclude that the fossils are very old, potentially dating back thousands or even millions of years.
4. Answer:
- Based on the above explanation, the answer to the question is B: Fossils found at deeper layers of the earth are very old, possibly more than a thousand years.

Wings of an insect & a bird are example of:
A: Analogous organs
- Wings of an insect and a bird are considered analogous organs.
- Analogous organs are those that have similar functions but different structures.
- In this case, both insect wings and bird wings are used for flying, but they have different structures and are formed from different body parts.
B: Vestigial organs
- Vestigial organs are organs that have lost their original function over time.
- Wings of insects and birds are not considered vestigial organs as they still serve a purpose and are fully functional in their respective organisms.
C: Homologous organs
- Homologous organs are organs that have similar structures but may have different functions.
- Wings of an insect and a bird are not considered homologous organs because they have different structures despite their similar functions.
D: Analytic organs
- "Analytic organs" is not a recognized term in biology and does not apply to the wings of an insect and a bird.
Therefore, the correct answer is A: Analogous organs.

Vestigial organ:
- The vermiform appendix is an example of a vestigial organ.
- A vestigial organ is a structure in an organism that has lost its original function through evolution.
- The appendix is a small, finger-like pouch attached to the cecum, which is part of the large intestine.
- In humans, the appendix is not considered to have a significant function.
- It is believed to be a vestige of our evolutionary past, where it may have had a role in digesting cellulose-rich plant material.
- However, with changes in diet and the evolution of our digestive system, the appendix has become functionally obsolete.
- The appendix can occasionally become inflamed, leading to a condition called appendicitis, which requires surgical removal.
- The presence of the appendix in humans is considered a vestigial trait, as it no longer serves a necessary purpose.
- Other examples of vestigial organs in humans include the coccyx (tailbone) and the ear muscles that help animals move their ears.
- The presence of vestigial organs provides evidence for the process of evolution and the common ancestry of organisms.

Introduction:
When an offspring is produced, its traits are influenced by various factors. One of the key factors is the DNA present in the gametes of the parents. The DNA in the gametes carries genetic information that is passed on to the offspring, determining its traits. In the case of the offspring, both the DNA from the mother's gamete and the DNA from the father's gamete contribute to the traits exhibited by the offspring.
Explanation:
The traits in an offspring are influenced by both the DNA of the father's gamete and the DNA of the mother's gamete. This is because:
- Each parent contributes one set of chromosomes to the offspring, which contains genes responsible for various traits.
- The DNA in the mother's gamete (egg) and the DNA in the father's gamete (sperm) combine during fertilization to form a complete set of chromosomes in the offspring.
- The genes present on these chromosomes determine the traits that the offspring will inherit from its parents.
- The combination of genes from both parents can result in a variety of possible traits in the offspring, as certain genes may be dominant or recessive.
- The interaction between the genes inherited from both parents also plays a role in determining the expression of traits.
Conclusion:
In conclusion, the traits in an offspring are influenced by both the DNA of the mother's gamete and the DNA of the father's gamete. The combination of genetic information from both parents determines the traits exhibited by the offspring. This understanding is crucial in the study of genetics and inheritance patterns.

Mendel's Experiment:
- Mendel crossed a tall plant (dominant trait) with a dwarf plant (recessive trait).
- This is a monohybrid cross, as only one trait (height) is being studied.
Genotypes:
- The tall plant is homozygous dominant (TT).
- The dwarf plant is homozygous recessive (tt).
F1 Generation:
- In the F1 generation, all the plants were tall.
- The genotype of all the F1 plants is heterozygous (Tt).
F2 Generation:
- Mendel allowed the F1 plants to self-fertilize.
- The possible genotypes in the F2 generation are TT, Tt, and tt.
Phenotypes:
- The tall phenotype is dominant, so plants with either TT or Tt genotype will be tall.
- The dwarf phenotype is recessive, so only plants with tt genotype will be dwarf.
Genotypic Ratio:
- In the F2 generation, the possible genotypes are: TT, Tt, and tt.
- The genotypic ratio is 1:2:1.
- This means that for every 4 plants in the F2 generation, 1 will be TT, 2 will be Tt, and 1 will be tt.
Phenotypic Ratio:
- In the F2 generation, the possible phenotypes are tall (TT and Tt) and dwarf (tt).
- The phenotypic ratio is 3:1.
- This means that for every 4 plants in the F2 generation, 3 will be tall and 1 will be dwarf.
Ratio of Dwarf Plants:
- The dwarf phenotype is expressed only in plants with the tt genotype.
- In the F2 generation, the ratio of dwarf plants is therefore 1 out of 4.
- This can be expressed as 1/4 or 25%.
Answer: The ratio of dwarf plants in the F2 generation is 25%. (Option A)

Detailed
Introduction:
Gamete cells are specialized cells involved in sexual reproduction. They are responsible for transmitting genetic information from one generation to the next. In this response, we will discuss the nature of gamete cells and whether they are diploid or haploid.
Definition of Diploid and Haploid:
- Diploid: Diploid cells have two complete sets of chromosomes, one from each parent. In humans, diploid cells have 46 chromosomes, arranged in 23 pairs.
- Haploid: Haploid cells have only one set of chromosomes. In humans, haploid cells have 23 chromosomes, which are not arranged in pairs.
Nature of Gamete Cells:
- Gamete cells are specialized reproductive cells that are involved in sexual reproduction.
- They are produced by a process called gametogenesis, which occurs in the gonads (testes in males and ovaries in females).
- Gametogenesis involves a type of cell division called meiosis, which results in the formation of haploid gamete cells.
- During meiosis, the diploid cells (germ cells) undergo two rounds of division, resulting in the formation of four haploid gamete cells.
- In males, the haploid gamete cells are called sperm, while in females, they are called eggs or ova.
Conclusion:
Based on the above information, we can conclude that gamete cells are haploid. They have only one set of chromosomes and are formed through the process of meiosis.

Explanation:
The 23rd chromosome pair in humans determines the sex of the individual. It consists of two chromosomes, one inherited from the mother and one from the father.
- Option A: XX - This combination represents a female. Females have two X chromosomes.
- Option B: XY - This combination represents a male. Males have one X and one Y chromosome.
- Option C: YY - This combination does not exist in humans.
- Option D: XYY - This combination represents a male with an extra Y chromosome. This condition is known as XYY syndrome and is a chromosomal disorder.
Since the question states that the baby will be a female, the correct answer is option A: XX.

Proposed Hypothesis: D. Haldane
Detailed
Haldane proposed the hypothesis that life must have developed from simple inorganic molecules that were present on Earth soon after it was formed. Here is a detailed explanation of Haldane's contribution to the hypothesis:
1. J.B.S. Haldane:
- J.B.S. Haldane was a British scientist and one of the prominent figures in evolutionary biology and genetics.
- He proposed the idea that life originated from simple inorganic molecules through a series of chemical reactions.
2. Primordial Soup Theory:
- Haldane's hypothesis was part of the primordial soup theory, which postulates that life originated in a mixture of organic compounds that existed in Earth's early oceans.
- According to this theory, the Earth's early atmosphere was composed of various gases like methane, ammonia, and water vapor, and these gases reacted to form complex organic molecules.
3. Formation of Organic Molecules:
- Haldane suggested that the early Earth's conditions, such as lightning strikes and volcanic activity, provided the necessary energy to drive chemical reactions.
- These reactions could have led to the formation of simple organic molecules like amino acids, which are the building blocks of proteins.
4. Abiotic Synthesis of Biomolecules:
- Haldane's hypothesis proposed that these simple organic molecules could have combined and formed complex biomolecules such as proteins, nucleic acids, and carbohydrates.
- The presence of these biomolecules is essential for the development of life.
5. Supporting Evidence:
- Haldane's hypothesis was supported by the famous Miller-Urey experiment conducted in 1952.
- In this experiment, Stanley Miller and Harold Urey simulated the conditions of the early Earth and successfully produced amino acids, further supporting the idea of abiotic synthesis of organic molecules.
6. Contributing to the Understanding of Life's Origins:
- Haldane's hypothesis played a significant role in shaping our understanding of how life could have originated from non-living matter.
- It provided a potential explanation for the emergence of life on Earth and laid the foundation for further research in the field of abiogenesis.
In conclusion, D. Haldane proposed the hypothesis that life could have developed from simple inorganic molecules present on Earth soon after its formation. His ideas, along with subsequent experiments, have contributed to our understanding of the origin of life on our planet.

Explanation:
Mendel observed 7 pairs of contrasting characters in Pisum sativum. One of the options listed is not a part of Mendel's observations. Let's analyze each option one by one:
A: Tall and dwarf
- This is a valid pair of contrasting characters observed by Mendel in Pisum sativum.
- He observed that plants can either be tall or dwarf in height.
B: Yellow and green seed colour
- This is a valid pair of contrasting characters observed by Mendel in Pisum sativum.
- He observed that seeds can either have a yellow or green color.
C: Terminal and axial flower
- This is a valid pair of contrasting characters observed by Mendel in Pisum sativum.
- He observed that flowers can either be terminal (at the end of the stem) or axial (in the leaf axils).
D: Smooth and rough stem
- This is not a part of Mendel's observations in Pisum sativum.
- Mendel did not observe or study the characteristics of stem texture (smooth or rough).
Therefore, the correct answer is D: Smooth and rough stem.

Mendel's Monohybrid Cross
Mendel's monohybrid cross involves the study of the inheritance of a single trait or characteristic in pea plants. He specifically studied the inheritance of seed shape, which can be either round or wrinkled.
F1 Generation
In the first generation (F1), Mendel crossed two pure-breeding pea plants with contrasting traits. He crossed a pure-breeding round-seeded plant with a pure-breeding wrinkled-seeded plant. All the offspring in the F1 generation had round seeds, indicating that the round seed shape is dominant over the wrinkled seed shape.
F2 Generation
Mendel then crossed the F1 generation plants with each other to obtain the second filial generation (F2). In the F2 generation, he observed the phenotypic ratio of the offspring.
Phenotypic Ratio
The phenotypic ratio refers to the ratio of different observable traits or phenotypes in the offspring. In the case of Mendel's monohybrid cross, the phenotypic ratio of the F2 generation for the seed shape trait was 3:1.
Explanation of Phenotypic Ratio
The 3:1 phenotypic ratio means that for every three plants with round seeds, there is one plant with wrinkled seeds. This ratio is obtained by observing a large number of offspring from the F2 generation.
Conclusion
Based on Mendel's monohybrid cross, the F2 phenotype ratio for the study of seed shape in pea plants is 3:1. This ratio indicates that the dominant trait (round seed shape) appears three times more frequently than the recessive trait (wrinkled seed shape) in the offspring.

According to Mendelism, the genotype of a tall pea plant can be determined based on the given information about the symbols T and t representing tallness and dwarfness, respectively.
To determine the genotype, we need to consider the possible combinations of alleles that an organism can inherit from its parents. In this case, since T is for tallness, it represents the dominant allele, and t for dwarfness represents the recessive allele.
Based on this information, the genotype of a tall pea plant can be either homozygous dominant (TT) or heterozygous (Tt).
Here's a breakdown of the possible genotypes based on Mendelism:
- TT: This represents a homozygous dominant genotype, where both alleles are dominant for tallness. The plant will be tall.
- Tt: This represents a heterozygous genotype, where one allele is dominant for tallness (T) and the other is recessive for dwarfness (t). The plant will also be tall because the dominant allele masks the effect of the recessive allele.
Therefore, according to Mendelism, the genotype of a tall pea plant can be either TT or Tt.

The genotype of the Yellow and Round seeded pea plant is YyRr. To determine the possible gametes produced by this plant, we need to consider the segregation of alleles during meiosis. Meiosis is the process of cell division that produces gametes, and it ensures that each gamete receives only one allele from each gene.
1. Segregation of the Yy genotype:
- The Yy genotype means that the plant has one allele for yellow seeds (Y) and one allele for green seeds (y).
- During meiosis, the Y and y alleles will separate, resulting in two possible gametes: Y and y.
2. Segregation of the Rr genotype:
- The Rr genotype means that the plant has one allele for round seeds (R) and one allele for wrinkled seeds (r).
- During meiosis, the R and r alleles will separate, resulting in two possible gametes: R and r.
3. Combination of gametes:
- Since the segregation of alleles occurs independently for different genes, we can combine the possible gametes for each gene.
- For the Yy genotype, we have two possible gametes: Y and y.
- For the Rr genotype, we have two possible gametes: R and r.
- Therefore, the possible combinations of these gametes are: YR, Yr, yR, and yr.
Therefore, the correct answer is option B: YR, yR, Yr, and yr. These are the four possible gametes that can be produced by a Yellow and Round seeded pea plant with genotype YyRr.

Explanation:
The sex of a fetus is determined by the combination of sex chromosomes inherited from both parents. In humans, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).
When a sperm fertilizes an egg, the sperm can contribute either an X chromosome or a Y chromosome to the resulting embryo. The egg always contributes an X chromosome.
Based on this information:
- If a sperm carrying an X chromosome fertilizes the egg, the resulting embryo will have two X chromosomes (XX). This will develop into a female fetus.
- If a sperm carrying a Y chromosome fertilizes the egg, the resulting embryo will have one X and one Y chromosome (XY). This will develop into a male fetus.
- Therefore, if a sperm (22 Y) fertilizes an egg (22 X), the resulting fetus will have an XY chromosome combination, indicating that it will be a male.
In conclusion:
- The sex of the fetus in this scenario will be male.

Evolutionary Relationship of Forelimb in Frog, Lizard, Bird, and Man:
The forelimbs of frog, lizard, bird, and man show an evolutionary relationship due to the presence of homologous organs. Below are the detailed points explaining this relationship:
1. Homologous Organs:
- Homologous organs refer to the presence of similar structures in different species that have a common evolutionary origin.
- In the case of forelimbs, although the functions of these organs may vary, the basic structure and arrangement of bones remain similar.
- The forelimbs of frogs, lizards, birds, and humans all contain a similar set of bones, including humerus, radius, ulna, carpals, metacarpals, and phalanges.
- These similarities in the bone structure suggest a common ancestry and evolution from a common ancestor.
2. Comparative Anatomy:
- Comparative anatomy studies the similarities and differences in the structure of different organisms.
- By comparing the forelimbs of frog, lizard, bird, and man, it is evident that they share a common skeletal structure.
- The presence of similar bones, although modified for different functions, indicates a shared evolutionary history.
3. Developmental Similarities:
- The development of forelimbs during the embryonic stage also supports the evolutionary relationship.
- In all these organisms, the forelimbs initially develop from similar regions and undergo similar developmental processes.
- This developmental similarity further indicates a common evolutionary origin.
4. Evolutionary Tree:
- By constructing an evolutionary tree or phylogenetic tree, scientists can visually represent the evolutionary relationships between different species.
- When analyzing the forelimbs of frog, lizard, bird, and man, they would be placed on different branches of the tree, indicating their shared ancestry but subsequent divergence.
Therefore, the correct answer is D: Homologous organs, as the forelimbs of frog, lizard, bird, and man exhibit homology, suggesting a common evolutionary relationship.

Autosomes in a human body cell:
- Autosomes are the non-sex chromosomes found in the nucleus of a cell.
- They are responsible for determining most of the organism's traits.
- Humans have a total of 46 chromosomes in each body cell, with 23 pairs.
- Out of these 46 chromosomes, 2 are sex chromosomes (X and Y) and the remaining 44 are autosomes.
- Sex chromosomes determine the sex of an individual, while autosomes carry genetic information unrelated to sex.
- In a human body cell, there are 22 pairs of autosomes, designated as pairs 1 to 22.
- These autosomes are numbered based on their size, with pair 1 being the largest and pair 22 being the smallest.
- Each autosome pair consists of two chromosomes, one inherited from the mother and one from the father.
- Therefore, the correct answer is A: 44, as humans have 44 autosomes in each body cell.

The Theory of Natural Selection

• Proposed by: Charles Darwin

Charles Darwin, a British naturalist, proposed the theory of Natural Selection in his book "On the Origin of Species" in 1859. This theory is considered one of the foundational concepts in the field of evolutionary biology.

Explanation of Natural Selection:

• Definition: Natural Selection is the process by which certain heritable traits become more or less common in a population over successive generations based on their impact on the individual's ability to survive and reproduce.


• Key Points:




• Individuals within a population exhibit variation in traits.


• Environmental factors lead to differential survival and reproduction.


• Individuals with advantageous traits that enable them to better survive and reproduce are more likely to pass on those traits to their offspring.


• Over time, these advantageous traits become more prevalent in the population, while less advantageous traits decrease.




• Evidence for Natural Selection:




• Fossil record: Fossils provide evidence of past organisms and show how species have changed over time.


• Anatomical homologies: Similarities in structures among different species indicate a common ancestry.


• Embryological development: Similarities in early stages of development suggest shared ancestry.


• Molecular genetics: DNA and protein sequences show similarities and differences among species, supporting the idea of common ancestry.




• Importance and Impact:




• Natural Selection explains how species adapt and evolve over time.


• It provides a mechanism for explaining the diversity of life on Earth.


• It is a fundamental concept in fields such as evolutionary biology, ecology, and genetics.

In conclusion, the theory of Natural Selection was proposed by Charles Darwin and has had a profound impact on our understanding of how species change and adapt over time.

How life might have originated on Earth was experimentally shown by Urey and Miller:
- Urey and Miller conducted an experiment in 1952 known as the Miller-Urey experiment.
- The experiment aimed to simulate the conditions believed to be present on early Earth, specifically the atmosphere and the presence of lightning.
- They created a closed system consisting of a mixture of gases believed to be present in the early Earth's atmosphere, such as methane, ammonia, water vapor, and hydrogen.
- They then introduced electrical sparks into the system to simulate lightning.
- After running the experiment for a week, they analyzed the contents of the system and found the presence of various organic compounds, including amino acids, which are the building blocks of proteins.
- This experiment provided experimental evidence that the basic building blocks of life could have formed under the conditions believed to exist on early Earth.
- The Miller-Urey experiment demonstrated the possibility of chemical reactions leading to the formation of organic compounds, suggesting a potential pathway for the origin of life.
- This experiment has since been replicated and expanded upon, further supporting the idea that life could have originated from non-living matter through natural chemical processes.
- The findings of the Miller-Urey experiment have contributed significantly to our understanding of the origins of life on Earth and have sparked further research in the field of abiogenesis.

Explanation:
- Genetic drift is a random change in the frequency of alleles in a population over several generations.
- This change is caused by errors in the transmission of genetic material (gametes) from one generation to the next.
- Genetic drift can have a significant impact on small populations, where chance events can lead to the loss or fixation of certain alleles.
- There are two main types of genetic drift: bottleneck effect and founder effect.
- The bottleneck effect occurs when a population undergoes a drastic reduction in size, leading to a loss of genetic diversity.
- The founder effect occurs when a small group of individuals establishes a new population, potentially carrying only a subset of the original genetic variation.
- Genetic drift is a random process and does not necessarily lead to adaptive changes in a population.
- It can result in the loss of beneficial alleles or the fixation of deleterious alleles.
- Genetic drift is distinct from other evolutionary forces such as natural selection, gene flow, and mutation.
- It is an important mechanism of evolution and can contribute to the genetic differentiation of populations over time.