Heredity & Evolution - Class 10 Science (Compulsory Test) - Class 10 MCQ

Inherited Variation:

• Germinal Variation: Germinal variation refers to the genetic variation that is inherited from one generation to the next. It occurs in the germ cells (sperm and egg) and is passed on to offspring during reproduction. This type of variation is responsible for the diversity seen within a species.

Non-Inherited Variation:

• Somatic Variation: Somatic variation refers to the genetic variation that occurs in the cells of the body other than the germ cells. These variations are not passed on to offspring and do not contribute to the genetic diversity of a species. Somatic variations can be caused by factors such as environmental influences or errors in DNA replication.

Conclusion:

Inherited variation is the type of variation that is passed on from one generation to the next. Germinal variation, which occurs in germ cells, is responsible for this inherited variation. Somatic variation, on the other hand, does not contribute to inherited variation as it occurs in non-germ cells and is not passed on to offspring.

Homologous organs:
- Homologous organs are organs that have the same basic structure but perform different functions.
- These organs are derived from a common ancestor and show similarities in their anatomical structure.
- Despite their different functions, homologous organs share a similar embryonic origin, showing evidence of common ancestry.
- These organs may have different shapes, sizes, and functions in different species, but they have a common underlying structure.
- An example of homologous organs is the forelimbs of vertebrates, such as the human arm, the flipper of a whale, and the wing of a bat.
- Homologous organs provide evidence for evolution and common descent among different species.
- By studying homologous organs, scientists can trace the evolutionary history and relationships between different species.

To determine the age of a fossil based on its depth of discovery, we can make the following conclusions:
1. Fossils found at deeper layers: Fossils that are discovered at deeper layers of the earth are generally older than those found at shallower depths. This is because the layers of sedimentary rock accumulate over time, with newer layers being deposited on top of older ones.
2. Age estimation: While the exact age of a fossil cannot be determined solely based on its depth, we can infer that it is very old. Fossils found at deeper layers could be thousands or even millions of years old. The deeper the fossil is found, the older it is likely to be.
3. Relative dating: By observing the position of a fossil in the geological layers, scientists can use relative dating techniques to estimate its age relative to other fossils and rock formations. This method allows for a comparison of the ages of different fossils but does not provide an absolute age.
4. Index fossils: Fossils found at specific depths can serve as index fossils, which are commonly occurring fossils with a known age range. By identifying these index fossils, scientists can further narrow down the age of the fossil-bearing layers.
5. Other dating techniques: To determine the absolute age of a fossil, scientists often use radiometric dating methods, such as carbon dating or potassium-argon dating. These techniques involve measuring the decay of radioactive isotopes in the fossil or the surrounding rocks.
In conclusion, while the exact age of a fossil cannot be determined solely based on its depth, fossils found at deeper layers of the earth are generally considered to be very old, potentially thousands or millions of years old.

Analogous organs:
- Analogous organs are those that have similar functions but different origins.
- They are not derived from a common ancestor.
- The wings of an insect and a bird are examples of analogous organs because they both serve the purpose of flight, but they have evolved independently in different organisms.
Vestigial organs:
- Vestigial organs are remnants of structures that were once functional in the ancestor but are no longer necessary or have reduced functionality in the descendant.
- They often serve no purpose or have a different function in the current organism.
- The wings of flightless birds, such as ostriches or penguins, are examples of vestigial organs because they are present but have lost their ability to fly.
Homologous organs:
- Homologous organs are those that have a similar structure and origin but may have different functions.
- They are derived from a common ancestor and often reflect evolutionary relationships.
- The wings of a bat and a bird are examples of homologous organs because they have a similar structure and are derived from a common ancestor, even though they have different functions (flight vs. gliding).
Analytic organs:
- There is no such term or concept as "analytic organs" in biology.
- It is not a valid option for the given question.
Therefore, the correct answer is A: Analogous organs, as the wings of an insect and a bird have similar functions but different origins.

Vermiform appendix is an example of a vestigial organ.

A vestigial organ is an organ that has lost its original function through evolution. It may have had a purpose in the past, but it is no longer necessary for the survival or functioning of the organism. The vermiform appendix is a small, tube-like structure attached to the cecum, which is the first part of the large intestine.

Here are some key points explaining why the vermiform appendix is considered a vestigial organ:

• No known function: The vermiform appendix does not have a clearly defined function in the human body. It does not play a role in digestion or other vital processes.



• Reduced size: Over time, the vermiform appendix has become smaller in humans compared to other species. In some animals, such as herbivores, the appendix is larger and plays a role in digesting cellulose-rich diets. However, in humans, the appendix has lost its original function and is much smaller.



• Predisposition to inflammation: The vermiform appendix is prone to a condition known as appendicitis, which is the inflammation of the appendix. This condition can be life-threatening and often requires surgical removal of the appendix. The high incidence of appendicitis suggests that the vermiform appendix is a non-functional organ in humans.



• Evolutionary remnants: The presence of a vestigial organ like the vermiform appendix in humans is considered evidence of our evolutionary history. It is believed to be a remnant of a larger cecum that was more functional in our ancestors, who had diets that required more extensive digestion.

Therefore, the vermiform appendix is classified as a vestigial organ due to its lack of function, reduced size, predisposition to inflammation, and evolutionary remnants.

Explanation:
The correct answer is C: both DNAs of father and mother gamete.
- Traits in an offspring are determined by the combination of genetic material from both parents.
- Gametes are reproductive cells (sperm and egg) that carry half the genetic information of an individual.
- The DNA in the mother's gamete (egg) and the father's gamete (sperm) both contribute to the genetic makeup of the offspring.
- Each parent passes on a copy of their DNA to their offspring, resulting in a combination of genetic traits.
- The DNA from both parents undergoes recombination during the process of fertilization, leading to unique genetic variations in the offspring.
- These genetic variations determine the inheritance of physical characteristics, such as eye color, hair color, height, etc.
- Therefore, the traits in an offspring are influenced by both DNAs of the father and mother gamete.

Mendel's Experiment:
Mendel conducted an experiment by crossing a tall plant with a dwarf plant. He wanted to study the inheritance patterns of traits in the offspring, specifically the height of the plants.
Explanation:
In the experiment, Mendel observed the F2 generation, which is the second filial generation or the offspring of the F1 generation. The F1 generation is the offspring of the cross between the tall and dwarf plants.
Mendel's experiment followed the principles of Mendelian genetics, which state that the inheritance of traits is governed by discrete units called genes. These genes can be dominant or recessive, and they segregate and assort independently during gamete formation.
In the case of plant height, the tall trait is dominant (T) and the dwarf trait is recessive (t). When a tall plant (TT) is crossed with a dwarf plant (tt), all the offspring in the F1 generation will be tall (Tt) because the tall trait is dominant.
When the F1 generation plants are self-fertilized or crossed with each other, the offspring in the F2 generation will show a phenotypic ratio of 3:1 for tall to dwarf plants. This is because the tall plants can be either homozygous dominant (TT) or heterozygous (Tt), while the dwarf plants are homozygous recessive (tt).
Calculation:
So, in the F2 generation, the ratio of dwarf plants is 1:3 or 1/4. This can be expressed as 25%.
Conclusion:
Therefore, the ratio of dwarf plants in the F2 generation, when a tall plant is crossed with a dwarf plant, is 25%.

Gamete cells are:
Gamete cells are specialized sex cells that are involved in sexual reproduction. They are responsible for transmitting genetic information from one generation to the next. Gametes are produced through a process called gametogenesis, which involves cell division and differentiation.
Types of gametes:
There are two types of gametes:
1. Haploid gametes:
- Gametes are haploid cells, meaning they contain half the number of chromosomes compared to other cells in the body.
- Haploid gametes are produced through a type of cell division called meiosis.
- In humans, haploid gametes include sperm cells in males and egg cells (ova) in females.
2. Diploid gametes:
- Gametes can also be diploid, meaning they contain the full set of chromosomes.
- Diploid gametes are rare and usually result from abnormal cell division or genetic disorders.
- Examples of diploid gametes are found in certain plants and some invertebrates.
Function of gametes:
- Gametes are responsible for sexual reproduction and the formation of a new individual.
- During fertilization, a haploid sperm cell fuses with a haploid egg cell to form a diploid zygote.
- The zygote then undergoes cell division and development to eventually form a new organism.
Conclusion:
In summary, gamete cells are haploid cells that are involved in sexual reproduction. They play a crucial role in transmitting genetic information and are responsible for the formation of a new individual.

Explanation:
To determine the sex of a baby, we need to look at the 23rd chromosome pair, also known as the sex chromosomes.
- In humans, females have two X chromosomes, denoted as XX.
- Males, on the other hand, have one X chromosome and one Y chromosome, denoted as XY.
Based on this information, we can conclude that a human baby will be female if its 23rd chromosome pair is XX.
Therefore, the correct answer is A: XX.

The Hypothesis of Life's Origin from Simple Inorganic Molecules
The hypothesis that life must have developed from the simple inorganic molecules present on Earth soon after it was formed has been proposed by various scientists. Among them, four prominent figures are Miller, Urey, Darwin, and Haldane. However, the correct answer to the question is D: Haldane.
Explanation:
Sir J.B.S. Haldane, a British scientist, proposed the hypothesis that life originated from simple inorganic molecules. He suggested that the early Earth's atmosphere was reducing in nature, consisting of gases such as methane, ammonia, water vapor, and hydrogen. Haldane believed that under these conditions, organic compounds could have been synthesized through various chemical reactions.
Haldane's hypothesis was further supported by the famous Miller-Urey experiment conducted in 1952. Stanley Miller and Harold Urey attempted to simulate the conditions of the early Earth's atmosphere and demonstrated that simple organic molecules, including amino acids, could be synthesized from inorganic components.
Although Charles Darwin laid the foundation for the theory of evolution, he did not specifically propose the hypothesis of life's origin from inorganic molecules. His work focused more on the mechanisms of natural selection and the diversification of life forms.
In conclusion, while Miller and Urey conducted experiments that supported Haldane's hypothesis, it was J.B.S. Haldane who proposed the idea that life must have developed from the simple inorganic molecules present on Earth soon after its formation.

Contrasting Characters in Pisum sativum:
Tall and dwarf:
- Mendel observed that some plants were tall while others were dwarf in Pisum sativum.
- This was a clear example of a pair of contrasting characters.
Yellow and green seed colour:
- Another pair of contrasting characters observed by Mendel was the color of the seeds.
- Some seeds were yellow, while others were green.
Terminal and axial flower:
- Mendel also noticed that some plants had flowers at the tip of the stem (terminal), while others had flowers along the sides of the stem (axial).
- This was a distinct difference in the flower arrangement.
Smooth and rough stem:
- The final pair of contrasting characters observed by Mendel was the texture of the stem.
- Some plants had smooth stems, while others had rough stems.
Conclusion:
- Among the given options, the pair of contrasting characters that is not a part of Mendel's observations in Pisum sativum is the "Smooth and rough stem."
- Mendel did not observe this particular contrast in stem texture in his experiments with Pisum sativum.

Explanation:
Mendel's monohybrid cross involves the crossing of two individuals that differ in only one trait. In this case, we are considering a monohybrid cross where only one trait is being studied.
Mendel studied the inheritance of traits in pea plants, specifically the color of the seeds. He crossed two pea plants, one with yellow seeds (dominant trait) and one with green seeds (recessive trait).
The F1 generation resulting from this cross all had yellow seeds. This indicates that the yellow seed color is dominant over the green seed color.
When the F1 generation plants are self-fertilized, they produce the F2 generation.
The F2 phenotype ratio refers to the ratio of individuals in the F2 generation that exhibit a specific phenotype, in this case, the ratio of individuals with yellow seeds to individuals with green seeds.
In the F2 generation, Mendel observed a ratio of 3 individuals with yellow seeds to 1 individual with green seeds.
Therefore, the F2 phenotype ratio of the monohybrid cross studied by Mendel is 3:1.
Answer: C. 3:1

To determine the genotype of a tall pea plant according to Mendelism, we need to understand the principles of inheritance as proposed by Gregor Mendel. Mendel's principles state that there are dominant and recessive traits, and that the genotype of an individual determines its phenotype.
In this case, T represents the tall trait and t represents the dwarf trait.
Genotypes:
- TT: Homozygous dominant genotype, where both alleles are for tallness.
- Tt: Heterozygous genotype, where one allele is for tallness and the other allele is for dwarfness.
- tt: Homozygous recessive genotype, where both alleles are for dwarfness.
Since the tall pea plant is tall, it exhibits the tall phenotype. According to Mendel's principles, the tall phenotype can be determined by either a homozygous dominant genotype (TT) or a heterozygous genotype (Tt).
Therefore, the genotype of a tall pea plant according to Mendelism can be either TT or Tt. Hence, the correct answer is option C: Either TT or Tt.

Explanation:
The genotype of the Yellow and Round seeded pea plant is YyRr. This means that it has two pairs of alleles: one for seed color (Y and y) and one for seed shape (R and r). When the plant undergoes gamete formation, the alleles segregate and combine randomly to produce different combinations of alleles in the gametes.
Here's a breakdown of the possible gametes produced by the plant:
Seed color:
- Y allele can combine with either Y or y allele
- y allele can combine with either Y or y allele
Seed shape:
- R allele can combine with either R or r allele
- r allele can combine with either R or r allele
Combining the possibilities:
- Y allele can combine with either R or r allele, resulting in YR or Yr
- y allele can combine with either R or r allele, resulting in yR or yr
Therefore, the possible gametes produced by the Yellow and Round seeded pea plant with genotype YyRr are YR, yR, Yr, and yr. Thus, the correct answer is option B: YR, yR, Yr, yr.

1. Introduction:
To determine the sex of a fetus, it is important to understand the genetic makeup of the parents and the process of fertilization. In this case, a sperm with 22 Y chromosomes fertilizes an egg with 22 X chromosomes.
2. Sex Determination:
The sex of a fetus is determined by the combination of sex chromosomes inherited from the parents. In humans, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).
3. Sperm and Egg:
- A sperm carries either an X or a Y chromosome.
- An egg always carries an X chromosome.
4. Fertilization Process:
- During fertilization, a sperm penetrates and fuses with an egg, forming a zygote.
- The sperm's chromosome (either X or Y) determines the genetic sex of the resulting zygote.
5. Outcome:
In this scenario, the sperm carrying a Y chromosome fertilizes the egg carrying an X chromosome. Therefore, the sex of the fetus shall be male (XY).
6. Conclusion:
Based on the genetic information provided, the sex of the fetus can be determined as male.

Explanation:
The forelimbs of frog, lizard, bird, and man show evolutionary relationships in terms of homologous organs. Homologous organs are structures that have a similar basic structure but may have different functions in different organisms. In this case, the forelimbs of these organisms have a similar basic structure despite their different functions.
Here is a detailed explanation of the evolutionary relationships:
Homologous Organs:
- Homologous organs are those that have a common ancestry and share a similar basic structure, although they may have different functions in different organisms.
- The forelimbs of frog, lizard, bird, and man are considered homologous organs because they have a similar bone structure, with similar bones such as the humerus, radius, and ulna.
- The presence of homologous organs suggests a common ancestor from which these organisms evolved.
Other options explained:
Hand Relationship:
- The term "hand relationship" is not a scientific term used to describe the evolutionary relationships of these organisms.
- While all of these organisms have some form of a limb or appendage that can be considered a hand, this does not explain their evolutionary relationship.
Missing Links:
- The term "missing links" refers to hypothetical transitional forms that would fill the gaps in the fossil record between different species.
- The existence of missing links is a debated topic in evolutionary biology, and it is not directly related to the forelimbs of these specific organisms.
Analogous Organs:
- Analogous organs are structures that have a similar function but do not share a common ancestry.
- The forelimbs of these organisms are not considered analogous organs because they have a similar basic structure, indicating a shared ancestry.
In conclusion, the correct answer is D: Homologous organs. The forelimbs of frog, lizard, bird, and man share a similar basic structure, indicating a common ancestry. This supports the idea of evolution and common descent.

To determine the number of autosomes in a human body cell, we need to understand the basics of human chromosomes.
Human cells contain a total of 46 chromosomes, which are organized into 23 pairs. These pairs consist of 22 pairs of autosomes and 1 pair of sex chromosomes.
Autosomes:
- Autosomes are non-sex chromosomes.
- They determine the majority of an individual's traits, excluding the ones related to sex determination.
- Autosomes are present in both males and females.
Based on this information, we can conclude that the number of autosomes in a human body cell is 22 (as mentioned in option C).
Therefore, the correct answer is C: 22.

The Theory of Natural Selection:

• Lamarck: Jean-Baptiste Lamarck proposed the theory of inheritance of acquired characteristics, which suggested that traits acquired during an organism's lifetime could be passed on to future generations. However, this theory is now considered to be incorrect.


• Darwin: Charles Darwin is the correct answer. He proposed the theory of Natural Selection in his book "On the Origin of Species" in 1859. According to Darwin, the process of natural selection leads to the survival and reproduction of individuals with favorable variations, while those with less advantageous traits are less likely to survive and reproduce.


• Mendel: Gregor Mendel is known as the father of modern genetics. He discovered the fundamental principles of heredity through his experiments with pea plants, but his work focused on the inheritance of specific traits and did not directly contribute to the theory of natural selection.


• Haldane: J.B.S. Haldane was a British scientist who made significant contributions to population genetics and evolutionary biology. However, he did not propose the theory of natural selection.

In conclusion, Charles Darwin is credited with proposing the theory of natural selection, which revolutionized our understanding of how species evolve and adapt to their environments. His work laid the foundation for modern evolutionary biology and is still widely accepted and studied today.

How life might have originated on Earth was experimentally shown by Urey and Miller:
The experiment conducted by Urey and Miller provided evidence for the origin of life on Earth. Here is a detailed explanation of their experiment:
1. Background:
- Urey and Miller conducted their experiment in the 1950s when the understanding of the origin of life was still limited.
- They aimed to simulate the conditions of early Earth in order to understand how life might have originated.
2. Experimental Setup:
- Urey and Miller created a closed system in the laboratory.
- They used a glass apparatus containing water, methane, ammonia, and hydrogen, which were believed to be the main components of the Earth's early atmosphere.
- The mixture was heated to simulate the presence of lightning or heat energy.
3. Observations:
- After running the experiment for a week, Urey and Miller analyzed the contents of the apparatus.
- They found that the water had turned pink and contained various organic compounds, including amino acids, which are the building blocks of proteins.
- This indicated that complex organic molecules could be formed under the conditions that mimicked the early Earth's atmosphere.
4. Significance:
- Urey and Miller's experiment provided evidence that the basic building blocks of life, such as amino acids, could have formed spontaneously on early Earth.
- This experiment supported the theory of chemical evolution, suggesting that life may have originated from simple organic molecules in the primordial soup.
5. Impact:
- Urey and Miller's experiment revolutionized the field of abiogenesis, which is the study of how life originated from non-living matter.
- Their findings sparked further research and exploration into the origins of life, leading to new theories and experiments.
In conclusion, Urey and Miller's experiment demonstrated that the conditions on early Earth were capable of producing organic molecules necessary for the origin of life. This experiment provided valuable insights into the possibility of life's emergence from non-living matter.

Genetic Drift
- Genetic drift is a random change in the frequency of alleles in a population over several generations. It occurs due to random errors or chance events in the production of gametes (eggs and sperm).
- It is an evolutionary mechanism that can lead to changes in the genetic composition of a population.
- Genetic drift is more pronounced in small populations where chance events can have a greater impact on allele frequencies.
- There are two main types of genetic drift: bottleneck effect and founder effect.
- Bottleneck effect occurs when a population experiences a drastic reduction in size, leading to a loss of genetic variation.
- Founder effect occurs when a small group of individuals establish a new population, resulting in a limited gene pool.
- Genetic drift can lead to the fixation of certain alleles, where the frequency of one allele becomes 100% in the population, while other alleles may be lost.
- This random change in allele frequencies can have long-term effects on the genetic diversity and adaptability of a population.
- In contrast to genetic drift, gene flow refers to the transfer of genetic material from one population to another through migration or interbreeding.
- Genetic error and genetic crash are not accurate terms to describe the random change in allele frequencies in a population.