Chapter 9. Heredity and Evolution

Class 10 Science Chapter 9. Heredity and Evolution Internal Questions and Answers :

Internal Question :

1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?

Answer : Trait B is likely to have arisen earlier because it has a higher prevalence in the population. As asexually reproducing species do not rely on genetic recombination, traits can accumulate over time through mutation and natural selection, leading to higher frequencies in subsequent generations.
2. How does the creation of variations in a species promote survival?

Answer :The creation of variations in a species promotes survival by increasing the likelihood of individuals possessing traits that can better adapt to changing environments, enhancing their ability to survive and reproduce successfully in diverse conditions.

Internal Question :

1. How do Mendel’s experiments show that traits may be dominant or recessive?

Answer : Mendel's experiments with pea plants revealed that certain traits, such as flower color or seed texture, appeared dominant in the presence of a contrasting trait. This dominance was evident when crossing plants with differing traits, as the dominant trait consistently appeared in the offspring, while the recessive trait seemed to "disappear" but reappeared in later generations.
2. How do Mendel’s experiments show that traits are inherited independently?

Answer : Mendel's experiments with pea plants involved studying the inheritance of multiple traits simultaneously. By performing dihybrid crosses, he observed that traits such as seed color and seed texture segregated independently of each other. The inheritance patterns of one trait did not influence or affect the inheritance patterns of another trait, demonstrating that traits are inherited independently and follow the principles of Mendelian inheritance. This concept is known as the principle of independent assortment.
3. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?

Answer : No, this information alone is not sufficient to determine whether blood group A or O is dominant. Blood group inheritance is governed by multiple alleles and complex genetic interactions. The ABO blood group system involves three alleles: A, B, and O. The O allele is recessive, while A and B are co-dominant. In this scenario, the daughter having blood group O could mean that either the father (with blood group A) passed on the O allele or that both parents passed on the O allele. Further information or genetic analysis would be needed to determine the dominance relationship between blood group A and O in this particular case.
4. How is the sex of the child determined in human beings?

Answer : The sex of a child in human beings is determined by the combination of sex chromosomes inherited from the parents. Typically, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The mother always contributes an X chromosome, while the father can contribute either an X or a Y chromosome.

If the sperm carries an X chromosome, it will combine with the mother's X chromosome, resulting in an XX combination and the birth of a female child. If the sperm carries a Y chromosome, it will combine with the mother's X chromosome, resulting in an XY combination and the birth of a male child.

It is the presence of the Y chromosome in the sperm that determines the development of a male child, while the absence of the Y chromosome leads to the development of a female child.

Internal Question :

1. What are the different ways in which individuals with a particular trait may increase in a population?

Answer : : Individuals with a particular trait can increase in a population through natural selection, genetic drift, migration, mutation, non-random mating, and artificial selection.
2. Why are traits acquired during the life-time of an individual not inherited?

Answer : Traits acquired during an individual's lifetime, also known as acquired traits, are not inherited because they are not encoded in the DNA of germ cells (sperm or egg) and therefore cannot be passed on to offspring through genetic inheritance.
3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Answer : The small numbers of surviving tigers are a cause of worry from a genetics perspective because they lead to reduced genetic diversity and increase the risk of inbreeding, which can result in genetic disorders, reduced adaptability, and decreased survival chances for the population in the long term.

Internal Question :

1. What factors could lead to the rise of a new species?

Answer : The rise of a new species, or speciation, can be influenced by factors such as geographic isolation, reproductive isolation, genetic drift, natural selection, polyploidy in plants, and hybridization between different species under certain circumstances.
2. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?

Answer : Geographical isolation may not be a major factor in the speciation of a self-pollinating plant species. Since self-pollinating plants do not rely on cross-pollination between different individuals, they are less affected by geographic barriers and can maintain gene flow even in the absence of physical isolation.
3. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?

Answer : Geographical isolation is generally not a major factor in the speciation of organisms that reproduce asexually. Asexual reproduction involves the production of genetically identical offspring, and without the need for genetic exchange between individuals, geographic barriers have less impact on the divergence and speciation of asexual organisms.

Internal Question :

1. Give an example of characteristics being used to determine how close two species are in evolutionary terms.

Answer :  One example of characteristics used to determine the evolutionary closeness between two species is the comparison of DNA or protein sequences. By analyzing the similarities and differences in genetic sequences, scientists can assess the degree of genetic divergence and estimate the evolutionary distance between species. The more similar their sequences, the closer the species are believed to be in evolutionary terms.                                  

2. Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?

Answer :  The wing of a butterfly and the wing of a bat cannot be considered homologous organs. Homologous organs are structures that share a common evolutionary origin, meaning they are derived from the same structure in a common ancestor.

In the case of the butterfly and the bat, their wings have different evolutionary origins. The butterfly's wing is an adaptation of the insect exoskeleton and is composed of chitinous structures. On the other hand, the bat's wing is a modification of the forelimb bones, with a thin membrane of skin stretched between elongated fingers.

While both wings serve the purpose of flight, their anatomical structures and developmental origins differ significantly. Therefore, the wings of a butterfly and a bat are not considered homologous organs.

3. What are fossils? What do they tell us about the process of evolution?

Answer : Fossils are the preserved remains or traces of ancient organisms.

They provide evidence of past life, reveal transitional forms, help determine evolutionary relationships, establish timelines of species appearance, and provide insights into ancient environments, contributing to our understanding of the process of evolution.

Internal Question :

1. Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?

Answer : Despite the visible differences in size, color, and appearance among human beings, they are considered to belong to the same species, Homo sapiens, because they can interbreed and produce fertile offspring. The underlying genetic similarities and ability to exchange genetic material demonstrate their shared ancestry and common biological classification as a single species.
2. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?

Answer : In evolutionary terms, it is not appropriate to categorize any of these organisms as having a "better" body design. Evolution does not progress towards a single ideal form, but rather favors adaptations that enhance survival and reproduction within specific environments. Each of these organisms has evolved body designs suited to their respective ecological niches and lifestyles.

Class 10 Science Chapter 9. Heredity and Evolution Exercises :

1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw

Answer : (c) TtWW

2. An example of homologous organs is
(a) our arm and a dog’s fore-leg.
(b) our teeth and an elephant’s tusks.
(c) potato and runners of grass.
(d) all of the above.

Answer : (d) all of the above.

3. In evolutionary terms, we have more in common with
(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.

Answer : (a) a Chinese school-boy.

4. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?

Answer : Based on the information provided, we cannot definitively determine whether the light eye color trait is dominant or recessive. The correlation between parents and children having light-colored eyes suggests a possible genetic influence, but it does not provide conclusive evidence about the specific mode of inheritance without further genetic analysis or information about other family members' eye colors.
5. How are the areas of study – evolution and classification – interlinked?

Answer : Evolution and classification are interlinked because the process of evolution shapes the diversity of life on Earth, and classification systems are developed to organize and categorize organisms based on their evolutionary relationships, allowing scientists to understand the patterns and history of life's diversification.
6. Explain the terms analogous and homologous organs with examples.

Answer :  Analogous organs are structures that have similar functions but different evolutionary origins, arising independently in different lineages due to adaptation to similar environments. Examples include the wings of birds and insects.

Homologous organs are structures with similar underlying anatomy and evolutionary origins, inherited from a common ancestor. Examples include the forelimbs of mammals, such as human arms, cat paws, and whale flippers.

7. Outline a project which aims to find the dominant coat colour in dogs.

Answer : Project Title: Determining the Dominant Coat Colour in Dogs

Objective: The objective of the project is to identify the dominant coat color in dogs and understand the inheritance patterns associated with coat color variations.

Sample Collection: Collect a diverse sample of dogs representing different breeds and coat colors.

Phenotypic Assessment: Record and categorize the coat colors of the collected dogs based on standardized coat color classifications.

Pedigree Analysis: Collect pedigree information for the sampled dogs to establish parent-offspring relationships and track coat color inheritance across generations.

Genetic Analysis: Extract DNA samples from the collected dogs and perform genetic analysis using molecular markers or sequencing techniques to identify genetic variations associated with coat color.

Statistical Analysis: Analyze the data obtained from phenotypic assessment and genetic analysis to determine patterns of inheritance and the dominance of specific coat colors.

Results and Conclusion: Determine the dominant coat color(s) based on the analysis and provide conclusions on the inheritance patterns and dominant traits related to coat color in dogs.

Further Exploration: Discuss potential future directions for studying other coat color genes, considering breed-specific variations, and investigating the interaction between coat color and other genetic traits.

Presentation and Publication: Present the findings at scientific conferences, publish the results in relevant journals, and share the knowledge with the scientific community and dog breeders

8. Explain the importance of fossils in deciding evolutionary relationships.

Answer : Fossils play a crucial role in determining evolutionary relationships by providing direct evidence of past organisms. They allow scientists to study the anatomical structures of ancient species, compare them to living organisms, and identify transitional forms. Fossils provide a timeline of species appearance and extinction, aiding in the construction of phylogenetic trees and understanding the branching patterns of evolutionary lineages.
9. What evidence do we have for the origin of life from inanimate matter?

Answer : The evidence for the origin of life from inanimate matter is largely indirect and based on scientific theories and experiments. Key lines of evidence include laboratory simulations that demonstrate the synthesis of organic molecules under early Earth conditions, the presence of organic compounds in meteorites, and the identification of potential building blocks of life in various planetary environments.
10. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?

Answer :  Sexual reproduction gives rise to more viable variations than asexual reproduction through the process of recombination and genetic diversity. During sexual reproduction, genetic material from two parent organisms is combined, resulting in the shuffling and mixing of genetic traits. This generates new combinations of alleles and increases the genetic variability within a population.

The increased genetic diversity resulting from sexual reproduction enhances the adaptability and evolutionary potential of organisms. It provides a wider range of genetic variations for natural selection to act upon, allowing sexually reproducing organisms to adapt more effectively to changing environments and increasing their chances of long-term survival compared to asexual organisms with limited genetic variation.

11. How is the equal genetic contribution of male and female parents ensured in the progeny?

Answer : : The equal genetic contribution of male and female parents is ensured through sexual reproduction. During fertilization, the male gamete (sperm) fuses with the female gamete (egg) to form a zygote. Each gamete carries half of the genetic material of the parent, ensuring an equal contribution from both male and female parents to the genetic makeup of the progeny.
12. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?

Answer : I partially agree with the statement. Variations that confer a selective advantage to an individual organism are more likely to increase its chances of survival and reproduction, leading to their persistence in a population over time. However, it is important to note that not all variations need to confer an advantage. Some variations may be neutral or even disadvantageous but can persist in a population due to factors like genetic drift, mutation, or environmental changes.