Class 10 Science Chapter 8 Case Based Questions - Heredity and Evolution

Case Study - 1

Change in non-reproductive tissues cannot be passed on to the DNA of the germ cells. Therefore the experiences of an individual during its lifetime cannot be passed on to its progeny, and cannot direct evolution. Consider another example of how an individual cannot pass on to its progeny the experiences of its lifetime. If we breed a group of mice, all their progeny will have tails, as expected. Now, if the tails of these mice are removed by surgery in each generation, do these tailless mice have tailless progeny? The answer is no, and it makes sense because removal of the tail cannot change the genes of the germ cells of the mice.

Q1: What are acquired traits? Explain with example.
Ans: The traits which are gain while experiencing the life time, its not related to genetic material.
Example: If a person get injured during his life time and get handicapped. This trait will not pass to his progeny as it had acquired throughout his life.

Q2: Who wrote origin of life on earth?
Ans: Charles Darwin

Q3: What do you meant by term speciation?
Ans: It is an evolutionary process in which new species are formed by developing distinct features from their species or by modifying their genetic material.

Q4: What are the factors that gave rise to the formation of new species?
Ans: Geographical isolation, genetic drift, mutation and natural selection.

Q5: What is natural selection?
Ans: The process which occurs in nature by which organism adapt the changing environment and tend to survive in it and reproduce in it.

Case Study - 2

The two sexes participating in sexual reproduction must be somewhat different from each other for a number of reasons. How is the sex of a newborn individual determined? Different species use very different strategies for this. Some rely entirely on environmental cues. Thus, in some animals like a few reptiles, the temperature at which fertilised eggs are kept determines whether the animals developing in the eggs will be male or female. In other animals, such as snails, individuals can change sex, indicating that sex is not genetically determined. However, in human beings, the sex of the individual is largely genetically determined. In other words, the genes inherited from our parents decide whether we will be boys or girls.

Q1: How many chromosomes are there in human beings?
Ans: 23 pairs in which 22 pairs are autosomal and one pair i.e 23rd pair is sex chromosome.

Q2: What are the pair of sex chromosome present in both male and female?
Ans: People have same set of chromosome i.e XX but male have different sets of chromosome i.e XY.

Q3: How is the sex of the child determined in human beings?
Ans: The sex is determined by paternal chromosome i.e. XY if X alleles fused with X chromosome of female then it is a baby girl. If Y allele fuse with X chromosome of female during fertilisation then it will be a baby boy.

Q4: What is hermaphrodites?
Ans: Those organisms who don't have separate sex organs i.e. both the sex organs are present in the same body.
Example: Earthworm

Case Study - 3

The rules for inheritance of such traits in human beings are related to the fact that both the father and the mother contribute practically equal amounts of genetic material to the child. This means that each trait can be influenced by both paternal and maternal DNA. Thus, for each trait there will be two versions in each child. What will, then, the trait seen in the child be?

Q1: What were the contrasting traits used by mendel?
Ans: Tall and dwarf plant, round/ wrinkled seeds, white / violets flower and on the basis of pod colour etc.

Q2: What was the phenotypic ratio of monohybrid cross?
Ans: 3 : 1 here, 3 is for tall plants and 1 is dwarf plants.

Q3: What was the genotypic ratio of monohybrid cross?
Ans: 1 : 2 : 1

Q4: How does the traits get expressed?
Ans: Genes control traits, the diploid organism inherit two alleles from a gene i.e one is from father and one is from mother.

Case Study - 4

The evolutionary relationships of the species we see around us. It is a sort of going backwards in time. We can do this by identifying hierarchies of characteristics between species. Similarities among organisms will allow us to group them and then study the groups. For this, which characteristics decide more fundamental differences among organisms, and which ones decide less basic differences? What is meant by ‘characteristics’, anyway? Characteristics are details of appearance or behaviour; in other words, a particular form or a particular function. That we have four limbs is thus a characteristic.

Q1: What is homologous organs?
Ans: The organs which have similar structure but different functions.
Example: limbs of human, bird, frog and lizard

Q2: What are fossil?
Ans: The preserved remains or traces of remains body parts of an organism is called fossil.

Q3: What are analogous organ?
Ans: Different structure but  same function.
Example: wings of bats and birds.

Q4: How do we know how old the fossils are?
Ans: By using carbon dating , in these we used radioactive decay of carbon 14 isotopes.

Q5: What does it infer ” if more characteristics of two species are common”?
Ans: It means they are closely related and may one had evolved from other or both have common ancestors.

Case Study - 5

It is all very well to say that very dissimilar looking structures evolve from a common ancestral design. It is true that analysis of the organ structure in fossils allows us to make estimates of how far back evolutionary relationships go. Are there any current examples of such a process? The wild cabbage plant is a good example. Humans have, over more than two thousand years, cultivated wild cabbage as a food plant, and generated different vegetables from it by selection. This is, of course, artificial selection rather than natural selection.

Q1: What was the evolution history of cabbage?
Ans: Earlier, the human beings cultivates the wild cabbage for food and had produced different varieties of cabbage by doing artificial selection. The different varieties were kohlrabi, cauliflower, broccoli, cabbage, red cabbage and kale.

Q2: What is molecular phylogeny?
Ans: It is a method to gather information of an organism regarding their evolutionary relationship.

Q3: What are the different methods for tracing the evolutionary relationship?
Ans: Looking into the data of homologous organ and analogous organ, fossil and embryo development.

Q4: Do you agree with the term that ” evolution should not be equated with progress”?
Ans: Yes, evolution leads to more and more complex body design over time. It doesnt mean that older design are inefficient. For example, the bacteria the most primitive and simplest type of organism live in any harsh habitat and still they are surviving.

Q5: Give one examples of evolution by stages?
Ans: Earlier, birds have feather only for heating purpose but as time passes, they evolve and now the feathers are used for flight also.

Case Study – 6

Pure bred pea plant with smooth seeds (dominant characteristic) were crossed with pure bred pea plant with wrinkled seeds (recessive characteristic). The F1 generation was self pollinated to give rise to the F2 generation.

Q1: What is the expected observation of the F1 generation of plants?
Ans: All of them have smooth seeds.

Q2: What is the expected observation of the F2 generation of plants?
Ans: ¼ of them have wrinkled seeds and ¾ of them have smooth seeds

Q3: What will be the genotypic ration of F2 offspring , also mention whether it will be homozygous or heterozygous ?
Ans: Genotypic ratio = 1 : 2 : 1

• Homozygous dominant
• Heterozygous dominant
• Homozygous recessive

Case Study - 7

A scientist cross pure-bred tall (dominant) pea plant with pure-bred dwarf (recessive) pea plant he will get pea plants of F1 generation. If now self-cross the pea plant of F2 generation is done, then we obtain pea plants of F2 generation.

Q1: State the type of plants not found in F2 generation but appeared in F2 generation, mentioning the reason for the same
Ans: In the F1 generation, Dwarf trait is recessive trait which was not expressed. After self pollination, the recessive trait gets expressed in F2 generation

Q2: State the ratio of tall plants to dwarf plants in F2 generation.. Write the full form of DNA.
Ans: Ratio – 3 : 1
Full form of DNA – Deoxyribonucleic acid

Q3: What do the plants of F2 generation look like?
Ans: All plants of F1 generation will be tall plants.

Q4: How does the creation of variations in a species promote survival?
Ans: Variations promote the survival only when the species wants to allow by itself for survive to the continuous changing environment and conditions. During variations, different species get different kinds of advantages depending on the nature.