8. Heredity

CBSE Class 10 Science Chapter 8. Heredity

Chapter 8. Heredity

Class 10 Science Chapter 8. Heredity CBSE Previous Years Questions and Answers :

Question : 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

Question : Why is variation important for a species ? [2017 1M]

Answer : Variation is crucial for a species because it promotes genetic diversity, which enhances adaptability to changing environments. It increases the chances of survival and reproduction, allowing populations to withstand environmental pressures and evolve over time.

Question: Given one example each of characters that are inherited and the ones that are acquired in humans . Mention the difference between the inherited and the acquired characters . [2010 2M]

Answer : In humans, inherited characters include traits such as eye color, hair texture, and blood type, which are determined by genetic factors inherited from parents. Acquired characters encompass attributes like language proficiency, learned skills, and cultural beliefs, which are acquired through environmental influences and experiences. The key difference lies in the source of determination: inherited traits originate from genetic inheritance, while acquired traits result from environmental factors and personal experiences.

Question: A Mendelian experiments consisted of breeding pea plants bearing violet flowers with pea plants bearing white flowers . What will be the result in progeny ? [2018 2M]

Answer : In Mendelian experiments involving the crossbreeding of pea plants with violet and white flowers, the result in the progeny would typically exhibit all violet flowers. According to Mendel's principles of dominance, one trait (violet flowers) tends to dominate over the other (white flowers) in the first generation (). The white flower trait, although present in the genetic makeup, is not expressed in the generation.

Question: Describe any three ways in which individuals with a particular trail may increase in population . [2011 3M]

Answer : Individuals with a particular trait can increase in population through various mechanisms:

Natural Selection: If the trait provides a survival or reproductive advantage, individuals possessing it are more likely to survive, reproduce, and pass the trait to their offspring. Over time, this can lead to an increase in the frequency of the trait within the population.

Sexual Selection: Traits that are preferred by mates can lead to increased mating opportunities for individuals possessing those traits. This can result in higher reproductive success for individuals with the trait, leading to its increased prevalence in the population over generations.

Genetic Drift: In smaller populations, random chance events can lead to fluctuations in the frequency of certain traits. If individuals with the particular trait happen to be more successful in reproduction due to chance, their trait may increase in frequency within the population over time, purely due to stochastic processes.

Question: A blue colour flower plant denoted by BB is crossbred with a white colour flower plant denoted by bb .

(a) State the colour of flower you expect in their generation plants .

(b) What must be the percentage of while flower plants in generation if flowers of plants are self-pollinated ?

Answer : (a) In the generation, the plants will have a genotype of Bb. Since B is dominant for blue color, the flowers of the generation plants will be blue.

(b) If the flowers of the plants are self-pollinated, the expected percentage of white-flowered plants in the generation would be 25%, as predicted by Mendelian genetics.

Question : “ A trait may be inherited, but may not be expressed” . Justify this statement with the help of a suitable example . [2014 3M]

Answer : The statement "A trait may be inherited but may not be expressed" is justified by considering the example of plant height. The gene for a specific enzyme influencing plant hormone production can affect height. If the gene undergoes an alteration, reducing enzyme efficiency, the trait (tallness) is inherited but not expressed, leading to a short plant. Gene variations can influence trait expression despite inheritance.

Question : What are chromosomes ? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained . [2015 3M]

Answer : Chromosomes are thread-like structures made of DNA and proteins found in the nucleus of cells. They carry genetic information in the form of genes.

In sexually reproducing organisms, the number of chromosomes in the progeny is maintained through meiosis, a specialized cell division process. During meiosis, germ cells undergo two successive divisions, reducing the chromosome number by half, ensuring that the progeny receive the correct number of chromosomes from each parent.

Question : How do Mendel’s experiment show that traits are inherited independently ? [2016 3M]

Answer : Mendel's experiments with pea plants revealed that traits like seed shape and color segregate independently during gamete formation. Traits like seed shape (round/wrinkled) and seed color (yellow/green) appeared unlinked, allowing for diverse combinations in offspring. This segregation demonstrated the principle of independent assortment, showing that traits are inherited independently.

Question : How did Mendel’s explain that it is possible that a trail is inherited but not expressed in an organism ? [2017 3M]

Answer : Mendel explained that a trait can be inherited but not expressed through his law of segregation and law of independent assortment. According to Mendel, traits are controlled by discrete units (genes), and some may be masked by dominant traits. These masked traits can still be passed down to offspring, remaining dormant until they encounter the right genetic conditions for expression.

Question : Name the plant Mendel used for his experiment . What type of progeny was obtained by Mendel in and generations when he crossed the tall and short plants ? Write the ratio he obtained in generation plants . [2019 3M]

Answer : Mendel used garden pea plants (Pisum sativum) for his experiments.

In the generation, Mendel obtained all tall plants.

In the generation, Mendel obtained a phenotypic ratio of 3 tall plants to 1 short plant, resulting in a 3:1 ratio of tall to short plants.

Question : List two differences between acquired trails and inherited trails by giving an example of each . [2019 3M]

Answer : The two differences between acquired trails and inherited trails are :

Acquired Traits	Inherited Traits
Acquired traits are developed during an individual's lifetime due to environmental influences.	Inherited traits are passed down from parents to offspring through genetic material.
Example: Language proficiency acquired through education and exposure.	Example: Eye color inherited from parents based on genetic makeup.

Question : (a) Name the two types gametes produced by men .

(b) Does a male child inherit X chromosome from his father ? Justify .

Answer : (a) The two types of gametes produced by men are sperm cells, which carry either an X or a Y chromosome.

(b) No, a male child does not inherit an X chromosome from his father. Instead, he inherits the Y chromosome from his father, determining his maleness. The X chromosome is contributed by the mother.

Question : Case study Based Questions : Mendel blended his knowledge of science and mathematics to keep the count of the individuals exhibiting a particular trials in each generation . He observed a number of contrasting visible Characters controlled in pea plants in a field . He conducting many experiments to arrive at the laws of inheritance .

(a) What do the progeny of tall plants with round seeds and short plants with wrinkled seeds look like ?

(b) Name the recessive trails in above case .

(c) Mention the type of the new combinations of plants obtained in progeny along with their ration, if progeny was allowed to self pollinate . [2012 4 Marks]

Answer : (a) The progeny of tall plants with round seeds and short plants with wrinkled seeds all appear tall with round seeds.

(b) The recessive traits in the above case are short plants and wrinkled seeds.

(c) In the progeny, new combinations of plants include tall plants with round seeds, tall plants with wrinkled seeds, short plants with round seeds, and short plants with wrinkled seeds. The ratio of these combinations follows Mendel's dihybrid cross ratio of 9:3:3:1.

Question : If 1600 plants were obtained in progeny , write the number of plants having trails : [2012 4 Marks]

(i) Tall with round seeds

(ii) Short with wrinkled seeds

Write the conclusion of the above experiment .

Answer : Given the progeny of 1600 plants, using the 9:3:3:1 ratio of Mendelian inheritance:

(i) Number of plants with tall and round seeds: plants

(ii) Number of plants with short and wrinkled seeds: plants

The experiment supports Mendel's laws of segregation and independent assortment, as the observed phenotypic ratios closely approximate the expected ratios based on Mendelian genetics. The segregation of alleles for different traits and their independent assortment during gamete formation explain the diversity of traits observed in the generation.

Question : The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it . Justify this statement with the help of flow chart showing determination of sex of a newborn . [2012 5 Marks]

Answer : The determination of the sex of a newborn child show in flow chart :

The sex of a newborn is determined by the combination of sex chromosomes inherited from both parents. The father contributes either an X or a Y chromosome, while the mother contributes an X chromosome. The resulting combination determines whether the child is male (XY) or female (XX). The process is a matter of chance, and neither parent has control over the specific combination of sex chromosomes passed on to the child.

Question: How do Mendel’s experiments show that the [2015 5 Marks]

(a) Trails may be dominant or recessive .

(b) Trails are inherited independently .

Answer : (a) Traits may be dominant or recessive: Mendel's experiments, particularly his monohybrid crosses, revealed the concept of dominance. For instance, in the crossing of tall (dominant) and short (recessive) pea plants, the generation displayed only tall plants, indicating the dominance of the tall trait. However, in the generation, the recessive trait reappeared in a 3:1 ratio, illustrating that traits can be either dominant or recessive based on their expression in the offspring.

(b) Traits are inherited independently: Mendel's dihybrid crosses involving plants with two different traits (e.g., seed color and seed shape) showed independent assortment. The distribution of one trait did not affect the distribution of the other trait in the generation. This observation supports the principle of independent assortment, indicating that different traits segregate independently during gamete formation and are inherited independently of each other.

Question: With the help of one example for each, distinguish between the acquired traits and the inherited trails . Why are the trails/experiences acquired during the entire lifetime of an individual not inherited in the next generation ? Explain the reason of this fact with fact with an example . [2017 5 Marks]

Answer : Acquired Traits:

Example: Language Proficiency

Acquired through education and exposure.

An individual learns a language through interaction and practice.

Inherited Traits: Example: Eye Color

Determined by genetic information inherited from parents.

Offspring inherit eye color traits from their ancestors.

Traits acquired during an individual's lifetime, such as language proficiency or learned skills, are not inherited in the next generation because they are not encoded in the individual's genetic material. These traits result from environmental influences and personal experiences that shape an individual's life but do not alter their genetic makeup.

For instance, consider the example of a person who learns to play the piano proficiently through years of practice. While the individual may become skilled at playing the piano, their offspring will not inherit this acquired skill genetically. However, if the individual has a genetic predisposition for musical talent, their offspring may have an increased likelihood of being musically inclined, but the specific skill of playing the piano must be acquired through practice and experience. Thus, acquired traits are not passed down to subsequent generations because they do not alter the genetic information transmitted from parent to offspring.

Question: (a) What is genetics ? [2020 5 Marks]

(b) What are genes ? where are the genes located ?

Answer : (a) Genetics: Genetics is the scientific study of genes, heredity, and variation in living organisms. It explores how traits are passed from parents to offspring, how genes are inherited and expressed, and how genetic information is transmitted and modified over generations.

(b) Genes: Genes are segments of DNA that contain the instructions for building proteins, which in turn determine an organism's traits. Genes are located on chromosomes, which are thread-like structures found in the nucleus of a cell. Each chromosome contains many genes arranged along its length.

Natural Selection: Natural selection is the process by which organisms better adapted to their environment tend to survive and reproduce more successfully. Over time, this process can lead to the emergence of new species as populations adapt to different environmental conditions.

Genetic Drift: Genetic drift is the random fluctuation of allele frequencies in a population due to chance events. In small populations, genetic drift can have a significant impact and may lead to the divergence of populations and the eventual formation of new species.

Isolation: Isolation refers to the separation of populations of organisms from each other, preventing gene flow between them. This can occur due to geographical barriers, ecological differences, or behavioral patterns. Over time, isolation can lead to genetic divergence and the evolution of distinct species.