Chapter 8 - Heredity Class 10 Notes (Science Solutions)
Ncert Solution for Chapter 8 Heredity Class 10 Notes (Science)
Updated Solution 2024-2025 Updated Solution 2024-2025
NCERT Solutions for (Science) Chapter 8 Heredity Class 10 Notes, Question/Answers, Activity, Experiments & Projects
Chapter 8 Heredity
Questions
Q 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?
Ans 1: Trait A, which exists in only 10% of the population, is likely to have arisen earlier. This is because, in asexually reproducing species, traits tend to spread rapidly once they emerge, especially if they are beneficial. The more common trait, B (60%), likely emerged later, as it has had more time to spread through the population.
Q 2. How does the creation of variations in a species promote survival?
Ans 2: The creation of variations in a species helps promote survival by making individuals better adapted to their environment. These differences, such as size, color, or behavior, can give certain members an advantage in finding food, avoiding predators, or coping with changes in climate. When these individuals survive and reproduce, they pass on their beneficial traits to the next generation, helping the species thrive in a variety of conditions. This process is known as natural selection.
Activity 8.1
- Observe the ears of all the students in the class. Prepare a list of students having free or attached earlobes and calculate the percentage of students having each (Fig. 8.2). Find out about the earlobes of the parents of each student in the class. Correlate the earlobe type of each student with that of their parents. Based on this evidence, suggest a possible rule for the inheritance of earlobe types.
Ans: Activity 8.1: Earlobe Inheritance
1. Observe and Record the Earlobe Type of Students:
- Observe the earlobes of all the students in your class to identify whether they have free or attached earlobes.
- Free earlobes hang below the ear, whereas attached earlobes are directly connected to the side of the face, without a visible hanging portion.
- Prepare a list of the students with free or attached earlobes.
2. Calculate the Percentage of Each Type of Earlobe:
- Count how many students have free earlobes and how many have attached earlobes.
- Calculate the percentage of each type using the formula:
Percentage of Free Earlobes = (Number of students with free earlobes ÷ Total number of students) × 100
Percentage of Attached Earlobes = (Number of students with attached earlobes ÷ Total number of students) × 100
3. Ask About the Earlobe Types of Parents:
- Find out the earlobe type of each student’s parents (both mother and father). Record whether they have free or attached earlobes.
4. Correlate the Earlobe Type of Students and Their Parents:
- For each student, compare their earlobe type with those of their parents. Try to find patterns.
- For example, if both parents have free earlobes, does the student have free or attached earlobes?
- If one parent has free earlobes and the other has attached earlobes, what is the student’s earlobe type?
5. Possible Inheritance Rule:
- Based on the observed correlation, you might hypothesize a rule about the inheritance of earlobe types.
A possible rule for the inheritance of earlobe types:
- Free earlobes (F) could be dominant over attached earlobes (f).
- If a child inherits one free earlobe allele (F) from one parent and one attached earlobe allele (f) from the other, the child is likely to have free earlobes.
- If both parents have attached earlobes (ff), the child would likely inherit attached earlobes as well.
The basic inheritance pattern may follow Mendelian genetics, where free earlobes are dominant (F) and attached earlobes are recessive (f). However, the correlation in your class may show a more complex inheritance pattern, depending on genetic variability and inheritance from multiple generations.
Chapter 8 – Heredity Class 10 Notes, Question/Answer, Activity & Projects
Updated Solution 2024-2025
This complete solution is prepared as per the latest syllabus of 2024-25. If you have any further queries, feel free to ask!
Activity 8.2
- In Fig. 8.3, what experiment would we do to confirm that the F2 generation did in fact have a 1:2:1 ratio of TT, Tt and tt trait combinations?
Ans: Activity 8.2
To confirm that the F2 generation indeed exhibits a 1:2:1 ratio of TT, Tt, and tt trait combinations (genotypes), we can conduct the following experiment:
Steps:
1. Grow the F2 Generation:
- Allow the F1 plants (all heterozygous tall, Tt) to self-pollinate and produce F2 progeny.
- Collect seeds and grow the F2 plants.
2. Phenotype Observation:
- Classify the F2 plants based on their physical appearance (phenotype):
- Tall (TT or Tt)
- Short (tt)
- Record the total number of tall and short plants.
3. Test for Genotypes in Tall Plants:
- To distinguish between TT and Tt tall plants, allow each tall F2 plant to self-pollinate and observe the progeny:
- TT plants: All progeny will be tall (100% tall phenotype).
- Tt plants: Progeny will segregate in a 3:1 ratio of tall to short (75% tall and 25% short).
4. Confirm the Ratios:
- Use the results to calculate the proportion of plants with each genotype:
- TT (homozygous dominant): Produce 100% tall progeny.
- Tt (heterozygous): Produce 75% tall and 25% short progeny.
- tt (homozygous recessive): Produce 100% short progeny.
- Verify if the observed genotypic ratio matches the expected 1:2:1
5. Optional – Punnett Square Validation:
- Construct a Punnett square for F1 (Tt × Tt) and predict the theoretical F2 genotypes:
- 1 TT : 2 Tt : 1 tt.
Expected Outcomes:
- The ratio of genotypes should confirm Mendel’s findings:
- 1 TT : 2 Tt : 1 tt.
- The phenotypic ratio of tall to short plants should be 3:1.
This experiment ensures that the observed F2 ratios align with Mendel’s laws of inheritance.
Questions
Q 1. How do Mendel’s experiments show that traits may be dominant or recessive?
Ans 1: Mendel’s experiments with pea plants showed that traits can be dominant or recessive by observing how they are passed from one generation to the next.
He cross-pollinated pea plants with different traits, like tall and short plants. In the first generation (F1), only the tall trait appeared, showing it was dominant. The short trait seemed to “disappear.” But when he allowed the F1 plants to self-pollinate, the short trait reappeared in the next generation (F2), in a 3:1 ratio of tall to short plants.
This revealed that traits are controlled by pairs of factors (now called genes), where one can hide (recessive) while the other shows (dominant).
Q 2. How do Mendel’s experiments show that traits are inherited independently?
Ans 2: Mendel’s experiments showed that traits are inherited independently through his dihybrid cross. He studied two traits at the same time, like seed shape (round or wrinkled) and seed color (yellow or green).
He found that the traits were passed on to the next generation in combinations that were not just like the parent plants. For example, a plant with round, yellow seeds could produce offspring with round, green seeds or wrinkled, yellow seeds. This happened because the genes for each trait were inherited separately, following the law of independent assortment.
This means traits are not linked and mix freely during inheritance.
Q 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?
Ans 3: No, this information is not enough to conclude which trait—A or O—is dominant. Blood group A can be either AA (homozygous) or AO (heterozygous). If the father has the genotype AO and the mother is OO, their daughter can inherit the O allele from both parents, resulting in blood group O. This does not confirm dominance, as the daughter’s blood group reflects a recessive combination.
Q 4. How is the sex of the child determined in human beings?
Ans 4: The sex of a child in human beings is determined by the chromosomes passed on by the parents during fertilization. Here’s a simple explanation:
1. Chromosomes and Sex Determination
Humans have 23 pairs of chromosomes in every cell, including one pair of sex chromosomes. These are labeled as X and Y.
- Women have two X chromosomes (XX).
- Men have one X and one Y chromosome (XY).
2. Role of the Parents
- The mother always contributes an X chromosome to the child because she only has X chromosomes.
- The father can contribute either an X chromosome or a Y chromosome:
- If the father passes on an X chromosome, the child will have XX chromosomes, meaning it will be a girl.
- If the father passes on a Y chromosome, the child will have XY chromosomes, meaning it will be a boy.
3. Conclusion
The sex of the child is determined by whether the sperm carrying an X or a Y chromosome fertilizes the mother’s egg. This means the father’s chromosomes decide whether the baby will be a boy or a girl.
This is a natural process and happens randomly, so there’s no way to predict or control which sperm fertilizes the egg.
Figure 8.6. Sex determination in human beings
Exercise
Q 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
Ans 1: (d). TtWw: In this Mendelian experiment, tall pea plants with violet flowers were crossed with short pea plants with white flowers. All offspring had violet flowers, but half of them were short. Since violet flowers are dominant over white flowers and tall plants are dominant over short, this suggests that the tall parent must carry a hidden “short” gene and the “white” flower gene. The genetic makeup of the tall parent is most likely TtWw (heterozygous for both traits), so the correct answer is:
Q 2. 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?
Ans 2: The study shows that children with light-colored eyes tend to have parents with light-colored eyes. This suggests that eye color may be inherited from parents. However, to determine whether the light eye color trait is dominant or recessive, we need more information about the specific genetic patterns. Generally, if light eye color were dominant, we’d expect children with just one parent with light eyes to have a higher chance of inheriting it. If it were recessive, both parents would likely need to have the gene for light eyes, even if their own eyes are dark. So, the study alone doesn’t give enough information to conclude whether the trait is dominant or recessive.
Q 3. Outline a project which aims to find the dominant coat colour in dogs.
Ans 3: Project: Finding the Dominant Coat Colour in Dogs
Objective: To identify the most common or dominant coat colour in dogs by analyzing various breeds.
Steps:
- Research: Study the genetic basis of dog coat colours, focusing on dominant and recessive genes.
- Data Collection: Gather information from various dog breeds about their coat colours. This can include surveys, breed-specific databases, and research papers.
- Sample Selection: Choose a diverse set of dog breeds, ensuring a wide range of coat colours.
- Genetic Analysis: Analyze the genetic makeup of selected breeds to identify which colour traits are most commonly passed down.
- Results Interpretation: Compare the frequencies of different coat colours across breeds to determine which is most common.
- Conclusion: Identify the dominant coat colour in dogs based on genetic inheritance patterns.
Outcome: The project will help understand which coat colour is most frequently inherited and why it might be dominant in certain breeds.
Q 4. How is the equal genetic contribution of male and female parents ensured in the progeny?
Ans 4: The equal genetic contribution of male and female parents is ensured through sexual reproduction. During this process, each parent contributes half of the offspring’s genetic material. The male provides one half of the genetic information through his sperm, and the female provides the other half through her egg. Each sperm and egg carry a set of chromosomes, so when they combine during fertilization, the offspring receives an equal share of genetic material from both parents, resulting in a balanced genetic makeup.
Chapter 8 – Heredity Class 10 Notes, Question/Answer, Activity & Projects
Updated Solution 2024-2025
This complete solution is prepared as per the latest syllabus of 2024-25. If you have any further queries, feel free to ask! 