CBSE Class 10 Science — Heredity

When a human egg is fertilized by a sperm having 'Y' chromosome, the zygote has the following combination of chromosomes:

Sex is determined by different factors in various species. However, in human beings, it is determined genetically. Which amongst the following option(s) is/are correct for human beings? (i) Gamete carrying X chromosome from female parent. (ii) Gamete carrying X chromosome from male parent. (iii) Gamete carrying Y chromosome from male parent.

Assertion (A): Bacteria that can withstand heat have better chances of survival in a heat wave. Reason (R): Accumulation of variations in a species increases the chances of its survival in changing environment.

(a) Show a cross between a pea plant having round & green seed with a pea plant having wrinkled and yellow seeds upto $F_2$ generation. (b) Also write down results of $F_2$ generation.

Mendel took garden pea plants with different characteristics, such as height to study the inheritance pattern of factors (genes). He crossed tall pea plant with short pea plant and obtained all the tall plants in the $\mathrm{F}_{1}$ generation. Answer the following questions: (a) Why only tall pea plants were observed in $\mathrm{F}_{1}$ progeny? (b) By which method did Mendel obtain $\mathrm{F}_{2}$ progeny? (c) (i) Write one difference between dominant and recessive trait. OR (c) (ii) Write two observations made by Mendel about $\mathrm{F}_{1}$ progeny.

A tall pea plant with round seeds (TTRR) is crossed with a short pea plant with wrinkled seeds (ttrr). The $F_1$ generation will be:

When a pure-tall pea plant is crossed with a pure-dwarf pea plant, the percentage of tall pea plants in $F_1$ and $F_2$ generation pea plants will be respectively :

If pea plants with round and green seeds (RRyy) are crossed with pea plants having wrinkled and yellow seeds (rrYY), the seeds developed by the plants of $F_1$ generation will be :

Assertion (A) : A human child bears all the basic features of human beings. Reason (R) : It looks exactly like its parents, showing very little variations.

Assertion (A): A mango seed will germinate to form a mango tree. Reason (R): Heredity determines the process by which traits and characteristics are reliably inherited from parents to offspring.

Assertion (A): In reptiles, the temperature at which the fertilized eggs are kept decides the sex of the offsprings. Reason (R): Sex is not genetically determined in some animals.

(a) "Proteins control the expression of various characters." Explain this statement by taking an example of "tallness" as a characteristic in plants. OR (b) Explain the mechanism of inheritance used by sexually reproducing organisms to ensure the stability of DNA of the species.

Explain with the help of a flow chart that in human beings father is responsible for the sex (male or female) of the child.

(a) Explain how the proteins control the 'characteristics' in an organism with the help of an example of 'tallness' trait in pea plant. (b) Name the section of DNA that controls the 'characteristics' in an organism.

(a) What are chromosomes? (b) Explain in brief how stability of DNA content of a species is ensured in sexually reproducing organisms?

A pure pea plant having round (R), yellow (Y) seeds is crossed with another pure pea plant having wrinkled (r), green (y) seeds. Subsequently $F_1$ progeny is self-pollinated to obtain $F_2$ progeny. (a) What do the seeds of $F_1$ generation look like? (b) Give the possible combinations of traits in seeds of $F_2$ generation. Also give their ratio. (c) State the reason of obtaining seeds of new combination of traits in $F_2$ generation.

The gene combination of purple flowered pea plants is denoted as (WW) and that of white flowered pea plants as (ww), when these two plants are crossed $F_1$ generation is obtained. (a) List two observations made by Mendel in $F_1$ generation plants. (b) Give the (i) percentage of white flowered plants and (ii) ratio of the gene combinations WW, Ww and ww in $F_2$ generation. (c) Write one difference between dominant and recessive trait.

The lowest part of the ear called earlobe, is closely attached to the side of the head in some of us (Figure 'X'), and not in others, called free earlobe (Figure 'Y'). Attached and free earlobes are two variants found in human populations. The gene for free earlobe is dominant over attached earlobes. (a) A man with attached earlobes marries a woman having free earlobes. $50\%$ of their children have free earlobes and $50\%$ have attached earlobes. Explain the inheritance of this trait and write the trait combinations of the progeny. (b) Write the gene combinations of the father and the mother in the above case.

In human beings, there are 23 pairs of chromosomes. Out of these 23 pairs of chromosomes (i.e. 46 chromosomes), 22 pairs of chromosomes are called autosomes and one pair of chromosomes. i.e. two chromosomes are called sex chromosomes. The sex chromosomes are of two types - 'X' chromosomes and 'Y' chromosomes. The sex of a child (i.e. progeny), is decided at the time of fertilisation. In other words, at the time of zygote formation the sex chromosomes inherited from the parents of a child decide whether the new born will be a boy or a girl. (a) What are chromosomes? (b) Why is the pair of sex chromosomes in human males called mismatched pair? (c) (A) Show with the help of a flow chart that the statistical probability of getting a boy or a girl is $50:50$. OR (c) (B) Mention two examples of animals where sex is not determined genetically like human beings. Describe in brief the method of sex determination in these animals.

Consider the following statements : (i) The sex of a child is determined by what it inherits from the mother. (ii) The sex of a child is determined by what it inherits from the father. (iii) The probability of having a male child is more than that of a female child. (iv) The sex of a child is determined at the time of fertilisation when male and female gametes fuse to form a zygote. The correct statements are :

Chromosomes : (i) carry hereditary information from parents to the next generation. (ii) are thread like structures located inside the nucleus of an animal cell. (iii) always exist in pairs in human reproductive cells. (iv) are involved in the process of cell division. The correct statements are :

In an experiment to study independent inheritance of two separate traits: shape and colour of seeds, the ratio of the different combinations in $F_2$ progeny would be

A cross between two tall pea plants resulted in offsprings having a few dwarf plants. The gene-combination of the parental plants must be

A cross made between two pea plants produces $50\%$ tall and $50\%$ short pea plants. The gene combination of the parental pea plants must be

Assertion (A): Sex of the children will be determined by what they inherit from their mother. Reason (R): Women have XX sex chromosomes.

Assertion (A) : Human female has a perfect pair of sex chromosome. Reason (R) : Sex chromosome contributed by the human male in the zygote decides the sex of a child.

(a) List any two pairs of visible contrasting characters of garden pea plants used by Mendel for his experiments stating the dominant and recessive characters in each pair. OR (b) In human beings, the probability of getting a male or a female child is $50\%$. Explain with the help of a flow diagram only.

List two differences between dominant traits and recessive traits. What percentage of pea plants in the $\mathrm{F}_2$ generation were with yellow seeds in Mendel's cross between the pea plants having yellow (YY) and green coloured (yy) seeds?

Mendel crossed pure tall pea plants (TT) with pure short pea plants (tt) and obtained $\mathrm{F}_1$ progeny. When the plants of $\mathrm{F}_1$ progeny were self-pollinated, plants of $\mathrm{F}_2$ progeny were obtained. (a) What did the plants of $\mathrm{F}_1$ progeny look like? Give their gene combination. (b) Why could the gene for shortness not be expressed in plants of $\mathrm{F}_1$ progeny? (c) Write the ratio of the plants obtained in $\mathrm{F}_2$ progeny and state the conclusion that can be drawn from this experiment.

In an experiment with pea plants, a pure tall plant (TT) is crossed with a pure short plant (tt). The ratio of pure tall plant to pure short plants in $F_2$ generation will be

A cross between pea plant with white flowers (vv) and pea plant with violet flowers (VV) resulted in $F_2$ progeny in which ratio of violet (VV) and white (vv) flowers will be :

The statement that correctly describes the characteristic(s) of a gene is:

Consider the following two statements: (i) The trait that expresses itself in $\mathrm{F}_1$ generation. (ii) The trait that keeps on passing from one generation to another. The appropriate terms for the statements (i) and (ii) respectively are:

When an 'X' bearing sperm fertilises the egg, the resulting zygote has the following combination of chromosomes :

Assertion (A): Genes inherited from the parents decide the sex of a child. Reason (R): X chromosome in a male child is inherited from his father.

Assertion (A) : Human populations show a great deal of variations in traits. Reason (R) : All variations in a species have equal chances of surviving in the environment in which they live.

Assertion (A) : In humans, if gene (B) is responsible for black eyes and gene (b) is responsible for brown eyes, then the colour of eyes of the progeny having gene combination Bb, bb or BB will be black only. Reason (R) : The black colour of the eyes is a dominant trait.

Assertion (A): When a bacterium divides into two, and the resultant two bacteria divide again, the four bacteria produced would be almost similar. Reason (R): DNA copying involves small inaccuracies in the reproduction process.

Mendel crossed a pure tall pea plant (TT) with a pure short pea plant (tt) and obtained all tall plants in $F_1$ generation. (a) What is the gene combination present in the plants of $F_1$ generation? (b) Give reason why only tall plants are observed in $F_1$ progeny. (c) What will be the ratio of the plants obtained in the $F_2$ generation when $F_1$ plants are self-pollinated?

In some families, either rural or urban, females are tortured for giving birth to a female child. They do not seem to understand the scientific reason behind the birth of a boy or a girl. In fact the mother is not responsible for the sex of the child and it has been genetically proved that the sex of a newborn is determined by what the child inherits from the father. (a) State the basis on which the sex of a newborn baby is determined in humans. (b) Why is the pair of sex chromosomes called a mismatched pair in males? (c) How is the original number of chromosomes present in the parents restored in the progeny? OR (c) Explain by giving two examples of the organisms in which the sex is not genetically determined.

In order to trace the inheritance of traits Mendel crossed pea plants having one contrasting character or a pair of contrasting characters. When he crossed pea plants having round and yellow seeds with pea plants having wrinkled and green seeds, he observed that no plants with wrinkled and green seeds were obtained in the $F_1$ generation. When the $F_1$ generation pea plants were cross-bred by self-pollination, the $F_2$ generation had seeds with different combinations of shape and colour also. (a) Write any two pairs of contrasting characteristics of pea plant used by Mendel other than those mentioned above. (b) Differentiate between dominant and recessive traits. (c) State the ratio of the combinations observed in the seeds of $F_2$ generation (in the above case). What do you interpret from this result? OR (c) Given below is a cross between a pure violet flowered pea plant (V) and a pure white flowered pea plant (v). Diagrammatically explain what type of progeny is obtained in $F_1$ generation and $F_2$ generation: Pure violet flowered plant $\times$ Pure white flowered plant (VV) (vv)

All human chromosomes are not paired. Most human chromosomes have a maternal and a paternal copy, and we have 22 such pairs. But one pair called the sex chromosomes, is odd in not always being a perfect pair. Women have a perfect pair of sex chromosomes. But men have a mismatched pair in which one is normal sized while the other is a short one. (a) In humans, how many chromosomes are present in a Zygote and in each gamete? (b) A few reptiles rely entirely on environmental cues for sex determination. Comment. (c) "The sex of a child is a matter of chance and none of the parents are considered to be responsible for it." Justify it through flow chart only. OR (c) Why do all the gametes formed in human females have an X chromosome?

The most obvious outcome of the reproductive process is the generation of individuals of similar design, but in sexual reproduction they may not be exactly alike. The resemblances as well as differences are marked. The rules of heredity determine the process by which traits and characteristics are reliably inherited. Many experiments have been done to study the rules of inheritance. (i) Why an offspring of human being is not a true copy of his parents in sexual reproduction ? (1 mark) (ii) While performing experiments on inheritance in plants, what is the difference between $F_1$ and $F_2$ generation ? (1 mark) (iii) (A) Why do we say that variations are useful for the survival of a species over time ? (2 marks) OR (iii) (B) Study Mendel's cross between two plants with a pair of contrasting characters: $RRYY \times rryy$ (Round Yellow x Wrinkled Green). He observed 4 types of combinations in $F_2$ generation. Which of these were new combinations ? Why do new features which are not present in the parents, appear in $F_2$ generation ? (2 marks)

Using height (tallness / dwarfness) of a plant as an example, show that genes control the characteristics or traits in an organism. OR In a cross between red coloured and white coloured flowers, when plants with red coloured flowers of F1 generation were self pollinated, plants of F2 generation were obtained in which $75\%$ of plants were with red flowers and $25\%$ plants were with white flowers. Explain the inheritance of traits in the above cross with the help of a flow chart only along with the ratio of plants obtained.

(a) What is variation ? List two main reasons that may lead to variation in a population. OR (b) (i) In a cross between violet flowered plants and white flowered plants, state the characteristics of the plants obtained in the $F_1$ progeny. (ii) If the plants of $F_1$ progeny are self-pollinated, then what would be observed in the plants of $F_2$ progeny ? (iii) If 100 plants are produced in $F_2$ progeny, then how many plants will show the recessive trait ?

(b) Justify the statement "Sex of the children will be determined by what they inherit from their father".

(a) Mendel crossed two pea plants with visible contrasting characteristics and found that there were no half-way characteristics in the plants of $F_1$ progeny. Explain the reason for this observation of Mendel.

(a) Name the two types of gametes produced by men. (b) Does a male child inherit X chromosome from his father? Justify. (c) How many types of gametes are produced by a human female?

How do Mendel's experiments show that the traits are inherited independently? Explain.

The mechanism by which the sex of an individual is determined is called sex-determination. In human beings, sex of a newborn is genetically determined, whereas in some others it is not. There are 46 (23 pairs) chromosomes in human beings. Out of these, 44 (22 pairs) control the body characters and 2 (one pair) are known as sex chromosomes. The sex chromosomes are of two types — X chromosome and Y chromosome. At the time of fertilisation, depending upon which type of male gamete fuses with the female gamete, the sex of the newborn child is decided. (a) Why is a pair of sex chromosomes in human beings called a mismatch pair in terms of type and size? (b) Out of male or female, which of them has a perfect pair of sex chromosomes? In case of a perfect pair, will the gametes produced be of the same kind or of a different kind? (c) (i) Name two animals whose sex is not genetically determined. Explain the process of their sex determination. OR (ii) With the help of a flowchart only, show how sex is genetically determined in human beings.

OR (for part c) If 1600 plants were obtained in $F_2$ progeny, write the number of plants having traits: (i) Tall with round seeds (ii) Short with wrinkled seeds Write the conclusion of the above experiment.

Mendel blended his knowledge of Science and mathematics to keep the count of the individuals exhibiting a particular trait in each generation. He observed a number of contrasting visible characters controlled in pea plants in a field. He conducted many experiments to arrive at the laws of inheritance. (a) What do the $F_1$ progeny of tall plants with round seeds and short plants with wrinkled seeds look like? (b) Name the recessive traits in above case. (c) Mention the type of the new combinations of plants obtained in $F_2$ progeny along with their ratio, if $F_1$ progeny was allowed to self pollinate.

Sex of an individual is determined by different factors in various species. Some animals rely entirely on the environmental cues, while in some other animals the individuals can change their sex during their life time indicating that sex of some species is not genetically determined. However, in human beings, the sex of an individual is largely determined genetically. (a) In what way are the sex chromosomes 'X' and 'Y' different in size? Name the mismatched pair of sex chromosome in humans. (b) Write the number of pair/pairs of sex chromosomes present in human beings. In which one of the parent (male / female) perfect pair / pairs of sex chromosomes are present? (c) Citing two examples, justify the statement "Sex of an individual is not always determined genetically". OR Draw a flow chart to show that sex is determined genetically in human beings.

Assertion (A): The sex of a child in human beings will be determined by the type of chromosome he/she inherits from the father. Reason (R): A child who inherits 'X' chromosome from his father would be a girl (XX), while a child who inherits a 'Y' chromosome from the father would be a boy (XY).

Define the term evolution. "Evolution cannot be equated with progress." Justify this statement. OR "During the course of evolution, organs or features may be adapted for new functions." Explain this fact by choosing an appropriate example.

What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor. Justify your answer.

Explain giving an example how the following provide evidences in favour of evolution in organisms. (i) Homologous organs (ii) Fossils

(a) Classify the following as homologous or analogous pairs: (i) Broccoli and Cabbage (ii) Ginger and Raddish (iii) Fore limbs of birds and lizard (iv) Wings of a bat and Wings of a bird (b) State the main feature that categorises a given pair of organs as homologous or analogous.

(a) Why is the F1 progeny always of tall plants when a tall pea plant is crossed with a short pea plant? (b) How is F2 progeny obtained by self-pollination of F1 progeny different from F1 progeny? Give reason for this observation. (c) State a conclusion that can be drawn on the basis of this observation.

A green stemmed rose plant denoted by GG and a brown stemmed rose plant denoted by gg are allowed to undergo a cross with each other. (a) List your observations regarding: (i) Colour of stem in their $F_1$ progeny (ii) Percentage of brown stemmed plants in $F_2$ progeny if $F_1$ plants are self pollinated. (iii) Ratio of GG and Gg in the $F_2$ progeny. (b) Based on the findings of this cross, what conclusion can be drawn?

(a) What is the law of dominance of traits? Explain with an example. (b) Why are the traits acquired during the life time of an individual not inherited? Explain.

List two differences between acquired traits and inherited traits by giving an example of each.

Name the plant Mendel used for his experiment. What type of progeny was obtained by Mendel in $F_1$ and $F_2$ generations when he crossed the tall and short plants? Write the ratio he obtained in $F_2$ generation plants.

A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plants bearing white flowers. What will be the result in F₁ progeny?

How did Mendel explain that it is possible that a trait is inherited but not expressed in an organism?

“Evolution and classification of organisms are interlinked.” Give reasons to justify this statement.

What is an organic evolution? It cannot be equated with progress. Explain with the help of a suitable example.

With the help of two suitable examples, explain why certain experiences and traits earned by people during their lifetime are not passed on to their next generations. When can such traits be passed on ?

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

The following vegetables are kept in a basket: Potato, Tomato, Radish, Brinjal, Carrot, Bottle-gourd. Which two of these vegetables correctly represent the homologous structures?

How do Mendel’s experiment show that traits are inherited independently?

“Two areas of study namely ‘evolution’ and ‘classification’ are interlinked”. Justify this statement.

With the help of an example justify the following statement : “A trait may be inherited, but may not be expressed”.

Define evolution. How does it occur ? Describe how fossils provide us evidences in support of evolution.

If you are asked to select a group of two vegetables, out of the following, having homologous structures which one would you select?

“We cannot pass on to our progeny the experiences and qualifications earned during our life time”. Justify the statement giving reason and examples.

(i) ‘Planaria, insects, octopus and vertebrates all have eyes. Can we group eyes of these animals together to establish a common evolutionary origin? Justify your answer. (ii) “Birds have evolved from reptiles”. State evidence to prove the statement.

How many pairs of chromosomes are present in human beings? Out of these how many are sex chromosomes? How many types of sex chromosomes are found in human beings? "The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it". Draw a flow chart showing determination of sex of a newborn to justify this statement.

Four students A, B, C and D reported the following set of organs to be homologous. Who is correct?

What is speciation?

Tabulate two distinguishing features between acquired traits and inherited traits with one example of each.

“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.

Study the different conclusions drawn by students of a class on the basis of observations of preserved / available specimens of plants and animals. I. Potato and sweet potato are analogous organs in plants. II. Wings of insects and wings of birds are homologous organs in animals. III. Wings of insects and wings of bats are analogous organs in animals. IV. Thorns of citrus and tendrils of cucurbita are analogous organs in plants. The correct conclusions are:

You have potato, carrot, radish, sweet potato, tomato and ginger bought from the market in your jute bag. Identify two vegetables to represent the correct homologous structures.

State one genetically different feature between sperms and eggs of humans. What is its consequence ?

If we cross pure-bred tall (dominant) pea plant with pure-bred dwarf (recessive) pea plant we will get pea plants of $F_1$ generation. If we now self-cross the pea plant of $F_1$ generation, then we obtain pea plants of $F_2$ generation. (a) What do the plants of $F_1$ generation look like ? (b) State the ratio of tall plants to dwarf plants in $F_2$ generation. (c) State the type of plants not found in $F_1$ generation but appeared in $F_2$ generation, mentioning the reason for the same.

A blue colour flower plant denoted by BB is crossbred with that of white colour flower plant denoted by bb. (a) State the colour of flower you would expect in their F1 generation plants. (b) What must be the percentage of white flower plants in F2 generation if flowers of F1 plants are self-pollinated ? (c) State the expected ratio of the genotypes BB and Bb in the F2 progeny.

"An individual cannot pass on to its progeny the experiences of its life-time." Justify the statement with the help of an example and also give reason for the same.

List in tabular form two distinguishing features between acquired traits and inherited traits, with one example of each.

(i) We see eyes in planaria, insects, octopus and vertebrates. Can eyes be grouped together in case of the above-mentioned animals to establish a common evolutionary origin? Why? (ii) State one evidence to prove that birds have evolved from reptiles.

What is meant by the term speciation ? List four factors which could lead to speciation.

How are fossils formed ? Describe, in brief, two methods of determining the age of fossils.

Distinguish between homologous organs and analogous organs. In which category would you place wings of a bird and wings of a bat ? Justify your answer giving a suitable reason.

With the help of a flow chart explain in brief how the sex of a newborn is genetically determined in human beings. Which of the two parents, the mother or the father, is responsible for determination of sex of a child?

Describe any three ways in which individuals with a particular trait may increase in population.

Explain with examples how the following are evidences in favour of evolution in organisms: (i) Homologous organs (ii) Analogous organs (iii) Fossils

Explain how evolutionary relationships can be traced by the study of homologous organs.

"Only variations that confer an advantage on an individual organism will survive in a population." Justify this statement.

State the evidence we have for the origin of life from inanimate matter.

Explain the terms: (i) Speciation (ii) Natural selection

How is the sex of the child fixed during the fertilisation step in human beings ? Explain.

Explain how equal genetic contribution of male and female parents is ensured in the progeny.

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

Give 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.