Board Exam 2025
1 Mark
Q9. In garden pea, violet colour flower is
the
dominant trait over white colour flower which is the recessive trait. When parent plant with violet
coloured flowers (Vv) is crossed with a parent plant with white flowers, the possible percentage of
occurrence of traits in the F1 progeny would be :
Cross:
Parent 1 (Violet, Heterozygous): Vv
Parent 2 (White, Recessive): vv
Gametes: V, v (from P1) \(\times\) v, v (from P2)
Punnett Square / Offspring:
- V \(\times\) v \(\rightarrow\) Vv (Violet)
- v \(\times\) v \(\rightarrow\) vv (White)
Ratio: 1 Violet : 1 White (50% : 50%).
Correct Option: (B)
Parent 1 (Violet, Heterozygous): Vv
Parent 2 (White, Recessive): vv
Gametes: V, v (from P1) \(\times\) v, v (from P2)
Punnett Square / Offspring:
- V \(\times\) v \(\rightarrow\) Vv (Violet)
- v \(\times\) v \(\rightarrow\) vv (White)
Ratio: 1 Violet : 1 White (50% : 50%).
Correct Option: (B)
4 Marks
Q37. The process of determining the sex of a
newborn is purely genetic. But still many people in some societies believe that only the woman (mother)
is responsible for determination of the sex of the child and blame her. In fact, the sex of the child is
genetically determined. But there are some animals where sex is not genetically determined.
(a) Define sex chromosomes. (1)
(b) Mention one example of animals where sex is not genetically determined. How is sex determined in these animals ? Explain. (1)
(c) (i) Does the genetic combination of the mother play a significant role in determining the sex of newborn ? Explain. (2)
OR
(c) (ii) How is equal genetic contribution of male and female parents ensured in progeny ? (2)
(a) Define sex chromosomes. (1)
(b) Mention one example of animals where sex is not genetically determined. How is sex determined in these animals ? Explain. (1)
(c) (i) Does the genetic combination of the mother play a significant role in determining the sex of newborn ? Explain. (2)
OR
(c) (ii) How is equal genetic contribution of male and female parents ensured in progeny ? (2)
(a) Sex Chromosomes: Chromosomes that determine the sex of an individual (e.g., XX
in females and XY in males in humans).
(b) Example: Turtles / Alligators.
Determination: Environmental Sex Determination. The temperature at which fertilized eggs are incubated determines the sex (e.g., high temp \(\rightarrow\) female).
(c) (i) Role of Mother: No.
Explanation: Mother produces only one type of gamete (Egg with 22+X). She always contributes an X chromosome. The sex is determined by the sperm (carrying X or Y) from the father.
OR
(c) (ii) Equal Contribution:
- Male gamete (n) and Female gamete (n) fuse during fertilization.
- Both contribute equal number of chromosomes (23 each in humans) to form the zygote (2n).
- Thus, both parents contribute equally to the genetic makeup.
(b) Example: Turtles / Alligators.
Determination: Environmental Sex Determination. The temperature at which fertilized eggs are incubated determines the sex (e.g., high temp \(\rightarrow\) female).
(c) (i) Role of Mother: No.
Explanation: Mother produces only one type of gamete (Egg with 22+X). She always contributes an X chromosome. The sex is determined by the sperm (carrying X or Y) from the father.
OR
(c) (ii) Equal Contribution:
- Male gamete (n) and Female gamete (n) fuse during fertilization.
- Both contribute equal number of chromosomes (23 each in humans) to form the zygote (2n).
- Thus, both parents contribute equally to the genetic makeup.
1 Mark
Q10. The number of chromosomes in a cell
division
is halved. This kind of cell division is observed in :
Meiosis:
Reduction division (halving chromosomes) occurs during gamete formation.
Gametes are formed in reproductive organs: Testis (sperm) and Ovary (egg).
Correct Option: (C)
Reduction division (halving chromosomes) occurs during gamete formation.
Gametes are formed in reproductive organs: Testis (sperm) and Ovary (egg).
Correct Option: (C)
1 Mark
Q18. 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.
Reason (R): Heredity determines the process by which traits and characteristics are reliably inherited from parents to offspring.
Analysis:
- Assertion: True. Like begets like.
- Reason: True. Heredity ensures transfer of specific traits.
- R is the correct explanation of A.
Correct Option: (A) Both A and R are true and R is the correct explanation of A.
- Assertion: True. Like begets like.
- Reason: True. Heredity ensures transfer of specific traits.
- R is the correct explanation of A.
Correct Option: (A) Both A and R are true and R is the correct explanation of A.
3 Marks
Q30. A pure pea plant bearing terminal
flowers
was cross-pollinated with a pure plant having axillary flowers. In \(F_1\) generation, plants with
axial
flowers only were obtained. \(F_1\) generation plants are self-pollinated and \(F_2\) generation is
obtained.
(a) Work out the pattern of inheritance in this case.
(b) What will be the ratio of plants obtained in \(F_2\) generation ?
(a) Work out the pattern of inheritance in this case.
(b) What will be the ratio of plants obtained in \(F_2\) generation ?
(a) Pattern of Inheritance:
- Axial (A) is dominant over Terminal (a) (Since F1 is all Axial).
- Parents: AA (Axial) x aa (Terminal).
- F1 Generation: Aa (All Axial).
- Self Pollination: Aa x Aa.
- F2 Gametes: A, a x A, a.
- F2 Offspring: AA (Axial), Aa (Axial), Aa (Axial), aa (Terminal).
(b) Ratio:
- Phenotypic Ratio: 3 Axial : 1 Terminal.
- Genotypic Ratio: 1 AA : 2 Aa : 1 aa.
- Axial (A) is dominant over Terminal (a) (Since F1 is all Axial).
- Parents: AA (Axial) x aa (Terminal).
- F1 Generation: Aa (All Axial).
- Self Pollination: Aa x Aa.
- F2 Gametes: A, a x A, a.
- F2 Offspring: AA (Axial), Aa (Axial), Aa (Axial), aa (Terminal).
(b) Ratio:
- Phenotypic Ratio: 3 Axial : 1 Terminal.
- Genotypic Ratio: 1 AA : 2 Aa : 1 aa.
3 Marks
Q30. (a) How many chromosomes are present in
human beings ? Out of these how many are sex chromosomes ?
(b) Explain how, in sexually reproducing organisms, the number of chromosomes in the progeny is maintained.
(b) Explain how, in sexually reproducing organisms, the number of chromosomes in the progeny is maintained.
(a) Chromosome Number:
Human beings have 46 chromosomes (23 pairs).
Out of these, 2 chromosomes (1 pair) are sex chromosomes (XX in females, XY in males).
(b) Maintaining Chromosome Number:
1. Gamete Formation (Meiosis): During the formation of gametes (sperm and egg), the number of chromosomes is reduced to half (Haploid, n=23).
2. Fertilization: When male and female gametes fuse, the normal number of chromosomes (Diploid, 2n=46) is restored in the zygote.
3. This ensures that the progeny has the same number of chromosomes as the parents.
Human beings have 46 chromosomes (23 pairs).
Out of these, 2 chromosomes (1 pair) are sex chromosomes (XX in females, XY in males).
(b) Maintaining Chromosome Number:
1. Gamete Formation (Meiosis): During the formation of gametes (sperm and egg), the number of chromosomes is reduced to half (Haploid, n=23).
2. Fertilization: When male and female gametes fuse, the normal number of chromosomes (Diploid, 2n=46) is restored in the zygote.
3. This ensures that the progeny has the same number of chromosomes as the parents.
2 Marks
Q24. "Sex of the children is determined by
type
of sex chromosome which they inherit from their father." Justify the statement.
Justification:
Human males have two types of sex chromosomes (XY) and produce two types of sperms (50% carrying X and 50% carrying Y).
Human females have only one type of sex chromosome (XX) and produce only one type of egg (carrying X).
- If a sperm carrying X fertilizes the egg (X), the zygote (XX) develops into a Girl.
- If a sperm carrying Y fertilizes the egg (X), the zygote (XY) develops into a Boy.
Since the father contributes either X or Y, he determines the sex of the child.
Human males have two types of sex chromosomes (XY) and produce two types of sperms (50% carrying X and 50% carrying Y).
Human females have only one type of sex chromosome (XX) and produce only one type of egg (carrying X).
- If a sperm carrying X fertilizes the egg (X), the zygote (XX) develops into a Girl.
- If a sperm carrying Y fertilizes the egg (X), the zygote (XY) develops into a Boy.
Since the father contributes either X or Y, he determines the sex of the child.
3 Marks
Q30. A pure pea plant having round (R),
yellow
(Y) seeds is crossed with another pure pea plant having wrinkled (r), green (y) seeds. Subsequently
\(\text{F}_1\) progeny is self-pollinated to obtain \(\text{F}_2\) progeny.
(a) What do the seeds of \(\text{F}_1\) generation look like ?
(b) Give the possible combinations of traits in seeds of \(\text{F}_2\) generation. Also give their ratio.
(c) State the reason of obtaining seeds of new combination of traits in \(\text{F}_2\) generation.
(a) What do the seeds of \(\text{F}_1\) generation look like ?
(b) Give the possible combinations of traits in seeds of \(\text{F}_2\) generation. Also give their ratio.
(c) State the reason of obtaining seeds of new combination of traits in \(\text{F}_2\) generation.
(a) \(\text{F}_1\) Generation:
All seeds are Round and Yellow (RrYy). (Dominant traits express).
(b) \(\text{F}_2\) Generation:
Possible Combinations:
1. Round and Yellow (9)
2. Round and Green (3)
3. Wrinkled and Yellow (3)
4. Wrinkled and Green (1)
Ratio: 9 : 3 : 3 : 1.
(c) Reason:
Law of Independent Assortment: When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters. Hence, new combinations (Round-Green, Wrinkled-Yellow) appear.
All seeds are Round and Yellow (RrYy). (Dominant traits express).
(b) \(\text{F}_2\) Generation:
Possible Combinations:
1. Round and Yellow (9)
2. Round and Green (3)
3. Wrinkled and Yellow (3)
4. Wrinkled and Green (1)
Ratio: 9 : 3 : 3 : 1.
(c) Reason:
Law of Independent Assortment: When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters. Hence, new combinations (Round-Green, Wrinkled-Yellow) appear.
2 Marks
Q25. Explain with the help of a flow chart that
in human beings father is responsible for the sex (male or female) of the child.
Sex Determination Flow Chart:
Father (XY) \(\times\) Mother (XX)
Gametes: X, Y (from Father) ; X, X (from Mother)
Offspring possibilities:
1. X (Sperm) + X (Egg) \(\rightarrow\) XX (Girl)
2. Y (Sperm) + X (Egg) \(\rightarrow\) XY (Boy)
Explanation: Sex depends on whether the egg is fertilized by an X-bearing sperm or a Y-bearing sperm. Since father produces two types of gametes (heterogametic), he determines the sex.
Father (XY) \(\times\) Mother (XX)
Gametes: X, Y (from Father) ; X, X (from Mother)
Offspring possibilities:
1. X (Sperm) + X (Egg) \(\rightarrow\) XX (Girl)
2. Y (Sperm) + X (Egg) \(\rightarrow\) XY (Boy)
Explanation: Sex depends on whether the egg is fertilized by an X-bearing sperm or a Y-bearing sperm. Since father produces two types of gametes (heterogametic), he determines the sex.
4 Marks
Q39. Case Study on Chromosomes.
(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.
(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.
(a) Thread-like structures found in the nucleus carrying genetic information in the form of DNA.
(b) Human males have XY chromosomes. X is normal size, Y is shorter. They are not perfect homologues, hence mismatched.
(c) (A) Sex Determination Flow Chart:
50% sperms carry X, 50% carry Y. Egg always X.
XX (Girl) : XY (Boy) = 1:1.
OR
(c) (B) Examples: Turtles, Lizards (Reptiles), Snails.
Method: Environmental Sex Determination. The temperature at which fertilised eggs are kept determines the sex (e.g., high temp -> female in some turtles).
(b) Human males have XY chromosomes. X is normal size, Y is shorter. They are not perfect homologues, hence mismatched.
(c) (A) Sex Determination Flow Chart:
50% sperms carry X, 50% carry Y. Egg always X.
XX (Girl) : XY (Boy) = 1:1.
OR
(c) (B) Examples: Turtles, Lizards (Reptiles), Snails.
Method: Environmental Sex Determination. The temperature at which fertilised eggs are kept determines the sex (e.g., high temp -> female in some turtles).
1 Mark
Q9. 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
Parent 1: TTRR (Tall, Round). Gametes: TR.
Parent 2: ttrr (Short, Wrinkled). Gametes: tr.
F1 Generation: TtRr.
Phenotype: Tall and Round (Dominant traits).
All (100%) offspring are TtRr.
Correct Option: (D)
Parent 2: ttrr (Short, Wrinkled). Gametes: tr.
F1 Generation: TtRr.
Phenotype: Tall and Round (Dominant traits).
All (100%) offspring are TtRr.
Correct Option: (D)
2 Marks
Q24. (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.
OR
(b) Explain the mechanism of inheritance used by sexually reproducing organisms to ensure the stability of DNA of the species.
(a) DNA contains information for making proteins. A section of DNA (gene) for tallness codes for an
enzyme/protein that triggers growth hormone production. Efficient enzyme/protein = More Hormone =
Tall Plant. Inefficient/Less protein = Short Plant. Thus, proteins control phenotype.
(b) Mechanism: Meiosis (Gamete formation) reduces the chromosome number by half (n). Fertilization (Fusion of gametes) restores the original chromosome number (2n). This cycle ensures DNA stability across generations.
(b) Mechanism: Meiosis (Gamete formation) reduces the chromosome number by half (n). Fertilization (Fusion of gametes) restores the original chromosome number (2n). This cycle ensures DNA stability across generations.
3 Marks
Q30. (a) "In human beings the genes inherited
from the parents decide whether the newborn individual is male or female." Explain this statement with
the help of a flow diagram.
(b) "Some animals rely on environmental cues for sex determination." Justify this statement giving an example.
(b) "Some animals rely on environmental cues for sex determination." Justify this statement giving an example.
(a) Male (XY) produces two types of sperms (X and Y). Female (XX) produces one type of egg (X).
- If X-sperm fertilizes egg -> XX (Female).
- If Y-sperm fertilizes egg -> XY (Male).
Thus, father's sperm determines sex.
(b) Example: In some reptiles like turtles/crocodiles, incubation temperature determines sex (High temp -> Female, Low temp -> Male, varies by species). Snails can change sex.
- If X-sperm fertilizes egg -> XX (Female).
- If Y-sperm fertilizes egg -> XY (Male).
Thus, father's sperm determines sex.
Flow Diagram Expected
(b) Example: In some reptiles like turtles/crocodiles, incubation temperature determines sex (High temp -> Female, Low temp -> Male, varies by species). Snails can change sex.
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