Class 10 Science Chapter 8 Heredity

Key Concepts: Sex Determination, Chromosome Origin

b) The paternal chromosome determines whether offspring are XX or XY.
[Solution Description] In humans, sex determination is primarily controlled by the combination of sex chromosomes inherited from the parents. Males have XY sex chromosomes, while females have XX. The father’s contribution either of X or Y chromosome decides if the offspring will be female (XX) or male (XY).

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Key Concepts: Trait Variants

b) Variants
[Solution Description] A child inherits two alleles for each trait, one from each parent, which may be different variants responsible for expressing specific physical characteristics.

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Key Concepts: Reproduction Type

b) Sexual reproduction
[Solution Description] Sexual reproduction involves the mixing of genetic material from two parents, resulting in greater variation and diversity among offspring compared to asexual reproduction which results in clones.

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Key Concepts: Gene Copy Concept

b) Two
[Solution Description] Mendel proposed that two copies of factors (genes) control traits in sexually reproducing organisms; one inherited from each parent.

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Key Concepts: Inheritance Rules

b) The presence of one or more dominant alleles.
[Solution Description] Mendel found that the expression of a dominant trait occurs when at least one allele for the dominant trait is present. For example, if ‘T’ represents tallness and ‘t’ represents shortness, a plant with genotypes ‘TT’ or ‘Tt’ will be tall. Only ‘tt’ would result in a short plant.

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Key Concepts: Inherited Traits

c) They provide a common body design

[Solution Description] Inherited traits provide a common basic body design and allow for subtle adaptations that may be beneficial for the survival of the next generation.

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Key Concepts: Genetic Makeup, Enzyme Efficiency, Advanced Reasoning

c) 1 tall : 2 intermediate : 1 short
[Solution Description] The alteration in the gene affects enzyme production, which impacts hormone levels responsible for growth. A heterozygous tall plant is Tt, where ‘T’ produces sufficient enzyme for normal height, whereas ‘t’ does not. If enzyme efficiency is halved, the effect on a Tt plant would reduce its effective height to intermediate values under normal conditions. However, due to dominance, it might still manifest as a tall phenotype. When crossed:

– TT offspring will have reduced but enough hormone to remain tall.
– Tt offspring will display reduced height due to further inefficiency.
– tt offspring remain short.

Upon self-pollination:$\text{Expected Ratio = Tall: Intermediate: Short} = 1:2:1$ The effective outcome may vary slightly depending on environmental factors.

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Key Concepts: Trait Frequency

b) Trait B
[Solution Description] In asexually reproducing populations, traits that are more common are likely to have arisen earlier as they have had more time to spread through the population.

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Key Concepts: Germ Cell Formation

c) They have one set
[Solution Description] Germ cells have one set of genes, known as haploid, whereas other body cells contain two sets of genes, known as diploid. This difference is crucial for sexual reproduction.

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 Key Concepts: Gene Alteration

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a change in the gene responsible for coding an enzyme can impact plant height. This is tied to the concept that enzymes play a crucial role in biochemical pathways, including those leading to hormone synthesis. Hormones are crucial for regulating growth in plants, such as gibberellins affecting plant height.

The reason provided explains that the efficiency of enzyme processes directly influences hormone production and thus impacts trait expression like height. If an enzyme is altered, it may not function efficiently, reducing hormone levels and subsequently altering traits controlled by these hormones.

Therefore, both the assertion and the reason are true. Furthermore, the reason correctly explains why an alteration in the gene results in changes in plant height.

Key Concepts: Gene Contribution

b) One
[Solution Description] During sexual reproduction, each parent contributes one set of genes to the offspring. This ensures that the progeny inherits equal genetic material from both parents, resulting in two total gene sets in the offspring.

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 Key Concepts: Genetic Determination

b) By the father’s X or Y chromosome
[Solution Description]
The sex of a child in humans is determined by the combination of sex chromosomes from each parent. The mother always contributes an X chromosome. If the father contributes an X chromosome, the child will be XX and female. If the father contributes a Y chromosome, the child will be XY and male.

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 Key Concepts: Chromosome Role

b) Each germ cell receives only one chromosome from each parent.
[Solution Description] Genetic stability in sexually reproducing organisms like humans is maintained because each germ cell carries only one chromosome from each pair, either maternal or paternal. During fertilization, the combination of these germ cells restores the typical number of chromosomes, preserving species-specific genetic information across generations.

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Key Concepts: Chromosome Count

b) 23 pairs
[Solution Description] Humans inherit 23 pairs of chromosomes in total, with one set of 23 chromosomes coming from each parent, making it 46 chromosomes in total.

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Key Concepts: Chromosome Basics

b) A single long thread of DNA
[Solution Description] A chromosome is made up of a single long thread of DNA, which contains genes.

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Key Concepts: Germ Cell Genetic Material, Chromosome Combination Impact

c) Germ cells contain half the genetic material, contributing to genetic stability upon fertilization.
[Solution Description] Germ cells contain half the genetic material compared to somatic cells, meaning they have a haploid set of chromosomes. Upon fertilization, the combination of two haploid sets from each parent restores the complete diploid set necessary for maintaining genetic stability and inheritance patterns.

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Key Concepts: Enzyme Efficiency

b) The plant will be short
[Solution Description] An inefficient enzyme leads to reduced production of growth hormones, resulting in shorter plant height.

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Key Concepts: Gene Expression

c) Proteins

[Solution Description] Genes contain instructions for making proteins. These proteins play various roles in the body, ultimately affecting physical traits such as height.

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Key Concepts: Genetic Contribution

b) Each parent contributes half of their chromosomes to form a complete pair of each chromosome in the child.
[Solution Description] During sexual reproduction, each parent contributes one set of chromosomes to the offspring. Humans have two sets of chromosomes; one set is inherited from the mother and one from the father. This means that for every gene, there are two alleles present in the offspring, one from each parent.

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Key Concepts: Trait Inheritance

b) They are both controlled by genes on separate chromosomes.
[Solution Description] Mendel’s experiments showed that traits such as plant height and seed shape segregate independently during gamete formation due to independent assortment, resulting in new combinations of traits.

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Key Concepts: Independent Inheritance

c) $\frac{1}{16}$
[Solution Description]
Consider the gametes produced by each parent: RY, Ry, rY, ry. Performing a dihybrid cross gives a 9:3:3:1 phenotypic ratio.

Wrinkled green seeds have the genotype rryy, which corresponds to $\frac{1}{16}$ of the total progeny based on the phenotypic ratio.

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Key Concepts: Basic Concept

c) Reproduction
[Solution Description] The reproductive process is responsible for generating individuals with similar designs, as it allows traits and characteristics to be passed from one generation to another.

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Key Concepts: Mechanism Explanation

a) By controlling the expression of enzymes that produce hormones
[Solution Description] In humans, DNA is the information source for producing proteins in cells, which determine traits. A section of DNA that provides instructions for making one protein is called a gene. Proteins are responsible for various functions and characteristics within an organism. For example, the height of a plant can be determined by a particular hormone controlled by an enzyme encoded by a specific gene. Thus, if a gene affects the efficiency of this enzyme, it will impact the overall trait such as height.

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Key Concepts: Basic Mendelian Concepts

c) Garden peas
[Solution Description] Mendel used garden peas to study the inheritance of traits. He selected pea plants with contrasting characteristics such as tall/short plants and round/wrinkled seeds for his experiments.

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Key Concepts: Trait Ratios

b) 3:1
[Solution Description] For a Tt x Tt cross, create a Punnett square. Possible gametes from each parent (T or t) will combine as follows:

$$
\begin{array}{c|c|c}
& \text{T} & \text{t} \\
\hline
\text{T} & \text{TT} & \text{Tt} \\
\hline
\text{t} & \text{Tt} & \text{tt} \\
\end{array}
$$

This results in:
– TT (tall)
– Tt (tall)
– Tt (tall)
– tt (short)

The phenotypic ratio of tall to short plants is therefore 3:1.

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Key Concepts: Sex Chromosomes

b) XY
[Solution Description] Human males have an XY composition for the sex chromosomes, where X is inherited from the mother and Y from the father.

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Key Concepts: Hypothetical Scenarios, Real-World Application

c) Thicker fur and enhanced lung capacity
[Solution Description]
Higher altitudes typically mean colder temperatures and lower oxygen availability. Mammals with thicker fur would likely be preferable for thermoregulation, while enhanced lung capacity supports better oxygen uptake. Both attributes aid survival under harsher conditions at altitude.

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Key Concepts: Genetic Mechanism, Chromosomal Behavior

c) Genetic linkage between loci
[Solution Description]
Classical Mendelian ratios presume that genes assort independently unless otherwise affected. A noted deviation from these ratios in a dihybrid cross suggests a non-standard interaction or genetic linkage.

Possible reasons include:
– Linkage: Genes located near each other on the same chromosome tend to be inherited together, reducing independence in segregation.
– Genetic interactions such as epistasis, where one gene masks or modifies the effect of another, could alter expected outcomes.

Analyzing chromosomal maps or conducting further breeding tests may uncover linkage or interaction patterns causing the observed deviations. Recognizing these factors aids accurate prediction of inheritance patterns in applied breeding contexts.

From the options listed, the explanation aligned with genetic linkage is encapsulated in option ‘c’.

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Key Concepts: Basic Concept

c) The father’s contribution of X or Y chromosome
[Solution Description] The sex of a human child is determined by the combination of sex chromosomes inherited from the parents. An X chromosome from the mother and either an X or Y chromosome from the father will determine the child’s sex: XX results in a girl, while XY results in a boy.

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Key Concepts: Sex Chromosome Anomalies

c) Non-viable embryo
[Solution Description] Normally, the sex chromosomes pair as XX for females and XY for males. If an individual were to inherit two Y chromosomes without an X chromosome, it would not be a viable situation because the X chromosome carries essential genetic information required for development. Two Y chromosomes alone lack the necessary genes found on the X chromosome.

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Key Concepts: Germ Cell Formation

c) By meiosis
[Solution Description] Germ cells ensure they contain only one set of genes through a process called meiosis, which reduces the number of copies of each chromosome from two to one.

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Key Concepts: Gene Expression

b) It provides information for protein synthesis
[Solution Description] DNA acts as an information repository for making proteins, which are crucial for various cellular functions. Each gene within DNA sequences encodes specific instructions for building proteins that express traits.

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Key Concepts: Trait Identification

a) Tall
[Solution Description]
When a tall pea plant is crossed with a short one, the F1 generation shows only the tall trait because it is the dominant trait.

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 Key Concepts: Enzyme Efficiency

b) The plant will be short
[Solution Description] If an enzyme associated with producing a hormone that influences plant height is less efficient, it would result in the production of less hormone, thus leading to shorter plants.

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 Key Concepts: Self-Pollination Outcome

c) 3 round:1 wrinkled
[Solution Description]
When F1 progeny (Rr) are self-pollinated, the F2 generation will exhibit a phenotypic ratio of 3:1 for round to wrinkled seeds, according to Mendel’s law of segregation. Therefore, the expected phenotypic outcome is 3 round:1 wrinkled.

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Key Concepts: Chromosome Mismatch

b) Y
[Solution Description] In human males, the sex chromosomes consist of one X and one Y chromosome. The Y chromosome is shorter and mismatched compared to the X chromosome.

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 Key Concepts: Genetic Makeup Analysis

b) TtWw
[Solution Description] To have offspring that are short and have white flowers, both recessive alleles ‘t’ (for shortness) and ‘w’ (for white flowers) must be present in at least one parent. If the first parent is heterozygous for both traits, its genotype can be TtWw. This allows it to pass on either dominant or recessive alleles to the progeny.

Considering this possibility:
– Tall (T) is dominant over short (t)
– Violet (W) is dominant over white (w)

Hence, the genotype of the first parent would be TtWw.

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Key Concepts: Real-world Application, Enzyme Gene Mutation

c) By optimizing enzyme activity for improved nutrient processing
[Solution Description]
Mutations that optimize enzyme catalytic efficiency can enhance nutrient uptake and metabolism even in poor soils. Such improvements allow plants to make better use of limited resources, sustaining growth and yield when nutrients are scarce. Breeding programs can focus on enhancing such beneficial mutations.

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Key Concepts: Inheritance Patterns

b) Dominant traits mask the presence of recessive ones.
[Solution Description] Mendel proposed that traits are inherited through discrete units called genes, which come in pairs. One trait is dominant over another if it appears in the offspring even when only one parent contributes it. This means there are no ‘blended’ traits; instead, a specific pattern of dominance and recessiveness is observed.

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 Key Concepts: Genetic Ratio Calculation

b) 1:2:1
[Solution Description]
To find the genotypic ratio of a monohybrid cross between two heterozygous tall pea plants ($$Tt \times Tt$$), apply the monohybrid Punnett square method. Each parent can pass either a Tor a t, leading to the following combinations in the offspring:

\[
\begin{array}{c|cc}
& T & t \\ \hline
T & TT & Tt \\
t & Tt & tt \\
\end{array}
\]

From this, we obtain the genotypes TT, Tt, and tt with the respective proportions: 1 TT: 2 Tt: 1 tt.

Hence, the genotypic ratio is 1:2:1.

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Key Concepts: Independent Inheritance, Complex Inheritance

b) One parent has AA and the other has BB or AO/BO.
[Solution Description] Blood type AB in a child indicates receiving one allele for “A” from one parent and one for “B” from another, showcasing codominance. Possible parental genotype combinations include: one parent with “AA” and another “BB”, or “AO” and “BO”. These pairings ensure that the child gets both A and B alleles.

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Key Concepts: Direct Fact

b) Little variation
[Solution Description] In a field of sugarcane plants, very little variation is typically observed because they reproduce asexually, leading to clones with minimal differences.

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Key Concepts: Dominant vs Recessive

b) Tt
[Solution Description] A heterozygous trait combination includes one dominant and one recessive allele. In Mendel’s experiments, the tallness is a dominant trait represented by T, while shortness is recessive, represented by t. Therefore, the heterozygous combination would be Tt, where tallness is expressed.

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Key Concepts: Variation Impact

c) It allows some individuals to survive changes better than others.
[Solution Description] Genetic variation increases a species’ adaptability because different individuals may possess traits that confer advantages under new or changing environmental conditions. Those with beneficial variations are more likely to survive and reproduce.

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 Key Concepts: Variation Survival

c) By enabling some individuals to adapt better to changes
[Solution Description] Variations provide a pool of different traits within a species, which can be advantageous when the environment changes. Some variants may have adaptations that better suit new conditions, increasing their chances of survival and reproduction while passing on those beneficial traits.

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Key Concepts: Genetic Mechanism

c) Chromosomal sex determination
[Solution Description] The genetic mechanism demonstrated here is sex determination based on the combination of sex chromosomes. In this case, the XX combination leads to female offspring and the XY combination leads to male offspring. This is a clear example of chromosomal sex determination.

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 Key Concepts: Chromosomal Inheritance

c) XY
[Solution Description] In humans, the sex of the child is determined by the type of chromosome inherited from the father. Females have two X chromosomes (XX), and males have one X and one Y chromosome (XY). The mother always contributes an X chromosome, while the father can contribute either an X or a Y chromosome. If the child inherits a Y chromosome from the father along with an X chromosome from the mother, the child will be male.

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Key Concepts: Sex Determination Method

b) Environmentally
[Solution Description] In snails, sex is determined environmentally rather than genetically. They have the ability to change sexes based on external conditions.

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 Key Concepts: Independent Assortment

d) Some are round with green seeds
[Solution Description] According to Mendel’s principle of independent assortment, traits are inherited independently of each other. For the given genotypes, we have the following possibilities for seed traits:

– Round Yellow: RY or Ry
– Round Green: rY or ry

A cross RrYy x Rryy will create gametes (combinations): RY, Ry, rY, and ry. The possible combinations for progeny include:
1. Round Yellow (RRYY, RRYy, RrYY, RrYy)
2. Round Green (RRyy, Rryy)
3. Wrinkled Yellow (rrYY, rrYy)
4. Wrinkled Green (rryy)

Thus, some F2 progeny may be round and green.

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