Question 1. How do Mendel’s experiments show that traits may be Dominant or recessive? Hence define the Law of Dominance and the Law of purity of gametes.

Ans: Mendel’s experiments with pea plants demonstrated the concept of dominant and recessive traits. He studied traits such as flower colour, seed texture, and plant height. Mendel crossed pea plants with different characteristics, such as crossing a plant with yellow flowers (dominant) with a plant with green flowers (recessive). He observed that the offspring always displayed the dominant trait, in this case, yellow flowers.

From these experiments, Mendel formulated the Law of Dominance, which states that in a cross between organisms with different traits, one trait (the dominant trait) will be expressed in the offspring, while the other trait (the recessive trait) remains hidden. Dominant traits mask the expression of recessive traits.

Mendel also observed that when he crossed two plants that were heterozygous for a particular trait (having one dominant and one recessive allele), the recessive trait reappeared in the subsequent generation. This led him to discover the Law of Segregation, which explains the purity of gametes. According to this law, during the formation of gametes (sex cells), the two alleles for a trait separate from each other and end up in different gametes. Therefore, each gamete carries only one allele for a specific trait, ensuring the purity of the trait in subsequent generations.

Question 2. How do Mendel’s experiments show that the Inheritance of two traits is independent of each other? Hence define the law of Independent Assortment.

Ans: Mendel’s experiments also provided evidence for the independent inheritance of different traits. He studied traits such as seed colour (yellow or green) and seed shape (round or wrinkled). Mendel crossed pea plants that differed in both traits and observed the inheritance patterns.

Mendel found that the inheritance of one trait did not influence the inheritance of another trait. In other words, the transmission of traits for seed colour and seed shape occurred independently of each other. This led to the formulation of the Law of Independent Assortment, which states that the alleles for different traits segregate independently of each other during the formation of gametes.

The law of Independent Assortment implies that the inheritance of one trait does not affect the inheritance of another trait unless they are physically linked on the same chromosome.

Question 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: The given information is not sufficient to determine which of the traits, blood group A or O, is dominant. The blood group A man and blood group O woman can have genotypes AO (heterozygous for blood type A) and OO (homozygous for blood type O), respectively. When they have a child, the child can inherit an O allele from both parents, resulting in blood group O.

In this case, both blood groups A and O could be dominant or recessive. To determine the dominance relationship between blood groups A and O, further information or experiments involving a larger sample size would be necessary. Additional crosses and observations involving individuals with known genotypes would be required to establish the dominance relationship between the two blood types.

Question 4. Will geographical isolation be a major factor in the speciation of (a) A self-pollinating plant species? Why or why not?

(b) An organism that reproduces asexually? Why or why not?

Ans: (a) Geographical isolation is unlikely to be a major factor in the speciation of a self-pollinating plant species. Self-pollination allows plants to reproduce without the need for external pollinators. Therefore, even in the absence of cross-pollination with other plants, self-pollinating plants can continue to reproduce and maintain genetic continuity within a localized population. Geographical isolation, which would prevent gene flow between populations, is not a significant barrier to speciation in self-pollinating plants.

(b) Geographical isolation is also less likely to be a major factor in the speciation of an organism that reproduces asexually. Asexual reproduction involves the production of offspring without the need for fertilization or the exchange of genetic material between individuals. As a result, asexually reproducing organisms can produce genetically identical offspring through methods such as binary fission or vegetative propagation. Geographical isolation would not pose a significant barrier to the reproduction and spread of genetically identical individuals, thus limiting the role of geographical isolation in speciation for asexual organisms.

Question 5. 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: Based on the given information that children with light-coloured eyes are likely to have parents with light-coloured eyes, we cannot definitively determine whether the light-eye colour trait is dominant or recessive. The observed pattern suggests a correlation between parental and offspring eye colour, but it does not provide conclusive evidence about the dominance or recessiveness of the trait.

The inheritance of eye colour is influenced by multiple genes, and the expression of eye colour is a complex trait. It is possible that both dominant and recessive alleles can contribute to variations in eye colour. Further analysis and breeding experiments involving a larger sample size would be needed to determine the exact inheritance pattern and dominance relationship of the trait.

Question 6. What do you understand by analogous and homologous organs? Explain these terms with examples.

Ans: Analogous organs and homologous organs are terms used to describe different types of structures in organisms.

Analogous organs: These are structures that have similar functions and may superficially resemble each other, but they have different evolutionary origins and do not share a common ancestry.

Analogous organs arise due to convergent evolution, where different species independently evolve similar adaptations in response to similar environmental pressures.

For example, the wings of birds and insects are analogous organs as they serve the same purpose of flying but have different underlying structures and evolutionary origins.

Homologous organs: These are structures that have similar characteristics, both in terms of their structure and evolutionary origin, indicating a common ancestry.

Homologous organs share a similar basic structure but may have different functions in different species.

For example, the forelimbs of humans, bats, cats, and whales have a similar bone structure, indicating a common ancestor, but they have different functions in each species (e.g., grasping, flying, walking, swimming).

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