4 Most FAQ’s of Heredity and Evolution Chapter in Class 10th Biology (TS/AP)

8 Marks

LAQ-1 : What is phenotype and genotype? Explain them with the help of mendel’s monohybrid cross.

Introduction

The field of genetics uses key terms to describe how traits are passed to the next generation. Two essential terms are ‘phenotype‘ and ‘genotype‘. Phenotype refers to observable traits in an organism, like appearance and behavior. Genotype refers to an organism’s set of genes that determine these characteristics.

Understanding Genotype and Phenotype Using Mendel’s Monohybrid Cross

1. The Monohybrid Cross Experiment:
   This is a breeding experiment between parental generation organisms differing in a single trait. Gregor Mendel, the father of modern genetics, conducted such experiments with pea plants, crossing yellow-seeded plants (dominant trait) with green-seeded ones (recessive trait).
2. First Generation Results (F1):
   The F1 generation produced yellow seeds, demonstrating ‘dominance’, where the dominant yellow seed trait (Y) masks the recessive green seed trait (y).
3. Second Generation Results (F2):
   Self-pollination of F1 plants resulted in both yellow and green seeded F2 plants, with a 3:1 ratio, illustrating ‘segregation’, where the recessive green trait (y) reappeared.

Summary

In conclusion, the phenotype in Mendel’s experiment is the observable seed color of pea plants (yellow or green). The genotype refers to the genetic makeup like YY, Yy, or yy, determining the expressed traits. Understanding genotype and phenotype is crucial for explaining trait inheritance from parents to offspring, a fundamental concept in genetics.

---

LAQ-2 : What do you understand by the term natural selection? Write Darwin’s theory of evolution.

Introduction

Natural selection and Darwin’s theory of evolution are pivotal concepts in biology, explaining the development and change of species over time. These theories, based on extensive observations and evidence, are crucial for understanding life on Earth.

The Concept of Natural Selection

1. Proposed by Charles Darwin, natural selection suggests that nature determines which organisms will survive based on their traits.
2. Organisms with beneficial traits are more likely to reproduce and pass these traits to offspring.
3. Those with less advantageous traits are less likely to survive and reproduce, potentially leading to their elimination from the environment.

Darwin’s Theory of Evolution

1. Darwin posited that each organism in a population has unique variations.
2. These variations are hereditary, passed from parents to offspring.
3. Due to overpopulation, there is a constant struggle for survival among organisms.
4. Organisms with useful variations often live longer and reproduce more, passing on these traits. Conversely, organisms with less beneficial traits have shorter lifespans and fewer offspring.
5. If the environment changes, organisms adapt to increase survival chances.
6. Over time, these adaptations accumulate, leading to the formation of new species.
7. Evolution is a slow and continuous process, resulting in the diverse life forms we observe today.

Summary

In conclusion, natural selection and Darwin’s theory of evolution provide a scientific framework for understanding how species adapt and change over time. These theories underpin our knowledge of biodiversity and ecological interrelationships. However, they have been refined by subsequent theories, such as the synthetic theory of evolution and mutation theory.

---

LAQ-3 : Observe the given flow chart and answer the following questions.

Introduction

In humans, sex determination is based on the combination of sex chromosomes inherited from parents. We will explore how this process works and address related questions.

Sex Chromosomes

1. Sex chromosomes are the pair of chromosomes determining an individual’s sex.
2. In humans, these are known as the X and Y chromosomes.
3. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

Representation in a Punnett Square

1. Using a Punnett square, we place the mother’s possible chromosomes (X and X) on one side and the father’s (X and Y) on the other.
2. This representation shows the possible combinations: XX (female) and XY (male).

Mendel’s Principle Applicable

This situation demonstrates Mendel’s Law of Segregation, which states that alleles for each gene segregate during gamete formation, so each gamete carries only one allele for each gene.

Is the Statement Correct?

1. The statement “Mother determines the sex of the baby” is incorrect.
2. The mother provides an X chromosome, but the baby’s sex is determined by whether the father contributes an X (resulting in XX, female) or a Y chromosome (resulting in XY, male).

Summary

In conclusion, an individual’s sex is determined by the combination of the X and Y chromosomes. The mother contributes an X chromosome, while the father’s contribution of an X or a Y chromosome ultimately determines the sex of the offspring.

---

LAQ-4 : Explain in brief any two evidences of evolution.

Introduction

Understanding evolution is crucial to comprehend how species have changed over time. Evidence for evolution spans various fields of biology, including comparative anatomy and embryology. We will explore two key evidences: homologous and analogous organs, and embryology.

Homologous and Analogous Organs

1. Homologous Organs:
   These organs have similar structures across different species but may serve different functions. Examples include the forelimbs of humans, cats, whales, and bats, which differ in functions like grabbing, walking, swimming, or flying. Their similarity suggests a common ancestor, supporting evolution.
2. Analogous Organs:
   These are organs in different species performing similar functions but with different structures. The wings of birds and bats are examples, both enabling flight yet structurally distinct. Analogous organs indicate independent evolutionary adaptations to similar environmental challenges.

Embryology

1. Studying embryos reveals significant evidence for evolution. The early stages of embryos in various animals, like fish, tortoises, birds, rabbits, and humans, show remarkable similarities.
2. Even specialists might find it challenging to differentiate these embryos initially. This resemblance indicates a shared evolutionary origin, strengthening the case for evolution.

Summary

In conclusion, homologous and analogous organs and embryology provide compelling evidence for evolution. They highlight the interconnectedness and common ancestry of different species, reinforcing the theory of evolutionary change. These evidences are part of the extensive body of research uncovering the history of life.