Heredity And Evolution (SAQs)

Biology | 8. Heredity And Evolution – SAQs:
Welcome to SAQs in Chapter 8: Heredity And Evolution. This page contains the most Important FAQs for Short Answer Questions in this Chapter. Each answer is provided in simple English, with a Telugu explanation, and formatted according to the exam style. This will support your preparation and help you secure top marks in your exams.

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SAQ-1 : Explain the theory of “inheritance of acquired characters” with an example.

Introduction

The theory of “Inheritance of Acquired Characters” was proposed by Jean Baptiste Lamarck. This theory suggests that traits developed during an organism’s lifetime can be inherited by its offspring. Although now supplanted by more contemporary theories, it was an early attempt to explain species evolution. The example of the giraffe is often used to illustrate this theory.

Acquired Characteristics

1. Lamarck posited that acquired characteristics, traits developed during an organism’s life, could be passed to offspring.
2. The transmission of these acquired traits was a foundational aspect of Lamarck’s evolutionary theory.

Example: The Giraffe

1. Lamarck used giraffes to exemplify his theory. He theorized that ancient giraffes, similar in size to deer with short necks, had to stretch their necks to reach leaves on trees due to ground-level food scarcity.
2. He proposed that this neck stretching led to increased neck length over generations, eventually becoming an inherited trait in all giraffes.

Summary

In conclusion, Lamarck’s theory of “Inheritance of Acquired Characters” suggests that organisms can adapt during their lifetime to environmental changes, and these adaptations can be inherited. It is crucial to note that this theory has been overtaken by more robust theories, like Darwin’s theory of natural selection. However, Lamarck’s ideas were significant in the historical development of evolutionary theory.

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SAQ-2 : Observe the checker board and answer the following questions.

Introduction

Checker boards, or Punnett squares, are genetic tools used to predict the potential genotypes of offspring from a cross between two parent organisms. Here, we focus on a monohybrid cross, examining a single trait. We will discuss questions related to this checker board.

Phenotypic Ratio of Monohybrid Cross

1. In a monohybrid cross, one trait, such as seed color in pea plants, is examined.
2. The typical phenotypic ratio is 3:1, indicating that out of four offspring, three are expected to exhibit the dominant trait and one the recessive trait.

Number of Heterozygous Plants

1. Heterozygous plants carry two different alleles for a trait. For example, a pea plant with one allele for yellow seeds (Y) and one for green seeds (y) is heterozygous.
2. In a monohybrid cross Punnett square, there are typically two heterozygous plants, represented as Yy and yY.

Summary

To summarize, a monohybrid cross usually shows a phenotypic ratio of 3:1. In our example, two plants are heterozygous. This method helps predict offspring outcomes in genetic crosses and understand the roles of dominant and recessive traits in inheritance, fundamental concepts in the study of genetics.

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SAQ-3 : Define the term phenotype and genotype?

Introduction

When delving into genetics, two essential terms are frequently encountered: “phenotype” and “genotype.” These terms describe an organism’s observable characteristics and the underlying genetic code responsible for these traits.

Phenotype

1. Phenotype refers to the set of observable characteristics or traits of an organism.
2. This includes physical traits like height and eye color, as well as behavioral traits.
3. The phenotype is the result of the interaction between an organism’s genotype and its environment.

Genotype

1. Genotype denotes the actual set of genes an organism carries.
2. It is the genetic composition of an organism concerning a specific characteristic or group of characteristics.
3. The genotype is responsible for determining the potential traits an organism can pass to its offspring.

Summary

In conclusion, the phenotype represents the visible traits of an organism, both physical and behavioral, while the genotype comprises the specific genes determining these potential traits. Understanding both terms is fundamental to grasping the principles of genetics and exploring the transmission of traits from parents to offspring.

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SAQ-4 : Explain the process to understand monohybrid cross of mendel experiment with a checker board. (OR) If you cross a plant with pure yellow seeds (YY) with a plant with pure green seeds (yy), what would be the color of seed in F2 generation? Show in a checker board.

Introduction

A monohybrid cross is a breeding experiment developed by Mendel to study the inheritance of individual traits. This experiment involves crossing pea plants with differing traits, such as seed color. One plant has yellow seeds (YY), and the other has green seeds (yy). We’ll delve into this process in more detail.

Performing a Monohybrid Cross

1. The monohybrid cross begins with the parental generation. One parent possesses yellow seeds (YY), and the other has green seeds (yy).
2. In the first generation (F1), these parents are cross-fertilized. Each offspring (F1) inherits one allele from each parent, resulting in Yy genotype, which displays yellow seeds due to yellow (Y) being dominant over green (y).

Creating the F2 Generation

1. The F1 generation undergoes self-fertilization to produce the F2 generation.
2. The F2 generation can have three genotypes: YY, Yy, and yy. These genotypes are illustrated in a Punnett square:
   • 3 out of 4 F2 offspring will have yellow seeds (YY, Yy, and Yy).
   • 1 out of 4 will have green seeds (yy).

Summary

In conclusion, a monohybrid cross is a powerful method for predicting genetic cross outcomes. In the case of crossing plants with yellow and green seeds, the F2 generation will comprise 75% plants with yellow seeds and 25% with green seeds. This process illustrates the principles of Mendelian genetics.

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SAQ-5 : How can we say that human being is a moving museum of vestigial organs?

Introduction

Throughout evolution, humans have retained certain vestigial organs. These organs, once functional, now offer insights into our evolutionary history.

Understanding Vestigial Organs

1. Vestigial organs are remnants from our ancestors, once useful in other species but no longer functional in humans.
2. Examples include the appendix, wisdom teeth, and tailbone (coccyx). The appendix, previously used for digesting plant materials, is now largely redundant. Wisdom teeth were essential for chewing hard plants in ancestral diets, but modern cooking has rendered them unnecessary. The tailbone is a remnant of a tail used for balance and communication in most mammals, but it has no significant function in humans.

Why Humans are a “Moving Museum of Vestigial Organs”

1. Humans possess over 180 vestigial traits, including organs and anatomical structures.
2. Each of these organs is a window into our evolutionary past, revealing aspects of our ancestors.
3. The term “moving museum of vestigial organs” highlights our carrying of these evolutionary artifacts throughout our lives.

Summary

In conclusion, humans are a “moving museum of vestigial organs” as we carry evolutionary remnants within us. Though these organs are no longer functional, they serve as intriguing evidence of our evolutionary journey over millions of years.

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SAQ-6 : Draw a flow – chart showing the sex determination in human beings. (OR) Who decides the sex of the baby, mother or father? Explain with a flow chart.

Introduction

In human reproduction, the father plays a decisive role in determining the sex of the baby. This determination is based on the type of sex chromosome carried by the father’s sperm. We’ll use a flowchart to illustrate this process.

Understanding Sex Determination

1. Human beings possess 23 pairs of chromosomes, including one pair of sex chromosomes (X and Y).
2. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
3. During reproduction, each parent contributes one sex chromosome to the offspring. The mother, being XX, contributes an X chromosome. The father, being XY, can contribute either an X or a Y chromosome.
4. The baby will be female (XX) if the father contributes an X chromosome, and male (XY) if the father contributes a Y chromosome.

The Flowchart of Sex Determination

1. Start: Conception begins with the fertilization of an egg by sperm.
2. Mother’s Contribution: The egg from the mother always contains an X chromosome.
3. Father’s Contribution: The sperm from the father contains either an X or a Y chromosome.
4. Combination: If the father’s sperm contributes an X chromosome, the resulting baby is female (XX).
5. If the father’s sperm contributes a Y chromosome, the resulting baby is male (XY).

Summary

In conclusion, the father significantly influences the sex of a baby, determined by whether the sperm carries an X or a Y chromosome. This process underscores the crucial role of the father’s genetic contribution in determining a baby’s sex.

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SAQ-7 : What happen if there is no evolution?

Introduction

Evolution is the process driving the development of species over time through changes in their genetic characteristics. Let’s consider the hypothetical scenario of a world without evolution.

Consequences of No Evolution

1. No New Species Formation: In the absence of evolution, new species would not emerge. Evolution drives biodiversity, allowing species to adapt and diverge into new forms.
2. Absence of Genetic Variations: Genetic variations, the foundation of evolution, would not occur without evolutionary processes. These variations arise naturally within populations and are essential for evolutionary change.
3. Lack of Natural Selection: Evolution involves natural selection, where species develop traits enhancing survival and reproduction. Without evolution, these advantageous traits would not develop, potentially impacting species’ adaptability and survival.

Summary

In conclusion, evolution is integral to the rich biodiversity on Earth. Without it, the emergence of a variety of species, genetic variations, and beneficial traits shaped over time would not occur. Evolution is fundamental to the continued existence and diversity of life on our planet.

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SAQ-8 : How does the embryological evidences support that evolution has taken place?

Introduction

Embryology, the study of embryos, offers crucial evidence for evolution. There are multiple ways in which embryological data supports the occurrence of evolution.

Embryonic Similarities Across Species

A key piece of evidence lies in the similarities of embryos across different species. Early-stage embryos from various animals exhibit remarkable resemblances.

Examples of Embryo Similarities

Notably, the initial development stages of vertebrates like fish, tortoises, birds, rabbits, and humans show striking similarity. Distinguishing these embryos based solely on physical traits is challenging, even for skilled embryologists.

Connection to a Common Ancestor

These embryonic resemblances imply that these vertebrates might have evolved from a common ancestor. This aligns with evolutionary theory, suggesting that different species share common roots and have diverged over time due to evolutionary pressures.

Summary

In conclusion, embryological evidence significantly supports the theory of evolution. The similarities in embryonic development among various species point to a common ancestry, affirming that evolution has transpired over time.