Inheritance and Variations

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Questions and Answers

What is the fundamental reason for the inheritance of characters from parents to offspring?

  • The influence of environmental factors on the offspring's traits.
  • The presence of variations among individuals of the same species.
  • The dominance of the father's genes over the mother's genes.
  • The equal contribution of genetic material from both parents. (correct)

Which of the following best describes 'heredity'?

  • The transfer of characters from parents to offspring. (correct)
  • The process of natural selection leading to new species.
  • The differences in traits among individuals of the same species.
  • The changes in genetic composition due to environmental factors.

What is the most accurate description of 'variations'?

  • The changes in genetic material that occur during reproduction.
  • The development of new species through accumulation of changes.
  • The differences in traits among individuals of the same species. (correct)
  • The process by which traits are passed from parents to offspring.

Why are variations more prominent in sexual reproduction compared to asexual reproduction?

<p>Asexual reproduction always produces identical copies, while sexual reproduction introduces new gene combinations. (B)</p> Signup and view all the answers

In Mendel's monohybrid cross, what was the ratio of tall to dwarf plants in the F2 generation when the F1 generation was self-pollinated?

<p>3:1 (A)</p> Signup and view all the answers

What is the genotypic ratio of pure tall (TT), hybrid tall (Tt), and pure dwarf (tt) plants in the F2 generation of Mendel's monohybrid cross?

<p>1:2:1 (C)</p> Signup and view all the answers

In the context of genetics, what is a 'dominant trait'?

<p>A trait that is expressed in the F1 generation in a monohybrid cross. (D)</p> Signup and view all the answers

What is a 'recessive trait'?

<p>A trait that is masked in the presence of a dominant trait. (A)</p> Signup and view all the answers

In a dihybrid cross, if plants with round yellow seeds (RRYY) are crossed with plants having wrinkled green seeds (rryy), what is the phenotype of the F1 generation?

<p>All plants with round yellow seeds. (D)</p> Signup and view all the answers

What phenotypic ratio is expected in the F2 generation of a dihybrid cross when two traits are considered?

<p>9:3:3:1 (C)</p> Signup and view all the answers

In humans, what determines the sex of the offspring?

<p>The presence of either an X or Y chromosome in the sperm cell. (B)</p> Signup and view all the answers

Which of the following statements correctly describes the role of variations in the survival of organisms?

<p>Variations may or may not help organisms survive; some can be harmful. (B)</p> Signup and view all the answers

What is the significance of 'acquired traits' in the context of evolution?

<p>Acquired traits cannot be passed on to the next generation and thus do not contribute to evolution. (C)</p> Signup and view all the answers

Which of the following factors can lead to the formation of new species?

<p>Accumulation of variations, physical barriers, genetic drift, natural selection, and migration. (B)</p> Signup and view all the answers

What is 'genetic drift'?

<p>The random change in the frequency of alleles in a population due to chance events. (B)</p> Signup and view all the answers

What are 'homologous organs'?

<p>Organs that have similar structures but perform different functions. (D)</p> Signup and view all the answers

Which of the following exemplifies homologous organs?

<p>Forelimbs of amphibians, reptiles, birds, and mammals. (D)</p> Signup and view all the answers

Which of the following pairs represents analogous organs?

<p>The wings of a butterfly and the wings of a bat. (C)</p> Signup and view all the answers

How do fossils provide evidence for evolution?

<p>By showing a timeline of life forms, demonstrating the transition from simpler to more complex organisms. (D)</p> Signup and view all the answers

Flashcards

Heredity

The transfer of traits from parents to offspring.

Variations

Differences in traits among individuals of the same species.

Variations in Reproduction

Variations are less in asexual reproduction and more in sexual reproduction.

Monohybrid Cross

A cross involving one pair of contrasting traits.

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Dominant Trait

The visible trait in the first generation (F1).

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Recessive Trait

The suppressed trait in the first generation (F1).

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Dihybrid Cross

A cross involving two pairs of contrasting traits.

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Sex Chromosomes

Chromosomes that determine sex (X and Y).

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Speciation

The formation of new species from existing ones.

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Inherited Traits

Traits caused by changes in genetic composition, passed down generations.

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Acquired Traits

Traits acquired during an organism's lifetime; not passed to offspring.

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Homologous Organs

Organs with similar structures but different functions.

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Analogous Organs

Organs with different structures but similar functions.

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Fossils

Remains of ancient organisms.

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Analogous organs examples

The wings of butterfly, bird and bat have different structures but similar functions.

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Complex Organisms

Organisms and its organs developed from simpler organisms gradually over generations.

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Study Notes

Inheritance of Characters

  • Characters get transferred through genes
  • Genes exist in DNA molecules within chromosomes in the cell's nucleus
  • Inheritance happens as both parents provide equal genetic contribution
  • Each trait is influenced by two factors, one from each parent
  • Gregor Johann Mendel discovered inheritance rules using garden pea experiments

Heredity and Variations

  • Heredity refers to the transfer of traits from parents to offspring
  • Variations refer to the differences in traits among individuals of a species

Variations During Reproduction

  • Offspring exhibit variations due to DNA copying errors during reproduction
  • Asexual reproduction has less variation than sexual reproduction
  • Helpful variations aid organisms in adapting to environmental changes
  • Harmful variations hinder adaptation and may lead to extinction

Monohybrid Cross

  • Monohybrid cross involves crossing plants with one pair of contrasting traits
  • Mendel crossed pure tall (TT) and pure short (tt) pea plants, resulting in all tall plants (Tt) (F1 generation)
  • Self-pollinating F1 plants produced tall and dwarf plants in a 3:1 ratio (F2 generation)
  • The ratio of pure tall (TT), hybrid tall (Tt), and pure dwarf (tt) plants was 1:2:1
  • Dominant trait: trait expressed in the F1 generation
  • Recessive trait: trait suppressed in the F1 generation

Dihybrid Cross

  • Dihybrid cross involves crossing plants with two pairs of contrasting traits
  • Mendel crossed pea plants with round yellow seeds (RRYY) and wrinkled green seeds (rryy)
  • The F1 generation had all plants with round yellow seeds (RrYy)
  • Self-pollinating the F1 generation resulted in 9 round yellow, 3 round green, 3 wrinkled yellow, and 1 wrinkled green out of 16 plants, a 9:3:3:1 ratio

Human Sex Determination

  • Humans have 23 pairs of chromosomes, with one pair being sex chromosomes (X and Y)
  • Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY)
  • Sperm and egg cells contain one set of sex chromosomes
  • Sperm can carry either an X or a Y chromosome, while eggs carry only X chromosomes
  • X sperm + X egg = female child (XX)
  • Y sperm + X egg = male child (XY)

Variations and Survival

  • Variations can affect an organism's ability to survive
  • Ex: Green beetles survive over red beetles due to crows predicating on the red beetles
  • Color variations in beetles can affect the population size
  • Ex: Blue beetles survive over red beetles die to crows predicating on both, decreasing both populations
  • Acquired traits aren't passed down genetically
  • Ex: Changes in beetle size due to food availability is no genetic.

Speciation

  • Speciation = new species evolve from existing ones
  • Factors include: accumulation of variations, physical barriers, genetic drift, natural selection, and migration
  • Accumulation of variations: Differences accumulating over generations cause new species
  • Physical barriers: Separated populations evolve uniquely
  • Genetic drift: Random events change gene pool
  • Natural selection: Advantageous traits survive
  • Migration: Moving leads to new variations

Evolution

  • Evolution describes gradual changes over time
  • Inherited traits are genetic changes passed down

Types of Traits

  • Acquired traits are obtained during lifetime, not passed down and don't cause evolution

Evidence of Evolution

  • The process of evolution is supported by common features among organisms
  • This is shown by:
    • Homologous organs: Similar structure, different function, like limbs
    • Analogous organs: Different structure, similar function, like wings
    • Fossils: Remains show structure and time period, Radio Carbon Dating determines age. Fossils of simpler organisms are found deeper, and show evolution

Stages of Evolution

  • Examples of how evolution occurs:
    • Evolution of eyes: developed from eye spots to complex organs
    • Evolution of feathers: First used for warmth in dinosaurs, later for flight in birds
    • Evolution by artificial selection: Humans breeded vegetables over time

Human Evolution

  • Humans have diversity, and evolved in Africa
  • Migration and genetic variation caused changes and features

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