Introduction to Genetics

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Questions and Answers

What is the main focus of genetics?

  • The evolution of plant species over time
  • The structure of proteins in organisms
  • The formation of blood cells in humans
  • The study of biological inheritance (correct)

Which theory regarding inheritance was prevalent before Mendel's experiments?

  • Chromosome theory
  • Molecular theory
  • Dominance theory
  • Blood theory (correct)

What term did Willard Johannsen introduce to replace earlier terms related to inheritance?

  • Factor
  • Chromosome
  • Gene (correct)
  • Allele

What did Griffith's experiments demonstrate?

<p>Genetic material can transform characteristics of other organisms. (B)</p> Signup and view all the answers

In which year was the chemical basis of heredity identified as DNA?

<p>1944 (A)</p> Signup and view all the answers

Why did Mendel choose garden peas for his experiments?

<p>They had a short life cycle and distinct traits. (A)</p> Signup and view all the answers

What was the significance of the work done by Watson and Crick in 1952?

<p>They elucidated the structure of DNA. (A)</p> Signup and view all the answers

Which of these characters did Mendel study in his hybridization experiments?

<p>Seed color and plant height (A)</p> Signup and view all the answers

What defines a homozygous genotype?

<p>Two identical alleles for a gene (D)</p> Signup and view all the answers

Which trait manifests in a heterozygous state?

<p>Dominant trait (A)</p> Signup and view all the answers

What is the term for the observable traits of an individual?

<p>Phenotype (B)</p> Signup and view all the answers

What follows Mendel’s laws of inheritance?

<p>Many human traits and diseases (B)</p> Signup and view all the answers

What is characteristic of a heterozygous genotype?

<p>Two different alleles (D)</p> Signup and view all the answers

What does a dihybrid cross clarify about the inheritance of traits?

<p>A pair of traits segregates independently of another pair. (A)</p> Signup and view all the answers

Which law states that hybrid offspring will inherit the dominant trait in the phenotype?

<p>Law of Dominance (C)</p> Signup and view all the answers

In a monohybrid cross, what does it mean for a trait to be recessive?

<p>It will only be expressed if inherited from both parents. (A)</p> Signup and view all the answers

What tool did Mendel use to determine the outcome of his crosses?

<p>Punnett square (C)</p> Signup and view all the answers

What is true regarding the Law of Segregation?

<p>Each hereditary factor separates so offspring acquire one from each parent. (B)</p> Signup and view all the answers

How does the Law of Independent Assortment affect the inheritance of traits?

<p>It causes traits to segregate independently during gamete formation. (B)</p> Signup and view all the answers

Which of the following statements about Mendel's experiments is accurate?

<p>His experiments helped establish the laws of inheritance. (B)</p> Signup and view all the answers

What type of cross did Mendel conduct to analyze two traits simultaneously?

<p>Dihybrid cross (B)</p> Signup and view all the answers

Flashcards

Genetics

The study of how characteristics are passed from parents to offspring, explaining why family members share similar traits.

Blood theory of inheritance

An outdated belief that children inherit traits by absorbing blood from their parents.

Hereditary substance

The material responsible for passing on traits.

Mendel's experiments

Experiments using pea plants to demonstrate inheritance controlled by factors passed from parents to offspring.

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Gene

The term introduced to replace 'inheritance factor' or 'inheritance unit' in describing the units of inheritance.

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Genetic transformation

The process where genetic material from one organism can change the traits of another organism.

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DNA as genetic material

The discovery that DNA, not proteins, is the chemical basis of heredity.

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DNA structure

The structure of DNA as a molecule determined in a crucial period.

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Mendel's Laws of Inheritance

Rules established by Mendel describing how traits are passed from parents to offspring in organisms.

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Monohybrid cross

A cross between parents that differ in only one trait or character.

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Pea plants

Organisms used by Mendel in experiments to study inheritance.

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Dihybrid Cross

A cross between parents with two different traits (like seed color and shape).

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Mendel's Dihybrid Cross

Mendel's experiment to discover how pairs of traits segregate during gamete formation.

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Independent Assortment

Traits are inherited independently of each other during gamete formation.

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Dominant Trait

The trait that appears in the hybrid offspring.

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Law of Segregation

During reproduction, the two copies of each hereditary factor segregate, and an offspring receives one factor from each parent.

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Monohybrid Cross

Cross between parents differing in only one trait.

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Punnett Square

A tool used to predict the possible genotypes and phenotypes resulting from a cross between two individuals.

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Homozygous

Having two identical alleles for a particular gene.

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Heterozygous

Having two different alleles for a particular gene.

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Phenotype

The observable physical characteristics of an organism.

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Genotype

The genetic makeup of an organism.

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Autosomal

Referring to chromosomes that are not sex chromosomes.

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Sex chromosomes

Chromosomes that determine the sex of an organism (X and Y).

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Dominant trait

A trait that is expressed even if only one copy of the allele is present.

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Recessive trait

A trait that is only expressed if two copies of the allele are present.

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Mendelian Inheritance

Traits inherited according to patterns described by Gregor Mendel.

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Non-Mendelian Inheritance

Traits that do not follow the patterns described by Mendel's laws.

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Locus

A specific location on a chromosome.

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Allele

Different forms of a gene, one per chromosome.

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Sex-linked trait

Traits whose alleles are located on the sex chromosomes.

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Study Notes

Introduction to Genetics

  • Genetics is the study of biological inheritance, explaining how characteristics are passed from parents to offspring and why members of the same family (or species) share similar traits.

Historical View - Blood Theory

  • For centuries, it was believed that children inherit traits through their parents' blood.
  • By the 1850s, this blood theory of inheritance was challenged.

What is the Hereditary Substance?

  • In 1866, Gregor Mendel's experiments on pea plants demonstrated inheritance is controlled by factors passed from parents.
  • By the early 1900s, scientists rediscovered Mendel's work, connecting inheritance factors to chromosomes.
  • The term "gene" was introduced in the 1920s to replace "inheritance factor."

Historical View - Griffith's experiment

  • Griffith showed that genetic material from one organism can transform the characteristics of another organism in 1928.

Historical View - Avery's experiment

  • In 1944, Avery and colleagues demonstrated that DNA is the chemical basis of heredity, not other compounds like protein. Experiments showed that DNA, not RNA or protein, was the critical component for transformation.

Historical View - Watson and Crick

  • In 1952, Watson and Crick elucidated the structure of DNA.

Mendel's Laws of Inheritance

  • Mendel's experiments involved hybridization (cross-mating) of pea plants.
  • Studied seven characteristics of pea plants.
  • Led to the development of three laws of inheritance:
    • Law of dominance: Hybrid offspring inherit the dominant trait.
    • Law of independent assortment: Pairs of traits segregate independently during gamete formation.
    • Law of segregation: Two copies of each hereditary factor segregate, so offspring acquire one factor from each parent.

Genetic Terms

  • Locus: Specific gene location on a chromosome.
  • Allele: Each gene has two alleles (one per chromosome).
  • Homozygous: Two identical alleles.
  • Heterozygous: Two different alleles.
  • Phenotype: Observable traits of an individual.
  • Genotype: Genetic composition of an individual.
  • Autosomal: Refers to chromosomes other than sex chromosomes.
  • Sex chromosomes: Determine sex (X and Y).
  • Dominant trait: Manifests in heterozygous state.
  • Recessive trait: Manifests only in homozygous state.
  • Sex-linked trait: Allele located on the X chromosome.

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