Questions and Answers
What do the terms 'true breeding' and 'purebred' mean?
True breeding refers to a strain, breed, or variety of organisms that yields progeny like itself, homozygous. Purebred refers to cultivated varieties or cultivars of an animal species achieved through selective breeding.
List and describe the traits of pea plants used by G. Mendel in his basic plant hybridization experiments.
Mendel studied 7 characters in peas: seed shape (round vs. wrinkled), seed color (yellow vs. green), flower color (purple vs. white), pod shape (inflated vs. constricted), pod color (green vs. yellow), flower and pod position (axial vs. terminal), and stem length (standard vs. dwarf).
What are mutually exclusive traits?
Mutually exclusive traits are those that are incompatible in such a way that they cannot occur at the same time; either one is expressed (e.g., wrinkled or smooth, yellow or green).
Explain the importance of cross-pollination and self-pollination in Mendelian pea experiments.
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What do the terms 'gene' and 'allele' mean?
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Where are genes (alleles) located physically?
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Define homologous chromosomes. Do all human chromosomes possess a homolog?
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Why do we discriminate between autosomal and X-linked modes of inheritance?
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What are the characteristics of traits transmitted through the Y chromosome?
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Compare and explain the differences between sex-linked, sex-influenced, and sex-limited inheritance.
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Define the terms 'genotype' and 'phenotype'.
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Define the terms: dominant, recessive, codominant, incomplete dominance, and intermediate mode of inheritance.
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Study Notes
Key Genetics Terminology
- True Breeding: Refers to organisms that consistently produce offspring identical to themselves and are homozygous.
- Purebred: Cultivated varieties or breeds developed through selective breeding.
Mendel's Pea Plant Traits
- Studied seven distinct traits in pea plants:
- Seed shape: Round vs. Wrinkled
- Seed color: Yellow vs. Green
- Flower color: Purple vs. White
- Pod shape: Inflated vs. Constricted
- Pod color: Green vs. Yellow
- Flower & pod position: Axial vs. Terminal
- Stem length: Standard vs. Dwarf
- Experiments involved hybridizing smooth yellow peas with wrinkled green peas.
Mutually Exclusive Traits
- Defined as traits that cannot coexist; only one trait is expressed at any time.
- Examples include wrinkled vs. smooth peas and yellow vs. green peas.
Pollination in Mendel's Experiments
- Cross-Pollination: Occurs when pollen from one plant fertilizes another.
- Self-Pollination: Pollen from the same plant fertilizes its flowers.
- Hybridization: The mating of different breeding lines to produce hybrids (e.g., red flower + ivory flower = pink flower).
Genes and Alleles
- Gene: A hereditary unit defined by the complementation test.
- Allele: Different forms of a specific gene.
Gene Location and Loci
- Genes (alleles) are located on chromosomes.
- Locus (plural: loci): The specific site or position of a gene on a chromosome.
Homologous Chromosomes
- Homologous chromosomes: Chromosomes that pair during meiosis with identical loci and structure.
- Humans possess 22 pairs of homologous chromosomes, except for the sex chromosomes (X and Y).
Autosomal vs. X-linked Inheritance
- Autosomal Inheritance: Depends on alleles present on autosomes; can be dominant or recessive with equal frequency in males and females.
- X-linked Inheritance: More prevalent in males due to their single X chromosome; females need two alleles for expression.
Y Chromosome Traits
- Traits on the Y chromosome are transmitted unchanged from generation to generation due to lack of recombination along most of its length.
Inheritance Comparisons
- Sex-linked Inheritance: Traits passed down through sex chromosome alleles.
- Sex-influenced Inheritance: Traits where sex affects expression but both genders can express them.
- Sex-limited Inheritance: Traits expressed in only one sex, linked to either sex chromosomes or autosomal genes.
Genotype vs. Phenotype
- Genotype: The genetic constitution of an organism concerning specific genes.
- Phenotype: Observable characteristics of an organism resulting from the interaction of the genotype and environment.
Modes of Inheritance
- Dominant: An allele whose traits are always expressed in the presence of another.
- Recessive: An allele whose traits are masked by dominant alleles.
- Codominant: Both alleles in a heterozygote are expressed equally.
- Incomplete Dominance: Blending of traits from both alleles in the phenotype.
- Intermediate Inheritance: A spectrum of traits resulting from the interaction of alleles.
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Description
Explore essential terms and concepts in genetics, including 'true breeding' and 'purebred', as well as traits studied by Gregor Mendel. This quiz is designed for students to reinforce their understanding of Mendelian genetics through engaging flashcards.