Genetics Classics Flashcards

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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.

Cross-pollination occurs when pollen is delivered to a flower from a different plant, while self-pollination occurs when pollen is delivered to a flower from itself. Hybridization is the mating between different breeding lines or populations. Signup and view all the answers

What do the terms 'gene' and 'allele' mean?

A gene is the hereditary unit defined experimentally by the complementation test. Any of the different forms of a given gene are called alleles. Signup and view all the answers

Where are genes (alleles) located physically?

Genes (alleles) are located on the chromosomes. A locus is the site or position of a particular gene on a chromosome. Signup and view all the answers

Define homologous chromosomes. Do all human chromosomes possess a homolog?

Homologous chromosomes are chromosomes that pair in meiosis having the same genetic loci and structure. Humans have 22 pairs of homologous chromosomes except the sex pair which differ in males having X and Y. Signup and view all the answers

Why do we discriminate between autosomal and X-linked modes of inheritance?

These modes represent different patterns of inheritance. Autosomal inheritance depends on the presence or absence of certain alleles on the autosomes and affects both sexes equally, while X-linked inheritance affects males more than females due to males having only one X chromosome. Signup and view all the answers

What are the characteristics of traits transmitted through the Y chromosome?

Because the Y chromosome does not undergo recombination along most of its length, genetic markers on the Y chromosome are completely linked and remain together as they are transmitted from generation to generation. Signup and view all the answers

Compare and explain the differences between sex-linked, sex-influenced, and sex-limited inheritance.

Sex-linked inheritance transmits traits via alleles at gene loci on sex chromosomes. Sex-influenced inheritance shows character differences due to sex differences, while sex-limited inheritance is the expression of a phenotype in only one sex. Signup and view all the answers

Define the terms 'genotype' and 'phenotype'.

Genotype is the genetic constitution of an organism with respect to one or few genes of interest. Phenotype is the observable property of a cell or organism that results from the interaction of the genotype and the environment. Signup and view all the answers

Define the terms: dominant, recessive, codominant, incomplete dominance, and intermediate mode of inheritance.

Dominant trait refers to an allele that completely masks the effect of another allele. Recessive traits only manifest when two copies are present. Codominance occurs when both alleles are expressed. Incomplete dominance is when the phenotype is a blend of both alleles. Intermediate mode of inheritance includes both dominant and recessive traits interplaying in expression. Signup and view all the answers

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.