Study Guide: Mendel and the Gene

Study Guide: Mendel and the Gene

What was the widely accepted inheritance hypothesis Mendel was testing?
The widely accepted hypothesis was blending inheritance, which predicted that the traits of parents blended in the offspring.
Provide an example of blending inheritance.
A white-flowered plant crossed with a purple-flowered plant would produce an intermediate, light purple flowered plant.
What is a phenotype?
A phenotype is a visible characteristic of an organism. Mendel analyzed seven pea phenotypes: seed shape, seed color, flower color, flower location, pod shape, pod color, and plant height.
What are true-breeding varieties or pure lines?
When seeds are planted, they produce known phenotypes. For example, pure line seeds for purple flowers always produce plants with purple flowers.
How are pure lines created?
Pure lines are produced by self-pollination, fertilizing the same plant, so offspring inherit exactly the same phenotypes as the parent.
What is the P generation?
True-breeding pure lines are known as the parent generation (P generation).
How did Mendel create hybrids of the P generation?
He cross-pollinated two pure lines using sterilized brushes and mesh bags to prevent unwanted pollination, producing hybrid offspring.
What is the F1 generation?
Hybrids of the P generation, known as the first filial generation (F1).
What was the prediction of the phenotypes for F1 generation based on blending inheritance?
The prediction was an intermediate phenotype in F1, such as slightly wrinkly seeds from smooth x wrinkly parents.
How did Mendel's results of the F1 generation conflict with blending inheritance?
All F1 seeds displayed the dominant trait (round seeds), not a blended intermediate.
What was Mendel's conclusion from his results of the F1 generation based on seed shape?
The smooth seed phenotype masked the wrinkly seed phenotype; traits are inherited as discrete units.
What is a dominant phenotype? Recessive phenotype?
Dominant: expressed when at least one dominant allele is present.
Recessive: expressed only when two recessive alleles are present.
What are Mendel's 'particles'?
Discrete heritable units controlling traits, now called alleles.
How many alleles determine a phenotype?
Two alleles (one from each parent) determine a phenotype.
What is a genotype?
The combination of alleles an individual has: homozygous dominant (AA), homozygous recessive (aa), or heterozygous (Aa).
What is Mendel's Principle of Dominance?
If an individual has two different alleles, only the dominant phenotype is expressed; the recessive is masked.
What is the F2 generation?
Offspring of the F1 hybrids, called the second filial generation (F2).
What phenotypic ratio of seed shape did Mendel observe in the F2 generation?
Approximately 3:1 dominant (round) to recessive (wrinkly) seeds.
Expected phenotypic and genotypic ratios: FF x ff
Phenotypic: all purple flowers
Genotypic: all heterozygotes (Ff)
Expected phenotypic and genotypic ratios: Ff x Ff
Phenotypic: 3 purple : 1 white
Genotypic: 1 FF : 2 Ff : 1 ff