Chapter 12
How many alleles determine a phenotype?
2
How did Mendel create hybrids of the P generation?
After self-pollination, he grew out pure line seeds of both varieties until they flowered. To control against unwanted pollination, the developing flowers were covered with mesh bags. Once fertile, pollen was collected with a sterilized paint brush from the flowers of one phenotype (i.e. smooth seeds) and used to pollinate the opposite phenotype (i.e. wrinkly seeds), producing a hybrid of the pure lines. Once pollinated, the mesh bags were reinstalled and the seeds allowed to develop, producing hybrids.
What is the expected phenotypic ratio of the cross between a homozygous purple flower (FF) and a homozygous white flower (ff): FF x ff ? What is the expected genotypic ratio?
All purple flowered plants are expected in the F1 generation. All heterozygotes (Ff) are expected in the F1 generation.
What was Mendel's conclusion from his results of the F1 generation based on seed shape?
He concluded the smooth seed phenotype masked the expression of the wrinkly seed phenotype.
What were the predicted results supporting dependent assortment of a dihybrid cross?
If dependent assortment was supported by this experimental design, the predicted phenotypic ratio would be 3 dominant/dominant: 1 recessive/recessive for two phenotypic combinations under investigation
In a pedigree analysis, what are the parental genotypes if one of their children express a different phenotype?
If two parents have the same phenotype and produce a child that has a different phenotype, we know that the child's phenotype must be the recessive expression. Furthermore, we know that the child's genotype must be homozygous recessive (i.e. aa), and the genotypes of both parents must be heterozygous (i.e. Aa).
What is the hypothesis of independent assortment?
Independent assortment predicts alleles for different phenotypes are sorted into gametes independently from one another.
What was the prediction of the phenotypes for F1 generation based on the blending inheritance hypothesis?
Mendel expected to get an intermediate result of slightly wrinkly seeded plants from a cross of pure line smooth seeded plants with pure line wrinkly seeded plants.
How did Mendel's results of the F1 generation conflict with the prediction of blending inheritance?
Once the seeds developed from Mendel's monohybrid cross, he discovered that all the resultant seeds (the hybrids) were not semi-wrinkly. Rather, they were identical in shape to the round seeded pure lines.
How are pure lines created?
Pure lines are produced by self-pollination, where a flower is covered and the pollen of a plant is used to fertilize the same plant, essentially producing a clone.
Did the results of Mendel's dihybrid cross support dependent or independent assortment?
Results of his dihybrid cross were consistent with independent assortment, indicating that alleles for different phenotypes segregate independently of each other.
What are the three principles of Mendel's Particulate Inheritance model?
The Principle of Dominance predicts that each phenotype is determined by two alleles, one of which is expressed when present, known as the dominant allele. Recessive phenotypes are expressed only when an organism is homozygous recessive. The Principle of Segregation predicts that during gamete production, each gamete receives exactly one of the two alleles present in the parental cell at random. The Principle of Independent Assortment predicts alleles coding for different phenotypes are segregated independently from one another during gamete formation.
What is the hypothesis of dependent assortment?
The dependent assortment hypothesis predicts that the inheritance of physical characteristics are linked during gamete formation.
What is a dominant phenotype? recessive phenotype?
The dominant allele masks the recessive phenotype. A recessive phenotype is only expressed when an individual has two recessive alleles in their genotype
What were the predicted results supporting independent assortment of a dihybrid cross?
The independent assortment hypothesis predicted that all allele combinations were possible in gamete production.
What is Mendel's Principle of Dominance?
The principle of dominance states that some alleles are dominant and others are recessive
What was the widely accepted inheritance hypothesis Mendel was testing?
The widely accepted inheritance hypothesis of the day was known as blending inheritance, which predicted that the traits of parents blended in the offspring.
What phenotypic ratio of seed shape did Mendel observe in the F2 generation?
To his surprise, not only did the dominant genotype (round seeds) emerge in the F2 generation, but also the recessive phenotype (wrinkly seeds).
What type of experiment did Mendel use to test the dependent vs. independent assortment hypotheses?
To test these competing hypotheses Mendel conducted a dihybrid cross (hybrids for two characteristic), for example flower color and seed color: FfSs X FsSs.
What is the P generation?
True-breeding pure lines are known as the parent generation, or P generation.
What is the expected phenotypic ratio of the cross Ff x Ff ? What is the expected genotypic ratio?
Using a Punnett square, the expected phenotypic ratio would be three purple flowered plant to one white flowered plant (3 purple : 1 white) in the F2 generation. The expected genotypic ratio would be 1FF : 1Ff : 1ff in the F2 generation.
What are Mendel's 'particles'?
We now refer to Mendel's particles as alleles, or alternate versions of a gene
What is a phenotype?
a visible characteristic of an organsism.
What is a genotype?
genetic makeup of an organism
Provide an example of blending inheritance.
if a white flowered plant and a purple flowered plant would produce an intermediate, or light purple flowered plant.
What is the F2 generation?
offspring of the F1 generation
What is the F1 generation?
offspring of the P generation
What is Mendel's Principle of Segregation ?
pairs of factors separate during meiosis and recombine at fertilization
What are true-breeding varieties or pure lines?
pure line seeds for purple flowers would always develop into plants with purple flowers.
