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Explain the pea relationship with a pair of alleles.
The difference between a round pea and a wrinkled pea is that one can convert sucrose to starch, thus allowing retention of water uptake and rounding when the pea reaches maturity and dehydrates.
The SBE1 gene is the one that describes pea shape. It has two alleles.
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What are the functional SBE1 alleles.
the first is the functional version that codes for round peas and the second is the nonfunctional that codes for wrinkled peas
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Aside from regular dominance, what are the other types of dominance?
Incomplete: there is a blend between the phenotype of the dominant and the phenotype of the recessive.
Dominant recessive may result in a lethal homozygote: being homozygous recessive results in the intolerance of the loss of the gene product and the homozygote to die
Codominance: Both pairs of alleles are expressed fully and functionally
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Example of incomplete dominance.
anthocyanin, a flavonoid that gives petals a deep red color.
It is synthesized from a white precursor by the enzyme anthocyanin synthase, which is coded by the ANS gene. The gene has two alleles: A (functional) and a (inactive)
AA: produces lots of anthocyanin--> red
Aa: some anthocyanin synthase is made--> pink
aa--> white due to no anthocyanin
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Example of lethal alleles.
aurea gene of snapdragon, which allows chlorophyll synthesis.
AA: they have the gene and can make chlorophyll
Aa: one can make enough cholorophyll
aa: no chlorophyll made and so die
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What are qualitative traits
traits that originate from combined activities of large numbers of genes
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Example of functional alleles having additive effects.
Number of pigment units:
The # of genotypes--> phenotypes
- 4: Red
- 3: Light red
- 2: Pink
- 1: Light pink
- 0: White
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What is the point of having two interacting synthesis genes?
1) alleles of different genes can combine in an additive fashion to determine the nature of a phenotype
2) the number of genotypes is not the same for each of the five possible
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What distribution gets formed between the two?
the normal, or Gaussian, distribution
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What is epistasis?
it is where certain alleles of one gene mask or cancel the effects of alleles of a second gene
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Interaction between multiple genes result in __.
quantitative traits
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What does the bell curve demonstrate in terms of the phenotypes?
it is the characteristic description of phenotypes resulting from interactions between multiple genes. As more genes are added, the curve becomes smoother.
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Why are quantitative traits studied today?
they are studied today because of their applied importance. In medicine, theya re important because susceptibility to certain diseases depends on interactions between multiple genes. Those individuals falling at one extreme are likely to develop the disease
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What does recombination form the basis of?
for the method used to map the positions of genes on chromosomes.
It is very difficult to locate a gene simply by examining a DNA sequence, especially if the gene is split into exons that are distributed over many kb. Some idea of its approximate position in the chromosome is needed so the search can be focused on the right part of the DNA sequence
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What is linkage?
the two genes behaving as if they were a single unit during meiosis
the physical association between two genes that are on the same chromosome
all of the meioses will contain all the same genes
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Explain recombination frequency.
It is a measure of the distance between two genes. Two genes that are close together will be separated by crossovers less frequently than two genes that are more distant from one another.
The distance between genes are expressed in map units
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