Topic 1 Heredity: Gene Interaction Flashcards
1
Q
- It is important to realize that genes don’t just exist in isolation. Rather, they are involved in complex interactions that give rise to observed phenotypes. Essentially, the whole point of genes interacting with one another is to serve as a mechanism for fine control. This section outlines these important interactions.
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Note
2
Q
- The process in which one gene affects the phenotypic expression of a second gene. A common example of epistasis is fur pigmentation in mice → one gene controls the production of pigment by either turning on or turning off and the second gene controls the color or amount of color deposited in the fur. Therefore, if the first gene codes for no pigment, then the second gene has no effect
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- Epistasis
3
Q
- When a single
gene has more than one phenotypic expression - One example of pleiotropy is a gene in pea plants that expresses for seed texture, but also influences the phenotype of starch metabolism and water uptake
- Another example of this is how sickle cell anemia leads to different health conditions
a. Sickle cell anemia - A mutation in the single gene responsible can result in the expression of multiple different health conditions: pain, stroke, high blood pressure, etc.
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- Pleiotropy
4
Q
- The interaction of many genes to shape a single phenotype with continuous variation such as height, skin color, or hair color
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- Polygenic Inheritance
5
Q
- It can help to better understand pleiotropy vs polygenic by thinking of them as opposites — pleiotropy is when a single gene affects many phenotypes, while polygenic inheritance is when many genes affect a single phenotype
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Note
6
Q
- When two or more genes reside physically close to one another on the same chromosome and therefore cannot separate independently as they are inherited together
a. The closer two genes are on a chromosome, the less likely they are to be separated by genetic recombination (a process that occurs due to crossing over in meiosis I)
b. Genes that are completely unlinked have a 50% chance of recombination, and the lower the percentage of recombination, the more likely the genes are linked/closer together.
c. A note about recombination - in a cross of BbVv x bbvv, and assuming that BV and bv are linked with each pair present in a homologue, we only get BV or bv as the offspring. Moreover, we don’t get Bv or bV. However, if recombination does occur, then we may observe some Bv and bV genotypes as well.
d. A greater recombination frequency means that the genes are located farther apart on the same chromosome, and therefore more likely to undergo recombination.
e. Linkage maps can be generated to visualize recombination frequency in linked genes: - For example, on a chromosome, the genes B-V have a recombination frequency of 18%, A-V has a 12% frequency, and B-A has a 6% recombination frequency. The map below represents this, with each representing one unit apart
- B- - - - - - A - - - - - - - - - - - - V
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- Linked Genes
7
Q
- A type of linked gene that refers to a single gene residing on a sex chromosome that is inherited differently in males and females
- One example of a sex-linked gene involves males. When a male (XY) receives an X chromosome from his mother, whether or not a dominant or recessive trait on the X chromosome is expressed depends on the mother as there is no copy on the Y chromosome
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- Sex-Linked Genes
8
Q
- These differ from sex-linked genes in that the expression of genes can be influenced by the sex of the individual carrying the trait
- For example, a female with the genotype Bb could be bald while a male with the same genotype is not
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- Sex-Influenced Genes
9
Q
- Sex-influenced genes are similar to genomic imprinting, in which one allele, either paternal or maternal, is not expressed in the offspring. Genomic imprinting is also different from sex-linked genes since this is seen in autosomal chromosomes
A
Note
