ch. 6.1

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ch. 6.1
2015-02-10 20:27:00
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  1. What is pleiotropic?
    What is an allelic series or multiple alleles?
    What is the simplest type of dominance?
    What is haplosufficient and whats an example?

    What is haploinsufficiency?

    What is a null mutation?
    • Pleiotropic is a term that is used for any allele that affects several properties of an organism.
    • Allelic series is the known mutant alleles of a gene and its wild-type allele.
    • Full or complete dominance.
    • Haplosufficient is when the defective allele is recessive that the wild-type gene is sufficient to cause normal function and an example would be  the recessive gene in the PKU condition in where the wild-type gene produces enough PAH to break down the phenylalanine entering the body and so the PAH gene is said to be haplosufficient.

    Haploinsufficiency is when a single normal allele is not sufficient to produce the normal phenotype.

    A null mutation is a mutation in which it produces a nonfunctional protein.
  2. What is Dominant Negative?
    What is incomplete dominance and what is an example?
    What is codominance and what is an example?
    Dominant Negative is another dominant mutation in where the altered gene product antagonizes the normal product.

    Incomplete dominance is when the phenotype of a heterozygous is intermediate between those of the two homozygotes and an example would be crossing a pure-breed four-o'clock line having red petals with white petals and the F1 has pink petals.

    Codominance is the expression of both alleles of a heterozygote and an example would be the ABO blood type in where both the Ia and Ib genotypes are both dominant and express the two antigens.
  3. What is a lethal allele?
    Can a recessive mutation be lethal?
    A lethal allele is an allele that is capable of causing the death of an organism.

    Yes, recessive mutation is sometimes found to be lethal.
  4. What is the dihybrid cross ratio for no overlap (independent assortment): independently synthesized and inherited pigments?

    What is the order of the biosynthetic pathway in Neurospora?

    What is the order of the enzymes of X, Y, and Z?
    The Dihybrid cross ratio is 9:3:3:1.

    The order of the biosynthetic pathway in Neurospora is Precursor-Ornithine-Citrulline-Arginine.

    The order of the enzymes are arg 1, arg 2, and arg3.
  5. When classifying mutants to determine if they are within the same gene, how should we do this? There are two methods, one is better than the other.

    What is a complementation test?
    • 1. The first method is mapping each mutant allele and if two mutations map to two different chomrosomal loci, they are likely of different genes; to see if each mutant is in the same or distinct genome (often hard, labor-intensive and expensive).
    • 2. The second is doing a complementation test (intercrossing two individuals that are homozygous for different recessive mutations)

    A complementation test is a test to see if the mutants are recessive to the wild-type and it involves crossing individuals that are homozygous for each mutant and checking for any wild-type offspring.
  6. When do you use the complementation test?

    What is complementations according to the book?
    You use the complementation test when sorting mutants to decide whether two mutations belong to the same gene.

    Complementation is the production of a wild-type phenotype when two haploid genomes bearing different recessive mutations are united in the same cell.
  7. A cross with a 9:7 ratio is an indication of what?

    In the "9:3:3:1" ratio, what got combined to make the 7?

    How does a regulatory gene often function?
    A cross with a 9:7 ratio is an indication of genes in the same pathway; absence of either gene function leads to absence of the end product of the pathway.

    In the 9:3:3:1 ratio, the 3:3:1 bit got combined to make the 7.

    A regulatory gene often functions by producing a protein that binds to a regulatory site upstream of a target gene, facilitating transcription of the gene.
  8. What is the ratio for recessive epistasis?
    What does epistatic mean?
    Which mutation is epistatic and which is hypostatic?
    Why is it called recessive epistasis?

    A recessive epistasis is a/an downstream or upstream mutation that is "standing upon" (epistatic to) a second mutation?
    • The Ratio for recessive epistasis is 9:3:4.
    • Epistatic means "stand upon," referring to the situation in which a double mutant shows the phenotype of one mutation but not the other.
    • Epistatic is the one mutation overrides the other and hypostatic is where a mutation is overridden.

    It is called recessive epistasis because the recessive phenotype (white) overrides the other phenotype.

    An "upstream" mutation is "standing upon" (epistatic to) a second mutation.
  9. What is the ratio of dominant epistasis?
    The ratio of dominant epistasis is 12:3:1 with the 9:3 combined to make the 12.
  10. By what pathway do we follow to account for there recessive epistasis in Collinsia?

    What is another case for the recessive epistatsis?

    What are the genotypes for the yellow pigment?

    Is this upstream or downstream?
    colorless-(gene w+) magenta-(gene m+) blue

    The yellow coat color of some Labrador retriever dogs.

    The genotypes B/-;e/e and bb/b;e/e both produce a yellow phenotype, where one E leads to the release for melanin which leads to black or brown.

    Downstream mutation.
  11. How do you screen for suppressors?

    What is the difference between suppression and epistasis?

    What is a type of suppressor?

    What are suppressors?
    You screen for suppressors by starting with a mutation in some process of interest, exposing this mutant to mutation-causing agents such as high energy radiation, and screening the descendants for wild types.

    The key difference between suppression and epistasis is that a suppressor cancels the expression of a mutant allele and restores the corresponding wild-type phenotype.

    One type of suppressor is a protein-protein binding.

    Suppressors are mutant alleles that cancel the expression of a mutant allele of another gene, resulting in normal wild-type phenotype.
  12. What is a modifier mutation?
    A modifier mutation is a mutation at a second locus that changes the degree of expression of a mutated gene at the first locus.
  13. What is the ratio for dominant epistasis that is due to a white mutation?
    The dominant epistasis that is due to a white mutation is a 12:3:1 ratio.
  14. What is the model for synthetic lethality?
    The model for synthetic lethality is when two interacting proteins perform some essential function on some substrate such as DNA but must first bind to it and reduced binding of either protein allows some functions to remain, but reduced binding of both is lethal.
  15. What is penetrance?

    Why would an organism have a particular genotype and yet not express the corresponding  phenotype?
    Penetrance is a phenotype measurement that is defined as the percentage of individuals with a given allele who exhibit the phenotype associated with that allele.

    • An organism would have a particular genotype and yet not express the corresponding due to three reasons:
    • 1. The influence of the environment.
    • 2. The influence of other interacting genes:
    • uncharachterized modifiers, epistatic genes, or suppressors in the rest f the genome may act to prevent the expression of the typical phenotype.
    • 3. The subtlety of the mutant phenotype:
  16. What is expressivity?
    Expressivity is another measure for describing the range of phenotypic expression; measures the degree to which a given allele is expressed at the phenotypic level or measures the intensity of the phenotype (could be dark brown or light brown color scale).
  17. What are the formal definitions of penetrance and expressivity?
    The terms penetrance and expressivity quantify the modification of gene expression by varying environment and genetic background; they measure, respectively, the percentage of cases in which the gene is expressed (penetrance) and the level(range of color, example) of expression (expression)

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