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BISC 202 Lecture Notes - Lecture 20: Lethal Allele, Null Allele, Wild Type

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School
Simon Fraser University
Department
Biological Sciences
Course
BISC 202
Professor
Michael Hart

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Document Summary

Bisc202 lecture 20: more gene interactions for 1-2 genes and biosynthetic pathways. 2 pure-breeding recessive mutant strains are mated together. If all wild type: complementation occurred so the mutations affect different genes. If not all wild type: complement failure so the mutations affect the same gene. Null mutations: mutation for one essential step in the gene pathway. Consider 2 wingless mutations (a and b mutations) for different genes for drosophila, many steps are essential to make wings. A mutation has a null mutation in a gene that"s needed for one step. B mutation has a null mutation in a gene that"s required for a different step. If 2 pure-breeding strains of these mutations mate with each other, the offspring will be able to have wings because these mutations affect different genes (they will each have a copy of the wild type allele)

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Related Questions

1. You mate flies that you know are heterozygous for a loss-of-function bicoid mutation and a balancer chromosome. The balancer chromosome, in this case, has a marker that allows one to detect the presence of the balancer in embryos. However, embryos without balancers seem normal. Does this imply Bicoid has no effect? Why or why not?

2. you are working with Arabidopsisdopsis, a model for plant development and two different recessive null loss-of-function mutations have been isolated. The mutations are in different genes but both affect the leaf development (specifically the density of the stomata- openings for gas exchange). The homozygous loss of function phenotype for gene A shows twice as many stomata when compared to wild-type leaves, while the homozygous loss of function for gene B shows four times as many stomata compared to wild-type leaves. A double mutant for both gene A and gene B show four times as many stomata. What is the order of action of these two genes and what is their genetic relationship (i.e. activation or inhibition)?

18) In your research on gene regulation in E. coli, you produce 2 mutant strains with the same phenotype: they can grow on lactose but not on glucose. To investigate these 2 mutants further, you perform a complementation test using them and discover that the diploid combination strain can grow on glucose or lactose. From this, you can deduce that:

a.)Both mutants have a mutation in the same gene

b.)The 2 mutants have mutations in different genes
c.)Glucose and lactose metabolic pathways in E. coli utilize at least one shared gene in common
d.)At least 2 different genes are required for glucose metabolism in E. coli
e.) b) and d)

19. In your research on the lac operon, you produce a unique regulatory mutatant strain of E. Coli where the lac l gene's repressor protein binding site for the operator is normal (wild-type) but its lactose binding site no longer binds lactose. The expected phenotype of this mutant will be:

a. inability to grow on lactose only medium

b. ability to grow on lactose only medium

c. blue colony color when grown on glycerol plus x-gal medium

d. blue colony oclor when grown on lactose plus x-gal medium

e. b & d

20.

20) In your research on the lac operon, you create a diploid E.coli strain with the following genotype (+) = wild type gene, (-) = mutant gene.

I- /O+ /Z- /Y+

I+ /Oc /Z+ /Y+
Can this diploid mutant grow on medium containing lactose as the only carbon source?

a) Yes

b) No

c) Maybe, it depends on if the Oc mutation is dominant or recessive

1. The amino acid sequence of a particular polypeptide in awild-type bacterium and three single point mutant strains are shownin the following table:

Wild type= Met-Tyr-Ile-Thr-Trp-Glu-Glu-Pro-Val-Lys

Mutant 1= Met-Tyr-Ile-Thr-Trp-Asp-Glu-Pro-Val-Lys

Mutant 2= Met-Tyr-Ile-Pro-Gly-Arg-Asn-Gln

Mutant 3= Met-Tyr-His-Tyr-Leu-Gly-Gly-Thr-Ser-Lys

  1. For each mutant indicate the type of point mutations(transition, transversion, insertion or deletion) and the codon inwhich it occurred.
  2. B. Determine to the extent that is possible, the ribonucleotidesequence of the wild type mRNA molecule.

2. Mutations in several different genes that encode enzymes inthe pathway for the synthesis of the heme group may cause a geneticdisorder called methemoglobinemia. The symptoms of this disorderrange form mild to death in the most severe cases. The enzymecytochrome b5 reductase is one of the enzymes in this pathway. Thisenzyme is responsible for reducing the iron in the heme group tothe ferrous state so that it can bind oxygen. Kobayashi et al.reviewed several mutations in this gene. One of these mutationscauses a Ser to Pro substitution. Explain what nucleotide changeand in which position in the codon can cause this amino acidchange. Assign all possible appropriate terms to this mutation.