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Flashcards in interactions between genes Deck (28):
1

types f interactions between alleles of a genes

dominance : incomplete and co-dominance -pleiotropy -lethal alleles

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interactions between genes

gene combinations epistasis genetic complementation tests

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co--dominance

heterozygotes show phenotype of both alleles

e.g. human MN blood groups: M, N and MN allele combination

-neither M or N is dominant to the other

-SHOWS FULL CHARACTERISITC AND NOT AN INTERMEDIATE VALUE.

 

4

how is co -dominance different to incomplete dominance

co-domnance unlike incomplete dominance shows the full characteristic of an allele, instead of intermediate values e.g. the roan cow

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incomplete dominance

heterozygotes show an intermediate phenotype e.g. red x white = pink

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ratios incomplete dominance

genotypic ratio= phenotypic ratio

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multiple alleles

there may be more than two alleles for a gene e.g.The ABO system in humans is controlled by three alleles, usually referred to as IA, IB, and IO (the "I" stands for isohaemagglutinin).

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dominance is subjective

there is a scale of dominance -dominant isn't just black and white, its subjective to the allele it is competing with

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pleiotropy

one gene contributes to more than one trait e.g. genes involved in cilia and flagella function- if mutant e.g. one mutation can cause cili and sperm tails to not work proper;y causing respiratory problems as well as sterility

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lethal alleles

Lethal alleles (also referred to as lethal genes or lethals) are alleles that cause the death of the organism that carry them. They are usually a result of mutations in genes that are essential to growth or development. Lethal alleles may be recessive, dominant, or conditional depending on the gene or genes involved.

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phenotypic ratios and lethal alleles

cause a skewed phenotypic ratio --> indicates an essential gene e.g. phenotypic ratio can be 2:1 --> since one of the combination of alleles is lethal and therefore missing and that organism will not survive

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penetrance

measure the percent of individuals with a given genotype who exhibits the phenotype associated with the genotype 

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expressivity

measures the extent to which a given genotype is expressed at the phenotypic level

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complex interaction between evens e.g. hair colour

hair colour is determined by at least 5 major genes

1. A gene - distribution of pigment in hair A = agouti; a= solid

2. B gene- colour of pigment B =black; b=brown

3. C gene- permits colour expression C= expressed; c= not expressed

4. D gene- controls intensity of pigment specified by other genes D= full expression d=dilute

5. S gene - control of distribution of pigment S= solid colour; s- spotted

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Alleles of one gene can ask the effects of alleles on another gene

epistasis

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epistasis

a gene interaction in which the effects of an allele at one gene hides the effect of alleles at another gene e.g. when two genes determine whether a certain pigment is produced. if gene A is a mutant and codes for a non-functional protein, then enzyme A will not be produced, therefor the first colourless precursor will not be produced, therefore functional enzyme B will not be able to produce the pigment

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complementation tests

- can determine if a phenotype arises from mutation in the same of separate genes (sometimes called a "cis-trans" test) can be used to test whether the mutations in two strains are in different genes. Complementation will not occur if the mutations are in the same gene.

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example 1 of complementation tests -what if W1 and W2 are mutations in the same gene and both code for a non-functional enzyme?

if the gene for the flower is W 1 or W2, them the enzymes will not be functional to turn the colourless precursors purple -therefore if two white flowered mutants (one with W1W1 and one with W2W2) are crossed then the offspring will be W1W2 and white --> this means there is no complementation

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complementation tests are used to determine..

whether the mutation is within the same gene are causing the phenotype or are the mutations within diff genes

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method of complementation tests

a method which uses a cross to determine if 2 mutations are located on the same or different gene

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complementation tests can also determine if

genes ar present on the same or different chromosomes

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if the mutations complement with each other

the mutations are within different genes

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if the mutations do not complement with each other

the mutations are on the same gene

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e.g. 2 if mutations are in different genes

both genes must be present for the result to occur --> the two genes complement each both e.g. two genes A and B colourless precursor 1 is turned into colourless precuros 2 by enzyme A produced by gene A. Colourless precursor 2 can then be transformed to purple pigment by enzyme B produced by gene B. the two genes complement each other and this is because: if both gene A and B are present then the purple pigment (results) will be produced

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examples of disease and interactions between alleles of a gene

sickle cell syndrome -an example of complications of dominance and pleiotropy -biochemical level shows its caused by co-dominance -physiological level- incomplete dominance HbA HbA- normal HbA HbS- no anaemia - cells sickle under low O2 tension HbS HbS- severe anaemia

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HbAHbA

normal suspetability to malaria

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HbA HbS

resistant to malaria but carrier of sickle cell

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HbSHbS

resistant to malaria but diseased