interactions between genes

Question 1

types f interactions between alleles of a genes

Answer 1

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

Question 2

interactions between genes

Answer 2

gene combinations epistasis genetic complementation tests

Question 3

co–dominance

Answer 3

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.

Question 4

how is co -dominance different to incomplete dominance

Answer 4

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

Question 5

incomplete dominance

Answer 5

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

Question 6

ratios incomplete dominance

Answer 6

genotypic ratio= phenotypic ratio

Question 7

multiple alleles

Answer 7

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).

Question 8

dominance is subjective

Answer 8

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

Question 9

pleiotropy

Answer 9

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

Question 10

lethal alleles

Answer 10

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.

Question 11

phenotypic ratios and lethal alleles

Answer 11

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

Question 12

penetrance

Answer 12

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

Question 13

expressivity

Answer 13

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

Question 14

complex interaction between evens e.g. hair colour

Answer 14

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

Question 15

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

Answer 15

epistasis

Question 16

epistasis

Answer 16

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

Question 17

complementation tests

Answer 17

• 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.

Question 18

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

Answer 18

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

Question 19

complementation tests are used to determine..

Answer 19

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

Question 20

method of complementation tests

Answer 20

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

Question 21

complementation tests can also determine if

Answer 21

genes ar present on the same or different chromosomes

Question 22

if the mutations complement with each other

Answer 22

the mutations are within different genes

Question 23

if the mutations do not complement with each other

Answer 23

the mutations are on the same gene

Question 24

e.g. 2 if mutations are in different genes

Answer 24

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

Question 25

examples of disease and interactions between alleles of a gene

Answer 25

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

Question 26

HbAHbA

Answer 26

normal suspetability to malaria

Question 27

HbA HbS

Answer 27

resistant to malaria but carrier of sickle cell

Question 28

HbSHbS

Answer 28

resistant to malaria but diseased