Variation in Mendelian Genetics Flashcards
inheritance patterns may not?
always be predicted by mendelian genetics. inheritance patterns are way more complex than those described by mendel.
what were mendels laws?
- each character was determined by one gene
- there was only 2 alleles for each gene
- one allele was always completely dominant over the other
however, there are?
variations
for a single gene, there may be?
degrees of dominance
one allele may not be?
completely dominant over the other.
f1 may have a phenotype that is?
intermediate with those of the parents.
what is this observed in?
this is observed in snapdragons. red snapdragon and a white snapdragon results in a pink snapdragon. the offspring has a phenotype that is intermediate to that of the parents.
what is that “intermediate” called?
incomplete dominance
what does the symbol look like for incomplete dominance?
since no allele is dominant, instead of using uppercase and lowercase. the letter C for flower color is used with subscripts.
CRCR x CWCW = CRCW
what is incomplete dominance
in incomplete dominance, neither allele is completely dominant over the other. instead, the resulting phenotype is a blend or intermediate between the two parental traits.
what is codominance?
in codominance, both alleles contribute equally to the organisms phenotype. this means that both traits from the parents are fully expressed in the offspring, rather than one allele dominating over the other.
can you give an example of codominance
human mn blood group:
EXPLAIN codominance and human mn blood group example:
the MN blood group is determined by two forms a glycoproteins found on the surface of red blood cells.
M form of glycoprotein
N form of glycoprotein
these two glycoproteins are controlled by a single gene with two alleles.
LM LN.
both alleles are expressed equally when they are present in an individual.
Genotype: LMLM: this means the individual has two LM alleles homozygous for M. The red blood cells will express M phenotype: M.
Genotype: LNLN: this means the individual has two LN alleles homozygous for N. The blood cells will express N. phenotype: N.
Genotype: LMLN: this means that this individual has one LM and one LN allele. Since the alleles are codominant, both M and N forms will be expressed on rbc. Phenotype: MN
how can incomplete dominance be distinguished from codominance?
in incomplete dominance: the offspring will show an intermediate phenotype: mix of traits. example: red flowered snapdragon x white flowered snapdragon = pink flowered snapdragon.
in codominance: both traits will be expressed clearly. like in Mn blood group example, both M and N antigens will be expressed on the red blood cells. another example. or speckled chhicken example.
unlike the genes mendel studied in the garden pea plant, most genes…?
exist in more than two allelic forms: multiple alleles.
can you give an example of multiple alleles?
ABO blood group system in humans. single gene with 3 alleles: iA, iB, i.
The ABO gene determines the type of carbohydrate/antigen present on the surface of rbc. iA=a iB=b i=none.
what are the different blood group genotypes and phenotypes?
genotype: IAIA or IAi phenotype: A
genotype: IBIB OR IBi phenotype: B
genotype: IAIB phenotype: AB
genotype: ii phenotype: O
universal recipient vs universal donor?
universal recipient: type ab
universal donor: type o
what is pleiotropy?
pleiotropy is when a single gene causes multiple effects on different traits of an organism.
the cftr gene is a pleiotropic gene because it affects multiple organs and systems in the body. it helps regulate the movement of salt and water in and out of cells.
if mutated, it can cause cystic fibrosis. this causes thick sticky mucus to build up in different parts of the body. this causes infertility, liver damage, pancreas/digestive system issues, and lung infections/trouble breathing.
there are also variations that can occur with two or more genes.
the phenotypic expression of one gene at one locus may influence the phenotypic expression of another gene at another locus
epistasis in laborador retrievers
one gene controls coat color. that gene has two alleles: B: black coat b: brown coat.
a different gene controls pigment deposition in the coat.
E: pigment deposition
e: no pigment deposition
BBEE, BbEe, bbEE, bbEe
the dog has BB for coat color and EE for pigment
result: BBEE: dog will have a black coat
the dog has Bb for coat color and Ee for pigment deposition
result: BbEe: dog wil have a black coat
the dog has bb for coat color and EE for pigment deposition
result: bbEE: dog will have a brown coat
bbEe: dog will have a brown coat.
if there was no pigment deposition, the coat would be yellow regardless of coat color alleles
how would you word the coat color thing?
the gene for pigment deposition is epistatic to the gene that codes for fur color.
the characters mendel studied in garden pea plants had one of two traits white flowers or purple flowers. some characters do not behave this way..?
there may be variations of the trait within a population. this is called quantitative characters
what are quantitative characters?
traits that are controlled by multiple genes/polygenic inheritence.
example: height in humans, skin pigmentation in humans
what is polygenic inheritence?
there is an additive effect of two or more genes on a phenotypic character.
the environment…?
can play a role and may give rise to a range of phenotypes.
examples of how the environment can have an effect?
hydrangeas: acidic soil: purple
basic soil: pink.
- diet, athletics for height
