Inheritance Flashcards
gene
sequence of nucelotides tht code for polypeptides = characteristics.
allele
variation of the gene. we have 2 alleles, for each gene, one from each parent.
locus
a fxes position of a gene on a chromosome. Alleles are found on the same locus of a gene on each chromosome in the pair.
is it always true that dominant alleles are more common
give an example.
no it is a myth. cos thos dominant alleles may be very rare, a population where most are recessive.
eg- polydactyly - born with 1 extra finger. the genotype includes a dominant allele, however in comparison to people with 5 fingers, people with 6 are not so common.
genotype
the genetic makeup of an organism, representing the combination of alleles. can be homozygous or heterozygous.
phenotype
observable characterisic.
co-dominant alleles
when both alleles are expressed in the heterzygote phenotype, there are no recessive alleles, when talking about co-dominance.
give an examples of codominance
- blood groups AB - alleles = I^A I^B
explain how codominance affects the phenotypes if both parents are heterozygous for sickle cell aneamia.
and state the ratio.
homozygous - heamoglobin - H^N H^N
homozygous - sickle cell aneamia - H^S H^S
heterozygous - sickle cell - H^S H^N
- so here some cells are sickle shaped and some arent.
2 heterozygous parents result in the ratio - 1:2:1
1 - unaffected
2 - sickle cell trait (heterozygous)
1 - Sickle cell aneamia (homozygous)
give an example where a gene may have multiple alleles (more than 2)
Blood groups AB, A, B, and o, have the following alleles -
I^A, I^B, I^o
here A and B are dominant and o is recessive.
epistasis and what are the different types.
only occurs hen 2 or more genes contribute to the same phenotype = when the expression of one gene masks or modifies the expression of another gene (aka the hypostatic gene) at a different locus.
different types include -
- dominant epistasis
- recessive epistasis
- duplicate (redundant) gene action.
what is the expected ratio when more than 1 characteristic is inherited from 2 different genes.
Using a dihybrid cross
9:3:3:1
what is the ratio observed when you cross 2 copies of recessive epistatic alleles. (dihybrid cross)
(homo recessive x homo dominant)
9:3:4
(dominant both:dominant epistatic recessive other:recessive epistatic.)
what is the ratio observed when you cross 2 copies of dominant epistatic alleles. (dihybrid cross)
(homo recessive x homo dominant)
12:3:1
(dominant both:dominant epistatic recessive other:recessive epistatic.)
polygenic inheritance
involves the interaction of multiple genes to control the expression of a single trait.
- the cumulative effect of multiple alleles at diferent gene loci control the gene expression.
give an example of epistasis
windo’s peak is controlled by one gene whilst the gene for baldness is controlled by another.
if you have the alleles for baldness, it does’nt matter if you have the alelle for a widow’s peak or not cos either way you will be bald.
- the baldness genes are epistatic for the widow’s peak gene.
what are modifier genes. give an example.
they dont produce a trait themselves, however they influence the expression or severity ot traits produced by other genes.
- eg in cystic fibrosis, certain modifier genes can influnece the severity of lung disease amongst people with the same CFTR mutation.
describe a relationship between mutations and epistais
the effect of a mutation on one gene might be masked or altered by a mutation in another gene.
describe a regulatory mechanism that can mask the expression of another gene and is this the same as epistasis?
No this isnt the same as epistasis.
- when the repressor protein of one gene binds to the promotor of another gene, the transcrption is inhibited. and the expression is essentially ‘masked’
- but can’t be the same as epistasis, which is just the interaction, that affects phenotypic expression.
describe complementary gene interaction
when 2 different genes work together to form a specific trait. the presence of at least one dominant allele at both gene loci is needed to express the phenotype.
- if one is homozygous recessive, then it may be masked = different phenotype.
give an example, of complementary gene interaction in the flower colour in sweet peas. and give the phenotypic ratio.
Take for example the genes C and P.
alleles include
C and c = C needed for the production of the colour precursor.
P and p = P needed for the conversion of precursor into the final pigment.
to get a purple colour both dominant C and P are needed
- any other genotypes will give a white flowered phenotype. (homozygous recessive)
ratio = 9:7 purple:white
without the C and P alleles, this pathway cannot continue, showing how they are complementary to each other.
what is supplementary gene interaction
genes that contain non-alleic pairs of genes. they both have an effect on the triat.
- 1st gene is dominant and can be expressed on it’s own among the non-alliec genes.
- 2nd gene is also dominant but only expresses it when the first gene is present.
gene redundancy (in terms of genetic interactions)
presence of multiple genes with similar functions, if one gene is mutated or inactive, the other redundant genes can compensate and maintain overallu function.
pleiotropy
when a single gene can affect multiple phenotypic traits, eg - a gene associated with a certain enzyme may impact several biochemical pahtways.
