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Mendelian genetics
Uni of Notts, Genes, Molecules, and Cells, first year
| Term | Definition |
|---|---|
| Pleiotropy | Genes producing protein that each cause multiple phenotypic effects. This is due to proteins being involved in many bodily systems & affecting each differently |
| Cases where Mendelian genetics don’t determine frequency of a characteristic | They can predict frequency of a gene but not a phenotype which is determined by the environment Only applies to regular (autosomal) inheritance & not other kinds (I.e., Co-dominance, sex linked, autosomal linked, epistasis, pleiotropy etc.) |
| Alleles | Subtle mutations of the same gene with slightly different base sequences, there can be many alleles of the same gene |
| Haplosufficiency | When a single functional (wild-type) allele of a heterozygous gene in a diploid organism provides enough protein to fulfil its purpose in the body |
| Haploinsufficiency | When a single functional (wild-type) allele of a heterozygous gene in a diploid organism doesn’t provide enough of its protein compared to the mutated allele, stopping the reaction from going ahead |
| ‘Wild type’ | Specific alleles carried by individuals in a population which, when expressed, provides their phenotypic traits |
| How dominance works | Wild type allele is usually dominant to non-functional allele since in many cases reactions can still take place with reduced concentration of proteins, usually enzymes since they're catalysts - haplosufficiency |
| How non-functional alleles can become dominant: Haploinsufficiency | Some processes require exact levels of protein & one functioning allele may not be enough, this can lead to haploinsufficiency syndromes like William's syndrome & breast cancer |
| How non-functional alleles can become dominant: Quaternary structure | If non-functional proteins are incorporated into a quaternary structure then it makes the whole multimer non-functional which means that other proteins & pathways are affected |
| Polygenic | Opposite of Pleiotropic, many different genes contribute to the same characteristic. Example of genetic interaction |
| Genetic interaction example - Why the expression of 2 genes can lead to so many skin colours of peppers | One gene codes for the expression of a pigment in the skin colour & the other codes for the expression of chlorophyll in the skin, depending on the combination of expression, this will lead to different phenotypes |
| Epistasis | When the expression of one gene affects (masks or enhances) the expression of a gene on a different locus |
| Hypostatic relationship | When the expression of a gene is controlled by the expression of another gene, opposite of an epistatic relationship |
| How a biochemical pathway can be affected by epistasis | They're determined by enzymes catalysing intermediates, each enzyme depends on previous enzymes in the pathway to create an appropriate substrate meaning their genes are hypostatic to the previous enzyme's genes |
| Penetrance | Probability an individual with a certain genotype will display it in their phenotype (this varies as a percentage of a population) |
| Expressivity | Degree of phenotypic change change caused by a genotype, this varies between characteristics (particularly polygenic ones) |
| A cause behind variable penetrance & expressivity | Many modifier genes involved in epistasis cause a large variance in expression (expressivity & probability of being expressed (penetrance) |
| Genetic maps | Diagrams showing simplified relative distance between genes or markers on a chromosome as well as the type of inheritance & linkage |
| How genetic maps are designed | The distance between genes is based on the frequency of recombination during inheritance which increases the further genes are from one another, measured in centimorgans (1cM = 1% probability) |
| Physical genome map | Diagram showing the exact distance between each gene, measured in base-pairs from a sequenced genome |
Created by:
Beech47
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