Inheritance 2 Flashcards
What do Mendel’s first two laws describe?
The principles of allele segregation and independent assortment of loci during meiosis
Give some examples of non-mendelian inheritance
*Genetic linkage= when alleles at separate loci are inherited together and thus do not obey Mendel’s law of independent assortment.
*Cytoplasmic inheritance=Some traits are inherited from organellar DNA. Genetic material is inherited often only maternally.
Meiotic drive= where intragenomic conflict arises from the preferential inheritance of one allele over another (‘ultra-selfish’ genes).
When are alleles less likely to be split up?
Alleles from loci that are located close together on the same chromosome are less likely to be ‘split’ apart by crossing over and recombination. Such loci are described as being linked.
What is intragenomic conflict
When genes or alleles evolve ways of transmitting themselves preferentially in detriment of the transmission of other genes that reside in the same genome.
What is meiotic drive?
Any process which causes some genetic variants to be over-represented in the gametes which are formed during meiosis. e.g T locus in mice, if they are recessive tt, they are sterile
90% of Tt individuals transmit t and not T to their offspring so
t is a segregation distorter
B chromosomes
B chromosomes (= ‘supernumerary’ or ‘accessory’ chromosomes) can also be transmitted in germline cells more frequently than expected from Mendelian inheritance
expectations, and can accumulate ‘selfishly’.
What did Mendel’s laws mean in relation to recessive alleles?
Recessive traits would disappear over time however recessive allele frequency does not become rarer throughout generations
What are the assumptions of the H-W model?
Infinite population size
Random mating
No mutations
No selection
Equal allele frequencies among males and females
If populations deviate from H-W expectations, then we say that they are not in H-W equilibrium and it indicates that one or several or these assumptions are not being met. The H-W model is an important null model to test population genotype and allele frequencies against evolution
Polygenic/Quantitative characters
Individual heritable characters are often controlled by groups of several genes.
Variation is continuous or quantitative (‘adding up’) - also called quantitative inheritance
What are factors of continuous characters?
more loci leads to a smoother distribution e.g height
*Controlled by several loci, each with small effect
*they still follow Mendelian inheritance patterns
*Discrete traits tend to be generated by single loci, continuous traits by many loci
*The substitution of one allele for another is often undetectable
*The environment often has a substantial influence
*Different genotypes can produce the same phenotype
What is Phenotypic plasticity?
when a genotype expresses different phenotypes depending on the environment
If different genotypes have different kinds of phenotypic plasticity, we call the effect genotype-environment interaction.
What is the total phenotypic variation due to?
*Environment
*Genetics
*Interaction between genes and environment
What is the point of hardy and weinburg
Hardy and Weinberg demonstrated that population allele frequencies should remain constant if they are inherited in a Mendelian fashion, under certain conditions. This has become an important ‘null model’ against which we can test whether evolutionary processes such as selection are occurring in populations.
