Flashcards in Mendelian Genetics Deck (19):
What is Mendel’s first law?
Alternative versions of a gene account for variations in inherited characters
What is Mendel’s second law?
Each character is independently inherited during gamete formation - each pair of alleles of a given gene are independently inherited from alleles at a different gene locus
Causes of deviations from Mendelian ratios
Co-dominance and multiple alleles
What is the difference between co-dominance and incomplete dominance?
In co-dominance heterozygote expressed in both forms - offspring looks like both parents at once
Incomplete dominance the heterozygote forms an intermediate phenotype - looks like a blend of both parents
What is pleiotropy?
When one gene influences 2 or more phenotypic traits
What is allelic heterogeneity?
A similar phenotype produced by different alleles of the same gene
What is locus heterogeneity?
A similar phenotype is produced by mutations at different gene loci
What is incomplete penetrance?
Not all individuals carrying a deleterious gene express the associated trait
What is linkage?
When particular gene loci are inherited jointly
Who discovered linkage?
Bateson and Punnet
Soon after 1900
What is recombination frequency?
A measure of how often recombination occurs between genes, measured as the fraction of offspring that inherit recombinant proteins
What is recombination frequency measured in?
How do recombination frequencies determine where genes are relative to each other on a chromosome?
Recombination is less likely between genes that are closer, because there is less DNA between them
Why don’t gene mapping recombination frequencies always add up to 100%?
Double crossing over can occur
What is another name for a sex chromosome?
What is X inactivation?
The inactivation of one of the two copies of the X chromosome in all female mammals. Happens during embryonic development
What does the inactivated X chromosome become?
It condenses into a compact object called a Barr body. Most of its genes aren’t expressed and it lies alongside the nuclear envelope
Why does X-inactivation not cause colourblindness?
The X chromosome is inactivated on a cell-by-cell basis - any daughter cell from one of the original embryonic cells will have the same X chromosome inactivated. As the eye comes from several different cells, some will have one X chromosome inactivated whilst others will have the other one inactivated