Lecture 1 Flashcards
What is the difference between Mendelian and quantitative genetics?
Mendelian genetics is concerned with the inheritance of differences between individuals that are of kind, whereas quantitative genetics is concerned with the inheritance of differences between individuals that are of degree.
Give an example of a Mendelian genetic trait
Horns in cattle (POLL gene)
BTA1 - Polled P Horned p
Give two examples of quantitative traits.
Birth weight and milk yield
Define Gene.
Originally defined as a physical unit of heredity.
Best defined as the unit of inheritance that occupies a specific locus on a chromosome and that conveys a set of DNA sequences that are required to produce a polypeptide or a RNA.
Define locus.
The site on a chromosome where a gene is located.
Any one of the alleles of a gene may be present at this site.
Define alleles.
Different forms or variants of a gene found at the same locus on a chromosome.
Assumed to arise by mutation.
What are Mendel’s laws?
The principle of segregation
The principle of independent assortment
Why is it possible with Mendelian laws to get the same frequency of offspring?
Because the genes were in different chromosomes and were independent. If the allele was on the same chromosome this would not be the case and gametes would have different frequencies and be linked. The chromosomes need to crossover (recombination).
What indicates complete linkage?
P(recombination)=0
What value indicates crossover linkage?
P(recombination) less than 0.5 (<0.5)
What value indicates independent assortment?
P(recombination) = 0.5
They are behaving as though they are on different chromosomes
Where does the 0.5 come from, in reference to linkage and independent assortment?
It is 0.5 because half of the gametes produced will be the same as the originals and half will be new gametes. So the maximum possible probability of recombination is 0.5.
A crossover occurred between A and B, and the resulting gametes were the same, why?
A and B must be sister chromatids. Recombination can only occur/have an effect on the gametes if they are non-sister chromatids.
