Where do recessive mutations generally occur?
Haplosufficient genes
Where do dominant mutations generally occur?
Haploinsufficient genes
What is the cellular basis of equal segregation of alleles?
Segregation of homologous chromosomes at meiosis
When is Mendelian single-gene segregation useful?
In identifying mutant alleles underlying many human disorders
Why is pedigree analysis useful?
Can reveal the mode of inheritance and thereby predict genetic risk
How does sex-linked inheritance arise?
Genes on the X chromosome have no counterparts on the Y chromosome and therefore show a single -gene
inheritance pattern that differs in the two sexes
What are dihybrid crosses and what ratios are observed?
Where the two gene pairs are on different chromosome pairs, each individual gene pair shows equal segregation at meiosis. Because nuclear spindle fibers attach randomly to centromeres, the two gene pairs assort independently. In a testcross of a dihybrid with a double recessive, a 1:1:1:1 ratio of phenotypes is observed. If such a dihybrid is selfed, a 9:3:3:1 ratio is observed. Both these ratios are diagnostic of independent assortment.
What is the main function of meiosis?
To produce recombinants, new combinations of the haploid genotypes that united to form the meiocyte.
What is the main source of recombination?
Independent assortment
What did certain dihybrid testcrosses in Drosophila reveal and what was the explanation?
A deviation from Mendel’s Second law. Morgan postulated linkage as an explanation
What does linkage explain and how is it explained?
How parental alleles stay together but not how recombinant (non-parental) combinations
arise. The explanation for this lies in crossing over.
What does crossing over involve?
Crossing over involves a physical break and reunion of chromosome parts at the 4-chromatid stage of meiosis I.
What did Sturtevant devise with what use?
A way of determining the distance between genes on a linkage map, based on RF. RF values expressed as percentages can be used as map units to construct a chromosomal map showing the relative
positions of loci.
When are 3-factor crosses useful?
For finding the precise order and relative positions of genes on
chromosomes
