- Exception to law of independent assortment
- When F1 plants self-pollinated, four phenotypes did not follow 9:3:3:1 ratio
- gene linkage: pattern of inheritance in which all the genes of a given chromosome are linked
<<Crossing over and recombination of Linked Genes>>
- autosomes: chromosomes other than the X and Y chromosomes
- diploid nuclei have 2 of each type of autosome (in humans there’s 22)
- Autosomal gene linkage: linkage when genes are on the same autosome
- Sex linkage: linkage when genes are located on the X chromosome
- Crossing over: incomplete linkage between pairs of genes in a linkage group resulting new allele combinations
- Recombination: formation of a chromosome or DNA with a new combination of alleles
- Recombinant: different combination of characters from either of the original parents
<<Polygenic Inheritance and Continuous Variation>>
- Polygenic inheritance: two or more genes affecting the same character
- closer to the normal distribution = more than one gene is involved
- variation in polygenic inheritance is continuous
- differences in phenotype between the classes are subtle and effects of environment blue differences making it undetectable
- e.g. human skin color environment (sunlight) and some genes
<<Inheritance of Skin Color>>
- mutations of few genes can prevent melanin production (black pigment) = leads to albinism
- mutation SLC4A5 = causes paler skin
Gene Linkage in Zea Mays (p.159)
1) Cc = colored, starchy (dominant) Ss = white, waxy (recessive) The F1 genotype would be CcSs, thus when the F1 is multiplied by F1:
So the CcSs x CcSs would produce offsprings in the dihybrid ratio of 9 colored, starchy: 3 colored, waxy: 3 white, starchy: 1 white, waxy
2) The genes for colored/white and starchy/waxy are linked because they do not follow the dihybrid typical ratio of 9:3:3:1.
3) F1 = colored and non-shrunken
The ratio is 1 colored, shrunken: 1 colored, shrunken: 1 white, non-shrunken: 1 white, shrunken.
4) Actual frequencies do not become a 1:1:1:1 ratio and thus genes are linked.
5) Starchy/waxy and non-shrunken/shrunken are linked to each other because they are both linked to color.