The Chromosome Theory of Inheritance Chpt. 15 Chpt. 15.

1866 Mendel’s paper 1875 process of mitosis revealed 1890 process of meiosis revealed 1902 realization that chromosomes were Mendel’s “factors” Putting the pieces together

Sex chromosomes- Autosomes

--> vary within species -->-->-->

Sex chromosomes -

In 1902 Sutton suggested that "the association of paternal and maternal chromosomes in pairs and their subsequent separation during the reduction division...may constitute the physical basis of the Mendelian law of heredity." His "The Chromosomes in Heredity" was published in 1903.

Walter Sutton 1902 Genes have specific locations (loci) on chromosomes chromosomes undergo segregation and independent assortment. The Chromosome Theory of Inheritance

tracking 2 genes on different chromosomes in their homologous pairs.

Thomas Hunt - Morgan 1 st to associate specific genes on specific chromosomes

Thomas Hunt Morgan Utilized:Drosophila melanogaster fruit fly 3 pairs autosomes 1 pair sex chromosomes

Thomas Hunt Morgan Utilized: Drosophila melanogaster can reproduce a generation in two weeks.

Fruit Fly Chromosomes

Genetic Symbols Mendel - use of uppercase or lowercase letters. T = tall t = short Morgan: symbol from the mutant phenotype (for fruitflies). + = wild phenotype (predominant)

Examples Recessive mutant: w = white eyes w+ = red eyes or + = red eyes

Examples “Mutant” = Cy = Curly wings Wild Type = Cy+ = Normal wings

Evidence for Sex Linkage female red eyes X male white eyes F1 --> 4:0 RED F1 --> 4:0 RED You would expect this with Mendel… would you not?

Evidence for Sex Linkage female red eyes X male red eyes F2 --> 3:1 BUT ONLY males had white eyes?? F2

eye color linked to gender

Examples Recessive mutant: w = white eyes w+ = red eyes or + = red eyes

eye color linked to gender 50% males had red eyes. 50% males had red eyes. 50% males had white eyes. 0% females had white eyes.

Evidence for Sex Linkage 50% males had red eyes. 50% males had red eyes. 50% males had white eyes. 50% males had white eyes. 0% females had white eyes. 0% females had white eyes.

Fruit Fly Chromosomes

Linked Genes (not sex-linked genes) Genes are on the same chromosome, therefore passed along as a “unit”Genes are on the same chromosome, therefore passed along as a “unit” these DEVIATE from Mendel’s “norm” A B uRuRatios mimic monohybrid crosses.. But it is a dihybrid cross.

Linked Genes Linked Genes (not x-linked)1:1:1:1 5:5:1:1

IF genes are linked, we would NOT expect any offspring to have different characters from that of the parents… THAT was not the case though, the offspring were, in fact different

“Well now, THAT’s confusing

Linked Genes Linked Genes (not x-linked)

Something’s goofy

Recombination due to crossing over in linked genes

“YES!!! I remember this stuff!!”

u Breaks up linkages and creates new ones. u Recombinant offspring formed that doesn't match the parental types. Crossing-Over

Alfred Sturtevant

Recombination Frequency= # of recombinants total offspring gives a rough estimate of how often recombination occurs. gives a rough estimate of how often recombination occurs. used to map genes in relation to one another. used to map genes in relation to one another. X 100

Recombination Frequency= The farther apart two genes, the higher the probability that a X-over will occur. The higher the Recombination Frequency

“YES!!! I remember this stuff!!”

Map of 3 genes relative to each other (genes: b, r, vg) b - vg = 17 r - vg = 9.5 b - r = 7.5

Map of 3 genes relative to each other b - vg = 17 r - vg = 9.5 b - r = bvg 17% (genes: b, r, vg)

Map of 3 genes relative to each other b - vg = 17 r - vg = 9.5 b - r = brvg 17% (genes: b, r, vg)

Map of 3 genes relative to each other b - vg = 17 r - vg = 9.5 b - r = brvg % (genes: b, r, vg)

Map of 3 genes relative to each other

Gene Map - Relative position using map units.Relative position using map units. Obtained from Recombination Frequency DataObtained from Recombination Frequency Data

Calico Cats.

u Result - body cells are a mosaic of X types.