The The ChromosomeChromosome Theory of Theory of InheritanceInheritance

Chpt. 15Chpt. 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 Sex chromosomeschromosomes--

AutosomesAutosomes

Sex Sex chromosomeschromosomes--

vary within species --> -->

-->-->

--> -->

Sex Sex chromosomechromosomess--

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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 1902Genes have specific locations (loci) on chromosomes

chromosomes undergo segregation and independent assortment.

The Chromosome Theory of

Inheritance

tracking tracking 2 genes 2 genes on on different different chromosomchromosomes ines in their their homologouhomologous pairs.s pairs.

Thomas Hunt -Morgan

11stst to to associate associate specific specific genes on genes on specific specific chromosomeschromosomes

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 eyesor + = red eyes

Examples

•“Mutant” =Cy = Curly wings

Wild Type =Cy+ = Normal wings

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Evidence Evidence for for Sex Sex LinkageLinkagefemale red female red eyes eyes X X

male white male white

eyeseyes

F1 --> 4:0 F1 --> 4:0 REDRED

You would expect this with Mendel… would you not?

Evidence Evidence for for Sex Sex LinkageLinkagefemale red female red eyes eyes X X

male red male red

eyeseyes

F2 --> 3:1 F2 --> 3:1

BUT BUT ONLYONLY malesmales had had white eyes??white eyes??

F2F2

eye color eye color linked to linked to gendergender

Examples

•Recessive mutant:w = white eyes

w+ = red eyesor + = red eyes

eye color eye color linked to linked to gendergender

50% males 50% males had red had red eyes.eyes.

50% males 50% males had white had white eyes.eyes.

0% females 0% females had had white white eyes.eyes.

Evidence Evidence for for Sex Sex LinkageLinkage50% males 50% males had red eyes.had red eyes.

50% males 50% males had white had white eyes.eyes.

0%0% females females had had white white eyes.eyes.

Fruit Fly Chromosomes

Linked GenesLinked Genes (not (not sex-linked sex-linked

genes)genes)

•Genes are on the Genes are on the same same

chromosome, chromosome, therefore passed therefore passed along as a “unit”along as a “unit”

these DEVIATE from Mendel’s

“norm”

A

B

Ratios mimic monohybrid crosses.. But it is a dihybrid cross.

Linked GenesLinked Genes (not x-linked)

1:1:11:1:1:1:15:5:15:5:1:1:1

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

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“Well now, THAT’s

confusing

Linked GenesLinked Genes (not x-linked)

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Something’s goofy

Recombination due to

crossing over

in linked genes

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“YES!!! I

remember this stuff!!

”

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

Crossing-Over

Alfred Sturtevant

RecombinationRecombination FrequencyFrequency==

# of recombinants # of recombinants total offspringtotal offspring

•gives a rough estimate gives a rough estimate of how often of how often recombination occurs.recombination occurs.

•used to map genes in used to map genes in relation to one relation to one another.another.

X 100

RecombinationRecombination FrequencyFrequency==

•The farther apart

two genes, the higher

the probability that

a X-over will occur.

•The higher the Recombination

Frequency

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“YES!!! I

remember this stuff!!

”

Map of 3 genes relative to each other (genes: b,

r, vg)

b - vg = 17r - vg = 9.5

b - r = 7.5

Map of 3 genes relative to each other

b - vg = 17r - vg = 9.5

b - r = 7.5

7.5

b vg

17%

(genes: b, r, vg)

Map of 3 genes relative to each other

b - vg = 17r - vg = 9.5

b - r = 7.5

7.5

b r vg

17%

(genes: b, r, vg)

Map of 3 genes relative to each other

b - vg = 17r - vg = 9.5

b - r = 7.5

7.5

b r vg

9.5

17%

(genes: b, r, vg)

Map of 3 genes relative to each other

Map of 3 genes relative to each other

Gene MapGene Map - -

•Relative Relative position position using map using map units.units.

•Obtained Obtained from from

Recombination Recombination Frequency DataFrequency Data

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Calico Cats.

Calico Cats.

Result - body cells are a mosaic of X

types.