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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.