Chromosomal Inheritance
description
Transcript of Chromosomal Inheritance
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Chi-square Statistical Analysis You and a sibling flip a coin to see who has to take out the trash. Your sibling
grows skeptical of the legitimacy of your coin because “tails” always seems to win.
You decide to test it out by flipping the coin 20 times.
Poss. Outcomes
TailsHeads
Obs.
137
Exp.
1010
(o-e)2/e
.9
.91.8c2 value
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Chi-square Statistical AnalysisDetermines the probability that observed data could result from expected conditions1. For each phenotype, calculate
(Observed – Expected)2 / (Expected)2. Add up your figures. This is the chi-square value
3. Degree of freedom (df) = (# of phenotypes – 1)4. Find the probability in the table.
c2 = (o-e)2 eS
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Fruit Fly Eye ColorP: Red-eyed female x White-eyed male F1: 100 Red-eyed flies F2: 75 Red-eyed, 25 white-eyedWrite out Punnett squares for both crosses.
75 25100
w+ = redw = white
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Fruit Fly Eye ColorP: Red-eyed female x White-eyed male F1: 100 Red-eyed flies F2: 75 Red-eyed, 25 white-eyed
75 25
25 males
50 females, 25 males
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Chi-square Statistical Analysis Our F1 cross produces 100 offspring If we assume eye color and gender are unlinked,
w+ = red w+w ♀ x w+w ♂w = white Then we expect… But we got…
Expected Phenotype
37.5 Red ♀12.5 White ♀37.5 Red ♂12.5 White ♂
Observed
500
2525
Calc.
4.212.54.2
12.5
33 c2 value
Only a 0.000027% probability
Therefore, eye color and gender are linked
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X-Linkage
The gene with the white-eyed mutation is on the X-chromosome
Homozygous Dominant
Xw+Xw+
Hemizygous Recessive
XwY
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Practice Problems1. Colorblindness is due to a recessive x-linked
allele. What are the chances of a normal male and a carrier female having a colorblind son as their first child?
2. Why are males more likely than females to have recessive x-linked traits?
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Practice ProblemsIn sesame plants, the one-pod condition, (A) is dominant to the 3-pod condition (a), and normal leaf (B) is dominant to wrinkled leaf (b). An AaBb plant is testcrossed to produce the following offspring:
11 one-pod, normal12 one-pod, wrinkled7 three-pod, normal10 three-pod, wrinkled
Is this data likely if this is a case of independent assortment?
What about…11012070100?
What about…182317?
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A
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A a
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Gametes
ABab
Parental
ABab
Recomb.
AbaB
AaBb
AaBb
A a
Bb
ORAbaB
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Earlobes & Toes (Independent Assortment)P: FFTT x fftt
all FfTt(free earloes and 2nd toe longer)
Testcross of F1 individualsFfTt x fftt:
¼ Free, 2nd toe¼ Free, great toe¼ attached, 2nd toe¼ attached, great toe
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Earlobes & Toes (Linked) P: FFTT x
fftt F1: FfTt F1 Testcross
FfTt x fftt
F
T
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f
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F
T
f
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½ Att,Grt Toe
½ Free,2nd Toe
IndependentAssortment
¼ Free, 2nd
¼ Free, Grt¼ Att, 2nd
¼ Att, Grt
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Earlobes & Toes (Linked + Recombination)
F
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fF
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Parental OffspringFfTt (free, 2nd)
fftt (attached, great)
Recombinant OffspringFftt (free, great)ffTt (attached, 2nd)
Recombination frequency = (# of recomb. offspring) (total offspring)
18 17 2 3
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Genetic Recombination
Genes farther apart are more likely to cross over
Greater distance greater RF Enables us to map genes on a chromosome
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Genetic Recombination b / c = 9% (9 map units or
centimorgans) v / c = 9.5% (9.5 mu) b / v = 17% (17 mu) According to our map, b/v = 18.5 mu
(not 17) Double crossover leads to lower than
expected recombinant frequencies
b
c9mu
v
v
OR
9.5mu
9.5mu
18.5mu
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ReviewConstruct a linkage map given the following
information:a-b 7.2 %b-c 3.5 %a-c 3.9 %b-d 9.6 % c-d 6.3 %How many recombinant organisms would you
expect to find out of 1000 offspring from a cross between AaDd and aadd organisms?