extensions to mendel unit 4 genetics. color blindness x-linked recessive condition xxcxc xxxxx c...
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Physiology of Color Blindness• Defective Cone Cells which detect color
• Shift the wavelengths of light so the signal sent to the brain is the wrong color.
• L, M and S wavelengths (Long, Medium and Short)
• Mixture of abnormalities with cones (missing…)Most Common- M Cone
Questions1) Can a female inherit colorblindness from dad?
Yes - nearly 100%
2) Does this mean that she will be colorblind? No - need to factor in the other X chromosome from
mom
3) Why?
It’s a recessive XcX-Normal vision XcXc-colorblind
4) Can a male inherit color blindness from dad?
No, a male only inherits the Y chromosome from dad
1 Incomplete or Codominance - Two or more alleles exist, but none is dominant to the other/s
2 Multiple alleles for a single gene3 Epistasis - interactions b/t more than one
gene4 Sex-linkage - locus of a gene is on a sex
chromosome5 Sex influenced or limited expression is
influenced or limited by gender (hormones…)
Exceptions to Mendelian ratios:
• Incomplete or codominance - Two or more alleles exist, but none are dominant to the other
• Incomplete dominance results in blending of the parental traits
• Example: In some flowers red crossed with white results in pink F1 generation
Incomplete Or Codominance
RED +
• F2 results shown below
Incomplete Or Codominance
CRCWCRCR CWCW
CRCR
CRCW
CRCW
CWCW
CR CW
CR
CW
F2 Generation
In the F2 generation a 1:2:1 ratio results of red to pink to white
1:2:
Epistasis
B CA 21
If the gene for enzyme 1 was knocked out, the flower would be colorless
B CA 21
X
pathway produces a red pigment, C, in flowers and that A is a colorless precursor and B is a yellow intermediate
1F1n2F2n X 1F1n2F2n
Confusing
1F2n
1n2F
1n2n
1F2F
1n2n1n2F1F2n1F2F
1F1n2F2n1F1n2F2F1F1F2F2n
1F1n2n2n1F1n2F2n1F1F2n2n1F1F2F2n
1n1n2F2n1n1n2F2F1F1n2F2n1F1n2F2F
1n1n2n2n1n1n2F2n1F1n2n2n1F1n2F2n
1F1F2F2F
1F2n
1n2F
1n2n
1F2F 1F1n2F2n1F1n2F2F1F1F2F2n
1F1n2n2n1F1n2F2n1F1F2n2n1F1F2F2n
1n1n2F2F1F1n2F2n1F1n2F2F
1n1n2n2n1n1n2F2n1F1n2n2n1F1n2F2n
1F1F2F2F
1F1n2F2n X 1F1n2F2n
Mendelian- 9:3:3:1
1F2n
1n2F
1n2n
1F2F
1n2n1n2F1F2n1F2F
1F1n2F2n1F1n2F2F1F1F2F2n
1F1n2n2n1F1n2F2n1F1F2n2n1F1F2F2n
1n1n2F2n1n1n2F2F1F1n2F2n1F1n2F2F
1n1n2n2n1n1n2F2n1F1n2n2n1F1n2F2n
1F1F2F2F
1F1n2F2n X 1F1n2F2n Epistatic
1F2n
1n2F
1n2n
1F2F
1n2n1n2F1F2n1F2F
1F1n2F2n1F1n2F2F1F1F2F2n
1F1n2n2n1F1n2F2n1F1F2n2n1F1F2F2n
1n1n2F2n1n1n2F2F1F1n2F2n1F1n2F2F
1n1n2n2n1n1n2F2n1F1n2n2n1F1n2F2n
1F1F2F2F
– 10:3:3 = (9+1):3:3– 10:6 = (9+1):(3+3)– 13:3 = (9+1+3):3
A 9:4:3 Ratio
– 9:7 = 9:(3+3+1)– 12:3:1 = (9+3):3:1– 12:4 =(9+3):(3+1)
A ratio made up of some combination of 9:3:3:1 is generally a good hint that epistasis is at work
A biochemical pathway like this one = 9:4:3 ratio as long as there are two alleles each of which
behaves in a simple dominant/recessive way The 9:4:3 ratio is really a 9:(3+1):3 ratio Other possible phenotypic ratios for a dihybrid
cross involving epistasis are below: