Beyond Mendel’s Laws of Inheritance Incomplete dominance Hybrids have “in-between” appearance...
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![Page 1: Beyond Mendel’s Laws of Inheritance Incomplete dominance Hybrids have “in-between” appearance – RR = red flowers – rr = white flowers – Rr = pink flowers.](https://reader036.fdocuments.net/reader036/viewer/2022070410/56649eab5503460f94bb051b/html5/thumbnails/1.jpg)
Beyond Mendel’s Lawsof Inheritance
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Incomplete dominance• Hybrids have “in-between” appearance– RR = red flowers– rr = white flowers– Rr = pink flowers• make 50% less color
![Page 3: Beyond Mendel’s Laws of Inheritance Incomplete dominance Hybrids have “in-between” appearance – RR = red flowers – rr = white flowers – Rr = pink flowers.](https://reader036.fdocuments.net/reader036/viewer/2022070410/56649eab5503460f94bb051b/html5/thumbnails/3.jpg)
Incomplete dominance
100%
100% pink flowers1st
generation(hybrids)
true-breedingred flowers
true-breeding white flowersX
25%white2nd
generation
25%red
1:2:1
50%pink
self-pollinate
![Page 4: Beyond Mendel’s Laws of Inheritance Incomplete dominance Hybrids have “in-between” appearance – RR = red flowers – rr = white flowers – Rr = pink flowers.](https://reader036.fdocuments.net/reader036/viewer/2022070410/56649eab5503460f94bb051b/html5/thumbnails/4.jpg)
Incomplete dominance
RW x RW
R Wmale / sperm
fem
ale
/ eg
gs
RR RW
RW WW
50%
25% 25%
50%
25% 25%
%genotype
%phenotype
1:2:1
1:2:1
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Codominance• Equal dominance– human ABO blood groups– 3 version • A, B, i• A & B alleles are codominant• both A & B alleles are dominant
over i allele
– the genes code for different sugars on the surface of red blood cells• “name tag” of red blood cell
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![Page 7: Beyond Mendel’s Laws of Inheritance Incomplete dominance Hybrids have “in-between” appearance – RR = red flowers – rr = white flowers – Rr = pink flowers.](https://reader036.fdocuments.net/reader036/viewer/2022070410/56649eab5503460f94bb051b/html5/thumbnails/7.jpg)
Sex chromosomes
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Sex-linked Traits• Sex chromosomes have other genes on them,
too– especially the X chromosome– hemophilia in humans• blood doesn’t clot
– Duchenne muscular dystrophy in humans• loss of muscle control
– red-green color blindness• see green & red as shades of grey
X X
X Y
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Sex-linked traits
XH
Y
XHXhXH
Xh
XHY
2 normal parents,but mother is carrier
male / sperm
XH Ymale / sperm
XHXH XHY
XHXh XhY
XH
Xhfe
mal
e /
eggs
![Page 10: Beyond Mendel’s Laws of Inheritance Incomplete dominance Hybrids have “in-between” appearance – RR = red flowers – rr = white flowers – Rr = pink flowers.](https://reader036.fdocuments.net/reader036/viewer/2022070410/56649eab5503460f94bb051b/html5/thumbnails/10.jpg)
![Page 11: Beyond Mendel’s Laws of Inheritance Incomplete dominance Hybrids have “in-between” appearance – RR = red flowers – rr = white flowers – Rr = pink flowers.](https://reader036.fdocuments.net/reader036/viewer/2022070410/56649eab5503460f94bb051b/html5/thumbnails/11.jpg)
![Page 12: Beyond Mendel’s Laws of Inheritance Incomplete dominance Hybrids have “in-between” appearance – RR = red flowers – rr = white flowers – Rr = pink flowers.](https://reader036.fdocuments.net/reader036/viewer/2022070410/56649eab5503460f94bb051b/html5/thumbnails/12.jpg)
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One gene: many effectsmost genes are affect many traits
1 gene affects more than 1 traitdwarfism (achondroplasia)gigantism (acromegaly)
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Acromegaly: André the Giant
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Many genes: one trait• Polygenic inheritance– additive effects of many
genes– humans• skin color• height• weight• eye color• intelligence• behaviors
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Human skin color• AaBbCc x AaBbCc – can produce a wide
range of shades– most children =
intermediate skin color – some can be very light
& very dark
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Albinism
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Coat color in other animals• 2 genes: E,e and B,b– color (E) or no color (e)– how dark color will be: black (B) or brown (b)
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Environment effect on genes• Phenotype is controlled by
both: environment & genesHuman skin color is influenced by both genetics & environmental conditions
Color of Hydrangea flowers is influenced by soil pH
Coat color in arctic fox influenced by heat sensitive alleles
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Dominant ≠ most common allele
• Because an allele is dominant does not mean…– it is better, or– it is more common
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Polydactyly individuals are born with extra fingers or toes
recessive allele far more common than dominant only 1 individual out of 500
has more than 5 fingers/toes so 499 out of 500 people are homozygous recessive (aa)
the allele for >5 fingers/toes is DOMINANT & the allele for 5 digits is recessive