Les son 17: P atterns of Inheritance
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Lesson 17: Patterns of Inheritance
blackwellpublishing.com
www.microscopy-uk.org.uk/mag/imgjul06/Image14.jpg www.purplemoon.com/Stickers/peas-earth.jpg
Roots: Di = 2mono = 1Homo = sameHetero = differentHemo = blood
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Gregor Mendel
• Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas– used good experimental design– used mathematical analysis
• collected data & counted them
– excellent example of scientific method
http://joefelso.files.wordpress.com/2007/04/mendel2.jpg
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Pollen transferred from white flower to stigma of purple flower
anthersremoved
all purple flowers result
Mendel’s work
• Bred pea plants– cross-pollinate
true breeding parents– raised seed & then
observed traits– allowed offspring
to self-pollinate & observed next generation
?
self-pollinate
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Mendel collected data for 7 pea traits
Each trait is represented by a specific allele on a specific chromosome.
Allele = genes that determine a specific trait.
http
://w
ww
.bio
.mia
mi.e
du/~
cmal
lery
/150
/men
del/7
trai
ts.jp
g
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2nd
generation
3:175%purple-flower peas
25%white-flower peas
Parents
100%1st
generation(hybrids)
100%purple-flower peas
Xtrue-breedingpurple-flower peas
true-breeding white-flower peas
self-pollinate
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What did Mendel’s findings mean?• Some traits mask others
– purple & white flower colors are separate traits that do not blend
• purple x white ≠ light purple• purple masked white
– dominant allele • functional protein
– affects characteristic• masks other alleles
– recessive allele • no noticeable effect• allele makes a
non-functioning protein
homologouschromosomeshomologous
chromosomes
allele producingfunctional protein
mutant allele malfunctioning
protein
mygenetic.wordpress.com
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Genotype vs. phenotype
• Difference between how an organism “looks” & its genetics– phenotype
• Form of the trait that gets expressed“what you see”
– genotype • An organism’s actual alleles
Explain Mendel’s results using…dominant & recessive …phenotype & genotype F1
P X
purple white
all purple
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Inheritance of genes• On the chromosomes passed from Mom &
Dad to offspring are genes– may be same information– may be different information
eye color(blue or brown?)
eye color(blue or brown?)
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Remember how Meiosis separates the alleles into sex cells?
This separation is called the Law of Segregation.
palaeos.com
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Effect of genes
• Genes come in different versions– brown vs. blue eyes– brown vs. blonde hair– Alleles = different forms of a gene
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Homozygous = same
Heterozygous = different
Homozygous = same
Heterozygous = differentHomozygous dominant = AAHomozygous recessive = aaHeterozygous = Aa
TtTt
BbBb
WwWwYyYy
rrrr
RRRR
AaAa
ABAB
SsSs
bbbb EeEeBBBB
aaaaXYXY
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Genes affect how you look…
XBBbb
Bb Bb Bb Bb
Where did the blue eyes go??
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XBbbb
Bb Bb bb bb
Why did the blue eyes stay??
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XBbBb
BB or Bb BB or Bb BB or Bb bb
Where did the blue eyes come from??
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• Genes come in “versions”– brown vs. blue eye color– Alleles (different forms of a gene)
• Alleles are inherited separately from each parent– brown & blue eye colors are separate & do
not blend • either have brown or blue eyes, not a blend
• Some alleles mask others– brown eye color masked blue
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How does this work?
eye color(brown?)
hair color
hair color
eye color
(blue?)
• Paired chromosomes have same kind of genes– but may be different alleles
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Traits are inherited as separate units
1 from Mom
1 from Dad
• For each trait, an organism inherits 2 copies of a gene, 1 from each parent– a diploid organism inherits
1 set of chromosomes from each parent• diploid = 2 sets (copies) of chromosomes
homologous chromosomes
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Making gametesBB = brown eyesbb = blues eyesBb = brown eyes
BB
bb
Bb
brown is dominant over blue
blue is recessive to brown
Remember meiosis!
B
B
b
b
B
b
Dominant = can mask others
Recessive = can be hidden by others
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How do we say it?
BB = brown eyesbb = blues eyes
Bb = brown eyes
2 of the same allelesHomozygous
2 differentHeterozygous
BB
B
B
bb
b
b
Bb
B
b
homozygous dominanthomozygous recessive
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Punnett squaresBb x Bb
male / sperm
fem
ale
/ eg
gs
X
BB
Bb bb
BbB
b
B b
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Genetics vs. appearance
• There can be a difference between how an organism looks & its genetics– appearance or trait = phenotype
• brown eyes vs. blue eyes
– genetic makeup = genotype• BB, Bb, bb
2 people can have the same appearance but have different genetics: BB vs Bb
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Genetics vs. appearance
vs.
eye color(brown)
eye color
(brown)
BB
B
B
eye color(blue)
eye color
(brown)
Bb
B
b
How were these brown eyes made?How were these brown eyes made?
http://designora.com/wp-content/uploads/2009/11/32-brown-eyes.jpg
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Making crosses• Can represent alleles as letters
– flower color alleles P or p– true-breeding purple-flower peas PP– true-breeding white-flower peas pp
PP x pp
PpF1
P X
purple white
all purple
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Punnett squaresPp x Pp
P pmale / sperm
P
p
fem
ale
/ eg
gs
PP
75%
25%
3:1
25%
50%
25%
1:2:1
%genotype
%phenotype
PP Pp
Pp pp pp
Pp
Pp
1st
generation(hybrids)
Aaaaah,phenotype & genotype
can have different ratios
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Beyond Mendel’s Lawsof Inheritance
http://crittergeek.com/wp-content/uploads/2006/11/calico.jpg http://pixdaus.com/pics/12072579159eXGQHR.jpg
http://www.drstandley.com/images/health%20topics/Acromegaly2.jpg http://staff.tuhsd.k12.az.us/gfoster/standard/3head.gif
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Extending Mendelian genetics• Mendel worked with a simple system
– peas are genetically simple– most traits are controlled by single gene– each gene has only 2 version
• 1 completely dominant (A)• 1 recessive (a)
• But its usually not that simple!
mac122.icu.ac.jp
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Incomplete dominance
• Hybrids have “in-between” appearance– RR = red flowers– rr = white flowers– Rr = pink flowers
• make 50% less color
RR Rr rr
RR
WW
RW
http://www.mnstate.edu/www.margaretaflowers.com www.99andbarry.com
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Incomplete dominance
true-breedingred flowers
true-breeding white flowers
XP
100%
100% pink flowers1st
generation(hybrids)
self-pollinate
25%white
2nd
generation
25%red 1:2:1
50%pink
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Incomplete dominance
RW x RW
R Wmale / sperm
R
Wfem
ale
/ eg
gs
25%
1:2:1
25%
50%
25%
1:2:1
%genotype
%phenotype
RR
RW
RW
WW
25%
50%
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Codominance• Equal dominance
– Chickens• A black-feathered chicken is crossed with a white-
feathered chicken.• All of the babies are white with black speckling.• Both white and black show up equally.
x =
www.self-sufficient-life.com /echotig8.files.wordpress.comwww.harvestofhistory.org
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More Codominance…
x
www.smartpawsacademy.com
/z.about.com
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Multiple Alleles• More than one allele to select from.
– Blood “types” can be A, B, AB, or O.– The alleles to make these types include A, B and i.– “i” is the recessive allele and A and B are both
dominant.– So to get…
• Type A you must have AA or Ai• Type B you must have BB or Bi• Type AB you must have AB• Type O you must have ii
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BLOODBlood cells have antigens and antibodies.
Antigens are tiny receptors on the outside of the blood cell that matches the “type.”
Antibodies are what the cell doesn’t like (which is anything different from the “type.”)
Multiple Alleles
Multiple Alleles
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Blood Types
A
A
A
Type A
B
BB
Type B
Type O
A
B
A
Type ABB
Antigens(none)
Anti-B Anti-
A
noneAnti-A and B
Multiple Alleles
Multiple Alleles
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Genetics of Blood type
pheno-type
genotypeantigenon RBC
antibodiesin blood
donationstatus
A A A or A itype A antigens
on surface of RBC
anti-B antibodies __
B BB or B itype B antigens
on surface of RBC
anti-A antibodies __
AB ABboth type A &
type B antigens on surface
of RBC
no antibodiesuniversal recipient
O i ino antigens on surface
of RBC
anti-A & anti-B antibodies
universal donor
Multiple Alleles
Multiple Alleles
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One gene : Many effects• The genes that we have covered so far
affect only one trait• But most genes are affect many traits
– 1 gene affects more than 1 trait• dwarfism (achondroplasia)• gigantism (acromegaly)
dymaxionweb.com /mentalfloss.cachefly.net
www.lifeinthefastlane.ca
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Acromegaly: André the Giant
lat34.com
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AA
Aa x aa
Inheritance pattern of Achondroplasia
a a
A
a
A a
A
a
Aa x Aa
Aa
aa aa
Aa
50% dwarf:50% normal or 1:1
aa
Aa
67% dwarf:33% normal or 2:1
Aa
library.thinkquest.org
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Many genes : One trait
• Polygenic inheritance– additive effects of many genes– humans
• skin color• height• weight• eye color• intelligence• behaviors
Polygenic =
“many genes”Polygenic =
“many genes”
www.scientificamerican.com
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Human skin color• AaBbCc x AaBbCc
– range of shades– most children =
intermediate skin color
– some can be very light & very dark
Polygenic =
“many genes”Polygenic =
“many genes”
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Albinism Johnny & Edgar Winter
albinoAfricans
melanin = universal brown color
cnb.uam.es
xenophilius.files.wordpress.com
theglenblog.blogspot.com
www.heartlandhunters.com
Albinism is the absence of pigment.
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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)
E–B–E–bbeeB–eebb
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Environment effect on genes• Phenotype is controlled by
both environment & genesCoat color in arctic fox influenced by heat sensitive alleles
www.saskschools.ca
s3.amazonaws.comColor of Hydrangea flowers is influenced by soil pH
/www.grahamrollason.co.uk/images.pictureshunt.com
Human skin color is influenced by both genetics & environmental conditions
wxyc.org
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SEX and GENES
• Women & men are very different, but just a few genes create that difference
• In mammals = 2 sex chromosomes
– X & Y– 2 X chromosomes = female: XX– X & Y chromosome = male: XY
X Y
X X
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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 Y
X X
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XH Ymale / sperm
XH
Xhfe
mal
e / e
gg
s XHXH
XHXh
XHY
XhY
XHXh
XH
Xh
XHY
Y
XH
XHXH XHY
XHXh XhY
sex-linked recessive
2 normal parents,but mother is carrier
HH HhxXHY XHXh
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library.thinkquest.org
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Most Common AlleleDominant or Recessive • Because an allele is dominant
does not mean…– it is better, or– it is more common
Polydactylydominant allele
Either One!
accessexcellence.org
biocrawler.com thelastoutpost.com
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Polydactyly
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
individuals are born with extra fingers or toes
stanford.wellsphere.com
absurdintellectual.com
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Hound Dog Taylorhttp://www.last.fm/music/Hound%2BDog%2BTaylor%2B%2526%2Bthe%2BHouse%2BRockers
www.mark-cole.co.uk
blogs.sun.com
/aagallery.aadl.org
mevio.com