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2007-2008 Regents Biology
Genetics&
The Work of Mendel
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Regents Biology
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
Gregor Mendel
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Regents Biology
Pollen transferred from white flower to stigma of purple flower
anthersremoved
all purple flowers result
Mendel’s work
?
self-pollinate
Bred pea plants cross-pollinate
true breeding parents raised seed & then
observed traits allowed offspring
to self-pollinate & observed next generation
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Regents Biology
Mendel collected data for 7 pea traits
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Regents Biology
2nd
generation
3:175%purple-flower peas
25%white-flower peas
Looking closer at Mendel’s work
Parents
100%1st
generation(hybrids)
100%purple-flower peas
Xtrue-breedingpurple-flower peas
true-breeding white-flower peas
self-pollinate
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Regents Biology
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
homologouschromosomes
I’ll speak for both of us!
allele producingfunctional protein
mutant allele malfunctioning
protein
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Regents Biology
Genotype vs. phenotype Difference between how an organism
“looks” & its genetics phenotype
description of an organism’s trait genotype
description of an organism’s genetic makeup
Explain Mendel’s results using…dominant & recessive …phenotype & genotype F1
P X
purple white
all purple
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Regents Biology
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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Regents Biology
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 & genotypecan have different
ratios
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2007-2008 Regents Biology
Any Questions??
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2007-2008 Regents Biology
Beyond Mendel’s Lawsof Inheritance
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Regents Biology
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!
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Regents Biology
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
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Regents Biology
Incomplete dominancetrue-breeding
red flowerstrue-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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Regents Biology
Incomplete dominance
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%
RW x RW
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Regents Biology
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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Regents Biology
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
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Regents Biology
Blood donation
clotting clotting
clotting clotting
clotting clotting clotting
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Regents Biology
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)
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Regents Biology
Acromegaly: André the Giant
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Regents Biology
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
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Regents Biology
Many genes: one trait Polygenic inheritance
additive effects of many genes humans
skin color height weight eye color intelligence behaviors
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Regents Biology
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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Regents Biology
AlbinismJohnny & Edgar Winter
albinoAfricans
melanin = universal brown color
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Regents Biology
OCA1 albino Bianca Knowlton
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Regents Biology
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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Regents Biology
Phenotype is controlled by both environment & genes
Color of Hydrangea flowers is influenced by soil pH
Human skin color is influenced by both genetics & environmental conditions
Environment effect on genes
Coat color in arctic fox influenced by heat sensitive alleles
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Regents Biology
Genetics of sex 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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Regents Biology
Sex chromosomes
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Regents Biology
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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Regents Biology
Sex-linked traits
XH Ymale / sperm
XH
Xhfe
mal
e / e
gg
s XHXH
XHXh
XHY
XhYXHXh
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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Regents Biology
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Regents Biology
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Regents Biology
Dominant ≠ most common allele
Polydactylydominant allele
Because an allele is dominant does not mean… it is better, or it is more common
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Regents Biology
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
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Regents Biology
Hound Dog Taylor
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2007-2008 Regents Biology
Any Questions?