Transcript Notes

Genetics
&
The Work of Mendel
Critical Question: What are alleles?
And Where are they located?
Regents Biology
Goals
Understand
 Homologous chromosomes
 Parent Generation / and their offspring
 Heterozygous
 Homozygous
 Alleles
 Phenotype
 Genotype
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Gregor Mendel
 Austrian Monk
 “Father of Modern Genetics”
 Documented patterns in peas:
 Studied at University of Vienna
in 1851,
 Influenced by physicist who
encouraged experimentation &
the application of mathematics
to science
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Homologous chromosomes
In all living things, characteristics are passed on in the
chromosomes that offspring inherit from their parents.
chromosome from
female parent
chromosome from
male parent
Homologous Chromosomes are matched from each
parent.
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© Boardworks Ltd 2004
Chromosomes
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Different versions of genes
gene for
petal colour
gene for
petal colour
version for red
petals
version for
yellow petals
Each chromosome may have a different version of a gene.
Different versions of a gene are called alleles.
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Pairs of alleles – homozygous
If alleles are matching they are called
homozygous alleles.
allele for
yellow petals
allele for
yellow petals
allele for
red petals
allele for
red petals
What colour are the flowers with these
homozygous pairs of alleles?
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(Click twice on each bud
to reveal the flower;
click again to close them.)
Pairs of alleles – heterozygous
If alleles are matching pair are different, they are
heterozygous alleles.
allele for
red petals
(Click twice on the bud
to reveal the flower;
click again to close it.)
allele for
yellow petals
Which characteristic is expressed if alleles are different?
Some alleles are dominant meaning they are expressed.
Some alleles are recessive meaning they are masked. (hidden)
Which is the dominant allele in this heterozygous pair?
Which is the recessive allele in this heterozygous pair?
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Looking closer at Mendel’s work
Parents
true-breeding
true-breeding
X
purple-flower peas
white-flower peas
100%
purple-flower peas
F1
1st
generation
100%
self-pollinate
F2
75%
purple-flower peas
2nd
generation
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25%
white-flower peas
3:1
Genotype vs. phenotype

phenotype (physical appearance)
 description of trait

genotype (genes)
 genetic makeup (what is on the
chromosome)
X
P
Explain Mendel’s results using
…dominant & recessive
…phenotype & genotype
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purple
white
F1
all purple
Making crosses
 We 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
X
P
purple
white
F1
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all purple
Pp
Punnett squares
Pp x Pp
1st
Aaaaah,
phenotype & genotype
can have different
ratios
generation
(hybrids)
%
genotype
male / sperm
female / eggs
P
p
PP
25%
75%
Pp
P
PP
%
phenotype
50%
Pp
Pp
p
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Pp
pp
pp
25% 25%
1:2:1
3:1
Any Questions??
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Let’s Practice
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Draw the Punnett Square for EACH Question!!!
S = Long Hair s = short hair
One cat carries heterozygous, long-haired traits (Ss), and its mate
carries homozygous short-haired traits (ss). Use a Punnett square to
determine the probability of one of their offspring having long hair.
A)
0%
B)
25%
C)
75%
D)
50%
One cat carries homozygous, long-haired traits, and its mate carries
homozygous short-haired traits. Use a Punnett square to determine the
probability of one of their offspring having short hair.
A)
25%
B)
50%
C)
75%
D)
0%
Regents Biology
Gregor Mendel Facebook Page
 Imagine you come across Gregor
Mendel’s Facebook Page
 Help Gregor fill in the missing
information on his page and
 Respond to a user’s post about Peat
plants
 When you are finished raise your hand
so I can check you off for today’s grade
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Beyond Mendel’s Laws
of Inheritance
WARM UUUPPPP
1. Grab the skinny sheet
off the front table
2. Answer the questions
Regents Biology
2007-2008
Goals
 Review Punnett Squares
 Incomplete Dominance
 Codominance
 Sex-Linked Chromosome

Diseases
 Polygenic Genes
 Environmental Effects on Phenotypes
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Heterozygous cross activity
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© Boardworks Ltd 2004
Extending Mendelian genetics
 Mendel worked with a simple organism
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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Incomplete dominance =
When heterozygotes have an “in-between”
appearance or create a new phenotype
 RR = red flowers
RR
 rr = white flowers WW
 Rr = pink flowers
RW
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RR
Rr
rr
Incomplete dominance
P
X
true-breeding
red flowers
true-breeding
white flowers
100% pink flowers
100%
F1
self-pollinate
25%
red
F2
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50%
pink
25%
white
1:2:1
Incomplete dominance
RW x RW
%
genotype
male / sperm
female / eggs
R
R
W
RR
W
RR
RW
RW
25% 25%
50% 50%
RW
RW
WW
WW
25% 25%
1:2:1
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%
phenotype
1:2:1
Codominance =
 Equal dominance!!!!!
Meaning both phenotypes
are equally expressed
human A B o blood groups
 3 version

 A, B, o
 A & B alleles are codominant
 both A & B alleles are
dominant over o allele
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Blood Types are….Codominant
A
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B
AB
o
Co-dominance
activity
FLASH
5 – Blood groups
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© Boardworks Ltd 2004
Regents Biology
Genetics of sex linked chromosomes
 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
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X
X
X
Y
Sex-linked traits
 Sex chromosomes have other genes on
them, too
especially the X chromosome!!
 hemophilia in humans

 blood doesn’t clot

red-green color blindness
X
X
X
Y
 see green & red as shades of grey
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sex-linked recessive
Sex-linked traits
2 normal parents,
but mother is carrier
For color blindness (h)
HY x XHh
H Xh
XHH
male / sperm
XH
XH
Y
XH
XH XH
XH Y
Xh
XH Xh
XhY
Y
XH
XH Xh
Xh
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female / eggs
XH Y
Many genes: one trait
 Polygenic inheritance =
many genes working together
 Examples in Humans:

 skin color
 height
 weight
 eye color
 intelligence
 behaviors
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Environment effect on genes
 Phenotype is controlled by
both environment & genes
Human skin color is
influenced by both genetics
& environmental conditions
Color of Hydrangea flowers
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Biologyby soil pH
is
influenced
Coat color in arctic
fox influenced by
heat sensitive alleles
In complete or Codominance
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Codominance
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Any Questions now?
Yes, No, Maybe so?
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Hospital Mix Up!!
 UH OHHHH!!!!!
 Which Baby Belongs to who?!
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End PPT
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Warm Up Question
New page! (Right)
P = purple
P = white
You are a geneticist.
A student gives you a purple flower and asks,
“Is this flower heterozygous or homozygous
dominant?”
You do a testcross to determine
the answer.
Based on the results explain
why the flower is heterozygous
or homozygous dominant.
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A Testcross
 A genetic procedure to determine an
individual’s actual genetic composition
 A purple-flowered plant can be
 homozygous dominant (PP)
or
 heterozygous (Pp)
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If offspring was
½ purple and ½
white, then the
parents was
heterozygous
male / sperm
male / sperm
P
P
P
p
p
Pp
Pp
p
PP
pp
p
Pp
Pp
p
Pp
pp
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female / eggs
female / eggs
If all offspring was
purple, then the
parents was
homozygous
dominant
Overview
 Mendel’s Laws
Law of Independent Assortment
 Law of Segregation

 Linkage
 Dihybrid Crosses
Regents Biology
MENDEL’S LAWS (2)
 1. LAW OF SEGREGATION -Reproductive cells
(sperm and eggs) only
receive one trait of
each parent.
male / sperm
P
p
Pp
Pp
p
Pp
Pp
female / eggs
P
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Mendel’s 2nd Law
 2. LAW OF INDEPENDENT
ASSORTMENT:
-Genes for different
characteristics sort
randomly
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Exception = Linkage
 Two genes that are

too close together
physically to sort
independently.
Meaning they will
always go into the
same gamete together
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What is a Dihybrid Cross?

Determines the
probability of
genetic outcomes
for TWO traits
instead of ONE.

What 2 traits are
being considered
here?


Coat Colour
Tail Length
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1. Figure out the alleles:
2. Draw your box
(16 squares for dihybrids!)
3. Foil (First)(Outer)(Inner)(Last)
4. Label The possible male gametes
5.Label Possible Female gametes
6. Plug & Chug!
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S = short tail s = long tail
B = brown fur b = white fur
Dihybrid cross
P
true-breeding
yellow, round peas
Y = yellow
R = round
true-breeding
green, wrinkled peas
x
YYRR
yyrr
y = green
r = wrinkled
yellow, round peas
F1
100%
generation
(hybrids)
YyRr
self-pollinate
F2
generation
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9/16
yellow
round
peas
3/16
green
round
peas
3/16
yellow
wrinkled
peas
1/16
green
wrinkled
peas
9:3:3:1
Your Turn!
Dihybrid cross of color and seed shape
YyRr x YyRr
YR
Yr
yR
yr
YR
YYRR
YYRr
YyRR
YyRr
Yr
YYRr
YYrr
YyRr
Yyrr
yR
YyRR
YyRr
yyRR
yyRr
yr
YyRr
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Yyrr
yyRr
yyrr
9/16
yellow
round
3/16
green
round
3/16
yellow
wrinkled
1/16
green
wrinkled
Genetics of Blood type
phenogenotype
type
A
B
antigen
on RBC
antibodies
in blood
donation
status
A A or A i
type A antigens
on surface
of RBC
anti-B antibodies
__
BB or B i
type B antigens
on surface
of RBC
anti-A antibodies
__
AB
both type A &
type B antigens
on surface
of RBC
no antibodies
universal
recipient
ii
no antigens
on surface
of RBC
anti-A & anti-B
antibodies
universal
donor
AB
O
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Blood donation
clotting clotting
clotting
clotting
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clotting
clotting
clotting
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
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Inheritance pattern of Achondroplasia
Aa
x aa
a
a
A
Aa
Aa
a
aa
aa
50%Biology
dwarf:50%
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normal or 1:1
Aa
x Aa
A
a
A
AA
Aa
a
Aa
aa
67% dwarf:33% normal or 2:1
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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Johnny & Edgar Winter
Albinism
albino
Africans
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melanin
= universal brown color
OCA1 albino
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Bianca Knowlton
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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
dominant allele
Polydactyly
individuals are born with
extra fingers or toes
the allele for >5 fingers/toes
is DOMINANT & the allele for
5 digits is recessive
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
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homozygous recessive (aa)
Hound Dog Taylor
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I decided to label
and record their g
Wait… Can you help me figure out what the off spring of my Pea plants will look like?
My parent generation is homozygous tall and the other parent was homozygous short.
X
100%
purple-flower peas
1st
generation
(hybrids)
100%
self-pollinate
2nd
75%
purple-flower peas
generation
Regents Biology
25%
white-flower peas
3:1
I decided to label the different generations of flowers,
and record their genotypes and phenotypes below:
Ge
Pp
Ph
Pp
Wait… Can you help me figure out what the off spring of my Pea plants will look like?
My parent generation is homozygous tall and the other parent was homozygous short
T= Tall and t = short.
Regents Biology