Transcript Genetics

Genetics
Solving Punnett Squares
Vocabulary
 Heredity – parent traits appear in offspring
 Allele – One version of a gene
 Gene – DNA code for a protein  a trait
 Dominant trait – Trait appears even with
only one copy of the gene.
 Recessive trait – Trait appears only with
two recessive alleles
 Homozygous – (Purebred) – two of the
same alleles (AA or aa)
 Heterozygous – (Hybrid) – two different
alleles (Aa)
 Genotype – the DNA for a trait
i.e. R or r.
 Phenotype – the appearance of a trait
determined by a genotype,
i.e. round or wrinkled peas.
Try these possibilities in HW
Dominant
Trait
Tall Stem
Recessive
Trait
Short Stem
Letter for Letter for
Dominant Recessive
T
t
Green Pod Yellow Pod
G
g
Yellow
Seeds
W
w
Green
Seeds
Now use two letters from above to fill in 2 genes
for each of the following individuals
Trait
Homozygous Tall
Hybrid Green Pods
Genes Present
Cross a hybrid white flower with a
homozygous purple flower
The heterozygote (hybrid) trait must be dominating the
recessive trait
Ex. If Hh is hybrid.
Then hybrid means one of each. If the Dominant is
expressed then white is dominant because white is the
trait that is expressed.
Seven Steps to Solve
The heterozygote (hybrid) trait must be dominating the recessive trait
5/6.
1. Dom = white
Rec= purple
rec=h
2. Dom= H
3. Ma= Hh
4.
H
h
Pa
Pa=
hh
7.
h
h
Ma
H
h
h
Hh
hh
h
Hh
hh
Genotypes =
50% Hh and 50% hh
Phenotypes =
50% White 50% Purple
Try This
 In a certain plant, tall stems are dominant to
short stems. A farmer crosses a shortstemmed flower with a homozygous longstemmed flower. Complete each of the steps.
1. Dom = T Rec =t
2. T = Tall
t = short
3. Ma: TT
Pa: tt
4.
T
T
t
t
5/6 Ma
T
T
Tt
Tt
Tt
Pa
t
t
Tt
7. Genotypes: 100% T t
Phenotypes: 100% Tall
CoDominance
 There are many different ways that we type blood. Today,
we’ll look at two systems, ABO and the Rh- factor.
ABO Typing:
 Each red blood cell has proteins on its surface that let the
body identify it as belonging to yourself.
Genes “A” and “B” are Co-Dominant genes.
Gene “o” is the recessive gene.
Sample Problem for Blood Type:
Mom is hybrid type B blood, Dad is hybrid type A blood.
5/6.
B
1. Dom = A & B Rec= o
A
AB
2. A or B
o
o
Bo
3. Ma= Bo
Pa= Ao
7. Genotypes =
4.
B
o
A
o
o
Ao
oo
25% AB, 25% Ao, 25%
Bo, 25% oo
Phenotypes = 25%
AB, 25% A, 25% B,
25% O
Rh Factor - is a protein found in blood
Rh + means the protein is present. Rh – means it is not.
Example: Dad is heterozygous Rh+ factor and mom is homozygous
for Rh- factor blood.
1. Dom = +
Rec= -
2. +
3. Ma= - 4. - -
-
5/6.
-
-
+
+-
+-
-
--
--
Pa= + +
-
7. Genotypes =
50% - - 50% + Phenotypes = 50%
Rh + 50% Rh-
What are sex-linked traits?
 Traits on the Y or X chromosomes
Females are XX
Males are XY
Which sex chromosome is home of the most
sex-linked traits?
 X…much, much larger and if any essential
gene were on the Y females would not live.
Karyotypes:
Is this a male or female?
What are examples of traits that are
sex-linked?
What are examples of traits that are sex-linked?
1)
Color blindness – (red-green)
2) Hemophilia
3) Muscular Dystrophy
4) Male pattern baldness
Fill in this table of phenotypes
with the correct genotype
B = normal b = color blind
H = normal h = hemophilia
M = normal m = muscular dystrophy
How should we write these genotypes to help
us remember they are sex-linked?
XmXm or XMY
M = Normal
m = muscular dystrophy
Colorblindness Test
Should See
 Circle, Square, star,
Colorblindness
Should see
 Square, circle
Try to find in the next picture
Dog, Sailboat, balloon, car
Should have seen
 Faint Brown boat, colorblind individuals
would have seen nothing.
Try to see.
Should see
 Colorblind individuals should see a yellow
square.
 Normal sight should see circle and square.
Ishihara Test
 http://www.toledobend.com/colorblind/Ishihara.html
Hemophilia – blood doesn’t clot
Czar Nicholas II of Russia and his family, photographed c. 1916,
showing his wife Alexandra (who was a carrier of hemophilia),
his four daughters, and (in the foreground) his son Alexis,
perhaps the most famous European royal with hemophilia.
http://www.humanillnesses.com/original/GasHep/Hemophilia.html
Muscular Dystrophy
 Muscles form incorrectly, including heart
and lungs, slowly deteriorate
  death by early 30’s
Male Pattern Baldness
 Some evidence hints at X linked status
Androgens (male sex hormones) play a
key role in balding--castrated men don't
go bald--and the AR gene helps them do
their work. The researchers found the
balding men were much more likely to
have a particular version of the AR gene
than the non-balding men, which they
took to mean they'd found a genetic
variant that triggers baldness.
http://www.straightdope.com/columns/050819.html
Sample Problems:
 Genotypes and Phenotypes
XHXh
XhY
XBXB
XMY
XMXm
Woman carrier of hemophilia
Man with hemophilia
Normal Vision Girl
Normal boy
Woman carrier of muscular dystophy
 Color Vision Phenotypes
XBXb
XbY
XBXB
XBY
Woman carrier of color blindness
Man with color blindness
Normal Vision Girl
Normal boy
Sex Linked traits:
Cross a normal male with a female whocarrier for
hemophilia.
XH
Y
1. Dom = healthy
5/6.
Rec= hemophilia
2. XH
Xh
3. Ma= XHXh Pa=XHY
4.
7.
XH
Xh
XH
Y
XH
XH XH XHY
Xh
XH Xh
XhY
Genotypes =
1/4
XH Xh 1/4 Xh Xh
1/4 XhY 1/4 XHY
Phenotypes = 50% girls with
hemophilia 50% carrier for
hemophilia girls, 50% boys
have hemophilia 50% boys
normal
Incomplete Dominance
 Sometimes, depending on the way the
different proteins from each allele interact
genes don’t completely dominate the
alternate allele
 Mendel studying 4 o’clocks (flowers) gave
up genetic research because of this fact.
Seven Steps to Solve
Cross an incompletely dominant White flower with a red flower.
1. Dom = Red and White
Inc. = Pink
2. R or W or RW
3. Ma=WW
Pa=RR
4.
5/6.
7.
W
W
R
R
8.
R
R
W
RW
RW
W
RW
RW
Genotypes =
100% RW
Phenotypes =
100% Pink
Pedigrees
 Looking at ancestor’s traits to predict the
genotypes of individuals in a family
Symbols
Symbol
Description
Unaffected male
Unaffected female
Affected male
Affected female
Deceased male
Deceased female
Possibly affected male
Possibly affected female
Carrier male
Carrier female
Add P1, F1, and F2 and genotypes
1. Decide if disorder
is dominant or
recessive
2. Assign disease
letters
3. Fill in only
remaining letters
you can guarantee
4. Be brave…use ? If
you don’t know
Complete:
Dihybrid Problems
1. Definition – Genetics Problems with two traits tracked
at the same time
Try This:
 Given B = brown hair, b = blond hair AND T = Tall while
t = short.





BbTt =
Bbtt =
bbTT =
bbtt =
____________phenotype
____________ phenotype
____________ phenotype
____________ phenotype
Dihybrids continued
2. When drawing your sperm and egg for the 7 steps in
a.
b.
3.
this type of problem each:
Sperm contains ____ genes?
Egg contains ____ genes?
Predict the sperm or eggs possible for a critter of BbTt.
Arrow Rule
B b T t = BT & Bt
Then B b T t = bT & bt
1.
What sex cells could be obtained from the genotypes below?
a.
b.
c.
d.

Bt
Bt
bt
bt
Bbtt: ___________,
___________,
___________,
___________
bt
bt
bt
bt
bbtt: ___________,
___________,
___________,
___________
BBTT: ___________,
___________,
___________,
___________
BT
BT
BT
BT
BbTt: ___________,
___________,
___________,
___________
BT
Bt
bT
bt
Hint: repeated sperm or eggs can be crossed out.
Dihybrid:
Cross a totally heterozygous brown eyed tall girl with a heterozygous brown
eyed homozygous tall guy.
1. Dom =Brown & Tall 5/6.
Rec= blue & Short
2.
B&T
b&t
3. Pa= BbTT ma=BbTt
4.
BT
Bt
bT
bt
BT
bT
BT
bT
BT
BBTT BbTT
Bt
BBTt
BbTt
bT
BbTT
bbTT
bt
BbTt
bbTt
Genotypes:
1/8 BBTT
2/8 BbTt
2/8 BbTT
1/8 bbTt
Phenotypes:
6/8 Brown eyed and tall
2/8 blue eyes and Tall
1/8 BBTt
1/8 bbTT
Multiple Genes
 Much like dihybrids, but more capital letter
alleles contribute to more of the specific
trait
 Ex. RRSS would be very dark red (4 caps)
RRSs is dark red (any 3 caps)
RrSs would be medium red (any 2 caps)
Rrss would be light red (only 1 cap)
rrss would be albino (no caps)
1. Dom = dark
2. R or S
3. Ma: RrSs
RS
rS
Rs
rs
rec = light
r or s
Dad: RrSS
RS
rS
RS
rS
Geno:
1/8 RRSS
RS
Rs
rS
RRSS
RRSs
RrSS
RrSS
RrSs
rrSS
2/8 RrSS
1/8 Very
dark red
1/8 RRSs
3/8 dark red
2/8 RrSs
3/8 medium
1/8 rrSS
1/8 light red
1/8 rrSs
rs
RrSs
rrSs
Pheno: