Transcript Genetics Enrichedx

Mendel’s 3 Laws of Inheritance
Law of Dominance- Each trait is controlled by 2
1.
factors:
•
•
Dominant- what is expressed
Recessive- masked in presence of dominant
P1
F1
F2
Mendel’s 3 Laws of Inheritance (cont.)
2. Law of Segregation- Each allele separates into
different gametes (when does this happen??)
Ex. Ww – one W goes in one sperm and the other w
goes into another sperm
Ww
w
W
Mendel’s 3 Laws of Inheritance (cont.)
3. Law of Independent
Assortment- Gene pairs
(homologous) will
separate randomly into
gametes during meiosis
*Chromosomes line up
randomly at metaphase
plate
What is a dihybrid Cross?
A
dihybrid cross allows us to predict possible
outcomes of offspring that will have 2 traits
simultaneously.

Ex: what would you get if you crossed a Brownhaired brown-eyed male with a blonde-haired
blue-eyed female? How many of the children
would have brown hair and brown eyes? Brown
hair and blue eyes? Blonde hair and brown
eyes? Blonde hair and blue eyes?
Setting up Dihybrid Crosses
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1. Labels!!
2. Determine parent genotypes
3. Determine gametes (alleles to be passed
down)
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The FOIL method
4. Set up punnet square
5. Determine outcome
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Phenotype Ratio
Dihybrid Crosses

Looking at two different traits
 Ex. Hair color and eye color
B=brown eyes
 b=blue eyes

R=Brown hair
 r=blonde hair
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Mother is heterozygous for both traits
 Father is heterozygous for eye color and
homozygous dominant for hair color
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Example
More Practice
 Mickey Mouse is heterozygous for Round
ears and homozygous for Black eyes.
Minnie Mouse is homozygous for Floppy
ears and heterozygous for Black eyes.
Determine phenotype ratios. (B=black eyes,
b=brown eyes, R=round, r= floppy.)
Do Now!! 
 Ariel and Prince Eric are curious to see
what their babies will look like! Eric is
heterozygous for black hair and Ariel has
the recessive trait of red hair. Both are
recessive for blue eyes. If they have 32
children, how many can we EXPECT to
have red hair and blue eyes?
Gene Linkage
 There are several
genes on a chromosome
 Gene Linkage:
 When two genes are close to each other on the
same chromosome
Gene Linkage (cont.)
o Linked genes on a chromosome results in an
exception to Mendel’s law of independent
assortment
o Linked genes usually do not segregate
independently
Drosophila melanogaster (Fruit Flies)
o First organism
with linked genes
o Linked genes
typically travel
together during
crossing over
Chromosome Map
 A map of genes on a chromosomes
 Crossing over occurs more frequently
genes that are far apart
between
Polyploidy
o
o
Cells that contain more than 2 homologous sets of
chromosomes
Ex. A triploid organism (3n) - means that it has
three complete sets of chromosomes.
Strawberries are octoploid!!
Pedigree
Shows history
of a trait in a
family
Allows
researchers to
analyze traits
within a family
In a pedigree…
You can see how a genetic disorder runs in
a family.
Carriers are individuals who are
heterozygous for an inherited disorder but
do not show symptoms.
Carriers can pass the allele for the disorder
to their offspring
Symbols for Pedigree
Worksheet!!
Do Now!! 
 Fill in the genotypes for the following pedigree (shows
recessive trait)
 B=brown eyes
 b = blue eyes
Incomplete dominance
o
o
o
Heterozygous phenotype is intermediate
between two homozygous phenotypes:
o In between two extremes
Heterozygous phenotype appears blended.
Ex: Four O’clock flowers
+
 Both traits are dominant and expressed (no
blending)
 Ex: Roan Cows
 white hair (HW) is codominant with red hair (HR)
 cows with genotype (HRHW) have coats with a
mixture of red and white hairs (roan)
 Red + White = RED AND WHITE
Multiple alleles – 3 or more alleles that control a
trait
 Example: blood type!
 Possible alleles: IA, IB,
i
 Which genotypes are heterozygous? Homozygous?
GENOTYPES
RESULTING PHENOTYPES
IAIA
IAi
IBIB
IBi
IAIB
Type A
Type AB
ii
Type O
Type B
Antigens vs. Antibodies
 Antigen: substance foreign to the body that causes
an immune response:
 Can act as surface markers
 EX: type A antigens on surface of type A blood
cells
 Antibody: protein that reacts with specific antigen:
 EX: Type B blood contains anti-A antibodies
Which is the universal donor?
Universal acceptor?
Determine Blood Type
 Determine the possible offspring of the following
crosses
 1. AB and O
 2. Homozygous A and heterozygous B
 3. AB and AB
Worksheet!!
What do you see?
What do you see?
Sex Linked Traits
 Traits located on the sex chromosomes
(X or Y)
 X linked: gene is located on the X chromosomes
 Y linked: gene is located on the Y chromosome
 Ex: color-blindness
is X-linked!
*If X-linked, can males be carriers?
What are the chances of having a girl?
 How
would you go about solving it?
Sex-Linked Traits
A man who is color blind marries a
woman that is heterozygous for color
blindness. What is the chance of having
a color blind boy?
Polygenic Traits
o Polygenic traits arise from the interaction of
multiple pairs of genes.