Transcript Different Types of Inheritance

Different Types of Inheritance
Dihybrid Crosses
 Cross that involves two
traits
 Concludes with 16
offspring
Steps for Solve for Dihybrid Cross
 Make a key for the two traits that you are crossing


Black Hair (B) vs Brown Hair (b)
Curly Hair (S) vs Straight Hair (s)
 Write out the different genotypes of the parents


Mother is heterozygous for both traits BbSs
Father is heterozygous for hair color but has straight hair Bbss
 Figure out the possible gametes (similar to FOIL) there
are four for each parent and each gamete must have one
allele from each trait

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Mother: BbSs BS; Bs; bS; bs
Father: Bbss Bs; Bs; bs;bs
Steps for Solve for Dihybrid Cross
 Set up your punnett square
BS
bs
Bs
BbSs
bs
BbSs
Bs
BBSs
Bs
BBSs
bS
Bbss
bbSs
Bbss
bbSs
BBss
BBss
BbSs
BbSs
bs
bbss
bbss
Bbss
Bbss
Steps for Solve for Dihybrid Cross
 Count up the possible genotypes and phenotypes
that you have from your punnett square

Genotypes:
Phenotypes:
BbSs:4/16
 BBSs:2/16
 Bbss:4/16
 BBss: 2/16
 bbSs: 2/16
 bbss:2/16
Black/Curly: 6/16
Black/Straight: 6/16
Brown/ Straight:2/16
Brown/Curly: 2/16

Please see worksheet for more
examples
Fourth Type of Inheritance:
INCOMPLETE
DOMINANCE
Incomplete Dominance
 Inheritance that occurs
when one trait is not
completely dominant
over another
 Results in the
heterozygous form being
blended together
Solving an Incomplete Dominance Problem
 Perform a regular monohybrid punnett square
 Only difference is the heterozygous offspring will be
mixture of two traits (i.e. if black and white than
gray)
Example
 Red carnations are not completely dominant to white carnations-
perform a punnett square mating a red and white carnation
r
r
Rr
R
R
Rr
Rr
Rr
Results
 Genotype: 4/4 Rr
 Phenotype 4/4 Pink
 Example: Black fur (B) is dominant over white fur
(b) in guinea pigs. Cross a grey guinea pig with a
white guinea. What do we get?
 Answer: ½ Bb (grey) and ½ bb (white)
Third Type of Inheritance
SEX LINKED TRAITS
Sex Determination
 In humans and many other organisms, sex is
determined by the X and Y chromosomes.
 Females: XX
 Males: XY
Sex Determination
 Sons get their X chromosome from their mothers
only.
 Fathers must pass their X chromosomes to their
daughters.
Sex Linked Traits
 Genes that are found on the X chromosome follow
a have a special pattern of inheritance:
 X linked traits are only passed to sons from
the mother
 Males are much more likely to be affected than
females.

If trait is recessive, daughters have a second X
chromosome so they can be heterozygous. Sons only
have one X chromosome
Sex Linked Traits
 Daughters can be
 Examples
carriers and pass
the trait onto their
son.
Baldness
Example: Colorblindness
Sex Linked Problem
 A woman is not colorblind but her husband is.
Construct a punnett square to determine what is the
chance that their children will be colorblind.
XB
XB
XBXb
XBXb
XBY
XBY
Xb
Y
0%what
about
% of
being
carrier
50%
Sex Linked Example
 A woman who is a carrier for hemophilia marries an
unaffected male. What is the % chance that their
children will be affected?
XH
Xh
XH
Y
XH XH
XH Xh
XH Y
Xh Y
25% affected- how many carriers?
25%
Fifth Type of Inheritance
CODOMINANCE
Codominance
 When two different alleles are present and both are
expressed
Example: Blood Types
 Red blood cells are coated with different markers.
 Each person contains either A, B, A and B or
neither protein.

Blood Types are: A, B, AB, O
Blood Type Key
Genotype
Phenotype
IAIA, IAIO
A Blood
IBIB, IBIO
B Blood
IAIB
AB Blood
IOIO
O Blood
Example: Blood Type
 Susan (blood type AB) and Bryan (blood type O)
have a son that has blood type B? Since neither
Susan nor Bryan have this blood type, was their a
mistake in the hospital?

Construct punnett square on next slide
Example: Blood Types
IA
IO
IO
IB
IA IO
IBIO
IAIO
IBIO
Results: ½ A blood type or ½ blood type B
Yes he is their son!