Download Complex Inheritance

Complex Inheritance
Mendel observed
monogenic traits and no
linked genes…It s not
usually that simple….
Other Types of Inheritance
 
Incomplete Dominance
– 
– 
– 
The phenotype of the heterozygote is
intermediate between phenotypes of the
homozygotes
Example: when a homozygous red carnation is
crossed with a homozygous white carnations,
then pink carnations are produced
We usually don t use lower case letters in this
type of inheritance because nothing is really
dominant
Incomplete Dominance
 
 
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RR = Red
RW= pink
WW= white
Incomplete Dominance Punnett
Square
  Pink
x White
  RW x WW
–  50%
offspring
are pink
–  50% are white
RW
RW
WW
WW
Other Types of Inheritance
 
Codominance
–  Occurs when both alleles for a trait are
expressed in heterozygous offspring
–  Codominant alleles are often symbolized
with different letters
Codominance
 
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BB = Brown
BW= Roan
WW= White
Notice both brown and white are present in the heterozygote
Codominance Punnett Square
  Roan
x Roan
  BW x BW
–  25%
brown
–  50% roan
–  25% white
BB
BW
BW
WW
Other Types of Inheritance
 
Multiple Alleles:
–  Genes with 3 or more alleles (or
variations)
–  Human blood type shows codominance
and it has multiple alleles- A, B, and O
Blood Type
 
Human blood types have 3 alleles A, B, and O.
–  Each person still only gets 2 alleles, but there
are 3 possibilities
–  O is recessive to A and B,
–  A and B are codominant:
–  Genotype AO or AA = A blood
–  Genotype BO or BB = B blood
–  Genotype OO = O blood
–  Genotype AB = AB blood (both alleles
expressed)
Blood Type
Blood Type
Terminology
GENOTYPE
Heterozygous B
BO
Heterozygous A
AO
Homozygous recessive
OO
Homozygous A
AA
Homozygous B
BB
AB (technically heterozygous)
AB
Codominance Punnett Square
 
 
Heterozygous A x
Heterozygous B
AO x BO
–  25% AB
–  25% A blood
–  25% B blood
–  25% O blood
AB
BO
AO
OO
Other Types of Inheritance
 
Sex-Linked Genes and Traits
–  Remember sex chromosomes are the
chromosomes that determine the sex of an
organism
–  So these are traits/genes carried on sex
chromosomes
–  These traits are symbolized using a
superscript on the X or Y, such as Xr or XR
Other Types of Inheritance
 
Sex-Linked Genes and Traits Examples:
–  In fruit flies, the gene for eye color is on the X
chromosome. Red (XR) is dominant, white (Xr) is
recessive.
–  To have white eyes, females must have the genotype
Xr Xr , or in other words TWO white alleles
–  To have white eyes, males must have the genotype Xr
Y, or in other words ONE white allele
–  This is why X chromosome sex-linked traits are more
common in males
Sex-linked Punnett Square
 
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 
Homozygous red
eyed female x white
eyed male
XRXR x XrY
Notice, 50% males
and 50% females for
offspring
All offspring will have
red eyes
XRXr
XRY
XRXr
XRY
Other Types of Inheritance
 
Polygenic Inheritance:
–  Traits that are controlled by more than
one gene
–  Most human traits are polygenic
–  Examples are height, skin color, eye
color, and hair color
Other Types of Inheritance
 
Complex Characters:
–  Characters that are influenced by
genetics AND the environment
–  Skin color and height are examples
Other Types of Inheritance
 
Sex-Influenced Traits:
–  Traits in which males and females show
different phenotypes even though they
have the same genotypes
–  Baldness is an example- it is dominant in
men, but recessive in women
–  The differences are mainly due to males
and females producing different hormones
(chemical signals)
Other Types of Inheritance
 
Single Allele Traits
–  Traits where there is only one allele
–  If you have the allele you have the traitthere is no recessive
–  Huntington s disease is an example
  http://www.mayoclinic.org/diseases-
conditions/huntingtons-disease/basics/
definition/con-20030685
Chromosome Mutations
 
Chromosome mutations involve
changes in the structure of a
chromosome or the loss or gain of
a chromosome.
–  Deletion: The loss of a piece of
chromosome due to breakage
–  Inversion: A chromosomal
segment breaks off, flips
around, and reattaches
Translocation- A piece of chromosome
breaks off and reattached to a
nonhomologous chromosome
Nondisjunction- When a chromosome fails to
detach from its homologue during meiosis, so
one gamete gets an extra chromosome
ex. Down’s Syndrome
http://www.nichd.nih.gov/health/topics/down/conditioninfo/Pages/causes.aspx
Duplication: repeats a
chromosomal segment