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The patterns of heredity
discovered by Mendel are
called simple Mendelian
inheritance or simple dominant/
recessive
-because only 2 options for
phenotypes & 2 alleles
Non-Mendelian Inheritance
1. Incomplete dominance:
-phenotype of the heterozygote
is intermediate to that of the
homozygous parents
e.g. flowers
Red x White = Pink
RR
x R1R1 = RR1
2. Codominance
(codominant alleles)
-phenotypes of both
homozygote parents are
expressed in the heterozygote
e.g. flowers
Purple x White = Purple&White
PP
x WW = PW
3. Polygenic inheritance:
-trait is controlled by 2 or more
genes
-produces multiple phenotypes
e.g.
Skin color = 3 genes(6 alleles)
AaBbCc
4. Sex-linked traits:
-traits are controlled by genes
found on the sex chromosomes
rd
-sex chromosomes: the 23
pair in humans, determines sex
-2 forms -- X & Y
-female = XX male = XY
-autosomes: 1st 22 pair of
chromosomes that code for
everything else
-examples of sex-linked traits
-red-green colorblindness
-hemophilia
-more common in males
because they only have
1X
-e.g. eye color in fruit flies is
carried on the X chromosome
R
X – red eyes
r
X – white eyes
(Discovered by Thomas Hunt
Morgan)
Cross
R
r
X X
x
r
XY
5. Multiple alleles:
-a trait is controlled by more
than 2 alleles
-e.g. blood types = 3 options for
alleles (IA, I B, & i)
-important for transfusions &
paternity cases
Genotype
IAIA or IAi
Surface Phenotype
Molecules
A
A
IBIB or IBi
B
B
IAIB
AB
AB
Ii
None
O
-e.g. Mom = Type O (ii)
Dad = Type AB (IAIB)
-e.g. – Mom = Type A
Baby = Type AB
Can Dad = Type O?
Carrier-individual that is
heterozygous for a defective
trait
-has the recessive allele, but
doesn’t have the gene & can
pass that on to offspring
Pedigree: graphic
representation of an ind. family
tree
Key
Female
or
Male
or
Affected
or
Carriers
or
Parents (P)
Offspring (F1)
-used mostly to show
inheritance of diseases
Hemophilia – carried on the X
XH – Normal Xh – Hemophilia
Karyotype: map showing paired
homologous chromosomes
-used to determine sex &
genetic disorders
-Autosomes: 1st 22 pairs of
chromosomes
-Sex Chromosomes: 23rd pair
XX=female
XY=male
Selective Breeding- org. are
bred to have specific traits
e.g. dogs, livestock, crops
Methods:
1. Inbreeding-mating closely
related individuals
-creates offspring that are
homozygous for
desired trait
2. Hybrids-org. created from
breeding 2 varieties or
closely related species
-offspring usually larger &
stronger than parents
e.g. crop plants &
livestock