Download Patterns of Inheritence - School District of La Crosse

Patterns of Inheritance
I: Mendel's laws



Two factors called
genes control each trait
For each gene,
organisms receive one
allele (form) from each
parent randomly.
If an organism receives
different alleles for the
same trait, one allele is
dominant over the other
II: Test crosses

Monohybrid cross

Breeding individuals to
observe the inheritance
of one trait

Ex: Mendel’s round vs
wrinkled peas

Expected phenotypic
ratio

3 dominant: 1
recessive
Test Crosses Continued…

Dihybrid cross




Breeding individuals to
observe the inheritance of
two separate traits
Ex: Mendel’s cross for
shape and color
Expected phenotypic ratio:
9 dom dom: 3 dom rec: 3
rec dom: 1 rec rec
Practice time

Assume the following:



A = round head a = square head
B = belly button b = no button
If two parents are heterozygous for belly buttons what
are the odds/percentages that their child will not have
a belly button?


¼ or 25%
If parent #1 is homozygous dominant for both traits
and parent #2 is homozygous recessive for both traits
what are the odds/percentages their child will have a
round head but no belly button?

0/16 or 0%
III: Complex inheritance

Incomplete Dominance: Blending of traits

Heterozygotes, and homozygotes have
different phenotypes
Continued…

Co-dominance:

Heterozygotes express both dominant
phenotypes
Continued…

Sex determination



23rd chromosome=X or Y
XX=female
XY=male
Sex linked traits:

Genes for the traits
located on the sex
chromosome


Ex: fruit fly eye color
XR= Red
Xr= white
Human color blindness
Continued…

Polygenic:
Poly=many
gen=genes

Multiple genes are
responsible for the
expression of the
trait