Download Law of Independent Assortment

Other Inheritance Patterns
Mendel’s Laws
Law of Dominance: if the two alleles at a locus differ, then
one, the dominant allele, determines the organism′s
appearance; the other, the recessive allele, has no noticeable
effect on the organism′s appearance
Law of Segregation: the two alleles for a heritable character
separate (segregate) during gamete formation and end up in
different gametes
Law of Independent Assortment: each pair of alleles
segregates independently of other pairs of alleles during
gamete formation
Segregation

Alleles segregate
when homologous
chromosomes
separate during
Meiosis I.
Independent
Assortment
Linked Genes



Genes located on the
same chromosome
tend to be inherited
together
Such genes are said
to be “linked genes.”
When genes are
linked, they do not
assort independently.
Intermediate Inheritance
(Incomplete Dominance)


The heterozygote has a phenotype that
is intermediate between the phenotypes
of the two homozygotes.
Example: Petal color in certain flowers.
Codominance


The heterozygote expresses both traits
at the same time.
Example: roan coat color in cattle
Red
“Roan”
White
CRCR x CRCR
CWCW x CWCW
CRCW x CRCW
CRCR x CRCW
CRCR x CWCW
CRCW x CWCW
Sex-Linked Inheritance




Genes located on sex chromosomes
produce different patterns in males and
females.
Females generally have two alleles for
these genes.
Males generally have only one allele.
If a male inherits a sex-linked recessive
allele from his mother, the allele will be
expressed.
Red/Green Color Blindness
color-blind male x carrier female
Epistasis
Effects of one gene override or mask the
phenotype of a second gene.
Epistasis is not dominance.
Compare the definitions:
Epistasis: One gene masks the expression of
a different gene for a different trait
Dominance: One allele masks the expression
of another allele of the same gene

Example of Epistasis


Labrador retrievers can be black,
brown, or yellow. Two genes control
this.
One gene influences melanin production


B (black) is dominant to b (brown)
One gene influences melanin deposition

E (full deposition) is dominant to e
(reduced deposition)
Multiple Alleles


For many genes, several alleles exist in
the population.
This expands the number of possible
genotypes and phenotypes.
Example of Multiple Alleles



Human blood type is determined by
three alleles: A, B, & O.
IA & IB are codominant.
i is recessive.
Polygenic
Inheritance
Many genes
influence a
single trait
Continuous variation



Most traits show a range of variation
rather than distinct either/or types
This occurs when multiple genes and
environmental factors influence the
trait’s expression
Continuous variation is often described
with frequency distribution tables.
Example using actual data