Advanced Genetics. Review Dominant vs. Recessive If an individual inherits even one dominant...
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Transcript of Advanced Genetics. Review Dominant vs. Recessive If an individual inherits even one dominant...
ReviewDominant vs. Recessive
If an individual inherits even one dominant allele, that trait will be expressed.
– BB– Bb
Continued…
An individual must inherit two copies of a recessive allele for that trait to be expressed.
– bb
Genes
Each “recipe” on the DNA is called a gene.– Ex. Hair color and hair texture are two
different genes found at different loci (locations) on the
chromosomes.
Alleles
There is often more than one version for a gene.
These are called alleles.
Example:Gene = flower color
– Alleles = purple or white
Beyond Dominant and Recessive Alleles
Not all genes show simple dominant/recessive patterns.
In most organisms, genetics is much more complicated.
The majority of genes have more than two alleles.
A. Multiple AllelesFor some genes, there are more
than two alleles possible. –For example, for eye color there are
alleles for shades of brown, blue, green, and hazel.
B. CodominanceIf more than one allele is
dominant for a trait, they are called codominant.
Both phenotypes will be expressed.
–Both black and white are dominant in this breed of chicken. A cross results in a chicken that has some black feathers and some white feathers.
Red and white fur are both dominant in this breed of cow…
If a cow inherits both (RW), it is described as roan.
In humans, blood type is determined by the presence (or absence) of certain antigens (A and B).
These two antigens are codominant.
C. Incomplete dominanceSometimes, neither allele can
dominate the other.A blend of the traits will appear.
–Example: Red and white flowers produce pink offspring when crossed.
D. Polygenic TraitsThese traits are controlled by
more than one gene and have a wide range of phenotypes. –Height–Skin color