PICK UP QUIZ #5 FOR ITEM ANALYSIS
Famous Rule Changes
• Baseball = walks no longer count as hits,
strikeouts now 3 strikes instead of four and
pitcher’s mound 10 feet further back
• Football = forward pass, challenge flag, longer
season
• Basketball = shot clock, 3 point line
Change The Rules of Inheritance?
The Genetics of Dog Breeds
• Dogs all belong to the
same species, but there
are 350-400 breeds
• What determines dog
breeds is controlled by
only 50 genes (by
contrast human height
alone is controlled by
over 200 genes)
If Mendel’s Principle of Dominance Is
Correct, How is Such Variety Possible?
Mendelian Exceptions
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•
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Multiple Allele Inheritance
Incomplete Dominance
Polygenic Traits
Non-Autosomal Inheritance
Exception #1: Incomplete Dominance
Incomplete Dominance & Transcription
• Normally, only one gene
of the homologous pair
is transcribed and
translated
• In situations of codominance and/or
incomplete dominance,
both alleles are
transcribed
Genotypes & Phenotypes
• In incomplete dominance,
the heterozygous
genotype produces a
“blended” phenotype
• In co-dominance, the
heterozygous phenotype
is an equal expression of
both phenotypes
• As such, there are three
values in the phenotypic
ratio
Exception #2: Co-Dominance/Multiple
Allele Inheritance
Blood Types
• Four major blood
groups
–
–
–
–
A
B
AB
O
• The % of each blood
type varies in different
populations
Multiple Allele Inheritance
• More than one dominant allele, both alleles are
expressed/translated equally
• Different than codominance (where one dominant
is “more dominant”/translated more frequently
than the other)
• Allows for a wider range of phenotypes
• Examples:
–
–
–
–
Blood type,
Parrot Feathers
HLA System of Cell Identification
Cystic Fibrosis
Antigens
• Alleles code for
different proteins on
surface of RBC called
antigens
• Three possible alleles IA,
IB and I
• IA and IB code for
different antigens
Exception #3: Polygenic Inheritance
Polygenic Traits
• Trait is produced through the production of
proteins from several genes
• Phenotypic range is spread across a
continuum
• Examples: Skin tone, height, weight, neural
tube formation, club foot
• Related concept: Pleiotropy = one gene affects
multiple traits