Download BIOLOGY CLASS NOTES UNIT 7_Part 2 Other Patterns of

Unit 7: (Part 2)
Mendelian Genetics
Mrs. Howland
Biology 10
Rev. Jan 2016
Exceptions to the Rule…
What happens if nature doesn’t follow
Mendel’s principles?
Multiple alleles
Codominance
Incomplete dominance
Sex-linked dominance
Dominance according to
Mendel’s Principles
One allele masks the other
MALE
MALE
FEMALE
Multiple alleles are when a gene can present
several different phenotypes, so there are more
than 2 possible alleles.
MULTIPLE ALLELES
Organisms still have ONLY 2 alleles in their genotype
Allows for variety among organisms
Polygenic Traits
POLYGENIC TRAITS: Traits that result from several
genes interacting; controlled by 2 or more genes
EXAMPLE: Human skin color
Codominance
Codominance = Neither allele completely
masks the other
BOTH alleles are dominant
Phenotype is some of each trait
EXAMPLE:
Chicken feather color
Examples of CODOMINANCE
Examples of CODOMINANCE
ABO Blood Type
Genotype
Phenotype
Cat fur color
(black/tan)
Some flower
colors
RBC
Incomplete Dominance
INCOMPLETE DOMINANCE = When alleles are
neither recessive nor dominant
Phenotype for heterozygous offspring is in between the
homozygous phenotypes
EXAMPLES: Incomplete Dominance
Human hair
Remember the DIFFERENCES!
Can you define each of these?
VIDEO:
https://www.youtube.com/watch?v=I6hYr
yyGXoU
Looking at Punnett Squares
~ What is different from what we’ve seen before?
Alleles have same letter
because they are for
the same trait: “C”
SUPERSCRIPTS show
the different forms of
the trait (“R” and “W”)
Codominance ~ Punnett Square
CODOMINANCE:
FB = Black feathers
FW = White feathers
Heterozygous = Black
and white feathers
GENOTYPIC RATIO ____ FBFR : ____ : FBFW : ____FWFW
PHENOTYPIC RATIO ____ BLACK : ____ : BLACK & WHITE : ____WHITE
Incomplete Dominance
~ Punnett Square
CODOMINANCE:
FR = Red flower
FW = White flower
Heterozygous = pink
GENOTYPIC RATIO ____ FRFR : ____ : FRFW : ____FWFW
PHENOTYPIC RATIO ____ RED : ____ : PINK : ____WHITE
Environmental Influence
Are genes affected by the environment?
Genes lay out the ‘plan’
The environment may help determine phenotype
Environment may affect the expression of genes
EXAMPLE:
• Environmental temperature affects
gene expression of color
(pigmentation)
• Darker pigmentation increases body
heat
SUMMER
AUTUMN
Environmental Influence
EXAMPLE:
• Environmental temperature affects gene
expression of color (pigmentation)
• Darker pigmentation increases body heat
SUMMER
AUTUMN