Contributed by:
POINTS TO BE DISCUSSED:
1. Incomplete Dominance 2. Multiple Alleles 3. Co-Dominance 4. Polygenic Traits 5. Environmental Factors in patterns of Heredity.
1.
Gregor Mendel
would roll over in his
grave if he knew we
were discussing
this!
Non- Mendelian Genetics
Complex Patterns of Heredity
Traits that do not follow Mendel’s Laws
2.
1. Incomplete Dominance
• Mendel stated that if an offspring gets
two different alleles, the dominant
allele will be expressed
– BB-brown eyes
– bb- blue eyes
– Bb-
• Today: intermediate/blended traits
• No dominant allele is expressed
• Why does this happen with colors?
– Less pigment
– Proteins that form traits do not form
correctly b/c recessive allele is mutated
• Examples: (genetic babies)
• Hair: straight + curly =
• Eyes: brown + blue =
• Limb sizes= large + small =
• Colors: red + white =
4.
2. Multiple Alleles
• Mendel stated that all traits have 2 alleles
• Today: multiple alleles
– more than 2 alleles can exist
• Example: Human Blood groups
• Alleles: IA I B i
• IA = dominant IB = dominant and i =recessive
• ABO blood groups:
• A - the alleles can be IA IA or IA i
• B -the alleles can IB IB or IB i
• AB - the alleles can IA and IB
• O - the alleles can be i and i
• A and B (antigens) are carbohydrates found on
the RBC’s
6.
Punnett practice
• Give the genotypic and phenotypic ratio of
the potential children of a couple, if the
man is heterozygous A-type blood and his
wife is heterozygous B-type blood.
7.
IA IA
IB IB
IA i
IA IB
IB i
Practice: A man of blood type AB marries a woman of blood type A. What are the possible
blood types of their offspring if the woman’s mother was blood type O?
Practice: A child with blood type O has a mother with blood type A and a father with blood type
B. The parental genotypes for blood types must be?
What are the possible blood types of their offspring?
8.
3. Co-dominance
• Mendel stated that traits can have ONE
dominant allele
• Today: 2 dominant alleles can be
expressed for the same trait
• Examples: blood types and fur coat colors
• alleles IA and I B are both dominant and can be
expressed: AB blood type
• Roan cows: red and white coats
• Chickens: black and white feathers
9.
Co-dominance
Roan cow: both red and white
AB blood group
10.
4. Polygenic Traits
• Mendel believed that there was one gene
(genotype) for one trait or phenotype.
• Today: several genes (genotypes) can
influence a particular trait or phenotype
• Poly (many) genic (genes)
• The genes that influence the phenotype may be
found on the same chromosome or different
chromosomes
• Examples: eye color, height, weight, skin color,
blood pressure
• There is not a single gene that results in high/low blood
pressure: metabolism gene and obesity gene
11.
Polygenic traits
Many genes affect 1 phenotype
14.
5. Environmental Factors
• Mendel stated that genes will predict traits (phenotypes)
not the environment
• Today: phenotypes can be influenced by the
environment
• Example: hydrangea plant
• Acidic soil: flowers are blue
• Basic soil: flowers are red
• Example: artic fox
• Temperature: warmer-more enzyme production- darker coat
» Cooler: less enzyme production- white coat
• Example: human height/skin color
• Nutrition and height
• Uv rays and skin color
15.
Environmental Factors Hydrangea
Basic soil
Summer and winter artic
Acidic soil
16.
Pleiotropy
• Gregor Mendel believed that 1 trait had 1 phenotype
• Today we know that most genes have multiple
phenotypes—
– NOT polygenic--many genes
– BUT many phenotypes
• pleion- Greek for more
• EX: hereditary diseases
– Sickle-cell anemia has multiple symptoms or phenotypes
• Breaks down RBC’s: weakness, anemia, heart failure
• Clumping of cells: brain damage, fever
• Spleen damage
– PKU:
• genetic disorder that causes mental retardation
• decrease in hair and skin pigmentation
17.
Pleiotropy
• Sickle Cell anemia
18.
Epistasis
• Gregor Mendel believed that genes didn’t influence
other genes (Law of Independent Assortment)
– Genes are NOT linked
• Today we know that a gene at one locus (location)
alters the phenotype of a gene at a second locus.
• Epistasis: Greek for “stopping” or “causing to
stand”
• I.e.> fur coat colors
– One gene for fur coat color
– Another gene determines whether or not the pigment
will be deposited in the hair
19.
B: black pigment gene
Epistasis
C: depositing of pigment
20.
Epistasis in Labrador retrievers
• 2 genes: (E,e) & (B,b)
– pigment (E) or no pigment (e)
– pigment concentration: black (B) to brown (b)
21.
Epistasis
• More examples:
• Widows peak vs.
baldness
– One gene could code
for a widows peak
(WW or Ww) and the
other gene for
baldness could hide
the widows peak
22.
Non-Mendelian Warm-up
For 3 minutes write as much as
you can regarding the topic:
“Non-Mendelian genetics”. The
idea is to write consecutively for
3 full minutes.
23.
Non-Mendelian Genetics Matching Review
• 1. Incomplete dominance ___
• 2. Pleiotropy ____
• 3. Epistasis ____
• 4. Multiple alleles ____
• 5. Co-dominance____
• 6. Environmental factors ____
• 7. Polygenic traits ____
• A. more than 2 alleles: IA IB i
• B. 2 dominant alleles expressed
• C. more than one gene can code for a trait
• D. The temperature can affect fur coat color
• E. many phenotypes for one gene: example- diseases
• F. The blending or mixing of alleles in a heterozygote: Tt
• G. A gene at one location can “stop” the effect of another gene at a
different location
24.
•
Linked Genes
Mendel believed that genes assorted independently of
each other during gamete formation-genes are not
linked!
• Today we know that some traits are inherited together as
a package
– Genes are linked
– Genes that are on the same chromosome and close together (less likely
to cross over or swap)
25.
So how is a dihybrid
cross for linked genes
different than non-
linked genes?
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