basic mendelian genetics what lovely things we pass onto our children!
Post on 21-Dec-2015
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Basic Mendelian Genetics
What lovely things we pass onto our children!
Mendel’s Laws• Law 1: Law of Unit Characteristics
– Inherited traits are controlled by “factors” which occur in “pairs”.
Factors = __________ Pairs = __________
• Law 2: Law of Dominance– One allele hides another allele in a heterozygote
Stronger allele = _____________ Weaker allele = _____________
Mendel’s Laws Continued
• Law 3: Law of Segregation– Alleles of a gene are separated during gamete
formation
Each cell only gets 1 allele for a gene
A a
B b
Mendel’s Laws Continued
• Law 4: Law of Independent Assortment of Alleles– When alleles separate during meiosis, they do
so independently of alleles of other genes
Placement of alleles is random
Not influenced by other genes
A A
BB
a a
bb
Mendel’s Laws Continued
• Law 5: Law of gene pricing– Lee genes are usually less expensive than
Levi’s, except when Levi’s are on sale
Life Beyond the Law of Dominance
Not all traits are governed by the law of dominance
• Incomplete Dominance– Neither allele is completely dominant over the
other in the heterozygote Blending/Mixing
Ex) Snap dragons
WW – White flowers
RR – Red Flowers
RW – Pink Flowers
Incomplete Dominance
Life Beyond the Law of Dominance
• Codominance– Both genes express themselves FULLY at the
same time
Example: Roan cattle
RR = Red Hair
WW = White Hair
RW = Roan (both red + white)
Example 2: Blood type in humans (AB)
Life Beyond the Law of Dominance
• Multiple Alleles– A gene possessing more than 2 alleles
Example: Blood types
Blood types differ in antigens found on RBC’s
AA – Homozygous A Type A
BB – Homozygous B Type B
OO – Homozygous O Type O
AO – Heterozygous A Type A
BO – Heterozygous B Type B
AB – Heterozygous AB Type AB
Life Beyond the Law of Dominance
• Polygenic Inheritance– When a trait is controlled by more than 2
genes
Example: Eye color (3 genes)
Amount of pigment
Location of pigment
Tone of pigment
Cowboys denied home field by Eagles
A Review of Mendelian Genetics
1) Neither allele is dominant a) Complete Dominance
2) More than 2 alleles b) Codominance
3) Both alleles are dominant c) Incomplete dominance
4) Many genes code for 1 trait d) Multiple alleles
5) One allele is dominant e) Polygenic inheritance