Download Inheritance Patterns

INHERITANCE PATTERNS
GREGOR MENDEL DISCOVERED THE BASIC
PRINCIPLES OF HEREDITY BY BREEDING GARDEN
PEAS IN CAREFULLY PLANNED EXPERIMENTS
MENDEL’S RESULTS
MENDEL’S 3 LAWS
Law of Dominance
Law of Segregation
Law of Independent Assortment
LAW OF DOMINANCE
There are two alleles for each gene
One is dominant over the other, which is recessive
Dominant means it is always expressed, recessive is only expressed
if there are two copies of the allele
MENDEL’S LAWS: LAW OF SEGREGATION
Sexual organism have two copies of a gene
 One from mom and one from dad
The law of segregation states that the two alleles separate
(segregate) during meiosis and end up in different gametes (sex
cells)
Thus, an egg or a sperm gets only one of the two alleles that are
present in the somatic cells of an organism
MENDEL’S LAWS: LAW OF INDEPENDENT
ASSORTMENT
The law of independent assortment states that each pair of alleles
segregates independently of other pairs of alleles during gamete
formation
Strictly speaking, this law applies only to genes on different, nonhomologous chromosomes
Genes located near each other on the same chromosome tend to
be inherited together
NON-MENDELIAN INHERITANCE
INCOMPLETE DOMINANCE
No dominant allele - blending
The phenotype of F1 hybrids is
somewhere between the
phenotypes of the two parental
varieties
 Ex: a red and white flower makes a
pink flower
P Generation
F1 Generation
Red
CRCR
CR
White
CWCW
CW
Gametes
Pink
CRCW
1
F2 Generation
2C
R
1
2C
1
2C
W
Sperm
1
1
2C
W
2C
R
CRCR
Eggs
1
R
CRCW
2C
W
CRCW
CWCW
CODOMINANCE
Two dominant alleles
Each allele affects the phenotype in separate, distinguishable ways
 Ex: a red and white flower make a marbled, or speckled, flower
MULTIPLE ALLELES
Most genes exist in populations in
more than two allelic forms
For example, the ABO Blood type
system has 3 alleles:
 The IA allele adds the A carbohydrate,
 The IB allele adds the B carbohydrate;
 The i allele adds neither
BLOOD TYPE PUNNETT SQUARE
BLOOD TYPING LAB!
SKIN COLOR
How do we get skin color?
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POLYGENIC INHERITANCE
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Polygenic inheritance results from an
additive effect of two or more genes
on a single phenotype
15/64
Fraction of progeny
Skin color in humans is an example of
polygenic inheritance
20/64
6/64
Eye color is another example: at least
8 genes code for eye color in humans
1/64
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