Download Inheritance Patterns - Milton

Special Inheritance Patterns
Learning Targets:
“I Can…”
-Define “codominance.”
-Complete a Punnett Square for genes that are codominant.
-Define “incomplete dominance” and give an example.
-Complete a Punnett Square for genes that show incomplete
dominance.
-Describe how the environment can affect the expression of
genes.
-Define a “sex-linked gene.”
-Complete a Punnett Square for genes that are sex-linked.
A. Introduction
1. Determine if the following traits are dominant or
recessive
Tongue rolling
Ear lobe attachment
Widow’ peak
PTC taster
2. Many human traits are inherited by the general
dominant/recessive pattern
B. Some traits have unusual inheritance patterns (Incomplete
and Codominant Traits #1 and 6)
1. Incomplete dominance:
1
RR x rr
Red White
Genotype frequency:
Phenotype frequency:
2. Codominance:
Example = Blood Types
A and B are dominant; O is recessive
Blood Type (Phenotype)
Genotype
A
B
AB
O
Genotype frequency:
Phenotype frequency:
2
3. Polygenic Inheritance:
Example = skin color, eye color, hair color
C. Gene Linkage (See Fruit Fly Lab Data)
1. Review of Metaphase I during Meiosis
2. The __________________________________states
that chromosomes line up independently of one another
3. Genetic ___________ of sex cells is increased
4. Genes located on different _________________ line up
independently. But what about genes on the same
chromosome??
5. Linked genes: genes located on the ______ chromosome;
these traits tend to be inherited together
EXAMPLES: Blonde hair and blue eyes, Red hair and
freckles
D. Some dominant/recessive traits cause certain conditions.
(Human Genetic Disorder Worksheet #2 and 4)
Examples
1. Dwarfism (_____________ disorder)
2. Sickle Cell Anemia (_____________ disorder)
E. Other conditions are caused by sex-linked traits (Sexlinked Traits Worksheet #3, 4, 7 and 8)
Examples
1.
2.
3
3.Punnett squares for sex-linked traits:
Hh, HH = normal
hh = hemophilia
X Y
x
X X
Genotypic frequency:
Phenotypic frequency:
X Y
x
X X
Genotypic frequency:
Phenotypic frequency:
4. Males are more likely to have sex-linked traits. Why?
Males do not have an extra ____ chromosome to mask
certain genes!
E.Some traits are _____________. This means that the gene is
expressed differently in males and females.
1. Genes are on ____________
2. Genes must be activated by ____________
4