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.
Special Inheritance
Patterns
Introduction
1. Determine if the following traits are
dominant or recessive???
Tongue Rolling
Ear Lobe Attachment
Widow’s Peak
PTC Tasting
Introduction
2. Many human traits are inherited in
the typical dominant/recessive pattern.
Unusual Inheritance Patterns
1. Incomplete dominance: the dominant
allele does not completely dominate over the
recessive allele (Incomplete and
Codominant Traits worksheet #1 and 6)
SNAPDRAGONS
Unusual Inheritance Patterns
RR ♂
Red
x
rr ♀
White
• Genotype frequency:
• Phenotype frequency:
Unusual Inheritance Patterns
2. Codominance: two dominant alleles are
equal in dominance
Unusual Inheritance Patterns
Example = Blood Types
A and B are dominant; O is recessive
Blood Type (Phenotype)
A
B
AB
O
Genotype
Unusual Inheritance Patterns
• Genotype frequency:
• Phenotype frequency:
Unusual Inheritance Patterns
3. Polygenic Inheritance: many genes affect
the same trait
Example = skin color, eye color, hair color
Gene Linkage (Fruit Fly Lab Data)
1. Review of Metaphase I during Meiosis
2. The LAW OF INDEPENDENT ASSORTMENT states
that chromosomes line up independently of one another
Gene Linkage
3. Genetic variety of sex cells is increased
Gene Linkage
4. Genes located on different chromosomes line up
independently. But what about genes on the same
chromosome??
5. Linked genes: genes located on the SAME
chromosome; these traits tend to be inherited together
• EXAMPLES: Blonde hair and blue eyes, Red hair and
freckles
Some dominant/recessive genes cause
certain conditions (Human Genetic
Disorder Worksheet #2 and 6)
Examples
1. Dwarfism
(dominant disorder)
2. Sickle Cell Anemia
(recessive disorder)
Other conditions are caused by sexlinked genes (Sex-linked Traits
Worksheet #3, 7, and 8)
Examples
1. Hemophilia
2. Colorblindness
Other phenotypes are caused by sexlinked genes
3. Punnett squares for sex-linked traits:
Hh, HH = normal
X Y ♂
hh = hemophilia
x
X X♀
Genotypic frequency:
Phenotypic frequency:
Other phenotypes are caused by sexlinked genes
3. Punnett squares for sex-linked traits:
Hh, HH = normal
X Y ♂
hh = hemophilia
x
X X♀
Genotypic frequency:
Phenotypic frequency:
Other phenotypes are caused by sexlinked genes
4. Males are more likely to have sex-linked
traits. Why?
Males do not have an extra X chromosome
to mask certain genes
Some traits are sex-influenced. This means
that the gene is expressed differently in
males and females.
1. Genes are on autosomes
2. Genes must be activated by hormones
References
• http://scienceprofonline.googlepages.com/Bentpinky.jpg/
Bentpinky-full.jpg
• http://www.scienceteacherprogram.org/images/Nakita084.gif
• http://www.ncrtec.org/tl/camp/gene/curl.jpg
• http://www.ncrtec.org/tl/camp/gene/widow.jpg
• http://learn.genetics.utah.edu/content/begin/traits/ptc/ima
ges/DSC00100.jpg
• http://wiki.answers.com/Q/What_are_examples_of_domi
nant_traits
References
• http://porpax.bio.miami.edu/~cmallery/150/mendel/c14x9
incomplete-dominance.jpg
• http://creationwiki.org/pool/images/thumb/c/c6/Codomina
nt.jpg/200px-Codominant.jpg
• http://www.gsboc.co.uk/graphics/pupscolour.jpg
• http://www.myherbalwellbeing.com/article_images/littleg
uy.jpg
• http://scanned.files.wordpress.com/2007/12/ssa.jpg
• http://www.humanillnesses.com/original/images/hdc_000
1_0002_0_img0129.jpg
• http://comps.fotosearch.com/comp/BDX/BDX107/colorblindness-test_~bxp26007.jpg