We’ve learned about Mendelian Genetics.
• Now week we will learn about Complex Patterns of Inheritance.
• Complex inheritance does not follow the patterns that Mendel described.
Exceptions to Simple Exceptions to Simple DominanceDominance
1. Incomplete dominance
2. Co dominance
3. Multiple alleles
4. Sex-linked Traits
• Incomplete Dominance- When the heterozygous phenotype is an intermediate (mix) between those of the two homozygous parents.
Example• AA=red aa=white
Aa=pink
Incomplete Dominance(One allele for a specific trait is not completely dominant over the other
allele. This results in a combined (blended) phenotype.)
Genotype Phenotype Example
Homozygous dominant
Dominant Curly hair
Heterozygous dominant
Intermediate
(blend)
Wavy hair
Homozygous recessive
Recessive Straight hair
Practice Problem: Incomplete Dominance
• A wildcat comes in three colors, blue, red, and purple. A homozygous (BB) individual is blue, a homozygous (bb) individual is red, and a heterozygous (Bb) individual is purple. What would be the genotypes and phenotypes of the offspring if a blue wildcat were crossed with a red one?
Codominance - both alleles are expressed. Neither allele is
dominate over the other.
PP = Pinkww = whitePw = Pink and
white
Codominance(Forms of the gene are equally dominant to each other.)
Genotype Phenotype Example
Homozygous dominant
Dominant Red horse hair
Heterozygous dominant
Intermediate (mixed)
Roan hair(red AND white)
Homozygous recessive
Recessive White horse hair
Practice Problem: Codominance• In cattle, reddish coat color is not completely
dominant to white coat color. Heterozygous individuals have coats that are roan colored (ie. reddish, but with spots of white hairs).
• Show a cross of a homozygous dominate red bull to a roan cow.
• (hint roan is heterozygous)
Key:
BB= RedBb= Roan (both of red and white)
bb= White
P1 CrossRed X RoanBB X Bb
F1Genotype:Phenotype:
Co-Dominance Vs. Incomplete Dominance
Make a poster with a fictitious animal or plant illustrating Co-Dominance and Incomplete Dominance.
1. Give your new organism a name and title your poster “ Complex Inheritance pattern of ___________”
2. Make a “key” with the genotypes and phenotypes listed.
3.List the parents genotype and draw a small image of each then draw one offspring larger, list the genotype. (see example)
4. List and Define the Vocab word at the bottom of poster
5. Must be COLORED and NEAT!!
You may NOT copy my example think of something on your OWN!!
• What is Incomplete Dominance?
• What is Codominance?
• How are they different from each other?
• How are they different from Complete Dominance?
Multiple alleles- having more than 2 alleles for a specific
trait• Remember a gene is an inherited trait (hair
color) and an allele is a form of that gene that codes for the phenotype (brown, blond, red, etc.)
Multiple allele (Multiple alleles can demonstrate a hierarchy of
dominance)in this example, there a 4 possible alleles: M, mb , mc , m
Genotype Phenotype Example
MM, Mmb, Mmc, Mm Dominant to all others
Ace beats the King, Queen,
Jack
mbmb, mbmc, mbm Version b (dominant to mc & m)
King beats the Queen & Jack
mcmc, mcm Version c (dom. to rec.)
Queen beats the Jack
mm Recessive to all others
Jack
The hair color of chinchillas would be an example of a multiple allelic trait.
Chinchilla Genetics
http://www.chinchillachronicles.com/chinchilla_genetics.html
Blood cells are an example of multiple alleles and Co-Dominance
As you can count, there are 6 different genotypes & 4 different phenotypes for blood type.
Bottom line for Multiple alleles
• The presence of multiple alleles allows for an increased number of genotypes and phenotypes, thus creating more variation.
• Why might variation be a good thing????
Practice Problem: Multiple alleles
• A woman with Type O blood and a man who is Type AB have are expecting a child. What are the possible blood types of the kid?
Sex linked
• Sex linked traits- characteristic controlled by genes that are on the X chromosome.
*Remember*
Male Genotype: XY Female Genotype: XX
Sex-linked (traits carried on sex chromosome, usually X-linked)
Genotype Phenotype Example
XX
XYNon-afflicted, not a carrier
Normal female
Normal male
XcXCarrier but
not afflicted
Carrier female*males cannot be
carriers!
XcXc
XcYBoth are afflicted
Colorblind female & male
Why are more males affected by X-linked traits than females?
• Males have an XY genotype, since males have only one X chromosome, they are affected by recessive X linked traits more often than females.
• Females have an XX genotype and the other X chromosome would likely mask the recessive trait.
Sex-Linked Traits
• Can you see a number inside this circle?
• About 8% of males a color blind and only .5% of females
Punnett Square
• XB = Normal• Xb = affected trait• Y= Normal Y
chromosome
XB Y
XB XBXB XB Y
Xb XBXb Xb Y
Practice problem: Sex-linked
• Hemophilia is due to a sex-linked recessive gene (Xh) and the normal condition to the gene (XH). Show a cross between a hemophiliac man and a woman does not carry the trait.
hemophiliac man X normal woman
*Remember*Male Genotype: XYFemale Genotype: XX
KeyXh = NormalXH = Hemophiliac
Lets review our new terms!!• Sex linked traits- characteristic controlled by
genes that are on the X chromosome.• Incomplete dominance- When the heterozygous
phenotype is intermediate between those of the two homozygous parents.
• Codominance- both alleles are expressed, neither allele is dominate over the other
• Multiple alleles- having more than 2 alleles for a specific trait