Post on 20-Jan-2016
Part 2:Non-Mendelian
Genetics
Last week we learned about Mendelian Genetics
• This 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
• Incomplete Dominance- When the heterozygous phenotype is an intermediate (mix) between those of the two homozygous parents.
Example• AA=red Aa=pink
aa=white
Incomplete Dominance(One allele for a specific trait is not completely dominant over the other
allele. This results in a 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 dominant (BB) individual is blue, a homozygous recessive (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?
Key:
BB=blue
Bb=purple
bb=red
P1 CrossBlue X RedBB X bb
F1Genotype:Phenotype:
Co-dominance - both alleles are expressed. Neither allele is
dominant over the other.
Sickle Cell
Co-dominance(Forms of the gene are equally dominant to each other.)
Genotype Phenotype Example
Homozygous Dominant
Dominant Red horse hair
Heterozygous Dominant
Intermediate (both alleles
are expressed)
Roan hair(red AND white)
Homozygous Recessive
Recessive White horse hair
Practice Problem: Co-dominance• 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 dominant red bull with 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.
2. Make a “key” with the genotypes and phenotypes listed.
3.List the parent’s genotypes and draw a small image of each. Then draw one offspring. List the genotype. (See example.)
4. List and Define the Vocab word at the bottom of the poster.
5. Must be COLORED and NEAT!!
You may NOT copy my example! Think of something ORIGINAL!!!
Warm-up Questions• What is Incomplete Dominance?
• What is Co-dominance?
• How are they different from each other?
• How are the different from Complete Dominance (Simple Dominance)?
Multiple Alleles- having more than 2 alleles for one specific
trait• Remember a gene is an inherited trait (hair
color). An allele is a form of that gene which codes for the phenotype (brown, blond, red, etc).
Multiple Alleles (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.
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?
Type O X Type AB
This Chart will Always be provided for you
• Worksheet Multiple Alleles what’s not done is HW
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
C = colorblindness which is a recessive, sex-linked, genetic trait
Why are more males affected by X-linked traits than females?
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
• Sex linked traits WS what’s not done is HW
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