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