Biology

Unit 4 Notes:NON-Mendelian

Genetics

(1) What does Non-Mendelian mean?

• Not all traits are as simple as dominant and recessive.

• Some traits…– Have more than just 2 alleles or variations.– Have 2 dominant alleles.– Are only passed on via sex chromosomes.– Are the result of 100’s of genes being

expressed.

(2) Non-Mendelian Types

• Polygenic Traits• Multiple Allele• Codominant Traits• Incomplete Dominant Traits• Sex-Linked Traits

(3) Polygenic & Multiple Allele Traits

• Polygenic = A trait which is the result of many genes being expressed at one time.– Examples:• Body shape and structure• Hair / Skin / Eye color

• Multiple Allele = A trait which has more than just 2 types of alleles that can be inherited.– Example:• Blood Type

(4) Codominant Traits

• Co = Together• Codominant = When 2 dominant traits are

expressed equally together (at the same time).

• Example:– Some flowers can be homozygous dominant and

RED.– Some flowers can be homozygous dominant and

WHITE.– Some flowers can be heterozygous, they look

RED AND WHITE (but NOT blended!!).

Homozygous Dominant RedAA

Homozygous Dominant WhiteBB

Heterozygous AB

(5) Setting Up Codominant Problems

• Use all capital letters.• Use 2 different letters, one per variation.• The heterozygote will show both

colors/traits at the same time, in patches.

• Example:– Homozygous Dominant #1 = AA– Homozygous Dominant #2 = BB– Heterozygous = AB

(6) Codominant Example #1

• A certain species of pansies are codominant for flower color. You cross a homozygous red flower, with a homozygous white flower:

(7) Codominant Example #2

• Now you take 2 offspring from the last cross (2 heterozygous pansies) and cross them:

(8) Incomplete Dominant Traits

• Incomplete = not fully• Incomplete Dominant = When 2 dominant traits are

partially expressed together at the same time, resulting in a blending appearance.

• Example:– Some flowers can be homozygous dominant and RED.– Some flowers can be homozygous dominant and

WHITE.– Some flowers can be heterozygous, they look PINK (like

a blending of red + white).

Homozygous Dominant RedAA

Homozygous Dominant WhiteBB

Heterozygous AB

(9) Setting Up Incomplete Dominant Problems

• Use all capital letters.• Use 2 different letters, one per variation.• The heterozygote will look blended.

• Example:– Homozygous Dominant #1 = AA– Homozygous Dominant #2 = BB– Heterozygous = AB

(10) Incomplete Dominant Example #1

• Snapdragon flowers show incomplete dominance for their petal color. You cross a homozygous red flower with a homozygous white flower:

(11) Incomplete Dominant Example #2

• Now cross 2 heterozygous snapdragons from the last problem:

(12) Sex-Linked Traits

• Sex-Linked = Traits only found on the sex chromosomes.

• REMEMBER:–Male = X Y– Female = X X

• These are often the types of traits that appear to “skip” generations or genders, or often show up more frequently in males.

(13) Sex-Linked Example #1

• Hair loss is a recessive gene connected to the x-chromosome.

• Write out the genotypes for:– Normal Female = – Female Carrier = – Bald Female = – Normal Male = – Bald Male =

(14) Sex-Linked Example #2

• Hair loss is a recessive gene connected to the x-chromosome. A man with normal hair and a woman who is a carrier decide to have children:

(15) Sex-Linked Example #3

• Dealing with the same hair-loss trait…. A bald man and a normal female decide to have children: