BELL WORK (Buff Binder):

Complete a Punnett square for the following genetic cross and answer the question:

Almond eyes (A) are dominant to round eyes (a). What are the genotypic and phenotypic ratios of the offspring when you cross two heterozygous parents?

A

A

a

a

AA Aa

Aa aa

Genotypic ratio:

Phenotypic ratio:

1 : 2 : 1

3 : 1

Today’s Standard: B6F predict possible outcomes of various genetic

combinations such as non-Mendelian inheritance

Essential Question: Do you think most traits follow Mendelian or non-

Mendelian rules of inheritance? Why?

REMEMBER:Mendel’s principles form the basis of the modern

science of genetics.

The inheritance of biological characteristics is

determined by specific segments of DNA called

genes.

Genes are passed from parents to their offspring.

Types of Inheritance 1. Mendelian: genetic traits are controlled by a single gene

----- dominant or recessive; flower color

2. Sex-linked: genetic traits are controlled by the X or Y chromosome

-----X-linked recessive; colorblindness

3. Co-dominance: both alleles contribute to the phenotype equally (ex. Blood type)

4. Incomplete dominance: when the presence of both alleles leads to a blending of traits (ex. Red flower + white flower = pink flower)

5. Polygenic: when a trait is controlled by multiple genes

Type of Inheritance

Mendelian or

Non-Mendelian?

Description Example

Mendelian (Simple Genetics)

Mendelian traits controlled by a single gene Bb x BB

Sex-Linked Traits

Codominance

Incomplete Dominance

Polygenic Traits

Mendelian (Simple) Genetics

Type of Inheritance

Mendelian or

Non-Mendelian?

Description Example

Mendelian (Simple Genetics)

Mendelian traits controlled by a single gene Bb x BB

Sex-Linked Traits Non traits controlled by the X or Y

chromosomeX-Linked, Y-Linked,

colorblindness

Codominance

Incomplete Dominance

Polygenic Traits

Sex-linked traits

• Are traits that are determined by either the Y or X chromosome

– If they are determined by the Y chromosome they are referred to as “Y-linked”

• Y-linked disorders are very rare and often cause infertility in men

– If they are determined by the X-chromosome they are referred to as “X-linked”

X-Linked TraitsX-Linked Dominant:

• These conditions (such as vitamin D resistant rickets) are rare and can affect both men and women– Men are more affected than

women– Both men and women can pass

on the affected chromosome to their children

X-Linked Recessive:

• These disorders (such as hemophilia and color blindness) more frequently affect men than women– Both men and women can pass these

traits on to their children (at different rates)

• An affected man/unaffected woman = sons who are unaffected, daughters who are carriers

• An affected woman/unaffected man = 50% chance of passing the trait. If she passes on her affected X chromosome, then her daughters will be carriers and her sons will be affected

– This is why men are more likely to be color blind than women

X-Linked Dominant

X-Linked Recessive (carrier mother)

Type of Inheritance

Mendelian or

Non-Mendelian?

Description Example

Mendelian (Simple Genetics)

Mendelian traits controlled by a single gene Bb x BB

Sex-Linked Traits Non traits controlled by the X or Y

chromosomeX-Linked, Y-Linked,

colorblindness

Codominance Non both alleles contribute equally (both phenotypes show)

Blood TypeA + B = AB

Incomplete Dominance

Polygenic Traits

Co-dominance• When the genotype is heterozygous, then both traits will

show up equally– Note: when writing we show this with two different capital

letters

Type of Inheritance

Mendelian or

Non-Mendelian?

Description Example

Mendelian (Simple Genetics)

Mendelian traits controlled by a single gene Bb x BB

Sex-Linked Traits Non traits controlled by the X or Y

chromosomeX-Linked, Y-Linked,

colorblindness

Codominance Non both alleles contribute equally (both phenotypes show)

Blood TypeA + B = AB

Incomplete Dominance Non presence of both alleles leads to

blending (new phenotype made)Red flower +

White flower = Pink flower

Polygenic Traits

Incomplete Dominance• When the genotype is

heterozygous, then the trait will be a blend of the two alleles

• Note: Sometimes, we write this by using an abbreviation of the trait in a capital letter (C =color) and the alleles as a superscript (CR = red flower) or subscript (CR).

• Sometimes, we just say the heterozygous trait is a blend.

Type of Inheritance

Mendelian or

Non-Mendelian?

Description Example

Mendelian (Simple Genetics)

Mendelian traits controlled by a single gene Bb x BB

Sex-Linked Traits Non traits controlled by the X or Y

chromosomeX-Linked, Y-Linked,

colorblindness

Codominance Non both alleles contribute equally (both phenotypes show)

Blood TypeA + B = AB

Incomplete Dominance Non presence of both alleles leads to

blending (new phenotype made)Red flower +

White flower = Pink flower

Polygenic Traits Non trait controlled by multiple genes Skin color

Polygenic Inheritance• Multiple genes control the inheritance of traits

Both genes and the environment determine how traits are expressed in a population

Non-Mendelian InheritanceIn rabbits, white coat color (W) and black coat color (B) are

codominant, and both of these alleles are dominant over albino (c); heterozygotes (WB) are spotted.

1. Draw a Punnett Square that shows the genotypes of the offspring from a spotted rabbit and a white rabbit.

Mrs. PigglyWiggly is a carrier of the sex-linked hemophilia allele, and Mr. PigglyWiggly is normal (as far as blood chemistry goes).

2. Draw a Punnet square that shows the possible genotypes among their children.

Non-Mendelian InheritanceIn rabbits, black coat color (B) and white coat color (W)

are codominant; heterozygotes (BW) are spotted.

1. Draw a Punnett Square that shows the possible offspring from crossing two spotted rabbits.

BB

W

W

BB BW

BW WW

Genotypic ratio:1:2:1

Phenotypic ratio:1:2:1

Non-Mendelian InheritanceMrs. PigglyWiggly is a carrier of the x-linked recessive

hemophilia allele (XH), and Mr. PigglyWiggly is normal (as far as blood chemistry goes).

2. Draw a Punnett square that shows the possible genotypes among their children.

XX

Y

XH

XX XY

XHX XHY

Male: Female Ratio =2:2

Phenotypes = 1 affected son1 normal son1 carrier daughter1 normal daughter

Non-Mendelian Inheritance

Spongebob loves growing flowers for his gal pal, Sandy. She loves the Poofkin flowers—red, purple, and blue! Interestingly enough, the Poofkin flowers display incomplete dominance in their genes for color.

1. Using “R” for red and “B” for blue, what would be the genotypes for the following phenotypes?

red: ______ purple: _____ blue: _____

2. Complete a Punnett square to cross a red Poofkin and a purple Poofkin.

Debrief:

Do you think most traits follow Mendelian or non-Mendelian rules of

inheritance? Why?

Type of Inheritance

Mendelian or

Non-Mendelian?

Description Example

Mendelian (Simple Genetics)

Sex-Linked Traits

Codominance

Incomplete Dominance

Polygenic Traits