1. 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?

2. A a AA Aa A a Aa aa
Genotypic ratio:
1 : 2 : 1
Phenotypic ratio:
3 : 1

3. 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?

4. 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.

5. Types of Inheritance
Mendelian: genetic traits are controlled by a single gene
----- dominant or recessive; flower color
Sex-linked: genetic traits are controlled by the X or Y chromosome
-----X-linked recessive; colorblindness
Co-dominance: both alleles contribute to the phenotype equally (ex. Blood type)
Incomplete dominance: when the presence of both alleles leads to a blending of traits (ex. Red flower + white flower = pink flower)
Polygenic: when a trait is controlled by multiple genes

6. traits controlled by a single gene
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

7. Mendelian (Simple) Genetics

8. 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 chromosome
X-Linked,
Y-Linked, colorblindness
Codominance
Incomplete Dominance
Polygenic Traits

9. 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”

10. X-Linked Traits X-Linked Dominant: X-Linked Recessive:
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
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

11. X-Linked Dominant

12. X-Linked Recessive (carrier mother)

13. 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 chromosome
X-Linked,
Y-Linked, colorblindness
Codominance
both alleles contribute equally
(both phenotypes show)
Blood Type
A + B = AB
Incomplete Dominance
Polygenic Traits

14. 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

16. 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 chromosome
X-Linked,
Y-Linked, colorblindness
Codominance
both alleles contribute equally
(both phenotypes show)
Blood Type
A + B = AB
Incomplete Dominance
presence of both alleles leads to blending (new phenotype made)
Red flower + White flower = Pink flower
Polygenic Traits

17. 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.

19. 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 chromosome
X-Linked,
Y-Linked, colorblindness
Codominance
both alleles contribute equally
(both phenotypes show)
Blood Type
A + B = AB
Incomplete Dominance
presence of both alleles leads to blending (new phenotype made)
Red flower + White flower = Pink flower
Polygenic Traits
trait controlled by multiple genes
Skin color

20. Polygenic Inheritance
Multiple genes control the inheritance of traits

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

22. Non-Mendelian Inheritance
In 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.

23. Non-Mendelian Inheritance
In 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.
Genotypic ratio:
1:2:1 B W B BB BW
Phenotypic ratio: W BW WW
1:2:1

24. Non-Mendelian Inheritance
Mrs. 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.
Male: Female Ratio =
2:2 X Y X XX XY
Phenotypes =
1 affected son
1 normal son
1 carrier daughter
1 normal daughter XH
XHX
XHY

25. 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.

26. Debrief: Do you think most traits follow Mendelian or non-Mendelian rules of inheritance? Why?

27. Type of Inheritance Mendelian or Non-Mendelian? Description Example
Mendelian (Simple Genetics)
Sex-Linked Traits
Codominance
Incomplete Dominance
Polygenic Traits