1. 7.1 KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

2. Two copies of each autosomal gene affect phenotype.
Mendel studied autosomal gene traits, like hair texture.

3. Rules of Inheritance
Some traits follow the simple rules of Mendelian inheritance of dominant and recessive genes.
Complex traits follow different patterns of inheritance that may involve multiples genes and other factors. For example,
Incomplete or blended dominance
Codominance
Multiple alleles
Regulatory genes
Have students guess how these examples of genetic rules may work. Encourage students to guess a definition or provide an example for each term.

4. Incomplete Dominance
Incomplete dominance results in a phenotype that is a blend of a heterozygous allele pair. Ex., Red flower + Blue flower => Purple flower
If the dragons in Harry Potter have fire-power alleles F (strong fire) and F’ (no fire) that follow incomplete dominance, what are the phenotypes for the following dragon-fire genotypes? Genotypes Phenotypes
FF strong fire
FF’ moderate fire (blended trait)
F’F’ no fire
Define and provide an example for incomplete dominance, and help students understand and apply the concept to the dragon’s fire power. Students may ask about using F and F’ instead of lower and upper-case letters. Provide clarification that lower and upper-case letters are used to indicate alleles with dominant or recessive traits. And explain that incomplete dominance is indicated with apostrophe (’) on an upper case letter.

5. Codominance
Codominance results in a phenotype that shows both traits of an allele pair. Ex., Red flower + White flower => Red & White spotted flower
If merpeople have tail color alleles B (blue) and G (green) that follow the codominance inheritance rule, what are possible genotypes and phenotypes? Genotypes Phenotypes
Define and provide an example for codominance, and help students understand and apply the concept to merpeople’s tail colors. Clarify the important distinction between incomplete/blended dominance and codominance--the former results in a phenotype that is a blended or average trait between the two different traits, and the latter results in a mixed trait with both traits being observable.

6. Codominance results in a phenotype that shows both traits of an allele pair. Ex., Red flower + White flower => Red & White spotted flower (both traits)
If merpeople have tail color alleles B (blue) and G (green) that follow the codominance inheritance rule, what are possible genotypes and phenotypes? Genotypes Phenotypes BB blue tail GG green tail BG blue & green tail (both traits)
Provide the answers for both genotypes and phenotypes for merpeople’s tail colors.

7. Codominant alleles will both be completely expressed.

8. In incomplete dominance, neither allele is completely dominant nor completely recessive.

9. Mendel’s rules of inheritance apply to autosomal genetic disorders.
Recessive disorder requires a homozygous recessive genotype to affect a person. A heterozygote for a recessive disorder is a carrier.
Disorders caused by dominant alleles are uncommon.
(dominant)

10. Mendel’s rule only apply for autosomal genes(chromosome pairs 1-22)
Mendel’s rule only apply for autosomal genes(chromosome pairs 1-22). Genes on sex chromosomes are called sex-linked genes.
Y chromosome genes in mammals are responsible for male characteristics. Males have an XY genotype.
X chromosome genes in mammals affect many traits. Females have an XX genotype.

11. Because males only have one copy of the X chromosome all of a male’s sex-linked genes are expressed.
In females, expression of sex-linked genes is similar to autosomal genes because they have two copies of the X chromosome. Y X

12. Common examples of sex-linked disorders:
Duchenne’s muscular dystrophy
Hemophilia
Color Blindness

14. Left Right Top 25 29 Spots Middle 45 56 Bottom 6 8
Normal Color Vision
Red-Green Color Blind
Left
Right
Top 25 29
Spots
Middle 45 56
Bottom 6 8
The test to the left is simpler. The individual with normal color vision will see a 5 revealed in the dot pattern. An individual with Red/Green (the most common) color blindness will see a 2 revealed in the dots.

15. X chromosome inactivation randomly “turns off” one X chromosome, named inactive chromosome a Barr body.
Stays inactive throughout cell’s lifetime.
Only seen in cats.

16. Multiple alleles
Multiple alleles have more than 2 variations. Ex., human blood type has 3 different allele variants, A, B, and O.
Genotypes
Phenotypes
AA, AO
A blood type AB
AB blood type
BB, BO
B blood type OO
O blood type
Explain the multiple alleles—more than 2 variant forms of a gene—related to human blood types. Students may observe additional relationship among the blood types: O is recessive to A and B; A and B are codominant. However they may also notice that the recessive O blood type does not use lower case letter as all blood types are indicated with upper case letters.

17. The ABO blood types result from codominant alleles and multiple alleles.
Codominant alleles are neither dominant nor recessive.
Codominant alleles will both be completely expressed.
Many genes have more than two alleles.

18. There are 3 alleles that determine blood type: IA, IB, and i
IA and IB are dominant to i.
IA and IB are codominant.

19. Codominance

20. There are 4 blood types: A : Genotype: IAIA or IAi Antigen: A
Antibody: Anti-B   
Can receive from: A, O
Can donate to: A, AB

21. B :
Genotype: IBIB or IBi
Antigen: B
Antibody: Anti-A   
Can receive from: B, O
Can donate to: B, AB

22. AB :
Genotype: IAIB
Antigen: A & B
Antibody: none  
Can receive from: A, B, AB, & O (universal recipient)
Can donate to: AB

23. O :
Genotype: ii
Antigen: none
Antibody: Anti-A and Anti-B   
Can receive from: O
Can donate to: A, B, AB, & O (universal donor)

24. Rh Factor: Another surface marker which may or may not be present on the RBC. 

25. Rh+ :
Genotype: Rh+Rh+ or Rh+Rh-
Antigen: Rh
Antibody: none  
Can receive from: Rh+ & Rh-
Can donate to: Rh+

26. Rh- :
Genotype: Rh-Rh-
Antigen: none
Antibody: Rh+
Can receive from: Rh-
Can donate to: Rh- & Rh+

27. Another example of multiple alleles.

28. Polygenic traits are produced by two or more genes.
Order of dominance: brown > green > blue.

29. Skin color result of four genes that interact to produce range of colors

30. Regulatory Genes
Regulatory genes regulate the expression of other genes.
For example, a regulatory gene may ‘silence’ another gene from expressing its dominant trait. The Manx cat has no tail because it has a regulatory gene that silences the gene that expresses the tail. This tail silencing gene is dominant and has possible alleles:
S = silences tail gene = no tail (Manx cat)
s = doesn’t silence tail gene = has tail (non-Manx cat)
Question: Can 2 Manx cats without tails have a kitten with a tail? Show your answer using Punnett Square.
Define and provide the example of a silencing regulatory gene in Manx cats. Have students work in pairs to answer whether two Manx cats without tails can have a kitten with a tail.

31. Regulatory Genes: Manx Cat
Question: Can 2 Manx cats without tails have a kitten with a tail? Show your answer using Punnett Square.
The possible alleles for the tail-silencing gene are:
S = no tail (dominant)
s = has tail (recessive)
Only if both parent cats have the heterozygous genotype-- Ss, there is a 25% chance for their having a kitten with a tail.
S s
S SS Ss
s Ss ss
Have student pairs volunteer their answers and review the answer using Punnett Square.

32. An epistatic gene can interfere with other genes.
There are no new phenotypes produced by this type of gene interaction.

33. Epistatic: recessive trait blocks another allele
Black is dominant to chocolate B or b Yellow is recessive epistatic (E or e)
Phenotype
Possible Genotypes
        
BBEE BbEE BBEe BbEe
bbEE bbEe
BBee Bbee bbee

34. Phenotype can be a combination of genotype and environment.
Malnourished
Fed and cared for.
Identical twins separated at birth and treated differently.
Sex of sea turtles depends on genes and environment. Temperature when eggs develop determine sex, warmer, more females, cooler, more males.

35. 7.4 KEY CONCEPT A combination of methods is used to study human genetics.

36. A pedigree is a chart for tracing genes in a family.
Phenotypes are used to infer genotypes on a pedigree.
Autosomal genes show different patterns on a pedigree than sex-linked genes.

37. If the phenotype is more common in males, the gene is likely sex-linked.

38. 7.3 KEY CONCEPT Genes can be mapped to specific locations on chromosomes.

39. Because of their location on a chromosome, some genes travel together and are considered to be linked.
Wild type
Mutant

40. Linkage maps estimate distances between genes.
The closer together two genes are, the more likely they will be inherited together.
Linkage maps show the relative locations of genes.