Chapter 11Beyond Mendel

Conditions that Mendel didn't explore - genetic traits that are inherited in new and interesting patterns

Incomplete Dominance Codominance Multiple Allele Traits Epistatic AllelesSex DeterminationPolygenic Inheritance

Incomplete Dominance

Traits appear to "blend" in offspringRR x WW

      RW  (pink)

Show:

Pink x Red

Pink x Pink

White x White

Figure 11.14

This illustrates another style of "letters" to denote genotypes

R1 and R2

Codominance

Both alleles in a heterozygous individual are expressed

Sickle Cell Trait in Humans

Genotypes  & Phenotypes

SS= not sickle cellSs= a little sickle cellss= a lot sickle cell

Coloration in Rodents

Black x White = Gray

BB   x   WW  =  BW

ROAN COW -           What happens when you cross a white and a red cow?

Roan is codominant - both alleles R and W are expressed

What happens when two Roan Cows are Crossed?

Blood Types  - Multiple Alleles

When doing blood type crosses, you will need to know whether at type A or B person is heterozygous or homozygous. Type O's are automatically OO and type AB is automatically AB. Crosses are performed the same as any other.

Show Crosses:

A B   x   A O                        A O  x  B O                         A A  x  A B

A woman who is type A is married to a man who is type B, what are ALL of the possible blood types of their children?

Many Genes Have Multiple Alleles•A population might have more than two alleles for a given gene.• In Labrador retriever, coat color is determined by one gene with four

different alleles. Five different colors result from the combinations of these alleles.  (More on labradors later)

Eye color is also controlled by multiple alleles

LABRADOR RETRIEVERS AND EPISTATIC ALLELES

•A population might have more than two alleles for a given gene.• In labrador retriever, coat color is determined by one gene with four

different alleles. Five different colors result from the combinations of these alleles.

•Even if more than two alleles exist in a population, any given individual can have no more than two of them: one from the mother and one from the father.

Black is dominant to chocolate B or bYellow is recessive epistatic (when present, it blocks the expression of the black and chocolate alleles) E or e

Black Lab

BBEE BbEE BBEe BbEe

Chocolate Lab

bbEEbbEe

Yellow Lab BBeeBbeebbee

1. A black lab (BBEe) x yellow lab (bbee)

2. A chocolate lab (bbEe) x black lab (BbEe)

3. Two black labs (BBEE x BbEe)

Sex Linked Genes

Genes located on the X chromosome are inherited with that X. When doing crosses you must include the sex chromosomes in your cross. Use superscript letters for the allele. Example: In fruit flies, eye color is a sex linked trait. Red is dominant to white. 

Females                Males

X R X R                   X R  Y  

X R X r                     X r  Y            X r X r

FRUIT FLY CHROMOSOMESDrosophila melanogaster

Show the cross between a white eyed male and a red eyed female:  XrY x XRXR

Show the cross between a red eyed male and a white eyed female:  

Figure 12.2

Human Sex Linked Disorders1.Colorblindness2.Muscular Dystrophy3.Hemophilia4.Fragile X Syndrome

COLORBLINDNESS

More Tests

Color Blindness Simulation http://www.idea.org/vision-demo.html?gclid=CJejqJ38_JgCFQ4eDQodUzNEmQ

Testshttp://www.toledo-bend.com/colorblind/Ishihara.asp

Polygenic Traits

• Individual heritable characters are often found to be controlled by groups of several genes, called polygenes.

•Each allele intensifies or diminishes the phenotype.•Variation is continuous or quantitative (adding up) - also called quantitative inheritance

•Seed Color in wheat - aabbcc, Aabbcc, AaBbcc, AaBbCc, AABbCc, AABBCC (light, intermediate colors, dark)

• In humans - hair color, height, skin color

Pg 197

Polygenic InheritanceAABBCC x aabbcc (P)

AaBbCc x AaBbCc (F1)

Seven Possible Phenotypes in the F2

Figure 11.16

Figure 11.17

Environment and PhenotypeTemperature, water, food sources can have an affect on how a gene is expressed

Rabbits have a gene that codes for darker pigments - this gene is more active at low temperatures. Parts of the body that are colder will develop the darker pigmentation - ears and

feet 

Figure 11.18b