Chapter 11 Beyond Mendel Conditions that Mendel didn't explore - genetic traits that are inherited in new and interesting patterns

Codominance Multiple Allele Traits Polygenic Inheritance  Lethal Alleles Epistatic Alleles

Incomplete Dominance Traits appear to "blend" in offspring RR x WW       RW  (pink) Show: Pink x Red Pink x Pink White x White

This illustrates another style of "letters" to denote genotypes Figure 11.14 This illustrates another style of "letters" to denote genotypes R1 and R2

Sickle Cell Trait in Humans Genotypes  & Phenotypes

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?

Mix Those Genes 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 Try this activity on Eye Color      Mix Those Genes

If you played "Mix Those Genes"  you saw how the eye color of the parents determines the eye color of their offspring. The simulation is a bit simplified, but the idea is that MULTIPLE ALLELES control a single trait (eye color) It is likely that more than 2 alleles control eye color, the simulation just made it simple to understand.

Determine the genotypes of these aliens given that the trait is controlled by multiple alleles. 

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

Polygenic Inheritance Pg 197 Polygenic Inheritance AABBCC 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

SIAMESE CATS

LEGHORN CHICKEN – SINGLE COMB Multiple Alleles control the combs of chickens. Assignment: Multiple Alleles in Chickens LEGHORN CHICKEN – SINGLE COMB

BUTTERCUP CHICKEN - BUTTERCUP COMB

Buckeye Chicken – Pea Comb

Wyandotte Chicken - Rose Comb

Lethal Genes  (Not in book, added to 11.5) Some genes are lethal when both alleles are present. Lethality can occur before or after birth Huntington's disease in humans is caused by a lethal allele, death occurs later in life Other examples: Mouse coat color (yellow), Creeper legs in chickens, Manx Cats (no tails) An example is the "creeper" allele in chickens, which causes the legs to be short and stunted.

Manx  x  Normal Cat

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 b Yellow is recessive epistatic (when present, it blocks the expression of the black and chocolate alleles) E or e

Black Lab Chocolate Lab Yellow Lab BBEE BbEE BBEe BbEe bbEE bbEe   BBee Bbee bbee

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)