Into the Genetic Frontier Beyond Mendel 11.3 Into the Genetic Frontier

Genes can be inherited based on various patterns Mendel’s Dominance vs. Recessive Incomplete dominance Co-dominance Multiple alleles Polygenic genes

Incomplete Dominance In this pattern neither allele is considered recessive Heterozygous conditions produce a blend of the two traits creating a third phenotype.

Co-dominance In this pattern much like incomplete dominance, neither allele is considered recessive In a heterozygous condition where each type of allele is present the phenotype displays both traits from each allele There are 3 possible phenotypes

Multiple alleles In this pattern there is more than just two alleles (3 or more) Combinations of other patterns Ex. Some alleles behave in a dominant/recessive fashion while other alleles display a co-dominant or incomplete dominant relationship This can lead to multiple phenotypes

There are 4 Human Blood Types A, B, AB & O = 4 phenotypes Blood type is controlled by one gene, with 3 different alleles – A, B and O The 3 alleles can be combined to produce 6 different genotypes AA BB AO BO AB OO

Inheritance of Blood Type Is a mix of complete dominance and codominance - AA & AO produce type A blood - BB & BO produce type B blood - AB produces type AB blood - OO produces type O blood From this we can infer that both A & B alleles are dominant to the O allele The A allele is codominant with the B allele

Determining Possible Outcomes Notating Blood Type IA = A allele IB = B allele i = O allele Example a person who heterozygous for A blood = IA i And a person with O blood = i i How would a person who is homozygous for B blood be notated? - IB IB How would a person who is heterozygous for B blood be notated? - IB i

What exactly is blood type? Each blood type is the result of a specific combination of proteins found on the blood cells called antigens and proteins found in the blood plasma called antibodies - type A blood = A antigens & B antibodies - type B blood = B antigens & A antibodies - type AB blood = both A & B antigens & no antibodies - type O blood = no antigens & both A & B antibodies

Why is Blood Typing Important? If a person is given blood with antigens that their blood plasma contains antibodies for, the antibodies will attach to the blood causing it to clump - this clumping is called agglutination

Figure 9.20 Blood Group (Phenotype) Antibodies Present in Blood Reactions When Blood from Groups Below Is Mixed with Antibodies from Groups at Left Genotypes Red Blood Cells O A B AB Carbohydrate A IAIA or IAi A Anti-B Carbohydrate B IBIB or IBi B Anti-A AB IAIB — Figure 9.20 Multiple alleles for the ABO blood groups. Anti-A Anti-B O ii Figure 9.20

Polygenic traits Some traits which have many possible phenotypes are controlled by more than one gene. - the interactions of these genes allows for the large numbers of phenotypes. - human examples: Hair, eye and skin color

The Inheritance of Eye Color Only partially understood. at least 3 different genes with 2 alleles each are responsible for eye color. – bey 1 bey 2 and gey These genes code for the formation of the pigment melanin The function of only 2 of the 3 genes is currently understood

The Inheritance of Eye Color as it is Currently Understood Known as the 2 gene model One gene known as bey 2 has 2 alleles B for brown eyes and b for blue eyes The other gene known as gey has 2 alleles G codes for green eyes and g for blue eyes Evolution of eye color- not understood. One theory melanin was useful in tropical climates, but as people moved north, less sun required less melanin. One other idea, the color blue allows more light to pass through the iris reducing depression in the winter due to SADS

The 2 Gene Model - B is dominant to all other alleles- BBGG,BBGg,BBgg,BbGG BbGg,Bbgg = Brown eyes - G is dominant to b bbGG , bbGg = Green eyes - bbgg only = blue eyes How to figure out eye genetics – dihybrid cross

Genes and the Environment The characteristics of any organism are not determined solely by the genes that organism inherits. Genes provide a plan for development, but how that plan unfolds also depends on the environment. The phenotype of an organism is only partly determined by its genotype.

Environment Can Influence Gene Expression example: Siamese cats - Siamese coloring is a partial albinism. Most of the cat is white -Black fur is only expressed in areas where the temperature is lower than the rest of the body - if black hair is shaved and the area kept warm then the hair that grows back will be white - if white hair is shaved and the area is cooled, then the hair will grow back black The Siamese color is recessive and only shows up in homo recessive cats. The same gene for fur color also controls crossed eyes associated with siamese. Albinism is associated with crossed eyes in many species Pleiotropy

In a certain fish, blue scales and red scales are codominant In a certain fish, blue scales and red scales are codominant. When a fish has the genotype B R, it has a patchwork of blue and red scales. What happens if you breed this fish with a fish that only has Blue Scales.

In snapdragons, flower color is controlled by incomplete dominance In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red (R) and white (W). The heterozygous genotype is expressed as pink. What happens when you breed 2 pink dragons?