Complex Genetics Incomplete Dominance, Codominance, gene interactions, multiple effects of genes, and sex- linked Updated for school year (reupload)

Incomplete Dominance The dominant allele cannot completely mask the recessive allele This results in a combination of both phenotypes

Snapdragons P: Red Color x White Color F1: Pink Color RR R’R’ RR’

Snapdragons P: Red Color x White Color F1: Pink Color RR R’R’ RR’ White flowers have a mutated allele (R’) that cannot make the color pigment The second letter needs to be the same case (Capitol or lower) as the 1st since they both show. Usually you use some type of exponent to show the different alleles.

Snapdragons P: Red Color x White Color F1: Pink Color RR R’R’ RR’ In the heterozygous flower (pink color), the single red allele cannot make enough pigment to turn the flower red = incomplete dominance

What would you get if you cross two pink snapdragons? R R R’ RR RR’ R’R’ RR’ In Incomplete Dominance you see a 1:2:1 phenotype ratio instead of the 3:1 in normal dominant recessive RedPink White

Codominance Where two different alleles are equally dominant; they both show their trait Human blood types is an example of this –3 different alleles 2 Dominant: I A & I B 1 Recessive: i multiple allele trait

Blood Types 4 blood types Both A & B alleles attach different sugars to the surface of your red blood cells i alleles do not make a sugar PhenotypeGenotype(s) AIAIAIAiIAIAIAi BIBIBIBiIBIBIBi ABIAIBIAIB Oii

Parents: A blood type x B blood type What are the possible genotypes of the parents? –Answer: I A I A or I A i x I B I B or I B i They have a type A child, what does this tell you about the parents? The child? –Answer: B parent must be I B i –Answer: The child must be I A i Their second child is type B, what is the probability of their next child being type AB? –Answer: 1/4; both parents are heterozygous

PhenotypeGenotype(s) AIAIAIAiIAIAIAi BIBIBIBiIBIBIBi ABIAIBIAIB Oii Blood Types Both A & B alleles attach different proteins to the surface of your red blood cells i alleles do not make a surface protein

Blood Interactions If your body is ever exposed to blood sugars that you don’t have you will make anti-bodies for those foreign sugars The anti-bodies attach to the foreign blood sugar which causes clumping (see row 1:A) Based on this, which blood type would be considered to be the Universal donor? Universal acceptor?

Rh factor Rh factor is another protein that can be found on the surface of your red blood cells and is usually part of the blood type –Rh+ = makes protein = dominant trait –Rh- = no protein made = recessive trait What are the genotype if two parents are B+ x B+ and they have an O- child? –Answer: I B i+- x I B i+-, child is ii--

Rh factor In the picture below the Mother is Rh- and the fetus is Rh+. During delivery the mother is exposed to the childs Rh+ blood and begins to make antibodies. If she then becomes pregnant a second time with another Rh+ fetus she will miscarry (pic 2). –Doctors now prevent this problem by giving Rh- mothers antibody shots after delivery so they will not make their own antibodies targeting the Rh protein.

Epistasis Interaction of two (or more) different genes that have an affect on the same trait Fur coloration in mammals is one example –One gene controls the amount and coloration of melanin (pigment) B = black b = brown –A second gene controls if the pigment will be deposited in the fur E = melanin deposited in fur (black or brown fur) e = melanin not deposited in fur (yellow fur)

What are the phenotypes and genotypes of the following purebred dogs? Pheno: black Geno: BBEE Pheno: brown Geno: bbEE Pheno: yellow Geno: __ee

A third gene affects whether melanin is produced at all –C = melanin produced (black, brown, yellow fur) –c = melanin not produced (albino) A normal dog with genotype BBEE would be? – black But if it was BBEEcc it would be? –white

Sex-linked Traits Genes that are carried on the sex chromosomes; X (or sometimes Y). These are usually recessive traits These traits are more common in males. –Baldness –Red-Green color blindness –Hemophelia

How to tell if it is X-linked Usually see grandfather to grandson inheritance through the mother. Father can NEVER pass the trait onto their sons Predominately males are affected (rare for a female to have the trait)

Colorblindness If a female is normal what is her genotype? –XX or XX cb If a male is normal what is his genotype? –XY If a male is colorblind what is his genotype? –X cb Y Why is it more common for males to be colorblind? –Males only need to inherit one recessive, females need to inherit two

Could two normal parents pass on colorblindness? Only if the mother is a carrier –Father: XY Mother: XX cb If mom is a carrier, what would be the probability of getting a colorblind child? –25% for any child born, but does the sex of the child make a difference? 0% if you are a girl 50% if you are male