Non-Mendelian and Human Heredity

Non-Mendelian Genetics Essential Questions: 1. What happens when you have two alleles for a trait that are dominant? 2. What is a blended phenotype? 3. If two alleles are dominant, how do I identify which letter to use in the punnett square?

Incomplete Dominance Neither allele is completely dominant When the offspring is heterozygous, a third BLENDED phenotype appears

Incomplete Dominance Example If red flowers (RR) are incompletely dominant to white flowers (R’R’), show the offspring of a cross between 2 pink flowers (RR’) What is the probability that these two parents will produce pink offspring? 50% R R’ R R R R’ R’ R’ R R’ Phenotype ratio: Red 1, White 1, Pink 2

Codominance Both alleles are equally dominant When the genotype is heterozygous, both phenotypes are represented in an almost equal ratio Example: A black cow and a white cow may produce a black and white cow

Codominance Example BW B B BB W B If black chickens (BB) are co-dominant to white chickens (WW), show a cross between a black chicken (BB) and a black and white chicken (BW). What is the probability that these two chickens will have a white offspring? 0% BW BB W B Phenotype ratio: Black 2, black and white 2, white 0

Blood Typing – co-dominance and multiple allelism More than two alleles are available for a trait Each individual will only have 2 of the alleles Example: Blood type (3 alleles- A,B,O) “A” and “B” are co-dominant, “O” is recessive Genotypes: TYPE A - IA IA or IA i TYPE B - IB IB or IB i TYPE AB - IA IB TYPE O – i i

Sex Linked inheritance Traits found on the X chromosome More typical in males Females: XX Males: XY Examples of sex linked traits Color-blindness Hemophilia - Male pattern baldness

Sex-Linked recessive Color Blindness Hemophilia One type of this disease (red-green) cannot distinguish between the colors red and green Hemophilia Lack a blood clotting enzyme and so cuts and wounds bleed without stopping If you can see “52” you are normal but if you can only see the “5” then you suffer from red-green color blindness

Sex-linkage Example Xb Y Y Xb Xb A color blind woman (Xb Xb) and a man with normal vision (XBY) want to know what chance a son will have to have normal vision. What is the probability that these two people will have a color-blind son? 100% XB Xb XB XB Xb Xb Y Xb Y Y Phenotype: Both females are carriers (have normal vision but can pass on the trait) Both males are color-blind

Techniques Pedigree Population Sampling Twin Studies Constructing and analyzing a graphical diagram of one trait over several past generations as well as the current generation Population Sampling Study a small randomly selected group to predict patterns in the entire population Twin Studies Study identical twins (they have the same DNA) to determine the role environment plays in the expression of our genes Make a Pedigree of your own family (see pg. 315) Twin studies and the environmental role they can determine Is on the mini

Polygenic Inheritance More than one gene control a trait Creates a wide range of phenotypes Ex. Height, skin color

Pedigree diagram used to track one trait over several past generations as well as the current generation.

Karyotypes The number, shapes, and sizes of the metaphase chromosomes constitute the karyotype Some genetic abnormalities can be identified using karyotyping (ex. Down syndrome) Do not need to know thisb

Genes vs. Environment Environment can influence the expression of genes Ex. Siamese cats fur gets darker in colder temperatures (phenotype changes) Environmental hazards can create genetic mutations Called mutagens ex. UV radiation causes skin cancer Twin studies are often used to study the influence of the environment on human traits

Essential Question WHY are males more often affected with sex-linked genes? Because the affected gene is on the X chromosome from the mother, and the father gives the boy a Y chromosome. Therefore the trait is expressed since the father can not give a boy a normal X chromosome. He can only give a boy a Y chromosome.

Essential Questions Which type of inheritance produces a blended phenotype? Incomplete Dominance Which type of inheritance produces disorders most often seen in males? Sex Linkage