NonMendelian and Human Heredity NonMendelian Genetics n Essential

Non-Mendelian and Human Heredity

Non-Mendelian Genetics n 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 n Neither allele is completely dominant n When the offspring is heterozygous, a third BLENDED phenotype appears

Incomplete Dominance Example n R R’ RR R R’ R’ R’ Phenotype ratio: Red 1, White 1, Pink 2 n 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%

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

Codominance Example W B BW BW BB BB Phenotype ratio: Black 2, black and white 2, white 0 n n If black chickens (BB) are codominant 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%

Blood Typing – co-dominance and multiple allelism n n n 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: n TYPE A - IA IA or IA i n TYPE B - IB IB or IB i n TYPE AB - IA IB n TYPE O – i i

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

Sex-Linked recessive n Color Blindness – One type of this disease (red-green) cannot distinguish between the colors red and green n Hemophilia – Lack a blood clotting enzyme and so cuts and wounds bleed without stopping

Sex-linkage Example Xb XB Y XB Xb Xb Y Xb n XB Xb Xb Y Phenotype: n • Both females are carriers (have normal vision but can pass on the trait) • Both males are color-blind 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%

Techniques n Pedigree – Constructing and analyzing a graphical diagram of one trait over several past generations as well as the current generation n Population Sampling – Study a small randomly selected group to predict patterns in the entire population n Twin Studies – Study identical twins (they have the same DNA) to determine the role environment plays in the expression of our genes

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

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

Karyotypes n The number, shapes, and sizes of the metaphase chromosomes constitute the karyotype n Some genetic abnormalities can be identified using karyotyping (ex. Down syndrome)

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

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