Nonmendelian inheritance Genetics Part 2 Nonmendelian inheritance

Beyond Dominant and Recessive Alleles Some alleles are neither dominant nor recessive

Incomplete Dominance Incomplete dominance is a pattern of inheritance in which two alleles, inherited from the parents, are neither dominant nor recessive. The resulting offspring have a phenotype that is a blending of the parental traits. The F1 generation produced by a cross between red-flowered (RR) and white-flowered (WW) plants consists of pink-colored flowers (RW).

We can still use the Punnett Square to solve problems involving incomplete dominance.  The only difference is that instead of using a capital letter for the dominant trait & a lowercase letter for the recessive trait, the letters we use are both going to be capital (because neither trait dominates the other). 

RR = allele for red flowers WW= allele for white flowers Genotype: 100% RW Phenotype: 100% Pink

Co-dominance Co-dominance is pattern of inheritance in which both alleles contribute to the phenotype For example, in certain varieties of chicken, the allele for black feathers is co-dominant with the allele for white feathers.

B W BW BW W BW BW B BB = allele for black WW= allele for white Genotype: 100% BW Phenotype: 100% Speckled (black and white) B B W BW BW W BW BW

More than two forms of a gene controlling the expression of a trait is called multiple alleles This does not mean that one individual can have more than two alleles. It only means that more than two possible alleles exist in a population.

ABO Blood Type in Humans Human Blood Types Include: A, B, AB, and O Type A blood: IAIA, IAi Type B blood: IB IB, IB i Type AB blood: IAIB Type O blood: ii The alleles IA and IB are co-dominant over i

Polygenic traits are controlled by more than one gene, and each gene may have two or more alleles. The genes may be on the same chromosome or on non-homologous chromosomes Skin color and adult height are examples of polygenic characteristics in humans. Environment can also affect organisms traits - fur color can change due to climate changes

Human Chromosomes Human body cells have 46 chromosomes Two of the 46 are sex chromosomes which determine an individual’s sex Females have two large “X” chromosomes Males have 1 “X” and 1 small “Y” 44 of the 46 chromosomes are autosomal chromosomes or autosomes

Sex Chromosomes Males and females are born in a roughly 50:50 ratio because of segregation in meiosis All human egg cells carry a single X chromosome Half of the sperm cells carry an X and half carry a Y Thus, half the zygotes will be XX and half XY X X XX XY X Y

Sex Linked Traits Sex-linked traits are traits associated with a gene that is located on one of the sex chromosomes Males have just one X chromosome. Thus all X-linked alleles are expressed in males, even if they are recessive. Examples: Color Blindness, and Hemophilia

Color Blindness Red-green color blindness is a common sex-linked disorder characterized by a malfunction of light sensitive cells in the eyes. Bb= Carrier (Not Colorblind) B= dominant, not Colorblind b = recessive, Colorblind

Hemophilia Hemophilia is a disorder in which people bleed excessively when injured, because they lack one or more proteins required for blood clotting.

HH = no hemophilia Hh= no hemophilia (carrier) hh= hemophilia

Pedigree Many traits can’t be traced easily because they are polygenic and influenced by the environment For those that can, pedigrees can predict how a trait and the genes that control it are inherited Pedigree is a chart which shows the relationships within a family to help with identifying inherited traits.

Circles = female Square = male Shaded In= has the trait Half Shaded In = is a carrier