Patterns of Intermediate Inheritance

Patterns of Intermediate Inheritance

Exceptions to Mendel s Principles Mendel s 3 principles provide us with an important foundation in building our knowledge of genetics. However, there are many types of inheritance patterns that do not follow the Principle of Dominance.

Types of Intermediate Inheritance Patterns There are several types of intermediate inheritance patterns: Co-dominance Incomplete Dominance Polygenic Traits Multiple Alleles

Co-dominance A trait for which both alleles contribute equally to the phenotype. Example: Coat color in cows and horses When a homozygous red cow is crossed with a homozygous white cow they produce a heterozygous cow that is red and white (roan).

Genotype: RR Phenotype: Red

Genotype: WW Phenotype: White

Genotype: RW Phenotype: Roan

Practice Cross - Codominance A horse that is roan is a blend of red and white colors that result when a red horse is crossed with a white horse. Red (R) horses breed true; and white (W) horses breed true. Write the following answers in the boxes: What is the genotype of a red horse? RR What is the genotype of a white horse? WW What is the genotype of a roan horse? RW

Show the cross between two roan horses (use R and W). What is the probability that two roan horses will have at least one roan offspring? 50% What is the probability that two roan horses will have a white offspring? 25% R W R RR RW W RW WW

Incomplete Dominance Results in a heterozygous phenotype that is a blend of the two homozygous phenotypes. Examples: mirabilis (four o clock) plants, coat color in horses When a homozygous chestnut horse is crossed with a homozygous white horse, they produce a heterozygous tan (palomino) horse. The trick to recognizing an incomplete dominance problem is to notice that the trait in the offspring is a blend of the parental traits

Genotype: CC (Chestnut)

Genotype: WW

Genotype: CW (Palomino)

Practice Cross Incomplete Dominance In Four O Clocks, the gene for red flowers (R) is incompletely dominant to the gene for white flowers (W). The heterozygous condition results in pink flowers. Red Plant Genotype? RR White Plant Genotype? WW

Show the results of a cross between a red Four O Clock and a white Four O Clock. Are the F 1 flowers purebred or hybrid? R R hybrid What is the phenotype of the F 1 flowers? W RW RW pink W RW RW

Snapdragons Mirabilis plants

Polygenic Humans & Plants A trait that is controlled by the interaction between 2 or more genes. Examples: skin color, eye color, height, hair color Results in a continuum of expressed phenotypes.

Multiple Alleles When a gene has more than two possible alleles. ONLY TWO alleles are inherited. Example: Rabbit Coat Color is controlled by 4 alleles - C, c ch, c h, and c C = wild type c ch = Chinchilla c h = Himilayan c = Albino

CC, Cc ch, Cc h, Cc

c ch c ch, c ch c h, c ch c

chc or chch

cc (2 lowercase c s)

Practice cross: Multiple Alleles Practice cross: In rabbits there are four different color alleles: C is dominant over all C = wild type color c ch is dominant to c h & c c ch = chinchilla color c h is dominant to c c h = Himalayan color c is recessive to all c = albino Each rabbit can inherit only two alleles. A wild colored rabbit is crossed with an albino and in the offspring there is a Himalayan rabbit.

Show the cross between a wild type and albino rabbit that has a Himalayan baby. What are the genotypes of the parents? Parent one : cc Parent two : Cc h What is the probability that they will have an offspring that is Himalayan? 50% What is the probability that they will have an offspring that is albino? 0% What is the probability that they will have an offspring that is wild colored? 50% c c C Cc Cc c c c h c h c h Mult. Alleles & Co-dominance

Multifactorial Inheritance Enviro Factors The phenotype is a result of an interaction between your genotype and certain environmental factors. The expression of most all genes is influenced by environmental conditions. Examples: Diabetes, Height, Heart Disease Can inherit a predisposition to all of these diseases/characteristics. Their development (phenotype) is influenced by environmental factors (proper nutrition, exercise, quality medical care, etc.)

Alleles for codominance and incomplete dominance Alleles for codominance and incomplete dominance problems can be written in different ways depending on the text: Examples: Codominance R=red hair RR = red F=flower color W=white hair R R = white F R =red flower RW=roan hair RR = roan F W =white flower (red and white hairs together) Incomplete dominance R= red flower R= red flower W= white flower r = white flower RW= pink flower F R F W = red & white spotted Rr = pink flower

Examples in plants: In many plants, the presence of light triggers the production of chloroplasts. Chemicals that stimulate germination are only produced in the presence of certain temperatures. http://www.dkimages.com/discover/previews/874/30020399.jpg Review of Terms