Patterns of Intermediate Inheritance Exceptions to Mendels Principles

Exceptions to Mendel’s Principles Mendel’s 3 principles provide us with an important foundation in

There are several types of intermediate inheritance patterns: – Co-dominance – Multiple Alleles –

Co-dominance A trait for which both alleles contribute equally to the phenotype. – Example:

Practice Cross - Codominance A horse that is roan is a blend of red

Show the cross between two roan horses (use R and W). What is the

Multiple Alleles When a gene has more than two possible alleles. ONLY TWO alleles

Practice cross: Multiple Alleles Practice cross: In rabbits there are four different color alleles:

Show the cross between a wild type and albino rabbit that has a Himalayan

Incomplete Dominance Results in a heterozygous phenotype that is a blend of the two

Practice Cross – Incomplete Dominance In Four O’Clocks, the gene for red flowers (r)

Show the results of a cross between a red Four O’Clock and a white

Polygenic Humans & Plants A trait that is controlled by the interaction between 2

Multifactorial Inheritance The phenotype is a result of an interaction between your genotype and

Examples in plants: In many plants, the presence of light triggers the production of

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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.

There are several types of intermediate inheritance patterns: – Co-dominance – Multiple Alleles – Incomplete Dominance – Polygenic Traits – Multifactorial Inheritance

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

Genotype: WW

Genotype: RW

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. 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? R W R RR RW WW – 50% What is the probability that two roan horses will have a white offspring? – 25%

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, cch, and c

CC, Ccch, Cc

cchcch, cchc

chc or chch

Practice cross: Multiple Alleles Practice cross: In rabbits there are four different color alleles: – – C is dominant over all cch is dominant to ch & c ch is dominant to c C is recessive to all C = wild type color cch = chinchilla color ch = Himalayan color 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? C ch c Cc cch – Parent one : cc – Parent two : Cch 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% Mult. Alleles & Co-dominance

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.

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. r Are the F 1 flowers purebred or hybrid? – hybrid What is the phenotype of the F 1 flowers? – pink r 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.

Multifactorial Inheritance 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 such as proper nutrition, exercise, quality medical care, etc. Enviro Factors

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