Patterns of intermediate inheritance
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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.

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Patterns of Intermediate Inheritance

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Patterns of intermediate inheritance

Patterns of Intermediate Inheritance


Exceptions to mendel s principles

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.


Patterns of intermediate inheritance

  • There are several types of intermediate inheritance patterns:

    • Co-dominance

    • Multiple Alleles

    • Incomplete Dominance

    • Polygenic Traits

    • Multifactorial Inheritance


Co dominance

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).


Patterns of intermediate inheritance

Genotype: RR


Patterns of intermediate inheritance

Genotype: WW


Patterns of intermediate inheritance

Genotype: RW


Practice cross codominance

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

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

RR

RW

R

WW

W

RW


Multiple alleles

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, ch, and c


Patterns of intermediate inheritance

wild type color

CC, Ccch, Cch, Cc


Patterns of intermediate inheritance

chinchilla color

cchcch, cchch, cchc


Patterns of intermediate inheritance

Himalayan color

chc or chch


Patterns of intermediate inheritance

albino

cc


Practice cross multiple alleles

Practice cross: Multiple Alleles

  • Practice cross: In rabbits there are four different color alleles:

    • C is dominant over all C = wild type color

    • cch is dominant to ch & ccch = chinchilla color

    • ch is dominant to c ch = Himalayan color

    • C is recessive to allc = 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

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 : 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%

C

ch

Cc

c

ch

c

c

ch

c

Cc

Mult. Alleles

&

Co-dominance


Incomplete 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.


Patterns of intermediate inheritance

Genotype: cc (Chestnut)


Patterns of intermediate inheritance

Genotype: ww


Patterns of intermediate inheritance

Genotype: cw (Palomino)


Practice cross incomplete dominance

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

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

  • Are the F1 flowers purebred or hybrid?

    • hybrid

  • What is the phenotype of the F1 flowers?

    • pink

r

r

rw

rw

w

rw

w

rw


Mirabilis plants

Snapdragons

Mirabilis plants


Polygenic

Humans

& Plants

Polygenic

  • 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

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

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.

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