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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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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.



Co dominance
Co-dominance patterns:

  • 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 patterns:


Genotype: WW patterns:


Genotype: RW patterns:


Practice cross codominance
Practice Cross - Codominance patterns:

  • 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 patterns: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 patterns:

  • 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


wild type color patterns:

CC, Ccch, Cch, Cc


chinchilla color patterns:

cchcch, cchch, cchc


Himalayan color patterns:

chc or chch


albino patterns:

cc


Practice cross multiple alleles
Practice cross: Multiple Alleles patterns:

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

    • C is dominant over all C = wild type color

    • cch is dominant to ch & c cch = chinchilla color

    • ch is dominant to c ch = 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
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 has a Himalayan baby.

  • 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) has a Himalayan baby.


Genotype: ww has a Himalayan baby.


Genotype: cw (Palomino) has a Himalayan baby.


Practice cross incomplete dominance
Practice Cross – Incomplete Dominance has a Himalayan baby.

  • 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 a white Four O’Clock.

Mirabilis plants


Polygenic

Humans a white Four O’Clock.

& 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 a white Four O’Clock.

  • 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: a white Four O’Clock.

  • 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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Review

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