Patterns of inheritance
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Patterns of Inheritance. I. Simple inheritance (Mendelian inheritance). One gene controls the trait There are two versions (alleles) of the gene One allele is completely dominant over the other. II . Multiple allele inheritance. The trait is still controlled by only one gene.

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Patterns of Inheritance

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Patterns of inheritance

Patterns of Inheritance


I simple inheritance mendelian inheritance

I. Simple inheritance (Mendelian inheritance)

  • One gene controls the trait

  • There are two versions (alleles) of the gene

  • One allele is completely dominant over the other


Ii multiple allele inheritance

II. Multiple allele inheritance

  • The trait is still controlled by only one gene.

  • There are more than two versions (alleles) for the one gene


Example multiple allele inheritance of feather color in pigeons

Example: Multiple allele inheritance of feather color in pigeons

  • BA allele produces red feathers. It is dominant to all other alleles

  • B allele produces blue feathers. It is dominant to b but recessive to BA.

  • b allele produces chocolate colored feathers. It is recessive to all other alleles.


Genotypes and phenotypes of pigeons

Genotypes and phenotypes of pigeons


Iii codominance

III. Codominance

  • Both alleles are equally dominant so they are both expressed


Example codominance in roan cattle

Example: Codominance in Roan cattle


A cattle that is r 1 r 1 is red

A cattle that is (R1R1) is red


A cattle that is r 2 r 2 is white

A cattle that is (R2R2) is white


A heterozygous cattle r 1 r 2 is roan both red and white

A heterozygous cattle (R1R2) is roan (both red and white)


Iv incomplete dominance

IV. Incomplete dominance

  • Both alleles are equally dominant so they are both expressed


Example incomplete dominance in snapdragons

Example: Incomplete dominance in snapdragons

  • Snapdragons that are RR are red.

  • Snapdragons that are R’R’ are white.

  • If a snapdragon is heterozygous for these two alleles (RR’) then it is pink.


A white snapdragon r r

A white snapdragon (R’R’)


A red snapdragon rr

A red snapdragon (RR)


A pink snapdraon rr

A pink snapdraon (RR’)


V polygenic inheritance

V. Polygenic inheritance

  • The trait is controlled by more than one gene.


Example eye color in humans

Example: Eye color in humans

  • Eye color is controlled by genes found in two different spots on chromosome number 15 and also by a gene found on chromosome number 19.


Vi sex linked traits

VI. Sex linked traits

  • The trait is controlled by a gene that is found on the sex chromosome (the 23rd pair in humans)

  • Because males only have one X and females have two X’s some unique inheritance patterns emerge.


Example of a sex linked trait in humans

Example of a sex linked trait in humans.


Patterns of inheritance

  • The gene that controls your blood clotting factors is found on the X chromosome.


Patterns of inheritance

  • There are two alleles for this gene a normal, dominant H allele that clots blood, and an abnormal, recessive h allele that doesn’t clot blood. If a person doesn’t have the normal H allele then they will have the disease hemophilia.


Patterns of inheritance

  • Since a man only has one X chromosome, and therefore only one gene for blood clotting, he is more likely to get hemophilia.


Use a punnet square to solve the following problem

Use a punnet square to solve the following problem:


Patterns of inheritance

A man that does not have hemophilia and a woman that is heterozygous for hemophilia have a child. What is the probability that their child will have hemophilia.


Start by showing the sex chromosomes that mom could give

Start by showing the sex chromosomes that mom could give

X

X


Then show the alleles that are found on mom s sex chromosomes

Then show the alleles that are found on mom’s sex chromosomes

XH

Xh


Then show the sex chromosomes that dad could give

Then show the sex chromosomes that dad could give.

X

Y

XH

Xh


Then show the alleles that are found on dad s sex chromosomes

Then show the alleles that are found on dad’s sex chromosomes

XH

Y

XH

Xh


Patterns of inheritance

Notice that there is no allele shown on the Y chromosome because it doesn’t have the same genes as the X

XH

Y

XH

Xh


Finally show the different possibilities for the offspring

Finally, show the different possibilities for the offspring.

XH

Y

XH

XHXH

XHY

Xh

XHXh

XhY


Only one of the four children would have hemophilia

Only one of the four children would have hemophilia.

XH

Y

XH

XHXH

XHY

Xh

XHXh

XhY


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