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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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.



Iii codominance
III. Codominance pigeons

  • Both alleles are equally dominant so they are both expressed



A cattle that is r 1 r 1 is red
A cattle that is (R pigeons1R1) is red


A cattle that is r 2 r 2 is white
A cattle that is (R pigeons2R2) is white


A heterozygous cattle r 1 r 2 is roan both red and white
A heterozygous cattle (R pigeons1R2) is roan (both red and white)


Iv incomplete dominance
IV. Incomplete dominance pigeons

  • Both alleles are equally dominant so they are both expressed


Example incomplete dominance in snapdragons
Example: Incomplete dominance in snapdragons pigeons

  • 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.





V polygenic inheritance
V. Polygenic inheritance pigeons

  • The trait is controlled by more than one gene.


Example eye color in humans
Example: Eye color in humans pigeons

  • 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 pigeons

  • 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.






Use a punnet square to solve the following problem
Use a punnet square to solve the following problem: one gene for blood clotting, he is more likely to get hemophilia.


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 heterozygous for hemophilia have a child. What is the probability that their child will have hemophilia.

X

X





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. because it doesn’t have the same genes as the X

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. because it doesn’t have the same genes as the X

XH

Y

XH

XHXH

XHY

Xh

XHXh

XhY


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