Patterns of Inheritance. I. Simple inheritance (Mendelian inheritance) One gene controls the trait...
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![Page 1: Patterns of Inheritance. I. Simple inheritance (Mendelian inheritance) One gene controls the trait There are two versions (alleles) of the gene One allele.](https://reader036.fdocuments.net/reader036/viewer/2022062318/551b720c550346a10a8b49e8/html5/thumbnails/1.jpg)
Patterns of InheritancePatterns of Inheritance
![Page 2: Patterns of Inheritance. I. Simple inheritance (Mendelian inheritance) One gene controls the trait There are two versions (alleles) of the gene One allele.](https://reader036.fdocuments.net/reader036/viewer/2022062318/551b720c550346a10a8b49e8/html5/thumbnails/2.jpg)
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
• One gene controls the trait• There are two versions (alleles) of the gene
• One allele is completely dominant over the other
![Page 3: Patterns of Inheritance. I. Simple inheritance (Mendelian inheritance) One gene controls the trait There are two versions (alleles) of the gene One allele.](https://reader036.fdocuments.net/reader036/viewer/2022062318/551b720c550346a10a8b49e8/html5/thumbnails/3.jpg)
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
• The trait is still controlled by only one gene.
• There are more than two versions (alleles) for the one gene
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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.
• 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.
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Genotypes and phenotypes of pigeons
Genotypes and phenotypes of pigeons
GenotypeGenotype PhenotypePhenotype
BBAA B BAA RedRed
BBA A BB RedRed
BBAAbb RedRed
BBBB BlueBlue
BbBb BlueBlue
bbbb ChocolateChocolate
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III. CodominanceIII. Codominance
• Both alleles are equally dominant so they are both expressed
• Both alleles are equally dominant so they are both expressed
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Example: Codominance in Roan cattle
Example: Codominance in Roan cattle
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A cattle that is (R1R1) is red
A cattle that is (R1R1) is red
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A cattle that is (R2R2) is white
A cattle that is (R2R2) is white
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A heterozygous cattle (R1R2) is roan (both red and
white)
A heterozygous cattle (R1R2) is roan (both red and
white)
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IV. Incomplete dominanceIV. Incomplete dominance
• Both alleles are equally dominant so they are both expressed
• Both alleles are equally dominant so they are both expressed
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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.
• 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.
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A white snapdragon (R’R’)A white snapdragon (R’R’)
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A red snapdragon (RR)A red snapdragon (RR)
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A pink snapdraon (RR’)A pink snapdraon (RR’)
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V. Polygenic inheritanceV. Polygenic inheritance
• The trait is controlled by more than one gene.
• The trait is controlled by more than one gene.
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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.
• 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.
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VI. Sex linked traitsVI. 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.
• 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.
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Example of a sex linked trait in humans.
Example of a sex linked trait in humans.
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•The gene that controls your blood clotting factors is found on the X chromosome.
•The gene that controls your blood clotting factors is found on the X chromosome.
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• 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.
• 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.
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•Since a man only has one X chromosome, and therefore only one gene for blood clotting, he is more likely to get hemophilia.
•Since a man only has one X chromosome, and therefore only one gene for blood clotting, he is more likely to get hemophilia.
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Use a punnet square to solve the following
problem:
Use a punnet square to solve the following
problem:
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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.
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.
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XX
Start by showing the sex chromosomes that mom could
give
Start by showing the sex chromosomes that mom could
give
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XH
Xh
Then show the alleles that are found on mom’s sex
chromosomes
Then show the alleles that are found on mom’s sex
chromosomes
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X YXH
Xh
Then show the sex chromosomes that dad could
give.
Then show the sex chromosomes that dad could
give.
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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 YXH
Xh
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XH YXH
Xh
Notice that there is no allele shown on the Y chromosome because it
doesn’t have the same genes as the X
Notice that there is no allele shown on the Y chromosome because it
doesn’t have the same genes as the X
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Finally, show the different possibilities for the
offspring.
Finally, show the different possibilities for the
offspring.
XHXH XHY
XHXh XhY
XH YXH
Xh
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XHXH XHY
XHXh XhY
XH YXH
Xh
Only one of the four children would have
hemophilia.
Only one of the four children would have
hemophilia.