patterns of inheritance. i. simple inheritance (mendelian inheritance) one gene controls the trait...
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Patterns of InheritancePatterns 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
• 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
• 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.
• 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
GenotypeGenotype PhenotypePhenotype
BBAA B BAA RedRed
BBA A BB RedRed
BBAAbb RedRed
BBBB BlueBlue
BbBb BlueBlue
bbbb ChocolateChocolate
III. CodominanceIII. Codominance
• Both alleles are equally dominant so they are both expressed
• Both alleles are equally dominant so they are both expressed
Example: Codominance in Roan cattle
Example: Codominance in Roan cattle
A cattle that is (R1R1) is red
A cattle that is (R1R1) is red
A cattle that is (R2R2) is white
A cattle that is (R2R2) is white
A heterozygous cattle (R1R2) is roan (both red and
white)
A heterozygous cattle (R1R2) is roan (both red and
white)
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
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.
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 inheritanceV. Polygenic inheritance
• The trait is controlled by more than one gene.
• 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.
• 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 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.
Example of a sex linked trait in humans.
Example of a sex linked trait in humans.
•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.
• 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.
•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.
Use a punnet square to solve the following
problem:
Use a punnet square to solve the following
problem:
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.
XX
Start by showing the sex chromosomes that mom could
give
Start by showing the sex chromosomes that mom could
give
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
X YXH
Xh
Then show the sex chromosomes that dad could
give.
Then show the sex chromosomes that dad could
give.
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
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
Finally, show the different possibilities for the
offspring.
Finally, show the different possibilities for the
offspring.
XHXH XHY
XHXh XhY
XH YXH
Xh
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.