1. Not-so-Simple Inheritance Patterns

2. Remember…
Genes are sections of a chromosome that have coded instructions for making proteins.
Alleles are different forms of a gene.

3. Simple Inheritance 2 alleles 2 phenotypes One allele is dominant
The other allele is recessive
The DOMINANT allele completely masks the recessive allele

4. Mendel Got Lucky
In many ways Gregor Mendel was quite lucky in discovering his 4 genetic laws. 
He happened to use pea plants. 
Things in nature aren’t always so simple.

5. Not-so-Simple Inheritance
4 Main Types
Codominance
Incomplete Dominance
Multiple Alleles
Polygenic Traits

6. Red Cow x White Cow  Roan Cow
Codominance
“Co” means together!
Codominance = two alleles are dominant together.
This produces a third heterozygous phenotype where BOTH traits are expressed TOGETHER
Ex: Human Blood Type A B O AB
Red Cow x White Cow  Roan Cow
Roan cattle have both red and white hairs mixed in together!

7. red x white  red & white spotted
Codominance
red x white  red & white spotted

8. copyright cmassengale
Mendelian Genetics
4/1/2017
Codominance
Two alleles are expressed (multiple alleles) in heterozygous individuals.
Example: blood type
1. type A = IAIA or IAi
2. type B = IBIB or IBi
3. type AB = IAIB
4. type O = ii
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9. copyright cmassengale
Mendelian Genetics
4/1/2017
Codominance Problem
Example: homozygous male Type B (IBIB)
x heterozygous female Type A (IAi) IB IA i
IAIB
IBi
1/2 = IAIB
1/2 = IBi
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10. Another Codominance Problem
Mendelian Genetics
4/1/2017
Another Codominance Problem
Example: male Type O (ii) x female type AB (IAIB) i IA IB
IAi
IBi
1/2 = IAi
1/2 = IBi
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11. copyright cmassengale
Mendelian Genetics
4/1/2017
Codominance
Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents?
boy - type O (ii) X girl - type AB (IAIB)
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12. copyright cmassengale
Mendelian Genetics
4/1/2017
Codominance
Answer: IB IA i
IAIB ii
Parents:
genotypes = IAi and IBi
phenotypes = A and B
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13. Amel & Ultra are incompletely dominant to each other.
Incomplete Dominance
Incomplete Dominance = neither of the two alleles is completely dominant
This produces a third heterozygous phenotype where the traits are BLENDED.
Amel & Ultra are incompletely dominant to each other.
Amel x Ultra  Ultramel

14. red flower x white flower  PINK flower
Incomplete Dominance
red flower x white flower  PINK flower

15. Multiple Alleles Any of a set of three or more alleles.
Only two of alleles can be present in a diploid organism.
Examples:
Human Blood Type
Human skin, hair, and eye colors

17. Polygenic Traits Result of the interaction of several genes
Human skin, hair, and eye color
Influenced by more than one gene at different locations on the chromosomes
Human Blood Pressure
Not just 1 “blood pressure” gene with several alleles
Caused by several genes that control other traits such as weight, cholesterol level, kidney function, etc…
Human Height
The combined size of all of the body parts from head to foot determines the height of an individual. 

18. Role of Environment
Our environment also plays a key role in how traits are expressed.
Genes can be turned on/off due to external environmental factors.
Examples:
Stress
Nutrition
Chemical exposure
Light
Temperature

19. Example of Environmental Influence
Human Height is heavily influenced by hormones produced in the pituitary gland and our diet during childhood and puberty.
Usually, about 10% of an individual's height is due to the environment.

20. Sample Questions
1. Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull.
2. What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur?

21. Sample Questions
3. A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). a) What pattern of inheritance does this illustrate? b) What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?

22. Sample Questions
1. A cross between a blue blahblah bird & a white blahblah bird produces offspring that are silver.  The color of blahblah birds is determined by just two alleles. a) What are the genotypes of the parent blahblah birds in the original cross? b) What is/are the genotype(s) of the silver offspring? c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds?

23. Sample Questions
2. The color of fruit for plant "X" is determined by two alleles.  When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit.  What are the genotypes of the parent orange-fruited plants?