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steps to determine the distance between genes on the chromosome:
1. find out whether it is autosomal or sex-linked
- autosomal = affects both gender equally
- sex-linked = gender biased, affects one gender
2. choose an autosomal with know mutation
- parents (wild type and double mutant) cross to form F1
- F1 self to form F2 = determine whether it is linked or not
3. test cross (if it is linked - not 9 : 3 : 3 : 1 ratio)
- F1 cross double mutant to form F2
- F2 = determine whether it is linked or not, not 1 : 1 : 1 : 1\
- use recombinant frequency to find the cM/distance of the gene
4. redo step 3 with a different gene (on the same chromosome)
- pinpointing frequency = more accurate, can tell the estimation of where exactly the gene is located

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genes that are likely to be inherited together because they are physically close to one another on the same chromosome
more likely inherit together = breaking law of independent assortment

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discontinuous variation - characteristics fall into distinct groups (sometimes 2 forms of a characteristic)
e.g. blood group, attached/detached earlobes, etc

continuous variation - characteristics which do not show clear cut differences (show a range of differences)
e.g. height, weight, eye colour, etc

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quantitative inheritance, where multiple independent genes have an additive or similar effect on a single quantitative trait

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precursor -> intermediate -> final product

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occurs in:
1. whenever two or more loci interact to create new phenotypes
2. whenever an allele at one locus masks the effects of alleles at one or more other loci
3. whenever an allele at one locus modifies the effects or alleles at one or more other loci

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the set of functional association between genes

a trait may need interaction between multiple genes -> more than one gene is responsible for the phenotype of the trait

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sickle cell anemia, Marfan syndrome, porphyria, and PKU are caused by mutations in a single gene (a different gene for each disease) but have multiple effects all over the body

Marfan syndrome
- single gene for fibrillin on chromosome 15
- inherited disorder of the connective tissue that cause abnormalities of the patient's eye, cardiovascular system, and musculoskeletal system

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phenomenon in which a single locus affects two or more apparently unrelated phenotypic traits

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Manx cat (mutated) - M^L gene
expected ratio - 1 (homozygous) : 2 (heterozygous) : 1 (recessive)
double copy of M^L alleles = lethal
observed ratio - 2/3 Manx cat : 1/3 normal cat

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when cross between 2 mice heterozygous for coat colour gene
expected - 3 (75%) : 1 (25%)
however dominant genotype is lethal
ratio - 2/3 (heterozygous) : 1/3 (recessive)

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alleles that cause an organism to die only when present in a homozygous condition

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3. Order of Dominance (multiple alleles) 

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3. Order of Dominance (multiple alleles) 

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dominance is the phenomenon of one allele of a gene on a chromosome masking or overriding the effect of a different allele of the same gene on the other copy of the chromosome

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phenotypic ratio of F2 generation
1 : 2 : 1

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a form of gene interaction in which both alleles of a gene at a locus are partially expressed
- often resulting in an intermediate or different phenotype

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parents: pure breed white cow x pure breed red cow
|        |     CR    | CR
| CW | CR CW | CR CW
| CW | CR CW | CR CW

F1 generation: all offspring = roan cow

|       |    CR    | CW
| CR | CR CR | CR CW
| CW | CR CW | CW CW

F2 generation: 1 white : 2 roan : 1 red

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phenotypic ratio of F2 generation
1 : 2 : 1

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a type of inheritance in which two alleles of the same gene are expressed separately to yield different traits in an individual