Genetics and Inheritance

Gregor Mendel was an Austrian Monk in the late 1800s who experimented with pea plants to find trait inheritance patterns in successive generations.

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Mendel's Laws

  1. Principle of Segregation - Two alleles of a homologous pair of chromosomes separate (segregate) during gamete formation such that each gamete receives only one allele
  2. Principle of Independent Assortment - Alleles of a gene pair assort independently of other gene pairs. The segregation of one pair of alleles in no way alters the segregation of another pair of alleles*

*This law is not always true, when genes are linked on a chromosome, explained later

Terminology

Homozygous - An individual who has two copies of the same allele at a locus

Heterozyous - An individual who has two different alleles at the same locus

Dominant alleles only needs one copy to show the phenotype

Recessive alleles need two copies of the allele to show the phenotype

Co-dominance means the phenotype for the heterozygote is different from either homozygote

Example - Blood types A and B are co-dominant to each other, but dominant to type O:

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Gene inheritance only happens during Meiosis, not mitosis (although mutations can happen in both). If you have genes close to each other, they are more likely to be inherited together, which is why Mandel's second law does not always hold.

Pedigree Drawing

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Diagonal line mean the person is deceased. Filled in represents individuals effected by a certain condition of interest, a half filled in shape represents a "carrier" of the condition who does not express it.

Mendelian Diseases

Mendelian diseases are disorders caused by a mutation in a single gene. Follow a specific form of inheritance, the most common:

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Any trait that does not follow a Mendelian pattern is a complex genetic trait

Storing Family Data

There are really no standards for storing genetic data, everyone has their own way of representing it.

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Here is a typical representation of a pedigree data set. 2 indicates something is present and 1 indicates it is not. Be prepared to draw a pedigree chart from something like the above.

a1 and a2 are the alleles being studied and aff is if the indicivdual is affected by the trait. We might represent the allele pair as 11, 12, 22 or 1/1, 1/2, 2/2, etc.

SNP (SNV) "single nucleotide polymorphism/variant" genotypes may be:

Microsatellites may be recorded as:

Sometimes phenotype may be complex, where it is than affected/unaffected, in which case it is usually store separately from the genetic data.

Useful Summary Information of Genetic Data


Revision #5
Created 12 September 2022 22:15:25 by Elkip
Updated 14 September 2022 16:01:32 by Elkip