Chapter 2 - Transmission Genetics

Mendelian genetics

Inheritance of a single phenotype governed by a single gene

Good experimental choices by Mendel

- Studied seven traits with only two states/phenotypes (colour of seed, pod shape, etc.)
- Each trait had a clear dominant and recessive phenotype
- Each experiment began with "pure breeding" strains (homozygous)
- Self pollination and cross-pollination are possible, crosses can be easily controlled by removing anthers (male reproductive organ) and transferring pollen
- Many offspring were created from each cross, making data more statistically significant
- Plant generations include parental (P), first filial (F1), second filial (F2), etc.
- Phenotypic ratio varied among generations used to demonstrate segregation of alleles

Monohybrid cross

Cross between two individual that are homozygous for different alleles of the same trait

Test cross

Cross between an unknown individual and a homozygous recessive individual to determine zygosity

Dihybrid cross

Double heterozygotes (AaBb) are crossed to determine linkage, possibility of nine genotypes and four phenotypes

Law of Segregation

Alleles separate during gamete formation, each gamete will have one of two alleles from the parent

Law of Independent Assortment

Alleles from different genes get sorted into gametes independently from each other
Only true in unlinked genes

Product rule

Used to determine the probability that two unlinked events will occur simultaneously

Sum rule

Used to determine the probability that either of two independent events will occur

Chi squared test

Compares expectations to observation and determines whether deviation is due to chance

Degrees of freedom (df)

Equal to number of possible outcomes minus 1

x^2 value

compared to critical value (based on degrees of freedom and probability threshold)

x^2 value is equal to or higher than critical value

Reject the null hypothesis, change likely is correlated with variable

x^2 value is lower than critical value

Unable to reject the null hypothesis, variation is likely due to chance

Gain or loss of function possible in...

Both dominant and recessive alleles

Independent assortment on the same chromosome

Genes are far enough apart that recombination results in random assortment

Number of human autosomes

22

Autosomal inheritance

Transmission of genes found on autosomal chromosomes, not sex linked

Autosomal dominant

- Individuals with the trait has at least one parent who also has the trait
- Either sex can transmit the trait to offspring
- If neither parent has the trait, none of the offspring will
- If both parents are heterozygotes, they may both express the trait yet the offspring may not

Autosomal recessive

- If both parents have the trait, all of the offspring will
- Can skip generations, but frequently appears in multiple siblings in the same generation

Modern synthesis of evolution

Combines Mendel's theory with Darwin's

Translation

Process of mRNA becoming protein

Transcription

Formation of mRNA by RNA transcriptase, copies DNA template strand