Topic 8: Classical Genetics Flashcards
Genotype is…
All of an organisms genes/alleles
Phenotype is…
the physical manifestation of the genotype (observable)
Traits controlled by the action of a single genetic locus are… e.g.
Discrete traits or mendelian traits
e.g. wet vs dry earwax, hairy ears
Traits that require the influence of multiple genes to results in the phenotype are… e.g.
Quantitative or continuous traits
e.g. height, weight
Homozygous vs heterozygous vs hemizygous
Homo = cell/organism with identical alleles of a gene of interest
Hetero = cell/organism with different alleles of a gene of interest
Hemi = cell/organism that naturally only has one copy of a gene normally residing on a sex chromosome
Gene vs allele
Gene = a region of a chromosome that is transcribed and influences phenotype
Alleles = a variant of a gene
Dominant allele is…
Fully expressed when only one copy is present
If the mutant allele is recessive…
Wildtype allele is haplosufficient (dominant)
If mutant allele is dominant…
WT allele is haploinsufficient
R vs r alleles in Mendel’s peas
R = WT allele, dominant, R phenotype = round pea
r = mutant allele, r phenotype = wrinkled
Why would a pea be wrinkled
Does not properly fill with starch
Gregor Mendel studied…
inheritance of many different phenotypes in pea plants
What kind of traits did Mendel study
discrete traits (straighforward geno-pheno relationship) that showed complete dominance
Basic principles of heredity
- Existence of genes
- Genes are in pairs i.e. diploid
- 1st law
- 3rd law
- 2nd law
1st, 2nd, and 3rd laws of heredity
1 = segregation (alleles separate in gametes in equal proportions)
2 = independent assortment (dihybrid crosses only)
3 = dominance
What is truebreeding
Individuals that are homozygous for a trait
Crossed they will give back the same phenotype generation after generation
What is monohybrid
Individual that is heterozygous with respect to a specific gene
Generated by cross of two true-breds with different phenotypes
When do you perform a monohybrid cross
When you want to test dominance (proof of law of dominance) or the law of segregation
Slides 11, 12, 13
Monohybrid crosses
What is a test cross? A tester?
Test cross = cross of an individual organism of unknown genotype with a tester
Tester = individual organism homozygous recessive for all alleles being tested
Test crosses are performed to…
Determine the genotype of an unknown individual
Slides 14, 15
Test cross
What is a dihybrid cross? Proves what?
Examine two traits at a time
Proves principle of independent assortment
Mendel’s second law (in more detail)
Law of independent assortment – unlinked or distantly linked segregating gene pairs assort independently at meiosis
Slides 16-18
Dihybrid cross
What are probabilities? Two types
The likelihood of the occurrence of a particular event
Multiplication rule and addition rule
Why are probabilities used in genetics
Determine the outcome of a genetic cross
What is the multiplication rule?
Probability of 2 independent events both happening
Event 1 AND event 2
What is the addition rule
Event 1 OR/EITHER event 2
Slides 21 - 25
Probabilities / dihybrid test cross *********
