BGDA - Genetics

Mendel’s first law

diploid individuals carry 2 alleles of a gene that will segregate during gamete formation, i.e. individuals inherit one alleles from each parent.

Particulate inheritance

passed from parents to offspring through discrete units that retain their individual identities across generations, as opposed to blended inheritance.

Mendel’s second law

alleles for different traits are distributed to gametes independently assort so the inheritance of one trait does not influence the inheritance of another.

Independent assortment

in meiosis I, paired chromosomes are sorted randomly into the daughter cells.

Crossing over

in meiosis I, homologous chromosomes exchange genetic information.

3

1 from hybrid cross

9

3

Test cross

determines the genotype of an organisms with the dominant trait by crossing the organism with a known homozygous recessive organism and analysing the phenotypes of offspring.

Linkage

closer loci on the chromosome experience less recombination and are more likely to be inherited together, i.e. independent assortment does not occur.

Incomplete dominance

neither allele is completely dominant, resulting in a blended phenotype in heterozygous individuals.

Codominance

two different alleles are expressed simultaneously in an individual, so the phenotype shows characteristics of both alleles in heterozygous individuals.

Pleiotrophy

a single gene has gene products with multiple functions, leading to multiple, seemingly unrelated phenotypic traits.

Epistasis

effect of one gene depends on the genotype of another locus.

Polygenic traits

traits influenced by many genes, each of which may have a small affect in the phenotype which is often continuous, e.g. height, weight.

Environment, linkage, incomplete dominance, codominance, pleiotrophy, epistasis, polygenic traits

List the 7 ways phenotype is influenced that goes against Mendel's 2nd law.

Mitochondrial genes, non-disjunction

List the 2 ways phenotype is influenced that goes against Mendel's 1st law.

Non-disjunction

homologous chromosomes not separating in either meiotic division, leading to aneuploidy (2n+/-1 chromosome

Family history, empiric risk, genetic testing

What are the 3 means of risk estimation for genetic disease.

Empiric risk

risk based on observed data, used when mendelian risk does not apply. Could be based on family history, maternal age…

Diagnostic tests

used to define a disease state where symptoms of the disease are present, based on clinical suspicion, to confirm from screening, or without any known diagnosis.

Karyotyping

looking at chromosomes under microscope, not commonly used but important for balance changes (translocations).

Chromosome microarray

used to compare patient DNA with a control to identify deletions or duplications.

Single gene sequencing

looking for errors in a single gene, e.g. one commonly associated with a condition.

Targeted gene panel sequencing

focuses on detecting mutations in a select subset of relevant genes (dozens to hundreds) rather than the entire genome.

Exome sequencing

a genomic technique that sequences only the protein-coding regions of an individual's DNA.

Cascade testing, carrier screening

What are the 2 types of carrier testing?

Cascade testing

a systematic process of extending genetic testing to biological relatives of an individual diagnosed with an inherited disorder.

Carrier screening

test taken before or early in pregnancy to determine if either parents are carriers to determine risk of having an affected child.

Predictive testing

checks for gene variants that increase your risk of developing a heritable disorder before any symptoms appear.

Ultrasound, nuchal translucency, NIPS

List 3 common screening tests done for all women who are pregnant, to detect potential anomalies with no suspicion.