8.2: chromosomes and quantitative inheritance Flashcards
What is quantitative inheritance?
Quantitative (discrete) inheritance describes how traits vary between individuals as some interactions of many genes.
–> Not all genotypes will produce same phenotypes due to penetrance, expressivity, or epigenetics.
What is qualitative inheritance?
Qualitative inheritance describes inheritance of traits along a continuous spectrum e.g. how height can be fitted to a normal distribution curve.
What are chromosomal mutations?
Chromosomal mutations are disruptions of whole DNA molecules (rather than scale of individual gene).
What are the key types of chromosomal mutation?
Deletions: can occur when chromosome breaks and rejoins without a section (e.g. cri du chat)
Duplications: if homologous chromosome breaks but reconnects to wrong partners (e.g. charcot-marie tooth disease)
Inversions: when breaking and rejoining causes flipping (e.h. pericantric inversions).
Translocation: when a segment of chromosome breaks off and attaches to a different chromosome (may not be deleterious: indiv can still be balanced). When non-homolog chromosomes exchange segments. Eg. chronic myelogenous leukaemia.
What is chromosomal non disjunction?
Chromosomal non disjunction describes improper segregation of homologous chromosomes in anaphase of meiosis, leading to trisomy or monosomy.
Aneuploid meaning?
Aneuploid = extra or missing chromosomes. Some types are viable, others not.
E.g. if you have an extra X you mightn’t know about it.
Polyploidy meaning?
Polyploidy = more than 2 COMPLETE SETS of chromosomes (e.g. triploid)
Vs aneuploidy: only affects part of set e.g. one chromosome pair (e.g. trisomic).
Why is pascal’s triangle useful in genetics?
Pascal’s triangle gives ratio of traits by how many genes control it?]
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Heritability meaning?
Heritability describes proportion of total phenotypic variation in a population which is due to genetic factors.
- -> Relative to env. conditions e.g. height of well-fed vs malnourished
- -> Relates expression in pop to actual gene pool.
What is epigenetics?
Epigenetics describes stable changes in gene expression that DON’T involve changes in DNA sequences.
- These changes involve modifications of DNA by cytosine methylation OR by how histone proteins bind DNA by acetylation.
What affects epigenetic changes?
Epigenetic changes are affected by the environment, which can be responsible for changing and inactivating genes, e.g. as embryo develops and cells become more specialised, genes whose products aren’t needed in certain cells become methylated.
(Methylated genes = silenced genes).
What are the two parameters describing effect of genes vs environment?
Expression of genes in relation to their environment can be expressed using…
- Penetrance: proportion of individuals with a genotype that actually show the expected phenotype.
- Expressivity: the degree to which a genotype is expressed in an individual (e.g. express only some or all aspects of a trait).
If a piece of chromosome breaks out (e.g. as a result of exposure to X-ray) what can result?
Broken piece of DNA can…
- Reattach in the right locus in the right orientation: no effect
- Reattach in the right locus but with opposite orientation: inversion
- Stay lost in the void. Deletion.
- Join onto other member of homologous chromosome pair, so original chrom has deletion, the other one has duplication (e.g. from 4 maternal to 4 paternal
- Join onto random chromosome (e.g. from 4 to 6. Deletion in original, translocation into new.
If a piece of chromosome breaks out (e.g. as a result of exposure to X-ray) what can result?
Broken piece of DNA can…
- Reattach in the right locus in the right orientation: no effect
- Reattach in the right locus but with opposite orientation: inversion
- Stay lost in the void. Deletion.
- Join onto other member of homologous chromosome pair, so original chrom has deletion, the other one has duplication (e.g. from 4 maternal to 4 paternal
- Join onto random chromosome (e.g. from 4 to 6. Deletion in original, translocation into new.
