Exam Lecture Notes - Dr Uniackes Lecture Material Gene a genetic factor(region of DNA that helps determine characteristic Allele one of two or more

Exam Lecture Notes - Dr Uniackes Lecture Material Gene a...

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Dr. Uniacke’s Lecture Material Gene : a genetic factor (region of DNA) that helps determine characteristic Allele : one of two or more alternative forms of a gene Locus : specific place on a chromosome occupied by an allele Recessive Mutations Null/amrophic alleles: non-functional and no protein is produced Hypomorphic alleles: poorly functioning and reduces amount of protein produced Dominant Mutations Hypermorphic : Over production of normal protein OR increased activity levels Neomorphic : presence of altered protein has a new function Autosomal dominant traits are most likely to be heterozygous (Bb) Incomplete dominance : BB, Bb, and bb all differ phenotypically (flower colour, red, white, pink) Codominance BB, Bb, and bb all differ phenotypically but Bb exhibits phenotypes of both BB and bb (blood type) Allelic series/dominance series : when some genes have many alleles Haplosufficency : half as much protein is synthesized, yet this is enough to achieve wildtype phenotype e.g Huntington’s Disease Haploinsufficency : half as much protein is synthesized, this is not enough to achieve wildtype phenotype e.g tailless cats (Manx) needs two copies of allele to get tail Penetrance : proportion of individual organisms having a particular genotype; variation in the population Complete : identical known genotypes yield 100% expected phenotype Incomplete : identical known genotypes yield <100% (e.g polydactyl = extra digits) Variance : degree to which a phenotype is expressed; variation in individual Constant : identical known genotypes with no expressivity effect yield 100% expected phenotype Variable : expressivity effect yield range of phenotypes Incomplete : produce broad range of phenotypes, due to varying degrees of gene activation (e.g Huntington’s disease) Phenocopy : change in phenotype arising from environmental factors that mimic the effects of a mutation in a gene Complementation (9:7): when two strains of an organism with different homozygous recessive mutations that reproduce the sae phenotype, produce offspring of the wild-type phenotype White x White Black C/c A/a c/c A/A C/C a/a Genetic Epistasis
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Masking of the expression of one gene by another Recessive - 9:3:4; homozygous recessive at one gene pair mask expression from other gene A/- b/b and a/a b/b have the same phenotype Dominant - 12:3:1; one dominant allele at one gene mask the expression from the other gene A/- B/- and A/- b/b have the same phenotype Summary of F2 Ratios Monohybrid 3:1 Complete dominance 1:2:1 Incomplete dominance 2:1 recessive lethal Dihybrid 9:3:3:1 Complete dominance 9:3:4 Recessive epistasis 12:3:1 Dominant epistasis 9:7 Complementation Pleiotropy : single gene responsible for number of distinct phenotypic effects Eg. Sickle cell disease, cystic fibrosis Inbreeding depression : inbred lines of plants are often less vigorous than hybrid lines Heterosis : when two different inbred lines are crosses, the hybrids are heterozygous for many genes and display hybrid vigour Inbreeding increases frequency of homozygous and decreases heterozygous Polyploidy
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