Complications with inheritance Flashcards
What is Incomplete Penetrance?
• Penetrance – whether or not a gene phenotype is expressed.
What is expressivity?
- Expressivity – how strong the phenotype is expressed.
* The phenotype expected from a genotype is variably expressed.
What is a disease people don’t express till older?
- Huntington’s disease – penetrance: many people don’t express phenotype until older.
What is Incomplete dominance? Example?
o When one allele is not completely dominant over another.
o Heterozygote will show an intermediate phenotype between the two characters.
o E.g. feather colour in chickens. CwCB.
What is Co-dominance? Example?
o Heterozygote expresses both genes.
o E.g. blood groups: AB where both genes are expressed. IAIB.
What is Epistasis?
- interaction between genes changes Mendelian ratios because one gene interferes with the expression of another gene.
What is Recessive Epistasis?
- 9:7 – lack of one gene masks the presence of another.
What is a Complementation test? between mutation of (tightly linked) different genes:.
o Complementation test= functional definition of a gene.
o 2 recessive mutations are considered alleles of different genes if a cross between the homozygous recessives result in non-mutant progeny – they complement each other.
o 2 recessive mutations are considered alleles of the same gene if a across between the homozygous recessives results in mutant progeny – fail to complement.
Describe Sex determination in animals and plants, what are the major differences?
o Many species are hermaphrodite.
o Species with 2 sexes often have X-Y system or one sex is haploid (wasps, bees, ants etc.).
o Mammals and fruit flies have XX=F XY=M.
o Some fish and birds are the reverse WW=M WZ=F.
o Sex with one X/W = heterogametic.
o Sex with two X/W = homogametic.
o Human sex-linked genes:.
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