BGM1004/L14 Inheritance III Flashcards
Define penetrance.
Proportion of a population with a particular gene mutation or exhibiting signs and symptoms
Define expressivity.
The degree to which a genotype is expressed as a phenotype in an individual
Define pleiotrophy.
When a single gene locus affects two or more apparently unrelated phenotypic traits
Define epistasis.
When expression of one gene is modified by expression one or more other genes
Define complementation.
Interaction between genes where multiple genes affect the same phenotype
Give an example of codominance in humans.
A and B blood groups
Define incomplete dominance.
Where both alleles of a gene locus are partially expressed, often resulting in a different phenotype
Give an example of pleiotropy.
Dominant ML allele in cats
Causes manx phenotype and recessive is lethal
How would a gene that is masked by another described?
Hypostatic
Give an example of an epistatic gene.
Labrador coat colour
Yellow ‘e’ epistatic to ‘B’ black and ‘b’ chocolate on different gene
Adenine biosynthesis in yeast
Any mutation that causes mitochondrial function loss yields white colonies
If 15% of a population exhibit the wild-type phenotype, what is the penetrance?
85%
What can expressivity and penetrance depend on?
Interaction with other genes
Environmental influences
Why does polydactyly exhibit incomplete penetrance?
Children with extra digits are born to parents with a normal number
Why does polydactyly exhibit variable expressivity?
Some individuals have one extra finger, others have extra digits on each hand and foot
Give an example of where temperature affects gene expression.
Siamese cats
Homozygous for a thermosensitive allele encoding melanin enzyme production
Does not work at normal body temperature
What is a complementation group?
A set of mutations mapping to the same chromosomal locus that fail to complement each other when crossed
What kind of allele is required for complementation analysis?
Recessive
What is interagency complementation and what can it do to complementation analysis?
Proteins with multiple functions or multimer-forming
Destroys analysis
Describe gene linkage.
When genes are (close) on the same chromosome, they are linked and co-segregate in crosses
What is a chiasma?
A physical connection between non-sister chromatids during meiosis
How are non-parental genotypes created?
Independent assortment of genes on different chromosomes
Breakage and rejoining of homologous chromosomes during meiosis
What is required to follow linkage and recombination?
Follow each piece of DNA through a marker
Use a genetic cross where recombination/assortment can be seen through phenotypes
Give the 2 steps in test crosses for 2 genes/traits.
Construct a double heterozygote cross
Cross double heterozygote with tester homozygous recessive for both traits (back cross)
What is the recombination frequency?
No. (recombinants/total progeny) x100
What is one centimorgan (cM)?
If recombination is observed between two loci in 1% of meiosis
