Inheritance Flashcards
How genotype is linked to phenotype
basic:
- genotype refers to the
genetic makeup,
commonly used in ref to the
paired alleles carried by an organism
- that give rise to a phenotype, which is
a physical manifestation of a genetic trait
explanation:
- phenotype depends on the different combination of alleles at each gene locus
- may depend on
interactions between 2 or more genes
- a range of phenotypes may also be controlled by the
combined effect of multiple genes
dominant inheritance
(interaction between alleles at one gene locus)
- when genotype consists of either 1 or 2 copies of the dominant allele of a gene
- organism displays the dominant phenotype, as a result of
the presence of a protein - as effect of recessive allele is masked by that of dominant allele in a heterozygote
recessive inheritance (interaction between alleles at one gene locus)
- when genotype consists of 2 copies of recessive allele of gene
- organism displays the recessive phenotype, as a result of
the lack of protein
(- which could result in lethality if protein is critical to embryonic development )
incomplete dominance (interaction between alleles at one gene locus)
- when genotype has 2 incompletely dominant alleles
- organism displays an intermediate phenotype
co-dominance (interaction between alleles at one gene locus)
- when genotype has 2 co-dominant alleles,
- organism simultaneously expresses the phenotypes of both types of homozygotes
epistatic gene interaction (interaction between 2 or more genes)
allele(s) of epistatic gene mask the effect of alleles of hypostatic gene
combined effect of multiple genes / polygenes
- genes act of phenotype in an additive manner
- and effects of single genes are too slight to be detected
- effect: leads to continuous variation of trait in phenotype
effect of temp on coat /fur colour in Himalayan rabbits
- Himalayan rabbits are homozygous for Ch allele of tyrosinase gene
- which codes for a heat-sensitive form of enzyme tyrosinase
- which is needed for melanin production resulting in black fur
- however, heat-sensitive tyrosinase is active only when air temp is below 33 ºC
- thus black fur only grow in parts of the body that are cool enough (e.g. extremities)
Effect of diet on differentiation in honey bees
- queen bees and workers bees have the same mount of genetic material
- but are phenotypically different;
- in which workers are infertile while queen is fertile
- due to difference in diet of bee larvae;
- in which larvae destined to be workers are switched to a diet containing honey and pollen
- while those destined to be the queen is fed with royal jelly
- high content of protein in royal jelly stimulate formation and maturation of the female repro system
how chi-squared test results can support a sample being an example of (autosomal) linkage
- X^calc > X^crit
- probability that chance alone is reason for difference between observed and expected results is less than 5%
- observed results do not fit expected 9:3:3:1 phenotypic ratio (i.e. Mendelian inheritance)
- with there being a larger no of parental phenotypes than recombinant phenotypes
explaining the mode of inheritance
- autosomal or sex-linked
- sex-linked: father with disease would produced daughters that all have the disease
- autosomal: prove that it is not sex-linked
- recessive or dominant
- recessive: both parents which have the disease should have children which all have the disease
- dominant:
- prove that it is not recessive
- no skipping of generations
use specific context for evidence
e.g. if given pedigree,
II-6 who has red hair has a daughter, III-5 who does not have red hair