University:
University of Ottawa
Course:
BIO 1130 | Introduction to Organismal Biology
Academic year:

2024
Views:

35

Pages:

4
Author:

xxzakxx 45

Chapter 4: Modern additions to Mendel’s Law: o Incomplete dominance – cross pure red with pure white pink flowers, showing incomplete dominance. Every allele can produce protein that can modify the offspring, even the recessive genes. Snapdragons Incomplete dominance – Horse with chestnut genes (CC), Palomino horse (Cc), Horse with cream genes (cc). o Codominance – both alleles are dominant and both are expressed in offspring. o Polygenism – when a phenotypic trait is under the combined action of two or multiple genes (very common). It is a very common phenomena with regards to expression of the genes. Each gene character segregates independently. This leads to a large variety of skin colours. It is possible that 20 gene characters could be discovered to play a role in skin colour one day. o Epistasis –when the effect of a gene hides or blocks the expression of another gene. o Example: Labradors- dominant is black, golden is result of epistasis. Epistasis blocks the black gene. E becomes recessive e and the pigmentation is blocked making the fur appear golden. o Pleiotropy – when a gene influences more than one trait. Certain pleiotropic genes are lethal when homozygous. o Example: Manx cat – the Manx gene (M) shows an incomplete dominance tail in mice (m). The gene for tailless trait (m). tail is lethal (embryo reabsorbed) when homozygous. The heterozygous cats do not have tails or have short tails. When homozygous dominant, the vertebral column does not develop properly, leading to the cat’s death. A population is in Hardy-Weinberg’s Equilibrium when: The frequencies of alleles and genotypes within a population will remain constant (according to the equation p2+2pq+q2=1) from generation to generation as long as the following conditions are respected. o There are no mutations. o Mating is done randomly. o The size of the population is extremely large. o There is no genetic (gene) flow (no migration of alleles between populations). o There is no natural selection. Hardy-Weinberg’s principle describes a hypothetical population that does not evolve. Mutation: changes in the DNA sequence of an organism. This is the source of genetically variability. Mutations are: o Random o Transmissible (can be passed from parents to offspring, but only if they are in the expressed form) gametes) o Frequent throughout the gene pool, but rare at each locus. o Rates of mutations vary greatly among groups of living beings. o Will influence allele frequencies but is a weak evolutionary force from generation to generation especially in large population. o No other ways to create genetic variability o One mutation in one species from a population won’t affect the population much. Point mutations (addition, deletions or substitution of a base; A-C instead of A-T). o Negative effect (Ehlers-Danlos syndrome – modification in the synthesis of collagen which is necessary for connective tissue) o Lethal effect (will cause death) o Neutral effect (synonymy of codons for the formation of amino acids; particularly in the 3rd position / non-coding part (protein) of the genetic code)