Genetics and Evolution
Time allowed: 1 hour and 30 minutes
Total marks available for this paper: 50
For marker use only:
Answer all questions in the spaces provided
Temperature sensitive cell division cycle (cdc) mutants were isolated in fission yeast at the permissive temperature these conditional mutants had a wildtype phenotype, but at the restrictive temperature these mutants arrested at a specific point of the cell cycle. The cdc2 gene was identified as a key regulator of the cell cycle because cdc2 mutants arrest prior to entry into M phase. cdc2 mutants were grown in permissive conditions (1 mark) and transformed with a yeast plasmid library of human genes (1 mark). The transformed cells were shifted to a restrictive temperature (1 mark). Only the cells transformed with copy of the human cdc2 genes grew in the restrictive conditions (1 mark). These plasmid rescue experiments provided the cdc2 mutants with a functional copy of a cdc2 gene. This complementation occurred because the cdc2 genes in yeast and humans are highly conserved (1 mark).
To test whether or not the mutations were recessive
Comparative genomics has revealed that E. coli has a core genome of about 3000, although there may be as many as 13000 genes represented in the genomes of a diverse set of strains (1 mark). Many of these genes have unknown functions and are likely to include important virulence factors (1 mark). It has also revealed that some genes, or gene clusters, are restricted to one or few strains of E.coli (1 mark). Other genes, or clusters of genes, are shared with more, but not all strains (1 mark).
Answer: the origin of the this family is ancient (~800MYr) (1 mark) and it is a diverse family (neuroglobin, cytoglobin and myoglobin, alphaglobins and betaglobins) (1 mark). Multigene families that have diversified via successive rounds of gene duplication and divergence, and whole genome duplication (2 marks). Clusters of related globin genes have followed different evolutionary trajectories (1 mark) this evidenced by a human beta globin gene being an inactive pseudogene in other mammals, or more complicated gene inversion or fusion events.
Answer: McClintock also showed that some regions of the genome are more
likely to suffer chromosome breaks than others
She concluded that mobile elements within the chromosomes must be responsible for these breaks
She showed that these elements could move to a new position and the position of the chromosome break would move with them
Answer: a phenotype influenced by multiple genes as well as the environment
Answer: the ability of one genotype to produce more than one phenotype when exposed to different environments
Answer: the proportion of the total variation due to genetic differences among individuals
A species is a group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.
Those that reproduce only asexually, such as dandelions, because the definition depends on recombination.
In allopatric speciation, a population is split by a barrier and the two isolated populations evolve independently until, when they meet again, they are too divergent to merge. In parapatric speciation, mutants within a population are able to colonise an adjacent environment that is not available to the parental population. There is no physical barrier, but a hybrid zone with unfit hybrids.
(1) Many were lost because they were not needed; (2) many moved to the nucleus where they encode proteins that are imported into the mitochondrion;
(3) some remained in the mitochondrial genome.
What does this mean, and what is the evidence? (3 marks)
The ancestor of diatoms became photosynthetic by engulfing another eukaryote (a red alga), which had previously acquired a chloroplast by primary endosymbiosis with a cyanobacterium. The diatom chloroplast has four membranes, nuclearencoded chloroplast proteins have both signal and transit peptides, the phylogeny of chloroplast proteins suggests a red algal origin.
The first appearance in the fossil record of most modern animal phyla (and others) over a period of 510 million years after the start of the Cambrian period 541 Mya.
Frequency of Mar1 = ((25 x 2) + 70)/200 = 0.6. Frequency of Mar2 = 0.4.
|(0.6)2 x 100 =||36 Mar1/Mar1|
|2 x 0.6 x 0.4 x 100 =
(0.4) 2 x 100 =
The excess of heterozygotes might reflect selection against one or both homozygotes.
1 mark for something that looks like a phylogeny; 1 mark for a sensible outgroup in the right place; 3 marks for the correct sister groups; 1 mark for the correct common ancestor; 1 mark for any date(s) within the range 39 Mya (that is 7 marks, allowing full marks for a slight imperfection).
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