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39 Cards in this Set
- Front
- Back
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Which process leads to inheritance of new combinations of alleles on different chromosomes?
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Independent assortment at meiosis I
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What is a bivalent?
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Homologous chromosomes organised in pairs. 2 chromosomes, 4 chromatids.
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When do bivalents occur?
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At metaphase I.
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What important genetic event can occur with bivalents?
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Recombination
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When does independent assortment occur?
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Metaphase I and II.
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How many chromosomes are present in a cell in a standard independent assortment model looking at 2 traits in metaphase I?
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4.
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And in metaphase II?
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2
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And in the final gametes?
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1 (one chromatid from each of the chromosomes in metaphase II)
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Which structure leads to inheritance of new combinations of alleles of genes on the SAME chromosome?
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A chiasma at meiosis I
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What is the diplotene phase?
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The stage in which bivalents lines up at metaphase I.
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What is phenotype is more often seen if genes are on the same chromosome?
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Parental phenotype.
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What is phenotype is more often seen if genes are on different chromosomes?
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Equal ratios of other phenotypes.
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Does the gene swap occur to the right or the the left of the chiasma in recombination?
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Right
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Between which chromatids does recombination occur?
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The two on the inside of the bivalent.
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If genes are on the same chromosome, can crossing over occur?
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Yes.
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If genes are on different chromosomes, can crossing over occur?
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No.
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What does a 'linked gene' mean?
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The gene is on the same chromosome.
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So, if parents are more frequent, are the genes linked?
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Yes.
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How can you figure out the genetic distance between two genes?
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Look at the parental phenotype (most frequent) and count up how many recombinants there are. Divide the total number of recombinants by total number of specimen, and that is the recombination frequency.
Times by 100 for some reason and that's the distance. |
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What unit is used to denote genetic distance?
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Centimorgans.
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If there is 1 chiasma in a bivalent, what is the frequency of recombination?
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50%
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What would be the recombination frequency if there were 2 crossovers between genes A and B?
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75%
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If there are 2 crossovers in a bivalent, both on the inner most chromatids, what is the frequency of recombination?
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0%
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If there are 2 crossovers in a bivalent, one between the innermost chromatids, and one between chromatid 1 and 3 (of four, going down) what is the frequency of recombination?
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50%
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If there are 2 crossovers in a bivalent, one between the innermost chromatids, and one between chromatid 3 and 4 what is the frequency of recombination?
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50%
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If there are 2 crossovers in a bivalent, one between the innermost chromatids, and one between chromatid 1 and 4 what is the frequency of recombination?
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100%
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What is the maximum frequency of recombination between two genes with 1 crossover?
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50%
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What genetic experiment allows one to decide how many genes are influencing a phenotype?
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A complementation test
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What does a plus on a complementation table mean?
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That the genes do complement, and so they are on different genes.
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What does a minus on a complementation table mean?
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That the genes don't complement, and so they're on the same gene.
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What is intragenic complementation?
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A codon in a gene has two points of contact with another allele, 1 and 2.
There is a mutation of these points of contact, leading it to become dysfunctional. If either of these dysfunctional sites touches a normal site, the protein expressed will be absent. If the two dysfunctional sites line up, leaving one normal site, the protein will be expressed by to a lesser extent. |
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What is a bacteriophage?
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A virus which parasitises a bacterium.
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What is the mode of invasion of Bacteriophage T4?
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Phage absorbed into host.
Phage DNA injected, host DNA degraded Phage DNA replicated, proteins synthesised Mature phage assembled Host cell lysis, phage released |
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What is trait does the rII+ genotype give?
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Rapid lysis of the host bacterium.
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What phenotype does this result in?
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Small, ragged plaques.
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What are the usual phenotypes for the wild type gene (rII)?
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Large, round plaques.
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What does it mean for the two rII mutants if there are no plaques present (in E.Coli K)?
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That the two genes don't complement.
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If there is an intermediate on a complementation table, for example 'few plaques' as well as 'no plaques' and 'confluent lysis', are these complementary?
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No (and so, they are on the same gene).
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Can recombination take place within a gene? What is an example?
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Yes, T4 rII mutations.
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