ch20 part 1
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are the five modes of genetic recombination and in which type of organisms does
•Genetic recombination occurs during
- –Crossing over between
- homologous chromosomes in meiosis (eukaryotes)
- of bacterial cells with related bacteriophages (bacteriophage)
What are synapsis, bivalents (also known as
tetrads), chiasmata, and crossing over?
- synapsis -when homologous chromosomes pair up.
- bivalents- a pair of homologous chromosomes
- Crossing over
- (exchange of DNA segments) occurs in Prophase I
- At the end of
- prophase I, chromosomes separate from their homologues and are connected only
- at the positions of crossovers called chiasmata.
in which phase of meiosis does crossing over take
Does crossing over typically occur between
sister chromatids or non-sister chromatids of homologous chromosomes?
What are the ploidy and DNA content of the
parent cell at the beginning of prophase I?
are the ploidy and DNA content of the daughter cells at the end of meiosis I
and at the end of meiosis II?
- two haploid cells at the end of meiosis 1
- four haploid cells at the ends of meiosis 2
are the similarities and differences between meiosis and mitosis?
Prophase- each condensing chromosomes had two chromatids. In meiosis I, homologous chromosomes synapse, forming a bivalent. Crossing over occurs between nonsister chromatids, producing chiasmata. In mitosis each chromosome acts independently.
- In meiosis I, the bivalents align at the metaphase plate. In mitosis, individual chromosomes align at the metaphase plate.
- In meiosis I, chromosomes (not chromatids separate. In mitosis, chromatids separate.
the meiotic bases of Mendel’s law of segregation and law of independent
is the effect of crossing over on the genotypes of the gametes?
Produces recombinant genotypes.
is the relationship between the frequency of recombination and the physical
distance between the genes on the chromosomes?
- The frequency of
- recombination is a measure of the distance between pairs of genes.
- The percent of nonparental offspring
- corresponds to map distance in map units or centimorgans.
- 1% crossover = 1 mu
does genetic recombination occur between two related but different
- recombination of bacteriophages can occur when a
- bacterial cell is co-infected by two related phage populations of different
is transformation? How does it lead to recombinant genotypes?
- Transformation is the
- uptake of exogenous DNA by a bacterial cell and allows recombination between
- the DNA fragment and the bacterial genome.
is transduction? How is it capable of introducing chromosomal
information from one bacterial cell to another?
- Phage that
- incorporated DNA from a previous host cell can carry that DNA into another
- bacterial host at a subsequent infection.
is conjugation? What are F+, F-, and Hfr cells?
Bacterial conjugationallows transfer of DNA from a donor cell to a recipient cell. Donor cells (F+)have F factor and develop sex pili to selectively bindto recipient cells (F-).
How does conjugation allow the transfer of plasmids between bacterial cells?
How does conjugation allow the transfer of chromosomal genes between bacterial cells?
- Conjugation between
- an Hfr cell and an F-
- cell allows transfer of genomic DNA from Hfr
- cell into F-
- cell. Crossing over between similar sequences then creates recombinant F-
is homologous recombination? The current model for this event includes the
formation of a crossed structure called H_______ J_______.
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