AP Biology : Evolution and Genetics
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Example Question #1 : Understanding Crossing Over
Crossover of homologous chromosomes in meiosis occurs during which phase?
Anaphase I of meiosis
Prophase I of meiosis
Prophase II of meiosis
Anaphase II of meiosis
Prophase I of meiosis
The crossing over of homologous chromosomes occurs in prophase I of meiosis. Prophase I of meiosis is characterized by the lining up of homologous chromosomes close together to form a structure known as a tetrad. A tetrad is composed of four chromatids.
Anaphase I is marked by the separation of homologous chromosomes, whereas in anaphase II there is the separation of sister chromatids. In anaphase I sister chromatids are still intact and connected at the centromere. Prophase II is similar to prophase in mitosis in that there is the break down of the nuclear membrane and the formation of spindle fibers in preparation for the separation of sister chromatids.
Example Question #1 : Understanding Crossing Over
During crossing over, two homologous chromosomes pair to form which of the following choices?
Mitotic Bond
None of these
Chromatid
Tetrad
Base Pair
Tetrad
The tetrad, which divides into non-sister chromatids, exchanges genetic information in order to make the genetic pool more variant, and result in combinations of phenotypic traits that can occur outside of linked genotypic coding.
Example Question #1 : Understanding Crossing Over
Chromosomal crossover occurs in which phase of meiosis?
Metaphase I
Prophase II
Anaphase I
Prophase I
Anaphase II
Prophase I
During prophase I, homologous chromosomes pair with each other and exchange genetic material in a process called chromosomal crossover. The exchange occurs in segments over a small region of homology (similarity in sequence, ie., the same alleles). The new combinations of DNA created during crossover provide a significant source of genetic variation.
Example Question #8 : Understanding Crossing Over
Crossing over is a phenomenon that happens during Meiosis I in the attempt to create genetic diversity. Crossing over typically occurs between which of the following structures?
Sister chromatids
Tetrads
Chromatin
Homologous chromosomes
Homologous chromosomes
Crossing over occurs when chromosomal homologs exchange information during metaphase of Meiosis I. During this stage, homologous chromosomes line up on the metaphase plate and exchange genetic information.
Example Question #9 : Understanding Crossing Over
When in meiosis does crossing over occur?
Anaphase I
Metaphase I
Telophase I
Prophase I
Interphase
Prophase I
Crossing over occurs during prophase I when parts of the homologous chromosomes overlap and switch their genes.
Example Question #1 : Understand Causes Of Genetic Variation
Which of the following affect the frequency of chromosomes of two linked genes crossing over?
Whether the genes are dominant or recessive
Size of the chromosome
Size of the gene
Distance between the genes
Distance between the genes
The recombination frequency depends upon the distance between the genes; a larger distance between the genes increases the probability of crossing over occurring.
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