Questions and Answers
What is the result of crossing over during meiosis?
What is the term for haploid cells containing a combination of alleles not found in the original chromosomes?
What is the main reason for the formation of recombinant offspring?
What did Thomas Hunt Morgan's experiments involve?
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What is the term used to describe two or more genes located on the same chromosome?
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What is the explanation for the high proportion of combinations of traits found in the parental generation in Morgan's three-factor cross?
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What is the phenomenon where genes close together on a chromosome tend to be transmitted as a unit?
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What is the term for the physical association of replicated sister chromatids from homologous chromosomes?
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Why does crossing over allow genes far apart on the same chromosome to independently assort from each other?
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What type of cross would be used to study linkage between three genes?
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What is the result of no crossing over during meiosis?
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During which stage of meiosis does crossing over occur?
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What did Bateson and Punnett observe when they crossed two traits, flower color and pollen shape?
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What is the number of linkage groups in humans?
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What is the reason why genes close together on a chromosome do not always assort independently?
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What is the term used to describe the chromosomes that contain a group of linked genes?
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What was Janssens' contribution to the understanding of crossing over?
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Why did Morgan assume that crossing over did not occur between the X and Y chromosomes?
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What is the result of crossing over between homologous X chromosomes in females?
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What is the relationship between the distance between two genes and the likelihood of crossing over?
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What is the result of genetic linkage?
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Why did Morgan propose that the genes for body color, eye color, and wing length are located on the X chromosome?
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Study Notes
Meiosis and Crossing Over
- Crossing over occurs during Prophase of Meiosis I, where non-sister chromatids of homologous chromosomes exchange DNA segments.
- Replicated sister chromatids (homologues) associate as bivalents.
- Crossing over can produce recombinant genotypes.
Recombinant Cells and Offspring
- Haploid cells containing a combination of alleles not found in the original chromosomes are called non-parental or recombinant cells.
- Recombinant offspring are produced by the exchange of DNA between two homologous chromosomes during meiosis in one or both parents.
- Recombinant offspring have a novel combination of genetic material due to a crossover event during gamete formation in (at least) one of their parents.
Morgan's Experiments
- Thomas Hunt Morgan's experiments provided the first direct evidence of linkage in Drosophila.
- He investigated three traits: body color, eye color, and wing length, which showed a non-parental combination of traits.
- Morgan observed a higher proportion of trait combinations found in the parental generation, suggesting that the genes are located on the X chromosome and tend to be transmitted together as a unit.
Linkage and Synteny
- Linkage refers to the phenomenon where genes close together on a chromosome tend to be transmitted as a unit, influencing inheritance patterns.
- Synteny means two or more genes are located on the same chromosome and are physically linked.
- Chromosomes are called linkage groups, containing a group of genes that are linked together.
- The number of linkage groups is equal to the number of types of chromosomes in a species.
Bateson and Punnett's Cross
- Bateson and Punnett's cross involving two traits (flower color and pollen shape) did not yield the expected 9:3:3:1 phenotypic ratio.
- This suggests that independent assortment does not always occur.
Altering Linkage
- Janssens proposed that crossing over involves a physical exchange between homologous chromosomes, which Morgan realized was consistent with his data.
- Morgan assumed crossing over did not occur between the X and Y chromosomes.
- The three genes studied by Morgan were not found on the Y chromosome.
Morgan's Hypotheses
- Morgan hypothesized that the genes for body color, eye color, and wing length are located on the X-chromosome.
- He proposed that alleles will tend to be inherited together due to crossing over.
- The likelihood of crossing over depends on the distance between the two genes, with crossing over more likely to occur between genes that are far apart.
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Description
Explore the process of meiosis, including crossing over during prophase, and its impact on genetic recombination, producing recombinant cells and offspring.
