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?
Signup and view all the answers
What is the term used to describe two or more genes located on the same chromosome?
Signup and view all the answers
What is the explanation for the high proportion of combinations of traits found in the parental generation in Morgan's three-factor cross?
Signup and view all the answers
What is the phenomenon where genes close together on a chromosome tend to be transmitted as a unit?
Signup and view all the answers
What is the term for the physical association of replicated sister chromatids from homologous chromosomes?
Signup and view all the answers
Why does crossing over allow genes far apart on the same chromosome to independently assort from each other?
Signup and view all the answers
What type of cross would be used to study linkage between three genes?
Signup and view all the answers
What is the result of no crossing over during meiosis?
Signup and view all the answers
During which stage of meiosis does crossing over occur?
Signup and view all the answers
What did Bateson and Punnett observe when they crossed two traits, flower color and pollen shape?
Signup and view all the answers
What is the number of linkage groups in humans?
Signup and view all the answers
What is the reason why genes close together on a chromosome do not always assort independently?
Signup and view all the answers
What is the term used to describe the chromosomes that contain a group of linked genes?
Signup and view all the answers
What was Janssens' contribution to the understanding of crossing over?
Signup and view all the answers
Why did Morgan assume that crossing over did not occur between the X and Y chromosomes?
Signup and view all the answers
What is the result of crossing over between homologous X chromosomes in females?
Signup and view all the answers
What is the relationship between the distance between two genes and the likelihood of crossing over?
Signup and view all the answers
What is the result of genetic linkage?
Signup and view all the answers
Why did Morgan propose that the genes for body color, eye color, and wing length are located on the X chromosome?
Signup and view all the answers
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.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Explore the process of meiosis, including crossing over during prophase, and its impact on genetic recombination, producing recombinant cells and offspring.