How did nondisjunction experiments help to prove the chromosome theory of inheritance?
How did nondisjunction experiments help to prove the chromosome theory of inheritance? Drosophila in which nondisjunction was seen were more likely to have wild type phenotypes than others. b) Bridges isolated genetic mutants of eye color and was able to sequence the mutants. c) The results of nondisjunction were seen on d) Bridges isolated exceptional Drosophila offspring with extra or missing chromosomes and was able to analyze the phenotypes based upon these genotypes. e) Bridges isolated Drosophila with no X chromosome and was able to identify the phenotypes. What is the phenomenon hyperactivation? When a gene is overexpressed in the homozygous dominant. b) In incomplete dominance, the homozygous dominant has a more intense phenotype than the heterozygote. c) In male mammals, when the genes on the chromosome are upregulated in such a way as to match the expression from the two chromosomes in the female. d) When a gene is overexpressed in response to a disease state. e) In male Drosophila, when the genes on one chromosome are upregulated in such a way as to match the expression from the two X chromosomes of the Drosophila female. What is the chromosomal ratio required for wild type male Drosophila to develop? 2X:LY IXZA 2Xila 0.5X:LY IX:1Y
Answer
Calvin Bridges’ nondisjunction experiments played a critical role in demonstrating that genes are located on chromosomes by linking abnormal chromosomal separation to specific phenotypic outcomes. Here’s how these experiments contributed to proving the chromosome theory of inheritance:
- Nondisjunction and Chromosomal Imbalances:
- Bridges isolated Drosophila offspring with abnormal numbers of chromosomes due to nondisjunction during meiosis.
- These “exceptional” flies often had either extra or missing X chromosomes, which led to deviations in expected inheritance patterns. By analyzing the phenotypes of these flies (e.g., eye color), Bridges was able to correlate specific traits with chromosomal compositions.
- Key observation: Offspring with nondisjunction events (e.g., XXY or XO) exhibited predictable deviations from typical inheritance, directly linking the chromosome number with the expression of genetic traits.
- Phenotypic Analysis:
- By examining the Drosophila with abnormal chromosomal compositions, Bridges showed that certain phenotypes corresponded to specific chromosomal anomalies. This helped him establish that genes were physically located on chromosomes.
- Exceptional Offspring:
- Bridges identified and analyzed flies with extra or missing chromosomes, further confirming that their unusual phenotypes (e.g., eye color) were a direct result of these chromosomal abnormalities. This provided concrete evidence for the chromosome theory of inheritance, as it showed that genes were carried on chromosomes and could be inherited according to their presence or absence.
- Microscopic Confirmation:
- Bridges also used microscopy to visually confirm the abnormal chromosomal configurations in exceptional offspring. This provided both molecular and phenotypic evidence for his conclusions, solidifying the role of chromosomes in inheritance.
Hyperactivation Phenomenon
The phenomenon of hyperactivation refers to the upregulation of gene expression to balance differences in chromosome numbers between males and females. The most relevant explanation is:
- Hyperactivation in Male Drosophila:
- In male Drosophila (which have only one X chromosome), genes on the single X chromosome are upregulated to match the expression levels of the two X chromosomes in females. This ensures that gene dosage between the sexes remains balanced.
- Correct answer: e) In male Drosophila, when the genes on one X chromosome are upregulated in such a way as to match the expression from the two X chromosomes of the Drosophila female.
Chromosomal Ratio Required for Wild-Type Male Drosophila Development
In wild-type male Drosophila, the sex determination system is based on the ratio of X chromosomes to sets of autosomes (A). A typical male has one X chromosome and one Y chromosome, resulting in a 0.5 X
ratio (one X chromosome per two sets of autosomes).
- Correct chromosomal ratio for wild-type male Drosophila: 0.5X:1Y
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