Morgan was right - the fly's cells did indeed appear to contain an extra chromosome. Specifically, these cells contained two X chromosomes as well as a single Y chromosome.
The extra chromosome was determined to be the result of a defect during meiosis that caused a high frequency of nondisjunction. Nondisjunction is the failure of two sister chromatids to separate during the second meiotic division.
Thus, when an egg containing two nondisjoined X chromosomes, each of which carried the mutant white gene, was fertilized by a sperm cell containing the Y chromosome, the product was an XXY female with white eyes. Rather than disproving the chromosome theory, this "exceptional" female actually provided strong experimental support that genes were in fact located on chromosomes.
Morgan's lab also found that the trait for white eyes could appear even if a fly's father didn't have white eyes.
This showed that flies could carry the white-eye trait even if they didn't show it themselves. The trait could vanish and reappear only in certain exceptional moments. This concept forms the basis of our modern understanding of the hereditary substance that exists on chromosomes but is not always apparent in the outward physical traits of an organism. Whereas Mendel called this substance "elementen" and Darwin called it "gemmules," researchers now use the more familiar term "gene. When considered in view of all this information, the chromosome theory of inheritance was not the work of a single scientist.
Rather, the theory was built on collaboration between multiple researchers working over a period of many decades. The seeds of this theory were first planted in the s, when Gregor Mendel and Charles Darwin each proposed possible physical elements of heredity. It wasn't until several decades later, following Walther Flemming's Figure 6 discovery of chromosomes and description of their behavior during mitosis, that a probable mechanism for the transmission of traits was uncovered.
Subsequently, Theodor Boveri and Walter Sutton's research strengthened the idea of a connection between chromosomes and hereditary elements. But direct evidence that explicitly demonstrated that traits exist on specific chromosomes wasn't delivered until the Morgan lab's experiments with fruit flies at the beginning of the twentieth century.
Thus, after nearly fifty years of speculation, scientists were finally able to confirm what they had long suspected: chromosomes are indeed the physical carriers of hereditary information, and this information exists in the form of genes.
This page appears in the following eBook. Aa Aa Aa. Drosophila chromosome. Scientists first discovered chromosomes in the nineteenth century, when they were gazing at cells through light microscopes. But how did they figure out what chromosomes do?
And how did they link chromosomes — and the specific genes within them — to the concept of inheritance? After a long period of observational studies through microscopes, several experiments with fruit flies provided the first evidence. What is a gene? The first words for genes: Elementen and gemmules.
The Original Thinkers. Who was Gregor Mendel? The life and legacy of Charles Darwin. Figure 1: Gregor Mendel. Figure 2: Charles Darwin. Describing chromosomes. Figure 3: Sample image from Walther Flemming's drawings of chromosome behavior during mitosis. In , German biologist Walther Flemming was the first person to describe what scientists now know as chromosomes. Flemming's elegant drawings showed how chromosomes aligned and were eventually pulled apart during mitosis Figure 3.
Then, in , another German researcher named Theodor Boveri provided the first descriptions of meiosis, also supported by detailed drawings, except these drawings showed how the number of chromosomes in a parent cell was reduced by half in the resulting gametes. Connecting heredity to chromosomes. Figure 4: Walter Sutton. Confirming the chromosome theory of inheritance. Morgan's lab connects eye color with inheritance of sex chromosomes.
Open search bar Open navigation Submit search. Health conditions. Facebook Youtube Twitter. Home Health conditions Genetic conditions. Genetic conditions What is a genetic condition? Examples of genetic conditions include: some cancers cystic fibrosis high cholesterol haemophilia muscular dystrophy birth defects for example, spina bifida or a cleft lip. What are genes? They determine most of your physical characteristics, including: whether you are male or female blood type eye colour height.
Many health conditions and diseases are also carried in our genes. How your genes affect your health Almost all known conditions have a genetic basis. Social changes, such as women having children later in life, are also associated with: an increased number of pregnancies at risk of genetic conditions and birth defects increased need for pregnancy screening and diagnostic tests.
How common are genetic conditions? Testing for genetic conditions Genetic tests can be used to: confirm or rule out a suspected genetic condition assess your chance of developing or passing on a genetic condition. The role of genetics In general, genetics play a role in the development of disease in three main ways: Firstly, there can be changes or alterations to the DNA of particular genes — these are known as Mendelian or single gene disorders.
Secondly, there may be problems with the number or the structure of the chromosomes that are inherited from each parent — these are Chromosomal disorders. Learn more. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. What does it mean if a disorder seems to run in my family? From Genetics Home Reference. Degrees of relationship Degrees of relationship Examples First-degree relatives Parents, children, brothers, and sisters Second-degree relatives Grandparents, aunts and uncles, nieces and nephews, and grandchildren Third-degree relatives First cousins This condition affects members in each generation of a family.
Topics in the Inheriting Genetic Conditions chapter What does it mean if a disorder seems to run in my family?
0コメント