Answer:
a dominant mutation
Explanation:
A monohybrid testcross is a cross-breeding experiment used to determine if an individual exhibiting a dominant phenotype is homo-zygous dominant or heterozygous for a particular phenotypic trait (in this case, wing length). In a monohybrid testcross, a 1:1 phenotypic ratio shows that the dominant parental phenotype was a heterozygote for a single gene that has complete dominance. Moreover, a 3:1 ratio in the F2 is expected of a cross between heterozygous F1 individuals, which means that 75% of individuals with short wings have the dominant allele that masks the expression of the long-wing trait (i.e. the recessive allele).

In humans, the medulla region of the brain is mainly responsible for the regulation process of respiration. It is also called the respiratory rhythm centre. The chemosensitive area located near the respiratory centre sends signals across nerve impulses to alter the rate of expiration to eliminate compounds.
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The phase during which sister chromatids aggregate along the equator of the cell is called the metaphase.
The image shows the process of cell division through mitosis. The mother cell divides into two genetically identical daughter cells in mitosis. There are four main phases in the mitosis process. They are: prophase, metaphase, anaphase and telophase. In the metaphase, the highly condensed sister chromatids line up along the equator of the cell by binding to the microtubles that form the skeleton of the cell. These kinetochores line up the chromatids at the equator to initiate their separation.