Fruit fly X-linked trait inheritance explained

Most animals and many plants show sexual dimorphism; in other words, an individual can be either male or female. In most of these cases, sex is determined by special sex chromosomes. In these organisms, there are two categories of chromosomes, sex chromosomes and autosomes (the chromosomes other than the sex chromosomes). The rules of inheritance considered so far, with the use of Mendel’s analysis as an example, are the rules of autosomes. Most of the chromosomes in a genome are autosomes. The sex chromosomes are fewer in number, and, generally in diploid organisms, there is just one pair. Let us look at the human situation as an example. Human body cells have 46 chromosomes: 22 homologous pairs of autosomes plus 2 sex chromosomes. In females, there is a pair of identical sex chromosomes called the X chromosomes. In males, there is a nonidentical pair, consisting of one X and one Y. The Y chromosome is considerably shorter than the X. At meiosis in females, the two X chromosomes pair and segregate like autosomes so that each egg receives one X chromosome. Hence the female is said to be the homogametic sex. At meiosis in males, the X and the Y pair over a short region, which ensures that the X and Y separate so that half the sperm cells receive X and the other half receive Y. Therefore the male is called the heterogametic sex. The fruit fly Drosophila melanogaster has been one of the most important research organisms in genetics; its short, simple life cycle contributes to its usefulness in this regard (Figure 2-11 ). Fruit flies also have XX females and XY males. However, the mechanism of sex determination in Drosophila differs from that in mammals. In Drosophila, the number of X chromosomes determines sex: two X’s result in a female and one X results in a male. In mammals, the presence of the Y determines maleness and the absence of a Y determines femaleness. This difference is demonstrated by the sexes of the abnormal chromosome types XXY and XO. #FruitFly #XChromosome #SexChromosome #genetics #biology #Entomology #XlinkedTraits #genotype #phenotype #KhanAcademy #NikolaysGeneticsLessons #geneticDisease #geneticDisorder #DNA #RNA #geneticsDisorders #homozygous #hemizygous #chromosomes #XChromosomeInheritance #dominantTrait #geneticDesease #XlinkedRecessive #AutosomalRecessive #GeneticsExamQuestionsSolutions #SexlinkedDominant #skewedXinactivation #Xlinked #Genetics101 #sexlinkedRecessive