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#IN-‐S-‐1 Inheritance of a Trait - Introduction Gregor Mendel was the first to identify that we inherit characteristics from both of our parents – a heritable factor we now know as ‘genes’. Due to mutations, genes can differ slightly between individuals resulting in different appearances and traits – their phenotype. Flies, like humans, are diploid – they have two sets of chromosomes with one inherited each from the mother and father. They also have sex chromosomes: with females being XX, and males being XY. The Y chromosome contains only a small number of genes that mostly relate to sperm production, while the X chromosome contains many genes important to both sexes. Before fertilisation, cells undergo meiosis to produce gametes – haploid cells, with only one set of chromosomes. These chromosomes segregate randomly into the cells producing a different mix of the maternal and paternal chromosomes in each gamete, which produces variation in the population. The progeny can inherit different alleles from their parents, resulting in a particular genotype at that locus. The alleles can interact with each other in different ways – such as being dominant, recessive, codominant or sex-linked. This results in distinct patterns of inheritance of a trait, which can be used to determine more information about the gene and it’s alleles. In humans we can assess this by looking at pedigrees, however if information about a generation is missing it can make it difficult to draw conclusions. It is easier to assess in model organisms – such as the fly – as we can set up specific crosses to get the most information out of each generation. Aim: To determine the pattern of inheritance of the white mutation in flies by designing crosses. The gene white encodes a transporter protein that is involved in the movement of the eye pigment precursors in Drosophila. The mutant allele of the gene is non-functional resulting in a lack of eye colour. Key Vocabulary • • • • • • • Locus: The region of the genome where a particular gene is located. Homozygous: An organism with two identical alleles at a particular locus. Heterozygous: An organism with two different alleles at a particular locus (at a particular gene). True-‐breeding: A population homozygous for a particular trait – usually inbred with little or no variation. Allele: A particular form of a gene – usually due to a mutation. Can give different traits (such as eye colour). Genotype: The set of alleles an organism has a particular locus or loci. Phenotype: The visible characteristics of an organism. The Tauber lab 1 The University of Leicester