Download Inheritance of a Trait - Introduction

#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 •
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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