10.1 Introduction

Learning Objectives

  • Distinguish between autosomes and sex chromosomes.
  • Discuss sex-linkage as an exception to Mendel’s First Law.
  • Describe sex-linked pattern of inheritance, with specific reference to Drosophila melanogaster as a model genetic organism.
  • Discuss the role of the Y-chromosome in sex-determination.
  • Recall and describe selected Y-linked characteristics.

Previously, Mendel, working with plants, showed patterns of inheritance derived from gene loci on autosomal chromosomes. One complication to this model of inheritance in animals is that loci present on sex chromosomes (see Figure 10.1.1 for example), called sex-linked loci, don’t follow this pattern. This chapter covers the various patterns of inheritance for various sex-linked loci.


Picture of a turkey with multiple coloured body parts
Figure 10.1.1 The E/e Gene in Turkeys is Responsible for Bronze or Brown Feather Colour, and is Located on the Z-Chromosome.

Figure 10.1.2 shows that most of the chromosomes in humans are present in two copies. Each copy has the same length, centromere location, and banding pattern. As mentioned before, these are called autosomes. However, note that two of the chromosomes, the X and the Y, do not look alike. These are sex chromosomes. In mammals, males have one of each while females have two X chromosomes.

Picture of a karyogram showing 23 pairs of chromosomes in black and white
Figure 10.1.2 Karyogram of a Normal Human Male

Watch the video below, Sex Determination | Genetics | Biology | FuseSchool,  presented by FuseSchool – Global Education (2017) on YouTube, which describes how the sex-chromosomes play a role in sex-determination in humans.

Media Attribution

FuseSchool – Global Education. (2017, November 27). Sex determination | genetics | biology | FuseSchool (video file). YouTube. https://youtu.be/D2hVgujy2E8


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Open Genetics by Natasha Ramroop Singh, Thompson Rivers University is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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