- 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.
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.
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.
- Figure 10.1.1 Wild Turkey strut by Steve Voght, CC BY-SA 2.0, via Flickr
- Figure 10.1.2 Human male karyotpe high resolution by National Human Genome Research Institute/ Talking Glossary of Genetics, public domain, via Wikipedia
FuseSchool – Global Education. (2017, November 27). Sex determination | genetics | biology | FuseSchool (video file). YouTube. https://youtu.be/D2hVgujy2E8
- Figure 10.1.1 A turkey demonstrates the phenotype of a bronze feather color, which is a gene located on the Z-chromosome or a sex chromosome of this animal. Sex-linked characteristics (e.g., bronze or brown feather color in turkeys) show different inheritance patterns than autosomal linked traits. [Back to Figure 10.1.1]
- Figure 10.1.2 A karyogram, which is a visualization of all the chromosomes in their condensed state of a cell in a particular organism. Here, 23 pairs of chromosomes are observed in a somatic cell of a human male: we see 22 pairs of autosomes and one pair of sex-chromosomes which are labelled XY. The Y chromosome is significantly smaller than the X chromosome. [Back to Figure 10.1.2]