Case Study: Why Are There No Male Calico Cats?
Overview:
This presentation case study asks two important questions regarding cat coloration*. The instructor uses the slides as an interactive lecture to discuss the topic and develop an understanding of genetics. Students can work in small groups to answer questions as the instructor facilitates a discussion. Questions included in the presentation can be answered as part of this discussion and turned in at the end of class.
Objectives:
- Understand how genes located on sex chromosomes are inherited
- Make predictions about the genotypes of male and female calico cats
- Examine a karyotype and identify abnormalities
- Understand how errors in meiosis can produce these abnormalities
- Discuss how the inactivation of X chromosomes can affect phenotypes
Target Audience: Advanced or AP Biology, could be modified for other courses
Time Frame: Can be completed in about 50-60 minutes.
Question 1: Why are there no male calico cats? Why are there a few cases of male calicos?
Question 2: Why do cloned Calico cats look different?
Questions 3: What is Spaz's genotype?
Queston 4: Describe Nondisjunction
Question 5: How many chromosomes are in a human zygote?
...... Question 11: Why do CC and Rainbow look differerent even though they are clones?
As students expore these questions, they will be asked to analzye data and make predictions about the inheritance patterns of cat coloration. The case is intended to showcase the relationship between chromosomes, genes, and inheritance.
Concepts Included:
Karyotypes
Autosomes vs Sex Chromosomes
Sex-Linked Traits
Cloning
Meiosis
Nondisjuntion
Trisomy & Monosomy
Barr Body
*Cat coloration has been simplified in this exercise to only examine the orange and black alleles located on the X chromosome.
There are many genes that affect cat colors, if students are interested in learning more, the Feline Genetics Primer explains how other cat colors are inherited.
Other Resources on Sex-Linkage
SRY not SRY - A case study in sex determination
Practice Genetics - Sex-linked Genes
The Genetics of Calico and Tortoiseshell Cats