1. Case Study - Calico Cats
Chromosomes & Inheritance
Big Question 1: Why are there no male calico cats?
Cat coloration is actually more complex than just the tri-colors found in calicos, but for the purpose of this study, we will focus only on this one aspect of cat coloration.

2. CC (Carbon Copy)
Rainbow
Big Question 2: Why do CC and Rainbow not look exactly alike, even though they are clones?

3. Genes are found on chromosomes, in most cases, you receive 2 alleles.
Shown is a human karyotype which contains
22 pairs of autosomes
1 pair of sex chromosomes
1. When would a person only have 1 allele for a trait?

4. Cat Karyotype 2. How is it similar to the human karyotype?
How is it different?

5. Fruit Fly
*animals have a set of autosomes and a set of sex chromosomes
3. How many autosomes does drosophila have?

6. Alleles are codominant
The genes for coat color in cats are located on the X chromosome.
Alleles can be:
ORange or Black
Alleles are codominant
4. What is Spaz’s genotype?

7. 5. What are the genotypes of these 3 cats
5. What are the genotypes of these 3 cats. The black and orange ones are both male.
6. Revisit Question 1: Why are there no male calico cats?

8. There are some rare cases of male calico cats.
How does that happen?

9. During meiosis, each egg and sperm should receive only one copy of each chromosome (haploid)
7. What is the diploid number for humans? And the haploid number?

10. The offspring ends up having an extra chromosome
The offspring ends up having an extra chromosome. Most of the time, this is FATAL, but not always.

11. Trisomy = extra chromosome
Monosomy = one chromosome of the pair is missing
8. Can you identify the abnormality in this karyotype of a girl with Turner Syndrome?

12. 9. How would nondisjunction explain male calicos?

13. Question 2: Why do CC and Rainbow look different?
Consider how color is expressed on a calico cat.
Some areas express orange, some black….
10. Propose a reason for this.

14. A Barr body (named after discoverer Murray Barr) is the inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization, in those species in which sex is determined by the presence of the Y

15. 12. How do Barr Bodies explain CC and Rainbow?
CC (Carbon Copy)
Rainbow

18. 13. Consider a male calico cat
13. Consider a male calico cat. Do you think this calico would have cognitive disabilities similar to those found in children with Down Syndrome. Why or Why not?
Possible answers: Considering that one chromosome is inactivated, it is unlikely that the cat will have a disability because the inactivation leads to each cell having the correct number. Since the extra chromosome is a sex chromosome and not an autosome, it will not have the same effect on cognitive development.