Just down the hill from the Abbey is the Cattery, which illustrates several types of inheritance patterns in domestic cats. The sign in each section offers a notecard with background information and a spreadsheet for recording data. The spreadsheet has multiple pages: one for each section of the Cattery.
West Cattery: A Cat of a Different Color
In this section, three pairs of cats represent a simple monohybrid cross. Parent cats are either black or gray and produce kittens with various mixes of the two colors.
The three sets of parents are:
- Black male x black female
- Gray male x black female (1)
- Gray male x black female (2)
By examing the kittens produced by each pair, a visitor can figure out which trait is dominant, what the genotypes of the parents are, and what genotypes are possible for the kittens.
A second pair of alleles is also represented by the three matings: a gene for white spotting. The type of inheritance represented by the spotting genes can be analyzed by examining the cats for the spotting patterns they display.
West Cattery Annex: Stripes!
In this section, a pair of cats illustrates how striping is inherited. Two types of striping are possible: mackeral or tiger striping, and the blotched pattern, in which the stripes on the side are in a spiral. The parents both have mackeral stripes. These parents produce a set of six kittens. The visitor is asked to examine the kittens and determine two things: which of the two patterns is dominant, and what the genotypes of the parents are.
Central Cattery: X-linked Inheritance
The four pair of cats in the central section of the cattery illustrate the inheritance of X linked traits. In sexually reproducing organisms, most genes come in pairs, with one member of the pair on each of two homologous chromosomes.
Usually, the pattern of inheritance is the same regardless of which parent contributes which member of the pair. However, in some species, the sex-determining chromosomes may be unpaired in one of the two sexes.
For example, in humans, cats and fruit flies, females have a pair of X chromosomes, but males have only a single X and a dissimilar chromosome, the Y chromosome.
Because only females in an XX/XY species get a pair of X chromosomes, only females can have the usual 3 possible genotypes for traits on the X chromosome: homozygous for one of the two alleles (AA or aa) , or heterozygous (Aa).
Males only get one X chromosome, so they will display whichever X-linked genes they inherit, regardless of dominance.
The inheritance of the Orange gene in cats is a good example of an X-linked inheritance pattern. Coat colors and patterns in cats depend on many pairs of genes, but the Orange gene is located on the X chromosome. Any cat that inherits the dominant Orange allele will express it. Cats that inherit the recessive non-orange gene usually express the black gene.
Clicking on one of the four cathouses in the exhibit produces a set of parents. Each of the four mating pairs of cats represents a different combination of male and female coat colors.
- Clicking on each of the cat pairs produces a litter of four kittens which represent all possible combinations of kittens for the two parents involved. The four pairs are:
- Black female x orange male
- Orange female x black male
- Tortie female x orange male
- Tortie female x black male
- Two other matings are possible, but would produce only kittens like the parents, since in each case the same allele is the only one available in both parents.
- Black female x black male (only nonorange)
- Orange female x orange male (only orange)
- Female cats, like other female mammals, have only a single X chromosome active in each cell. Therefore, even if they are heterozygous for a particular pair of alleles, they will express only one of their two alleles in a particular patch of tissue. The inactive chromosome is determined early in development, so female mammals have patches of tissue in which all cells have the same active X. Females cats heterozygous for the orange allele will express orange in some tissues, but not in others, leading to a patchy coat pattern of orange and black called Tortoiseshell or Tortie. To express the same allele in all tissues, females must be homozygous.
- Male cats have only a single X chromosome, so will express whatever alleles they have on their X chromosome. Because males must inherit the Y chromosome from their fathers, their X always comes from their mothers, although they may inherit either of her two X chromosomes.
- The book displayed here, Cats Are Not Peas, tells the story of a rare tortie male, and explains how such males can occur.
- When kittens are produced from each of the pairs of cats, their sexes and color patterns are entered into the Chat Record, and can be cut and pasted into the spreadsheet provided with the activity.
- By examining the phenotypes of the parents and each of the kittens, you can assign genotypes to all members of each family.
- Note how the results differ in the kittens from reciprocal pairs: black male x orange female and black female x orange male. Also note how the color of the male parent influences the possible offspring of tortie females.
East Cattery: Cat Tales
In the east section of the Cattery, the inheritance of the gene for short tails -- the Manx gene -- is represented. The Manx gene is interesting because kittens homozygous for the gene suffer from serious developmental disturbances and die before birth. The Manx trait is dominant, so heterozygous cats have short tails.
Because of homozygous lethality, only two types of crosses involving the Manx mutation are possible: Manx x Manx and Manx x normal tailed cats. Both crosses are represented in the exhibit.
In addition to the Manx gene two additional genes are represented in this part of the Cattery. One produces the dominant White phenotype. The White trait is epistatic to other coat colors, i.e. cats with one or two White alleles express only white coat color.
The other is a color dilution gene, which is recessive. Dilution homozygotes have reduced color. The color expressed depends on the base coat color. Dilute black cats are gray (this is actually the "gray" gene represented in the west section of the Cattery.) Dilute orange cats are cream.
Overall, genes for the following sets of traits are represented in the Cattery:
- White/ nonwhite
- Dilute/ full color (gray/black; cream/orange)
- Spotting/ solid
- Short tail/ normal tail
- Orange/ nonorange