Genetics of the Aristocats

By Becca Smithers

Sometimes in science made simple our discussions can take an interesting turn. The query was raised “how can Duchess the cat from The Aristocats have three kittens of different colours?” This blog aims to find out the genetics behind Marie, Berlioz, and Toulouse!

Cat Colour Genetics

Cats inherit their colour from their parents. The gene that codes for colour is sex linked which means that is is only present on the X chromosome. Females have two X chromosomes (XX), they inherit one X from their mother and one X from their father. Males have one X and one Y chromosome (XY), they inherit the X from their mother and the Y from their father.

Sex Linked Genes on X Chromosomes. All rights reserved: science made simple

Sex Linked Genes on X Chromosomes. All rights reserved: science made simple

The colour of female cats is determined by a combination of their mother and father’s genes, but the colour of male cats is determined by the mother’s genes, as they only inherit an X chromosome from their mother. The genes code for alleles which determine the colour of the fur.

Colour of Duchess

Marie has white fur, Berlioz has black fur, and Toulouse has orange fur. Berlioz and Toulouse are both male, so they must have inherited their colour from Duchess, their mother. Duchess has white fur, so how can the boys be black and orange?

Duchess. The Aristocats, Disney, 1970.

Duchess. The Aristocats, Disney, 1970.

Cats have a gene that can override the fur colour genes and mask the appearance of fur colour by making the fur white. This can be in certain places like on their feet, bellies, heads, or it can be over their whole body. Duchess must express this colour masking gene which hides her “true” coat colours and makes her fur white.

For Berlioz to have inherited the dominant black fur allele and Toulouse to have inherited the dominant orange fur allele, Duchess must have both. Because Duchess is a female cat she has XX chromosomes so can have two alleles for her colour whilst males can only have one. If Duchess has both black and orange alleles she could be a black and orange tortoiseshell cat, a mixture of the two colours. We cannot see if this is true because of her colour masking gene.

Colours of the Kittens

Berlioz has black fur because he inherited the black allele from the fur gene on one of Duchess’ X chromosomes. The Y chromosome from his father plays no part, so Berlioz has black fur.

Toulouse, Marie, and Berlioz. The Aristocats, Disney 1970.

Toulouse, Marie, and Berlioz. The Aristocats, Disney 1970.

The same can be said for Toulouse but he inherits the orange allele from the fur gene on the other of Duchess’ X chromosomes. The Y chromosome from his father plays no part, so Toulouse has orange fur.

Marie has white fur. Like her mother, she expresses the colour masking gene meaning that her “true” fur colour is hidden and she has white fur instead. She must have inherited this from Duchess. Marie could have inherited either the black or orange fur allele from her mother, which leaves the question of what colour is their father?

Colour of the Father

The boys’ fur colour is determined by Duchess, and Marie’s colour is hidden by the masking gene giving her white fur. It doesn’t really matter what colour the father was because all three of the kittens have their fur colour determined by their mother’s genetics. It is very likely that the father is a ginger tom because to be a ginger cat you need to express all dominant orange alleles. Male cats only need one dominant allele to make a male cat ginger, whilst females need two dominant alleles to be ginger. Females only need one dominant black allele to be a black cat.

The O next to the X stands for orange, and the B stands for black.

Family tree genetics of the Aristocats. All rights reserved: science made simple

Family tree genetics of the Aristocats. All rights reserved: science made simple

Thomas O’Malley

A family photo. The Aristocats, Disney, 1970.

A family photo. The Aristocats, Disney, 1970.

O’Malley is no more an alley cat when he is welcomed as part of the family. He is a ginger cat with some white masking giving him white patches on his face, belly, and feet. He can only influence the colour of female offspring. If he and Duchess have future kittens it is possible that they would have ginger female kittens, tortoiseshell female kittens, black male kittens, or even more white kittens!

A way to represent the possible fur colours of the offspring is with a Punnett square. A Punnett square matches up the possible combinations of the genotype (the genetic code of a gene) to find out the phenotype (the characteristic of that gene shown in the offspring.

A Punnet square showing potential future offspring. All rights reserved: science made simple

A Punnett square showing potential future offspring. All rights reserved: science made simple

 

For more Disney science, check out:

The Real Life Jungle Book!

Dumbo – How Could an Elephant Fly?


 

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Posted in Biology, Exploring Science