Make your own free website on Tripod.com

SEX-LINKED AND AUTOSOMAL GENE COMBINATIONS



Most breeding crosses are made between parents containing multiple mutations. In this section, I will address a cross involving both a sex-linked mutation and an autosomal mutation.

PLEASE NOTE

The X and Y portrayed in the Punnett squares below represent the sex chromosomes and any allele in superscript is sex-linked. The autosomal allele is not written in superscript - it is written in normal script. The autosomal genes are not attached to the sex chromosomes but rather are grouped with the respective sex chromosome during gamete formation.

The following presents a worst case scenario (i.e. requires the most calculations) for a sex-linked and autosomal mutation cross. A Gray Male heterozygous for Pearl and Pied (Xpl,X+,+,pd) is crossed to a hemizygous Gray Female heterozygous for Pied (X+,Y,+,pd). The four possibilities of gametes the male can produce are as follows:



Xpl,pd and X+,+
Xpl,+ and X+,pd


The four possibilities of gametes the female can produce are as follows:


X+, pd and Y, +
X+, + and Y, pd


In this case, there are four different crosses that would have to be performed to derive the expected outcome. These crosses are as follows:


Male Female
Case 1: Xpl,pd and X+, + crossed toX+, pd and Y, +
Case 2: Xpl,pd and X+, + crossed toX+, + and Y, pd
Case 3: Xpl, + and X+, pd crossed toX+, pd and Y, +
Case 4: Xpl, + and X+, pd crossed toX+, + and Y, pd


Figures 11 through 14 work through each case. Since each case has the same probability of occurrence, the expected total outcome (ie., the sumation of Figures 11 through 14) of this breeding can be summarized as follows:


1/16 Gray Pied/pearl Males
1/8 Gray/pied Males
1/8 Pearl/pied Females
1/16 Gray Females
1/8 Gray/pied/pearl Males
1/16 Gray Males
1/16 Pearl Pied Females
1/8 Gray/pied Females
1/16 Gray Pied Males
1/16 Pearl Females
1/16 Gray/pearl Males
1/16 Gray Pied Females