Final answer:
Using a Punnett square to demonstrate a sex-linked cross such as red-green colorblindness involves considering the X and Y chromosomes' differences between females and males. An example of a cross between a colorblind male and a carrier female shows that 50% of the sons will be colorblind and 50% of the daughters will be carriers.
Step-by-step explanation:
Sex-linked traits, such as red-green colorblindness, exhibit different inheritance patterns in males and females due to their association with the sex chromosomes. When we use a Punnett square to predict outcomes of sex-linked crosses, we take into account that males have one X and one Y chromosome (XY) while females have two X chromosomes (XX).
As an example, consider the cross between a colorblind male (XcY) and a carrier female (XCXc). Here, the male can only pass on the Y chromosome or the X chromosome carrying the colorblind gene (Xc), while the female can pass on either the X chromosome with the normal vision allele (XC) or the one with the colorblind allele (Xc). The Punnett square would show that 50% of the male children will be colorblind (XcY) and 50% will have normal vision (XCY). Similarly, 50% of the female children will be carriers (XCXc) and 50% will have normal vision (XCXC).
If we consider a cross between a white-eyed male fruit fly (XwY) and a heterozygous red-eyed female fruit fly (XWXw), the resulting offspring will have a 1:1 ratio of red-eyed females (XWXw) to white-eyed males (XwY) since females can be carriers whereas males express the trait if they inherit the mutation.