Genetics__guide - pair with alleles for one trait: RrTt RT...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
! 2009-2010 University of Washington Biology 180 Updated 1/12/2011 Biology 180 Handy Genetics Guide The many possible combinations of dominance, linkage (genes on the same chromosome) and sex-linkage (genes on a sex chromosome) can get confusing. Use the chart below to sort it all out. Suggestions: Be consistent with notation. In Biology 180, we use uppercase letters ( A ) for a dominant allele, lowercase ( a ) for recessive. To avoid confusion for both yourself and readers of your work, use upper- and lowecase characters that differ by more than just size ! Example: S s is better than Ss . Group the alleles for each trait (e.g., S s Tt , not ST s t ) and list them alphabetically unless you know the order in which they occur. For this combination … … the chromosomes would look something like this: Use this notation for a diploid individual … … and this for (haploid) gametes 1 : Autosomal, one trait One pair of homologs, each with one allele: Rr R, r Autosomal, two unlinked traits Two pairs of homologs, each
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: pair with alleles for one trait: RrTt RT , Rt , rT , rt Autosomal, two linked traits One pair of homologs, each chromosome with alleles for both traits: Can be written any of four ways; all mean the same thing. The line(s) separate the homologs. Pq/pQ Pq Pq Pq//pQ pQ pQ Pq , pQ Note that the underline notation indicating linkage should be used for gametes, too. X-linked 2 , one trait ± ² ± : X B X b ² : X B Y ± : X B , X b ² : X B , Y X-linked 2 , two traits ± ² ± : X Bh X bH ² : X Bh Y ± : X Bh , X bH ² : X Bh , Y X-linked 2 and autosomal traits in the same cross ± ² ± : TtX B X b ² : TtX b Y ± : TX B , TX b , tX B , tX b ² : TX b , tX b TY, tY Notes: 1 The gametes shown assume no recombination between linked alleles. 2 In almost all cases, only the X chromosome has alleles for the gene(s) of interest. Recall that ± = female, ² = male. Now, what if there are three traits, or four, or five … ? R r t T X b X B X B Y X B h X b H X B h Y X b X B t T X b t T Y...
View Full Document

This note was uploaded on 11/02/2011 for the course BIOL 11102 taught by Professor Parks,john during the Spring '11 term at University of Washington.

Ask a homework question - tutors are online