Example 1: A male who is 7r/7r at DRD4 (and therefore exhibits ADHD) mates with

Question

Example 1: A male who is 7r/7r at DRD4 (and therefore exhibits ADHD) mates with a woman who is heterozygous (different) for the 7r allele (and therefore doesn’t exhibit ADHD). Assuming neither are Irish (DRD4 doesn’t appear to contribute to ADHD

in people of Irish descent), if they had 5 offspring, how many would you expect to exhibit ADHD?   

Dad: 7r/7r x Mom: 7r/+ (I have the answer but I do not understand what the + means for the mother) Only need this answered

Dad only has one type of allele, so could only possibly produce one type of gamete (one with a 7r allele). Mom has two types of allele, so could produce an egg with a 7r allele, or an egg with a + allele.

Another example with + plus Have the answer only need to know what the plus sign means

A man with ADHD (due to DRD4) and DMD mates with a woman who is 7r/+ for DRD4 and is heterozygous for DMD. What are all the possible genotypes and phenotypes of their children? From this we gather that dad is 7r/7r Xb /Y and mom is 7r/+ X B /X b

Dad: 7r Xb or 7r Y Mom: 7r XB , 7r Xb , + XB , or + Xb

Explanation / Answer

In diploid organisms, in order to display the genotype for two copies of each gene sometimes a plus(+) symbol is used. Referring to a gene, + means the wildtype, which is the "normal" version, or unmodified version of the gene.The rule that genes are always written in the same order allows geneticists to use this shorter notation in which the wild-type allele is written with a plus sign alone to indicate a wildtype or unmodified allele, whatever the kind of strain that is being described. that means, in the given example, the woman has got one 7r allele at DRD4 but another allele is a "wild-type".

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