Match STR Repeat Counts in a Missing Bike Case

Start with Zoom From Chromosome to Gene to Allele and Label DNA Bases and Copy a Strand to build vocabulary. Then teach mutations, then crosses and pedigrees, and save the DNA profile cases for the end of the unit.

Compare STR repeat counts at five spots for four adults to a water bottle found by a bike rack. A short tandem repeat (STR) is a spot in DNA where a short sequence, such as GATA, repeats several times in a row; the number of repeats varies from person to person. The directions on the page read: Read the case and the rule. In each person's column, circle every pair of counts that matches the Bottle column at that spot. An answer key is included.

Yes, both. We made it for 8th grade living things, and it works the same at home or at school. At home, a student can work through it alone and then go over it with you, which shows quickly what is solid and what needs another look. In class it works as independent practice, homework or a warm-up, and you can print one copy or a full set.

A test cross mates an organism showing the dominant trait with one showing the recessive trait. If any offspring show the recessive trait, the parent must carry a hidden recessive allele. Test Crosses and Expected Offspring Counts uses purple and green tomato stems to practice this.

At certain spots, a short piece of DNA repeats a different number of times in different individuals. Each one has two counts at each spot, one from each parent, and samples match only if every count matches. Match STR Repeat Counts in a Missing Bike Case and Use DNA Profiles to Find a Grape Variety's Parents both use this rule.

Every mitochondrion in a child comes from the egg, because the sperm's few mitochondria do not survive in the new cell. A mother passes it to all her children, but only her daughters pass it on again. Mitochondrial DNA Passed Down From Mothers traces it through a family tree.