Recessive Inheritance Model

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" colspan=2 height=90 BGCOLOR="#006699" TEXT="#080000" bgproperties="fixed" background="109285a1erlcgo.gif"> <div> <FONT SIZE="5" COLOR="#FFCC66" FACE="Arial" ><B>Human Genetics</B></FONT><B>     |     </B><A HREF="index.htm" TARGET="_top" TITLE="Human Genetics"><U><B>home</B></U></A></div> <div> <A HREF="id36.htm" TARGET="_top" TITLE="Syllabus"><U>Syllabus</U></A>   |   <A HREF="id82.htm" TARGET="_top" TITLE="Journal Club Days"><U>Journal Club Days</U></A>   |   <A HREF="id27.htm" TARGET="_top" TITLE="Journal Guidelines"><U>Journal Guidelines</U></A>   |   <A HREF="id38.htm" TARGET="_top" TITLE="Journal Club Guidelines"><U>Journal Club Guidelines</U></A>   |   <A HREF="id90.htm" TARGET="_top" TITLE="Genetics Education Model Project"><U>Genetics Education Model Project</U></A>   |   <B>Recessive Inheritance Model</B>   |   <A HREF="id98.htm" TARGET="_top" TITLE="figures"><U>figures</U></A>   |   <A HREF="id52.htm" TARGET="_top" TITLE="Sample Exam I"><U>Sample Exam I</U></A>   |   <A HREF="id62.htm" TARGET="_top" TITLE="Sample Exam II"><U>Sample Exam II</U></A>   |   <A HREF="id63.htm" TARGET="_top" TITLE="Sample Exam III"><U>Sample Exam III</U></A>   |   <A HREF="id78.htm" TARGET="_top" TITLE="Sample Exam IV"><U>Sample Exam IV</U></A></div> <div> </div> </td> </tr><tr> <td valign="top" width=210 BGCOLOR="#FFCC66" TEXT="#080000" background="108d2c00dkelyh.gif"> <bR> </td> <td valign="top" height=390 BGCOLOR="#FFFFFF" TEXT="#080000"> <div> <I>Recessive Inheritance Model</I></div> <div> <B>Genes, cookies, and phenotype</B></div> <bR> <div> <IMG SRC="113af1d0.jpg" border=0 width="431" height="285" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <bR> <div> Mary and Florence Martin were pair of sisters with albinism who lived in the nineteenth century. Taken from <FONT SIZE="3" COLOR="#0000FF" FACE="Arial" ><A HREF="http://members.optusnet.com.au/~msafier/albinism/albino2.html" TARGET="_top" TITLE="http://members.optusnet.com.au/~msafier/"><U><U>http://members.optusnet.com.au/~msafier/albinism/albino2.html</U></U></A></FONT>.</div> <bR> <div> <B>Case: </B> Alberta and Raymond both exhibit a lack pigment in their skin, hair, and eyes that is caused by a mutation in one gene.  This gene normally produces a protein that generates the pigment, as well as having other functions in the body.  However, Alberta's lack of pigment is much more severe and she has vision problems.   How can the differences between Alberta and Raymond be explained?</div> <bR> <div> <B>Objectives:</B> Learn how:</div> <div> a. different genetic mutations can affect enzyme activity,</div> <div> b. enzyme activity correlates to phenotype, and </div> <div> c. different mutations in the same gene can result in a variation in protein activity and variability of the resulting phenotype.</div> <bR> <div> <B>Background:</B> Oculocutaneous albinism is a recessively inherited genetic disorder that is caused by mutations in the gene encoding tyrosinase.  This enzyme converts tyrosine to DOPA which is then converted to melanin. </div> <bR> <div>              <IMG SRC="111ff1d0.gif" border=0 width="255" height="29" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <div> tyrosine                         DOPA                           melanin (pigment)</div> <bR> <bR> <div> <B>Activity:</B>  In this modeling exercise one of you will be the enzyme tyrosinase that converts tyrosine, a “closed” cookie, to DOPA, a “open” cookie, which is the precursor of melanin.  The others will select mutations, time, and graph the results when mutations are introduced into the gene encoding the “enzyme.”</div> <bR> <div> <B>Followup Questions: </B></div> <div> a. If 6 units of DOPA/15 seconds (opened cookies) are required to make enough pigment for a “normal” phenotype, which mutations will result in a phenotype?  <B>Remember, that you have two alleles.</B></div> <bR> <div> b. Which mutations result in the most severe phenotype?  Why?</div> <bR> <div> c. A person having two different mutations is called a compound heterozygote.  How could this affect the severity of phenotype?</div> <bR> <div> d. How would your answers above change if 12 units of DOPA/15 seconds were required for a normal phenotype?</div> <bR> </td> </tr></table></body>