HI! In 1902, Sir Archibald Garrod published the first example of a recessive human trait, alkaptonuria, a relatively harmless disorder. Patients produce dark, discolored urine - an easy phenotype to score.
Let's look at a test case. John has alkaptonuria; it "runs in the family." Although his father, paternal uncles, and aunt do not have alkaptonuria, his paternal grandmother did. Pick the correct pedigree that describes this situation.
Alkaptonuria is a recessive human disorder. John and his grandmother are both homozygous for alkaptonuria.
John's grandmother has two brothers and a sister. One of the brothers had alkaptonuria and his daughter is John's mother.
This means that John's mother and father are first cousins. This is a consanguineous, or a closely related "blood" union. In a pedigree, consanguineous relationships are represented by a double horizontal line.
Based on this information, John's parents are:
both homozygous for the alkaptonuria gene. No, if John's parents are homozygous, they would have alkaptonuria too.
both heterozygous for the alkaptonuria gene. That is correct.
not carrying the alkaptonuria gene. No, John wouldn't have alkaptonuria if he didn't inherit the genes from his parents.
unknown in terms of who carries the gene for alkaptonuria. There isn't enough information. There is enough information.
John is homozygous and inherited one copy of the alkaptonuria gene from each parent. John's parents are both heterozygous for the alkaptonuria gene. Archibald Garrod noticed that recessive disorders are more likely to appear in families with consanguineous relationships.
If John marries someone who is heterozygous for alkaptonuria, then which of the following statements are true? Remember alkaptonuria is a recessive disorder.
All the children will have alkaptonuria. No, only children who inherit two copies of the recessive gene will have alkaptonuria.
None of the children will have or be carriers of alkaptonuria. No, both John and his wife can pass on the alkaptonuria gene.
All of the children will inherit at least one copy of the alkaptonuria gene. That is correct.
All of the children are heterozygous for alkaptonuria. No, draw a Punnett square and see how the genes sort out.
John is homozygous and his wife is heterozygous for alkaptonuria. All their children will inherit at least one copy of the alkaptonuria gene. This is the case for each pregnancy.
CONGRATULATIONS! YOU'RE SO SMART!
mendelian laws, family pedigree, archibald garrod, recessive disorder, alkaptonuria, phenotype