Unformatted text preview: Answers 1. Affected individuals would be cc (homozygous recessive) – to see an autosomal recessive trait, the individual must be homozygous for the recessive trait which should be designated as lower case letters. 2. CC (homozygous dominant) or Cc (heterozygous) – as long as they have one dominant allele, they will not be affected. 3. Cc (heterozygous) – to be unaffected he must have at least one dominant allele, however, to have an affected child (6), he must carry one recessive allele as well. 4. Cc (heterozygous) – for two unaffected individuals to have an affected child, they must each carry one recessive allele (to give to the affected child) and one dominant allele (so they don’t express the recessive trait and be affected themselves). 5. Cc (heterozygous) or CC (homozygous dominant) – could get either dominant or recessive allele from either parent. 6. Individual 7 must be Cc (heterozygous) – since she is unaffected she could be Cc or CC, however, because she has both affected and unaffected children she must carry both a recessive and dominant allele; if she was CC, none of here offspring would be affected. Individual 12 must be heterozygous (Cc) as well, she must receive a recessive allele from her father (cc), but since she is unaffected, she must have one dominant gene as well and be Cc. 7. It can not be X linked recessive because if it was both sons of individual 2 would be affected because the mother is homozygous recessive. Because she is homozygous recessive she would give the recessive allele to all of her sons and because males only have one X chromosome, they would be affected. It cannot be a Y linked recessive trait because in order for individual 3 to have an affected son (9), he would also need to be affected. 8. It is not an autosomal dominant trait because neither parent of individual 9 is affected (the trait would have skipped a generation which is not possible with dominant traits). 1 Answers 1. Affected ‐ Hh (heterozygous) or HH (homozygous dominant) – individuals require only one dominant allele to express the phenotype – note the use of upper case letter (H) to designate the dominant allele. 2. Unaffected – hh (homozygous recessive) . Unaffected individuals must be homozygous recessive because if they had even one dominant allele, they would demonstrate the trait. 3. Hh (heterozygous) – it is the only way that they could have an unaffected (hh) child. 4. Hh (heterozygous) – because he has both affected and unaffected children. If he was HH, all of his children would be affected. 5. Hh (heterozygous) – because she is affected she must have one dominant allele, however, because her mother is unaffected (hh) she must also have a recessive allele. 6. No, since neither is affected they are both hh and therefore can only have hh offspring which will be unaffected. 7. If it were autosomal recessive then to be affected an individual would have to be hh – this would mean that individuals 1 and 2 would have to be hh (affected) and therefore all of their children would have to be hh (affected) and individual 4 is not affected. 8. It cannot be Y linked dominant because the son of individual 6 would be affected and it cannot be X linked dominant because if it was, both daughters of individual 6 would be affected. Likewise, both daughters of individual 1 would have to be affected if it were X linked dominant. 2 1. XbY – because he is a male, he has only one X chromosome and therefore to be affected he needs on the one recessive allele on that chromosome 2. Individual 5 – XbXb – genotypes of X linked genes in females is just like autosomal genes and so for the phenotype to be observed, she must have two recessive alleles. Because individual 2 is not affected she could be XBXB or XBXb however because she has an affected daughter, she must have one recessive allele and therefore must be XBXb; you also know she is heterozygous because one of her sons (individual 6) is not affected (received a dominant allele). 3. From his mother – even though both his father and his mother carries the recessive allele, the mother is always the source of a son’s X chromosome (the father must give the Y chromosome in order for the son to be male). 4. Individual 6 cannot be a carrier because he is a male. Individual 7 must be a carrier because her son is affected. 5. No – the father has only one X chromosome and because he is not affected it must carry the dominant allele – so he can only give a dominant (unaffected) allele to his daughters and therefore at most a daughter would be a carrier if she received the recessive allele from the mother. 6. XBXb ‐ since one of her daughters is affected and one is not. Both daughter must have received a recessive allele from their father. For one daughter to be affected and the other not affected, the mother must have both a recessive and a dominant allele to give to each daughter. 7. Yes. She would have to receive the recessive allele from her father because this is all he has, and therefore she will be a carrier. 8. XBY – is not affected, therefore he must have the dominant allele on his lone X chromosome. 9. It cannot be dominant X linked because the trait skips a generation in individuals 6 and 7. For the son of individuals 6 and 7 to be affected, he must have received the X linked allele from his mother and if the trait was dominant, then the mother would be affected as well. 10. It could be autosomal recessive as well. 3 ...
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This note was uploaded on 12/24/2009 for the course BIOLOGY 1003 taught by Professor Suzannepaterson during the Fall '09 term at Carleton CA.
- Fall '09