When investigators study human genetics, they often must examine \"family trees,

Question

When investigators study human genetics, they often must examine "family trees," or pedigrees. The following page shows two different pedigrees, each following the expression of a single genetic trait. To figure out the type of inheritance involved, consider each generation separately, and determine phenotypic ratios in each set of offspring. If you can "work" the following human pedigrees, you will have mastered several fundamental aspects of Mendelian genetics!Let us make the assumption that only four types o inheritance are involved in the pedigrees described.

autosomal dominant X-linked dominant   

autosomal recessive X-linked recessive

The symbols used are: =(Square) male =(circle) female.When the symbol is filled in, the individual expresses the trait. When the symbol is empty, the individual does not express the trait.For example, the figure below represents a marriage in which the female exhibits the trait, but the male does not. The symbols on below the "parental" symbols represent the children of this marriage. In this case, both sons exhibit the trait, but the daughter does not.

Pedigrees are constructed by a process of elimination. Begin by writing down all possible genotypes for each individual. Rule out each type of inheritance as it becomes evident that, from the information given, a certain type of inheritance is not possible. If a certain type of inheritance "fits" the pedigree, it means only that that type of inheritance is possible in the given situation--not that you are absolutely correct. On the next page you will find two pedigrees, each typical of a particular type of inheritance (autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked dominant, or Y-linked recessive). Examine the pedigree, and fill in the most likely genotypes for each individual on the family tree. Finally, given what you have hypothesized about the family, write the type of inheritance in the space provided below each pedigree.

Explanation / Answer

above pedigree----------- X - LINED RECESSIVE INHERITANCE

XCXC      X    XY

all sons are affected--------------XCY

DAUGHTER s are affected------------CARRIER --X XC

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PEDIGREE 1--------------AUTOSOMAL RECESSIVE

PEDIGREE 2--------------AUTOSOMAL RECESSIVE

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