Mr Hoyle Pedigree Worksheet Biology Worksheets

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Name ___________________________
Date _________ Period 1 2 3 4 5 6
Pedigree Worksheet
A pedigree is a chart that shows the inheritance of a trait in a family. It usually tracks a
particular trait or disease through several generations.
A square
represents a male individual. A circle
represents a female.
A shape that is filled in
means that individual has the trait. An empty shape
means he/she
does not show the trait.
A straight horizontal line between a male and female represents a "marriage" or mating line. A
vertical line descending from a marriage line represents the offspring of the parents.
Here’s an example:
In this pedigree the parents had four offspring; two
male and two female. The mother and one of the
sons show the trait, but no one else does.
The pedigree only shows the phenotype, not the genotype
and not whether a trait is dominant or recessive.
For example, some members of this family are allergic to
strawberries (s) and some are not (S). Here is the same
pedigree with the genotypes. See if it you can see why
some individuals show the trait and some do not.
Here are a few rules of logic to help you understand the genetics behind the pedigree
1. If neither parent show the trait:
a. the trait cannot be dominant.
b. the trait could be recessive and either parent or both could be heterozygous carriers.
2. If one parent shows the trait:
a. the trait could be dominant and the affected parent could be heterozygous while the
unaffected parent is not a carrier
b. the trait could be recessive and the affected parent is homozygous while the unaffected
parent could be a heterozygous carrier
3. If both parents show the trait:
a. the trait could be dominant and both parents could be heterozygous carriers which
means that some of the children could be unaffected
b. the trait could be recessive meaning that both parents would have to be homozygous and
all the children would have to be affected
Problems:
Pedigree 1 shows a family of parrots. One of the offspring shows the trait for
blue feathers. (R = red feathers, r = blue feathers)
1. Do you think blue feathers are dominant or recessive? ______________
2. What must the genotypes of the parents be? _______________
3. What two genotypes could the other offspring have? _______________

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