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GCSE Biology Paper 2
Inheritance
Family Trees
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Created by
Sophia Robinson
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Cards (18)
What should you be able to do by the end of the video on family trees?
Interpret
information from family trees
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Why can interpreting family trees be tricky?
You might need to watch the video
multiple
times
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What type of allele causes cystic fibrosis?
Recessive
allele
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What must a person inherit to have cystic fibrosis?
Faulty
allele
from both
parents
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What genotype does a carrier of cystic fibrosis have?
One copy of the faulty
allele
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How many copies of the faulty allele does a person with cystic fibrosis have?
Two
copies of the faulty allele
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What type of allele causes polydactyly?
Dominant
allele
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How many copies of the faulty allele must a person inherit to develop polydactyly?
One
copy from one parent
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What does a family tree show regarding phenotypes and genotypes?
Shows
phenotypes
, not
genotypes
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What is the genotype of person 2 who has cystic fibrosis?
Lowercase
e
lowercase
e
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What evidence supports that cystic fibrosis is caused by a recessive allele?
Person 11
has cystic fibrosis, parents do not
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What would happen if cystic fibrosis was a dominant trait?
At least one
parent
would have cystic fibrosis
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What is the probability that persons 7 and 8 will have another child with cystic fibrosis?
25%
chance
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What is the genotype of person 3 who has polydactyly?
Capital P
lowercase P
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Why can't person 3 inherit the polydactyly allele from person 1?
Person
1
does
not
have
polydactyly
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What is the probability that persons 6 and 7 will have a child with polydactyly?
50%
chance
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What are the key characteristics of cystic fibrosis and polydactyly inheritance?
Cystic fibrosis: caused by a
recessive allele
Requires two copies of the
faulty allele
Polydactyly: caused by a
dominant allele
Requires only one copy of the faulty allele
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How do you use a Punnett square for cystic fibrosis and polydactyly?
Cystic fibrosis: two
carriers
(e.g., eE x eE) yields
25%
chance
Polydactyly: one affected parent (e.g., Pp x pp) yields
50%
chance
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