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U18
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Task 2
Produce a genetic diagram to show what would happen if you crossed Short White plants (ttCwCw) with Tall
Red plants (TTCRCR)
Show the ratio of the offspring
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Thus, Rr (R- red, rwhite) will produce pink flowers
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short), so do them one at a time:
RR
r Rr Rr
r Rr Rr
The offspring will be 100% genotypic ally heterozygous, and 100% phenotypically pink
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Thus, all of the plants will be tall and pink
Task 3
A)
You are working as a genetic councillor, produce a poster that explains how one of the following
illnesses/disorders is inherited: Cystic Fibrosis
Colour Blindness
Haemophilia A
Fragile X Syndrome
Sickle Cell Anaemia
Cystic fibrosis is a recessive disorder, which means that both mother and father have got to cross on the
faulty gene for any of their children to get the disease
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Carriers don't sincerely have the disorder, but they may be able to
go it on to their kids
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They are expecting their first child and they are carriers for cystic fibrosis
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They're called "CF carriers
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Cff
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N
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, 2016
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14 June 2016
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Task 4
Use the two photographs shown on the next page to analyse the correlation between observed patterns of
Inheritance and the expected patterns
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You should calculate the probabilities of the correct ratios using the Chi Squared test you learned in Unit 8
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Monohybrid inheritance
Questions
Q1

Some forms of albinism, a genetic disorder, may be due to a single gene mutation
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A woman is heterozygous for albinism
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A
B
C

Does the woman suffer from the condition?
What percentage of their children are likely to be carriers?
Explain what is meant by the term ‘symptomless carrier’
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If the
method of inheritance for the disease is understood, then examination of the genetic family tree, sometimes
called a pedigree diagram, will let the counsellor advice on the likelihood of any children inheriting the disease
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Figure 1 A pedigree diagram showing the occurrence of sickle cell anaemia within one family
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Give a reason for your answer
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Huntington’s disease (HD) causes cells in the brain to degenerate
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The HD gene codes for a protein that
occurs in the brain
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a
b

What is the chance of a mother who is heterozygous for the condition passing it on to a child?
A couple who both have the condition would like to have children
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genetic family tree in Figure 2 shows the occurrence of this feature in one family
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a
b
c

Explain what the genotype of Maggie is
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What
does this suggest about the possible genotype of Catherine’s husband?

Sex linked conditions
There are genes that only occur on the X chromosome; these are said to be sex-linked
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A boy’s Y chromosome is always inherited from his father and his X
chromosome from his mother, so males can only inherit X-linked conditions from their mothers
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It does not occur on the Y chromosome
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Explain why fathers cannot pass the condition onto their sons
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Explain:
A
why any child of a heterozygous female has a 50% chance of being affected, assuming the father is
unaffected
B
why all daughters but no sons of affected fathers will have the disease, assuming the mother is
unaffected
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In pigs ear shape is controlled by a pair of alleles
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Black coat is controlled by the dominant allele B whilst red coat is controlled by the recessive allele b
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(i) With the aid of a genetic diagram show the genotypes and phenotypes of a cross between two black
pointy eared heterozygous pigs
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2
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This gene acts with a gene which possesses two alleles dominant E which allows the development of colour and the
recessive e which suppresses colour development, resulting in
Albino rats which have white coats and pink eyes
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(i) A black rat
(ii) A cream rat
(iii) An albino rat
(b)With the aid of a genetic diagram show the genotypes and phenotypes which could result from a cross between a
cream individual of genotype bbEe and a black rat heterozygous for both characters
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Long hair (L) is dominant and
short hair (l) is recessive
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About 70% of people get a bitter taste from the chemical phenyl thiocarbamide (PTC), while the other 30% do not
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Tonguerolling ability is dominant (R), while the inability to roll the tongue is recessive (r)
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She marries a man who can taste PTC but cannot roll his tongue
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Show the possible children this couple could produce
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