3. Genetics (Core) – 3.4 Inheritanc
Understandings, Applications and Skills (This is what you maybe assessed on)
Statement
Guidance
3.4.U1
Mendel discovered the principles of inheritance with
experiments in which large numbers of pea plants were
crossed.
3.4.U2
Gametes are haploid so contain only one allele of each
gene.
3.4.U3
The two alleles of each gene separate into different
haploid daughter nuclei during meiosis.
3.4.U4
Fusion of gametes results in diploid zygotes with two
alleles of each gene that may be the same allele or
different alleles.
3.4.U5
Dominant alleles mask the effects of recessive alleles but
co-dominant alleles have joint effects.
3.4.U6
Many genetic diseases in humans are due to recessive
alleles of autosomal genes, although some genetic
diseases are due to dominant or co-dominant alleles.
3.4.U7
Some genetic diseases are sex-linked. The pattern of
inheritance is different with sex-linked genes due to their
location on sex chromosomes.
3.4.U8
Many genetic diseases have been identified in humans but
most are very rare.
3.4.U9
Radiation and mutagenic chemicals increase the mutation
rate and can cause genetic diseases and cancer.
3.4.A1
Inheritance of ABO blood groups.
3.4.A2
Red-green colour blindness and haemophilia as examples
of sex-linked inheritance.
3.4.A3
Inheritance of cystic fibrosis and Huntington’s disease.
3.4.A4
Consequences of radiation after nuclear bombing of
Hiroshima and accident at Chernobyl.
3.4.S1
Construction of Punnett grids for predicting the outcomes
of monohybrid genetic crosses.
3.4.S2
Comparison of predicted and actual outcomes of genetic
crosses using real data.
3.4.S3
Analysis of pedigree charts to deduce the pattern of
inheritance of genetic diseases.
Alleles carried on X chromosomes should
be shown as superscript letters on an
uppercase X, such as Xh.
The expected notation of ABO blood group
alleles is: O = ii , A = IAIA or IAi,
B = IBIB or IBi, AB = IAIB
Recommended resources: Allott, Andrew. Biology: Course Companion. S.l.: Oxford UP, 2014. Print.
Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
3.4.U1 Mendel discovered the principles of inheritance with experiments in which large numbers of pea
plants were crossed.
1. Read about Mendel’s work on pg. 169 – 170.
a) Explain the experiments he performed and their results.
b) State the implications/discovery made from his results?
c) How long were his results ignored by the scientific community?
d) Besides his contribution to the field of genetics, why should we think of him as a “pioneer of research
methods in biology”?
2. Read the pink “TOK” box on pg. 172. Answer question number 2 below:
Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
3.4.U2 Gametes are haploid so contain only one allele of each gene.
1. Why do haploid gametes only have one allele of each gene?
3.4.U3 The two alleles of each gene separate into different haploid daughter nuclei during meiosis.
1. Review: What is the name of the location of a gene or allele on a chromosome?
3.4.U4 Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same
allele or different alleles.
1. Define the following to be used in future problems:
Genotype
Gene expression
Phenotype
Dominant allele
Recessive allele
Codominant alleles
Homozygous
Heterozygous
Carrier
Autosome
Sex chromosome
Gene locus
Monohybrid cross
Test cross
2. Outline the conventions for notation of genotypes, using one example of each:
Dominant/recessive alleles
Codominant alleles
Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
Sex-linked traits
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
3.4.U5 Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.
1. The allele for tall plants is dominant over the allele for dwarf plants.
a. State the possible genotypes of a tall plant.
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b. Explain how a test cross could be used to determine the genotype of a tall plant.
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2. Mendel is known as the father of genetics for his extensive experimental work with peas and different
types of crosses.
a. Complete the punnet grid below to show the outcome of the monohybrid cross that results in peas of
different colours.
Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
b. Complete the punnet grid below to show the possible outcomes of a cross between two members of
the F1 generation. Describe all genotypes produced.
3. Sickle cell is an example of codominance.
a. State the genotypes and phenotypes of these individuals.
HbAHbA
HbAHbs
HbsHbs
genotype
phenotype
b. Predict the phenotype ratios of offspring in the following crosses. Show all your working, and set it
out as expected. Take care with notation.
i.
Carrier mother with affected father
ii.
Affected father with unaffected mother.
iii.
Carrier mother with carrier father.
c. Explain how the prevalence of sickle cell in regions of Africa is an example of natural selection in
action.
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Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
A
d. The pedigree chart below shows a family affected by sickle cell:
i.
Deduce the genotype of each individual with a letter.
F
B
G
C
H
D
$
E
#
ii.
Calculate the likelihood of any further children produced by E and her husband # having
sickle cell anemia.
iii.
Male $ is healthy but of unknown genotype. Calculate the likelihood of any children produced
with female D having sickle cell anemia. Show all working.
Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
3.4.U6 Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some
genetic diseases are due to dominant or co-dominant alleles.
1. Identify the type of inheritance exhibited with the disease cystic fibrosis.
2. What are the symptoms of cystic fibrosis?
3. Identify the type of inheritance exhibited with the Huntington’s disease.
4. What are the symptoms of Huntington’s disease?
3.4.U7 Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes
due to their location on sex chromosomes.
1. Some traits are autosomal whereas others are carried on sex chromosomes.
a. Distinguish between autosomes and sex chromosomes.
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b. Annotate the diagram to distinguish between the X and Y chromosomes.
Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
c. Outline how non-disjunction can lead to gender-related chromosome abnormalities.
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2. Some inherited disorders are associated with gender.
a. Define sex-linkage.
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b. State two examples of sex-linked genetic disorders.
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c. Explain why sex-linked disorders are more common in males than females.
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d. Explain why human females can be homozygous or heterozygous for sex-linked genes, where males
cannot.
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e. The allele for colour blindness (n) is recessive to the allele for normal vision (N). This gene is carried
in a non-homologous region on the X chromosome. Complete the table below to show the genotypes
and phenotypes of individuals with regard to colour blindness.
Female
Normal
XN
Male
XN
Affected
Not possible! Why?
Carrier
f.
In the space below, complete a punnet grid to show a cross between a normal male and a carrier
female. What is the expected ratio of phenotypes?
Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
3.4.U8 Many genetic diseases have been identified in humans but most are very rare.
1. Read pg. 183 on Genetic Diseases in humans.
a. How many genetic diseases have already been discovered?
b. List some common examples of genetic diseases:
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c. How many rare recessive alleles out of the total 25,000 genes in the human genome are
genetic disease causing?
2. Research the job of a genetic counsellor. Describe the job below:
3.4.U9 Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases
and cancer.
1. Explain the relationship between radiation, mutations, and cancer.
2. What determines whether a mutation is passed on to offspring?
3. What are 3 examples of radiation that can cause chemical changes in DNA?
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4. What are 2 examples of chemical substances that are mutagenic?
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Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
3.4.A1 Inheritance of ABO blood groups.
1. Human ABO blood types follow a codominant inheritance pattern.
a. Describe what is meant by “some genes have multiple alleles.”
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b. Complete the table below to show how blood type is inherited.
alleles
i
IA
IB
i
IA
IB
c. Highlight the genotype and phenotype which is an example of codominance.
d. Complete this pedigree chart to show the inheritance of blood types in this family.
Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
3.4.A2 Red-green colour blindness and haemophilia as examples of sex-linked inheritance.
1. Hemophilia is a blood-clotting disorder that is also recessive and sex-linked.
a. State the normal function of the gene associated with hemophilia.
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b. Describe the effects and symptoms of hemophilia.
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c. Use the pedigree chart to deduce the possible genotype(s) of the named individuals.
Leopold
Helen
Alice
Mary
Rubert
Bob
Britney
d. Research & outline one form of genetic engineering used to help patients with hemophilia.
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Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
2. Red-green color blindness is an example of sex-linked inheritance. The recessive allele for color
blindness is located on the X chromosome.
a) Draw a pedigree chart complete with genotypes for this family:
Mary’s father is color-blind but her mother is not. Mary’s husband, Bill, has normal vision. Mary and Bill
have 3 children. Their oldest son has normal vision, their daughter has normal vision, but their youngest
son is color blind.
3.4.A3 Inheritance of cystic fibrosis and Huntington’s disease.
1. A mother is heterozygous for the cystic fibrosis allele, and the father is does not have cystic fibrosis
and is homozygous. Draw a Punnett grid to determine the probability of them having a child with
cystic fibrosis.
2. A mother has Huntington’s disease and is heterozygous. The mother is married to a man without
Huntington’s disease. Draw a Punnett grid to determine the probability of them having a child who
develops Huntington’s disease.
Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
3.4.A4 Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.
1. Use the graph on pg. 185 to answer this question: “When would you expect the cases of thyroid
cancer in young adults to start to drop, based on the data in Figure 26?”
2. Read the data-based question on pg. 186.
a. Calculate the percentage of excess deaths over control groups due to leukaemia in people
exposed to (a) 0.005-0.02 Sv (sieverts) of radiation and (b) >1 Sv of radiation. [4]
b. Compare the effects of radiation on deaths due to leukaemia and deaths in cancer. [3]
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c. Discuss, with reasons, what level of radiation might be acceptable in the environment. [4]
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3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.
1. Explain how to make a Punnett grid.
Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School
3. Genetics (Core) – 3.4 Inheritanc
3.4.S2 Comparison of predicted and actual outcomes of genetic crosses using real data.
1. Answer these questions from the first data-based question on pg. 176.
a) Construct a Punnett grid to predict the outcome of the cross between Darwin’s F1 plants. [3]
b) Discuss whether the actual results of the cross are close enough to support the predicted outcome. [2]
c) Peloric Antirrhinum majus plants are extremely rare in wild populations of this species. Suggest reasons
for this. [1]
3.3.S3 Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.
1. Do the data-based question on pg. 183.
a) Explain, using evidence from the pedigree, whether the condition is due to a recessive or
dominant allele. [3]
b) Explain what the probability is of the individuals in generation V having: [3]
i) two copies of a recessive allele
ii) one recessive and one dominant allele
iii) two copies of the dominant allele
c) Deduce, with reasons, the possible alleles of: [2]
i) 1 in generation III
ii) 13 in generation II
d) Suggest two examples of genetic diseases that would fit this inheritance pattern. [2]
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Citations: Allott, Andrew. Biology: Course Companion. S.l.: Oxford UP, 2014. Print.
Adapted by Mrs. Black, Ms. Emrich, Ms. Froese
from: Stephen Taylor Bandung International School