Download GRADE 12A: Biology 5

GRADE 12A: Biology 5
UNIT 12AB.5
9 hours
Genetic inheritance
About this unit
Previous learning
Resources
This unit is the fifth of seven units on biology for
Grade 12 advanced.
To meet the expectations of this unit, students should already understand
that changes in DNA bases cause variation. They should know some
causes of mutation. They should understand that a mutation causes a
change in DNA and that this can reduce the efficiency of, or block, an
enzyme. They should know the difference between genes and alleles and
that they are sections of DNA. They should understand how genetic
variation occurs through the segregation of alleles and chromosome crossovers. They should understand how sex is determined in humans and the
mechanism of sex linkage. They should understand the difference between
dominant and recessive alleles and be able to calculate genotype and
phenotype frequencies in monohybrid crosses.
The main resources needed for this unit are:
The unit is designed to guide your planning and
teaching of biology lessons. It provides a link
between the standards for science and your
lesson plans.
The teaching and learning activities should help
you to plan the content and pace of lessons.
Adapt the ideas to meet your students’ needs.
For consolidation activities, look at the scheme of
work for Grades 10A and 11A.
You can also supplement the activities with
appropriate tasks and exercises from your
school’s textbooks and other resources.
Introduce the unit to students by summarising
what they will learn and how this builds on earlier
work. Review the unit at the end, drawing out the
main learning points, links to other work and real
world applications.
• overhead projector (OHP) or whiteboard
• corn (Zea mays) cobs
• coloured beads
• chi-squared statistical tables
• DNA autoradiograph from a genetic fingerprint
• Internet access
Key vocabulary and technical terms
Students should understand, use and spell correctly:
Expectations
• incomplete dominance, co-dominance
By the end of the unit, students calculate the frequency of different
progeny from a cross with incomplete dominant alleles, from back crosses
and from dihybrid crosses. They understand co-dominance and the
inheritance of phenotypic traits through multiple alleles. They use the chisquared test to determine the significance of results of genetic crosses.
They know about the Human Genome Project, genetic fingerprinting and
genetic screening and counselling.
• chi-squared test
• dihybrid cross, Punnett square
• Human Genome Project
• genetic fingerprinting, polymerase chain reaction (PCR)
• genetic screening, amniocentesis, chorionic villus sampling
• genetic counselling
Students who progress further are able to follow and understand the
principles of the technological advances and applications of the Human
Genome Project, genetic fingerprinting and genetic screening and
counselling.
435 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.5 | Biology 5
© Education Institute 2005
Objectives for the unit
9 hours
2 hours
Calculating ratios
of phenotypes
and genotypes
SUPPORTING STANDARDS
11A.14.3 Explain the terms gene, allele,
phenotype, genotype, dominant,
recessive and co-dominant.
Unit 12AB.5
CORE STANDARDS
Grade 12 standards
EXTENSION STANDARDS
12A.12.1 Calculate the ratios of the genotypes and phenotypes in the progeny of
incomplete dominant monohybrid crosses, dihybrid crosses (9:3:3:1 ratio)
and back crosses.
11A.14.4 Use genetic diagrams to solve
genetic problems involving
monohybrid crosses.
1 hour
Co-dominance
and multiple
alleles
1 hour
Using the chisquared test
1 hour
The Human
Genome Project
11A.14.5 Explain how variation occurs through
segregation of alleles during gamete
formation and through the crossing
over of chromosome segments
during meiosis
11A.14.6 Know how X and Y chromosomes
determine sex in humans and the
inheritance pattern of sex-linked
characteristics.
12A.12.2 Explain co-dominance and the inheritance of phenotypic traits such as
blood grouping through multiple alleles.
12A.12.3 Use the chi-squared test to determine the significance of observed and
expected frequencies of different progeny in genetic crosses.
12A.12.4 Know the purpose of the Human Genome Project.
12A.12.5 Explain the basis of genetic fingerprinting and understand its advantages
2 hours
Genetic
fingerprinting
and potential dangers.
12A.12.6 Explain the basis of genetic screening for alleles of disadvantaging
inherited conditions; understand the advantages and potential dangers of
such screening and the need for genetic counselling.
2 hours
Genetic
screening
436 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.5 | Biology 5
© Education Institute 2005
Activities
Unit 12AB.5
Objectives
Possible teaching activities
2 hours
Reinforce previous knowledge by giving students a quiz on genes, chromosomes, monohybrid
crosses, genetic variation and sex-linked characteristics (from Unit 11AB.5).
Calculating ratios of
phenotypes and
genotypes
Calculate the ratios of the
genotypes and phenotypes in
the progeny of incomplete
dominant monohybrid
crosses, dihybrid crosses
(9:3:3:1 ratio) and back
crosses.
Tell students to use the library to read about, and make notes on, the work of Mendel and his
recording of experiments conducted on the garden pea. These experiments included
monohybrid crosses, dihybrid crosses and back crosses.
Notes
Enquiry skill 12A.2.1
School resources
Use this column to note
your own school’s
resources, e.g.
textbooks, worksheets.
Use large diagrams on the board or OHP to display examples of the phenotypes of pea plants
involved in a variety of crosses.
Introduce an example of incomplete dominance (which Mendel did not meet). Show students
large diagrams on the board or OHP to illustrate the typical cross between red and white
snapdragon (Antirrhinum ) flowers. The F1 offspring are all pink. Ask students to explain this
observation. Ask them to predict what will happen in the F2 when the F1 plants are selfed.
Confirm that when the pink plants are selfed, then a ratio of 1 red : 2 pink : 1 white is produced in
the F2. Ask students to explain the results using a Punnett square. Make sure students
appreciate that the alleles remain discrete and that they do not blend together.
Enquiry skill 12A.3.3
Get students to predict the outcome of a back cross on the pink plants.
Provide students with an example of a dihybrid cross. Use large diagrams on the board or OHP
showing the phenotypes of the parents and offspring for both F1 and F2.
For example, use one of Mendel’s crosses in which he crossed plants with tall purple flowers
with plants with short white flowers, and produced all F1 tall purple flowers. These were selfed
and he finally obtained the following F2 plants: 96 tall purple, 31 tall white, 34 short purple and
11 short white flowers. Get students to explain the results using a Punnett square and work out
the dihybrid ratio of 9:3:3:1.
Enquiry skill 12A.3.3
Provide students with a number of cobs of maize (Zea mays). Maize kernels display a number
of easily recognisable characteristics, such as colour and shape. Ask to students to examine
the kernels and make deductions about the genotypes of the parent plants.
Use a computer simulation to investigate genetic crosses.
ICT opportunity: Use of computer simulation.
Get students to predict the outcomes of dihybrid crosses and compare their predictions with
collected data
Enquiry skill 12A.1.2
Simulate a dihybrid cross. Provide four bags, each containing the same number of a different
colour of bead (e.g. 50 red beads in one bag, 50 blue in the second, 50 green in the third and
50 blue in the fourth). Arrange students in pairs and get each student to take two bags of the
beads, pour them into one bag and mix thoroughly. Tell students to decide which colour will be
the ‘dominant’ and which the ‘recessive’ allele. Each student then takes two beads out of their
bag and puts them together to represent the first of the dihybrid’s F2 progeny. This should be
repeated at least 16 times and the ‘genotypes’ of the progeny identified. Ask students to
compare their ratios with those of other pairs of students and discuss the results together.
437 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.5 | Biology 5
© Education Institute 2005
Objectives
Possible teaching activities
1 hour
Distinguish co-dominance from incomplete dominance by asking students to find out, using the
library, what the difference is between these genetic features.
Co-dominance and
multiple alleles
Explain co-dominance and
the inheritance of phenotypic
traits such as blood grouping
through multiple alleles.
Notes
School resources
Ensure students understand that, in co-dominance, both of the alleles are expressed in the
phenotype, whereas, in incomplete dominance, the phenotype has an expression of a feature
some way between the phenotypes of the two parental varieties.
A human example of co-dominance is in blood grouping. The three blood groups M, N and MN
display the genotypes MM, NN, and MN, respectively. Note that MN is not intermediate
between the M and N phenotypes, since both these factors are expressed on the membrane of
a red blood cell.
Explain multiple alleles by using the other example of human blood groups: the ABO system.
Use the OHP or whiteboard to set up the examples and ask students to show the possible
outcomes of parents with different blood groups producing children. Get a student to come to
the front of the class and explain their answer, by adding the details such as a Punnett square.
For example, ask them to explain how parents, one of blood group A and one of blood group B,
can produce children with blood group A, B, AB or O.
1 hour
Using the chi-squared test
Use the chi-squared test to
determine the significance of
observed and expected
frequencies of different
progeny in genetic crosses.
Explain the purpose of the chi-squared test to students. It is a basic statistical test of
experimental data that is used to indicate whether the observed data is significantly different
from the expected values. If a difference has been established, then the probability of this
occurring by chance can be determined from statistical tables.
Work through an example with students, using data from phenotypes resulting from a dihybrid
cross. Show them how to interpret the equation to calculate the chi-squared value.
Provide students with a worksheet containing results from a dihybrid cross displaying the
numbers of the progeny. Ask them to work out the chi-squared value to see if the difference
between the observed and expected data is significant. They will need access to chi-squared
tables.
Prepare worksheets on the appropriate dihybrid
crosses.
Students will need access to chi-squared tables.
Enquiry skills 12A.3.3
Using other examples, get students to calculate the probability of obtaining the progeny of
genetic crosses by chance.
1 hour
The Human Genome
Project
Know the purpose of the
Human Genome Project.
Get students to visit the Human Genome Project website to gather information and to find out
the purpose of this ambitious research project.
ICT opportunity: Use of the Internet.
The project is producing evidence of the sequence of the bases of the DNA in the entire human
genome. Ask students how this knowledge will help people. Ensure they understand the huge
potential benefits, for example:
• health care – identification and mapping of the genes responsible for genetic diseases will
help in the diagnosis, treatment and prevention of those conditions;
• science – knowledge of the genome will give insight into the control of gene expression,
cellular growth and differentiation;
• evolutionary biology – enabling clarification of genetic relationships between species.
Show students a video of the Human Genome Project.
Get students to write an article for a magazine about the Human Genome Project.
438 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.5 | Biology 5
© Education Institute 2005
Objectives
Possible teaching activities
2 hours
Before beginning this topic, get students to collect newspaper and magazine articles (e.g. New
Scientist) on genetic fingerprinting. Get them to use these and the Internet to find out about the
development of genetic fingerprinting by Alec Jeffreys and colleagues at the University of
Leicester, and to explain the principles of the procedure of genetic fingerprinting. Ask them to
produce a poster showing the main stages of genetic fingerprinting and its applications.
Examples of applications include:
Genetic fingerprinting
Explain the basis of genetic
fingerprinting and understand
its advantages and potential
dangers.
Notes
School resources
ICT opportunity: Newspaper and magazine
articles can be obtained from the Internet.
Enquiry skills 12A.2.1
• settling paternity disputes;
• settling disputes in hospitals where newborn babies have been accidentally switched;
• revolutionising forensic work (using DNA extracted from cells in traces of blood, saliva, hair
roots or, in rape cases, semen);
• animal identification (e.g. establishing the variation of the whale population).
Ask students to find out about the dangers or shortcomings of genetic fingerprinting, for example:
• discovering that a child may not be the natural child of a parent may create problems for
family relationships;
• relatives show many similarities in their genetic fingerprints, so if more than one family
member is a suspect of a crime, it may be difficult to be certain who is the culprit;
• the use of the polymerase chain reaction (PCR) to amplify the amount of DNA for forensic
work means the technique is now extremely sensitive to contamination; anyone who has
shed dandruff or sneezed at the scene of a crime may become a suspect!
Show students autoradiographs of genetic fingerprints of individuals from a murder case and
ask them to select the possible suspect.
Get students to write an article for a magazine about genetic fingerprints.
2 hours
Genetic screening
Explain the basis of genetic
screening for alleles of
disadvantaging inherited
conditions; understand the
advantages and potential
dangers of such screening
and the need for genetic
counselling.
Ask students what they understand by the term genetic screening. Explain that everyone
probably carries several genetic defects, and detecting the mutant genes in an individual is
known as genetic screening.
Ask students to find out from the library the situations in which genetic screening is particularly
relevant. These include: prenatal diagnosis, carrier diagnosis (e.g. CF, sickle cell), and
predictive diagnosis (e.g. Huntington’s disease).
Ask students to investigate and compare the advantages and dangers of prenatal diagnosis by
amniocentesis and chorionic villus sampling.
Enquiry skills 12A.2.2
Debate the ethics of genetic screening with students. Should the mother be able to choose to
abort her foetus? Which genetic disorders should result in a foetus being aborted? Where do
you draw the line? Will we be able to breed genetic abnormalities out of the human race in the
future?
Ask students what they understand to be the role of a genetic counsellor.
Ask students to find out whether their local hospital has a genetic counselling department and
why only certain people may need to visit a genetic counsellor.
Discuss the nature of a conversation that a counsellor might have with a husband and wife, one
of whom thinks they are carrying an allele for a disadvantaging condition.
439 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.5 | Biology 5
© Education Institute 2005
Assessment
Examples of assessment tasks and questions
Assessment
Set up activities that allow
students to demonstrate what
they have learned in this unit.
The activities can be provided
informally or formally during
and at the end of the unit, or
for homework. They can be
selected from the teaching
activities or can be new
experiences. Choose tasks
and questions from the
examples to incorporate in
the activities.
Examine the kernels of cobs of maize (Zea mays). Make deductions about the genotypes of the
parent plants. Justify and support your deductions by drawing diagrams to show the parental
cross and a Punnett square to show the offspring.
Unit 12AB.5
Notes
School resources
Provide suitable cobs of maize for this question.
Distinguish co-dominance from incomplete dominance by using examples.
Examine the worksheet containing results from a dihybrid cross and displaying the numbers of
the progeny. Work out the chi-squared value to see if the difference between the observed and
expected data is significant.
Provide a suitable worksheet and chi-squared
tables.
Write an article for a magazine about the Human Genome Project.
Explain the principles of the procedure of genetic fingerprinting.
Explain the advantages and dangers of genetic screening by prenatal diagnosis by
amniocentesis and chorionic villus sampling.
440 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.5 | Biology 5
© Education Institute 2005