Variation and Inheritance
WJEC Biology Module 12011 Specification
Variation
WJEC Biology Module 12011 Specification
Learning Outcomes
Examine the variation in height/length in individuals of the same species by collecting and analysing data and know that variation may be due to environmental or genetic causes.
Understand that variation may be continuous or discontinuous.
Keywords
Clones Fertilisation Inheritance Chromosome Exposure Gamma rays Mutation Ultraviolet radiation X-rays
Continuous Discontinuous Environmental
factors Genes Mutation Phenotype Variation Sexual reproduction Asexual reproduction
Variation
Look at variation in the class Try to write down at least 20 ways in which
individuals vary from one another.
Variation
Variation can be described as either Continuous variation
a range of measurements from one extreme to the other. E.g. height
Discontinuous variation individuals fall into distinct categories. E.g.
ability to roll the tongue; attached or free ear lobes
Continuous variation Use a tally chart and plot results in a
histogram
Discontinuous variation
Plot results in a bar chart
Variation
Differences in the characteristics of different individuals of the same kind may be due to differences in The genes they have inherited – genetic
causes The conditions in which they have
developed – environmental causes Variation is normally a combination of
both genes and the environment.
Phenotype
The phenotype is the outward appearance of an organism
It depends on both the organism’s genes and its environment.
Variation in Snails - Practical
Snails of two closely related species of Cepaea are common in woodland and grassland in Britain.
They show a pattern of variation known as polymorphism.
This means that there are several different ‘types’. The shell may be either yellow or pink/brown, and it may have dark stripes or be plain.
So, the four types of the snails are as follows: Pink/brown, plain Yellow, plain Pink/brown, striped Yellow striped
Even within each type, there is variation, so that the pink/brown variety may be distinctly pink, or brown, or even greyish, and the striped forms may have different numbers of stripes, for instance.
Variation in Snails - Practical
Pick 50 snails at random for the grassland
Use the table to create a tally chart recording the number of each type of snail found in the grassland
Write your results onto the main table Calculate the percentage of each snail
type Repeat the stages above for woodland
snails
Conclusion
1. What differences do you notice in the distribution of the different types of snail? Describe any trends seen. [2]
2. Describe one difficulty in the method that might have reduced the accuracy of the results [1]
3. The size of the sample can affect the accuracy of the results. In using a sample, do you think a sample size of 50 was big enough? Give a reason for your answer
Evaluation
Plan a similar activity to find out if the snails grow bigger in woodland or grassland.
Describe, in detail, the procedure you would use.
Suggest any difficulties you may have in obtaining valid results
Suggest how these difficulties may be avoided.
Learning Outcome
Understand that sexual reproduction leads to offspring that are genetically different from the parents unlike asexual reproduction where genetically identical offspring called clones are produced from a single parent. Sexual reproduction therefore gives rise to increased variation.
Genetic Variation
Sexual reproduction Egg and sperm fuse at fertilisation, to form
a zygote The zygote has a set of genes from the
mother and a set from the father. Offspring are genetically different from their
parents
Asexual reproduction No fertilisation, no mixing of genes Offspring are genetically identical to each
other and the parents Produces clones
Cloning
Cloning can be used to mass produce economically important organisms Animals
IVF – In vitro fertilisation Plants
micropropagation
Prep
WJEC Science Page 34 What are continuous and discontinuous
variation? Question 1
Inheritance
WJEC Biology Module 12011 Specification
Learning outcomes
Understand that genes are sections of DNA molecules that determine inherited characteristics and are in pairs. Genes have different forms, called alleles.
Know that chromosomes are linear arrangements of genes and that chromosomes that are found in pairs in body cells are strands of DNA. DNA contains coded information for the production of different types of proteins. These proteins determine how cells function.
Chromosomes and Genes
Our cells contain genetic information this is your DNA.
This information on DNA is in units called genes.
Our genes are on chromosomes. Chromosomes always come in pairs in
our body cells.
Genetics and DNA
Each chromosome is made up of thousands of genes; the genes carry genetic information that
affects how we grow and what we look like. A chromosome is made up of a long
thread, made up of deoxyribonucleic acid (DNA).
One gene is made up of a short length of DNA.
DNA
DNA is twisted into a double helix, where bases pair up: Adenine with thymine Guanine with cytosine
Every 3 bases along the strand codes for a particular amino acid, this means that DNA controls the proteins that are made
DNA and Genetics
GCSE Practical
What is DNA?
DNA is packed tightly into chromosomes inside the cell, it is a gigantic molecule, very long but very thin.
DNA from a single cell can be 2 metres long, but is so thin that it can hardly be seen with a powerful microscope.
When DNA is released from cells it clumps together to form strands, which are colourless and jelly like.
Extraction of DNA from cells is the first step in many experiments in genetic engineering. DNA can be extracted from both plant and animal cells.
How to extract DNA from kiwi fruit!
Equipment
Kiwi fruit White tile Scalpel Tap water Warm water 600C Ice cold ethanol
Washing up liquid Coffee filters Plastic measuring
cylinders Funnels 250ml beaker Boiling tube Boiling tube bung
Method – Stage 1
DNA extraction mixture: Mix 10ml washing up liquid + 3g salt +
100ml water in a 250ml beaker Finely chop the kiwi fruit and place in
boiling tube. add DNA extraction mixture Place bung on top and shake carefully.
Leave for fifteen minutes at 60oC
Method – Stage 2
Filter the mixture through the coffee filter into a 100ml beaker to separate the chopped kiwi fruit from the clear liquid. (the DNA is invisible as it is dissolved in the clear liquid)
Transfer 5 ml of the clear liquid into a clean test tube.
Add 5ml of cold (4oC) absolute alcohol down the side of the tube.
DNA will appear as “fluffy” white solid.
Final “tricky” stage
The DNA can be pulled out using a fine wire.
Learning Outcomes
be able to understand and complete Punnett squares and explain the outcomes of monohybrid crosses including ratios.
The following terms should be understood: genotype, phenotype, dominant, recessive,
F1, F2, selfing, heterozygous, heterozygote, homozygous and homozygote
An understanding of simple Mendelian ratios.
Inheritance
Things to remember: Chromosomes are strings of genes and
chromosomes occur in pairs in each cell. There are two copies of each gene in each
cell These genes may be identical or may be
different versions (alleles) of the same gene.
Glossary
Homozygous 2 identical alleles for a particular characteristic
Heterozygous 2 different alleles for a particular characteristic
Genotype alleles for a particular characteristic
Phenotype outward effect of those alleles
Glossary
Dominant allele which controls the
development of a characteristic when it is present on only one chromosome.
Recessive allele which control the
development of a characteristic if present on both chromosomes.
Further definitions
F1 – first generation F2 – second generation Selfing
Manually pollinating a flower by placing its pollen on its own stigma
Self pollination
Monohybrid Inheritance
The study of how a single gene is passed on from parents to offspring.
A punnet square can be used to predict an outcome
Genetic Cross - Tips
When you write out a genetic cross, make sure you state what the symbols represent
Make sure you label each line in the cross (phenotype, genotype, etc)
It is a good idea to circle the gametes to show that meiosis has happened
Read the question carefully – are you asked to state the outcome in terms of the genotype or the phenotype?
A cross between a pure-breeding tall pea plant and a pure-breeding dwarf pea plant
A cross between two F1 pea plants
A cross between a heterozygous tall pea plant and a dwarf pea plant
Now try this …….
You need to be able to predict the genotypes of the parents from descriptions of them.
Work out the following genotypes, based on peas that can be round or wrinkled, with round being dominant to wrinkled. A heterozygous round pea A wrinkled pea A pure-breeding round pea
Learning Outcomes
Understand that most characteristics are controlled by more than one gene.
consider the scientific process of observation, experimentation and deduction that led Gregor Mendel to propose the mechanism of inheritance.
Discuss why the significance of the work was not recognised and validated by scientists for many years.
Gregor Mendel
Gregor Mendel was a monk who did experiments looking at the inheritance of height in pea plants.
He did not publish any of his results in scientific journals, so no one took any notice of his work during his lifetime.
He is now regarded as one of the greatest scientists of all time.
Learning Outcome
know that in human body cells, one of the pairs of chromosomes, XX or XY, carries the genes which determine sex. These separate and combine randomly at fertilisation.
Inheritance of Sex in humans
The sex chromosomes X and Y determine the sex of an individual Males XY Females XX
The presence of the Y chromosome results in male features developing
Inheritance of sex
Learning Outcomes
understand that when gametes are formed the chromosome number is halved and the genetic composition of the daughter cells is not identical (the term, meiosis, and knowledge of stages are not required). Fertilisation restores normal chromosome number.
Chromosomes and Genes
Human body cells have 23 pairs of chromosomes. This gives a diploid number (2n) of 46.
Human gametes contains 23 chromosomes, this is the haploid number (n).
Pupil ActivityCopy and complete the following sentences.
Another name for sperm and egg cells is . These sex cells join to make one cell, the _____________.
This cell grows into a foetus by ___________ many times. Each body cell in the baby contains
pairs of chromosomes. One of the chromosomes in each pair comes from
the , the other chromosome in each pair comes from the .
Human Life Cycle
Adult46
HaploidSperm
23
HaploidEgg23
Diploid Zygote
46
fertilisation
Mitosis
Meiosis
Cell Division
Number of chromosomes
Learning Outcomes
understand that new genes result from changes, mutations, in existing genes and that mutations occur at random. Most mutations have no effect but some may be beneficial or harmful. Mutation rates can be increased by ionising radiation. (Reference to specific ionising radiation is not required.)
Mutations
A mutation is a change in the structure of a gene
Mutations are Rare Random
They can have No effect beneficial effects
If a mutation improves the “design” of an organism this can lead to increased survival.
harmful effects
Causes of Mutations
Mutations can occur naturally
Mutations rate can be increased by Ionising radiation X-rays chemicals
Learning Outcomes
understand that some mutations cause conditions which may be passed on in families, as is shown by the mechanism of inheritance of cystic fibrosis, and be able to interpret family trees.
Inherited Diseases
Genetic diseases can be caused by: Dominant or recessive alleles on normal
chromosomes E.g. cystic fibrosis (recessive), Huntington’s
Chorea (dominant) Recessive genes on X chromosome
E.g. haemophilia
Cystic Fibrosis This is the commonest inherited disease among white
people; it affects one in every 2000 children. In a person with the disease thick, sticky mucus builds up in respiratory passages and digestive glands, making the person susceptible to infection and disrupting digestion.
Cystic Fibrosis
This is a disorder of cell membranes; it is caused by a recessive allele of a gene. It must be inherited from both parents.
As it is a recessive allele parents may be carriers of the disorder without actually having the disorder themselves.
Pupil Activity
Let N = normal allele Let n = allele for cystic fibrosis Carry out the following crosses and
work out the chances of a child having cystic fibrosis for each cross. Nn x Nn NN x Nn
Pupil Activity
Cystic fibrosis and family tree w/sheet
Learning Outcomes
Discuss the issues surrounding the development and use of gene therapy which has been tried as a means to alleviate the symptoms in cystic fibrosis sufferers but has greater potential as advances are made in knowledge and technology.
Learning Outcome
understand that an organism's DNA can be analysed by 'genetic profiling' and how this can be used to show the similarity between two DNA samples. The process involves cutting the DNA into short
pieces which are then separated into bands. The pattern of the bands produced can be
compared to show the similarity between two DNA samples, for instance in criminal cases, paternity cases and in comparisons between species for classification purposes.
Advances in technology now make such analysis widely available.
Genetic Profiling
Genetic profiling is a method by which an organism's DNA can be analysed
this can be used to show the similarity between two DNA samples. The process involves cutting the DNA into
short pieces These are then separated into bands. The pattern of the bands produced can be
compared to show the similarity between two DNA samples
Stages in genetic profiling
Collect a sample of cells E.g. blood, hair follicles, semen, skin
Break cells up and extract DNA Enzymes are used to break the DNA into
segments of differing sizes. Gel Electrophoresis
DNA fragments are placed on a gel Electric current is passed through the gel Smaller fragments move further through the gel The pattern that develops is the genetic profile.
Learning Outcome
Discuss the benefits of DNA profiling, for example to identify the presence of certain genes which may be associated with a particular disease. As this likelihood may be based on statistical probability, understand that it raises issues such as risk-benefit considerations and disclosure of information along with wider ethical issues of ownership and human rights which are subject to value judgement by society.
Uses of Genetic Profiling
A genetic profile is a pattern of bands or lines It is unique to each individual and can be
used to identify an individual person. For example
Identification of a suspect in a crime Identification of a dead body Look for genetic relations
Maternity Paternity
Species identification for classification
Is genetic profiling a good thing?
What are the benefits of DNA profiling? to identify the presence of certain genes which may
be associated with a particular disease. Problems with this
As this likelihood may be based on statistical probability
understand that it raises issues which are subject to value judgment by society. risk-benefit considerations disclosure of information along with wider ethical
issues of ownership human rights
Learning Outcomes
know that genes can be transferred artificially from one species to another.
Genetic Modification
Genetic modification is the process by which a gene is taken from a chromosome of one species and put into a chromosome of another species
For example Genes inserted into crop plants so that they
produce an insecticide, making the plants resistant to pests
Learning Outcomes
Understand that the introduction of genes from herbicide-resistant plants into soya bean plants, so increasing their resistance to herbicides, may increase the crop yield due to reduced competition.
Herbicide resistance
A common feature of genetically modified crops is resistance to herbicide. A herbicide resistant gene is transferred from a soil
bacteria and transferred to Soya bean plants Advantages of herbicide resistance in Soya
Increases herbicide resistance, so farmers can kill weeds without damaging crop plants
Removing weeds reduces competition for the crop improving crop yield
Learning Outcomes
Understand the potential disadvantages and issues involved.
GM Crops and developing countries Advantages
Crops tailor made to suit the farming conditions More nutritional value Higher income
Energy-producing crops could save natural resources
Disadvantages GM crops in developed countries mean that they no
longer need to import from abroad – developing countries lose trade
Mismanagement and political reasons
Problems with GM Crops
All issues raised with GM crops raise important political, ethical and trade questions.
Learning Outcomes
investigate and evaluate the potential benefits and problems posed by advances in GM crop technology
Understand the need to collect reliable data, e.g. the use of farm scale field trials, in order that possible effects on the environment and on health should be understood. The data may be used to help formulate policy decisions regarding the planting of these crops and to inform consumers.
Learning Outcomes
Understand the need for unbiased information and interpretation as it affects the public perception of foods containing GM products and informs risk management considerations of possible consequences.
Activity
Read through the sources provided Comment on whether these sources are
biased or unbiased Make notes on any facts that you think are
important Write a short evaluation on the advantages
and disadvantages of GM Crops
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