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