Variation & Inheritance

Unit 2 Key Area 4: Variation & Inheritance

Today we will…

• Discuss what variation is and why it is important

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• Look at the two types of variation

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• Investigate variation among pupils in the class.

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• Look at new genetic terms we need to learn

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• Learn how to write an organism's genotype

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• Learn how to figure out an organism’s phenotype from the genotype.

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• Learn how to do monohybrid crosses to look at the inheritance of one characteristic.

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Variation

All members of the same species are not identical.

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Variation exists within a species.

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Variation = a different form of something

Variation

How does variation exist?

Combining the genes from each parent will contribute to variation.

Different Types of Variation

A characteristic is controlled by one gene or more than one gene.

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This will lead to different types of variation.

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There are two kinds:

• Discrete variation
• Continuous variation

Discrete Variation

• Characteristics determined by the inheritance of a single gene can show what is called discrete variation within a population.

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• Characteristics fall into distinct/clear categories (we can divide into groups)

Memory tool!

DIScrete variation = DIStinct groups

Discrete Variation

Tongue roller or non-tongue roller.

Eye colour

Earlobes attached or not.

Continuous Variation

• Characteristics determined by the inheritance of many genes (polygenic) can show what is called continuous variation within a population.

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• Characteristics show a range of values between a minimum and a maximum

Continuous Variation

Height

Tail Length

Hand Span

Investigating Variation

Collecting data on examples of characteristics which show discrete variation will allow us to produce a bar chart.

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Collecting data on examples of characteristics which show continuous variation will allow us to produce a histogram.

Investigating Variation

Carry out the survey and plot a graph for one example of discrete variation and a graph for one example of continuous variation.

Inheritance

Starter Quiz:�1) Give an example of a discrete characteristic.

2) Give an example of a continuous characteristic.

3) What type of graph is used for discrete inheritance?

4) What part of your cells contain the DNA?

5) What is fertilisation?

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Inheritance

The passing on of genetic information from parent to offspring via gametes. The information comes in the form of genes.

Before we continue, we are going to create a glossary of new words important for this topic that we can refer back to.

The unit of heredity that controls a characteristic.

Different forms of a gene

The physical attributes that are observed.

The combination of genes that is possessed by an organism.

The allele that is expressed in the phenotype.

The allele that is only observed in the phenotype, if homozygous.

When an organism possesses two identical alleles.

When an organism possesses two different alleles.

https://www.youtube.com/watch?v=6NvESo3mG90

Mendell and The Pea

Alleles

• Alleles are different forms of a gene.

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• An individual inherits two alleles for each gene, one from each parent.

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• When both alleles are the same we call them homozygous.

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• When they are different – heterozygous.

Alleles

Chromosome inherited from one parent

Chromosome inherited from the other parent

Alleles

Alleles can be described as either dominant or recessive.

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Dominant Alleles – always shows up in the appearance (phenotype) of the organism. (represented by a capital letter, e.g. B).

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Recessive Alleles – only show up in appearance if an organism has inherited two of them. (represented by a lower case letter, e.g. b).

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Alleles

Alleles

Phenotype and Genotype

• Phenotype is the physical characteristics shown by an organism.

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For example, blue eyes, brown fur, curly hair etc….

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• An organisms genotype is the combination of genes it possesses for a particular characteristic.

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When the genotype of an organism is written, letters are used to represent the alleles, e.g. AA or Aa or aa

Let’s Practise

The allele for curly hair is represented by C and the allele for straight hair is represented by c.

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Look at the following genotypes and try to figure out the phenotype of the individual.

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• CC
• Cc
• cc

both dominant = curly hair

Both different (but one is dominant) = curly hair

both recessive = straight hair

Heterozygous & Homozygous

CC – both alleles the same and dominant = homozygous

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Cc – both alleles different = heterozygous.

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cc – both alleles the same and recessive = homozygous.

Homo = the same

Hetero = different

More Practise!

Black coat

Heterozygous

Homozygous

bb

Pick an activity

• Use your keyword glossary to create genetics bunting for key words of your choice.

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• Create a play-doh model to show a nucleus, chromosome, DNA and gene

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• Create a poster on genetics describing how genes are inherited

More Practise!

• Grain colour (purple dominant vs yellow recessive)
• Tongue rolling (roller dominant vs non-roller recessive)

Purple grain

Purple grain

yellow grain

roller

roller

Non- roller

More Practise!

With height of pea plants, the allele for a tall plant is T and dwarf plant is t.

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What could the genotype be of a:

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• A plant which is tall.
• A dwarf plant
• A plant which has both alleles the same and is tall
• A plant which has two different alleles.

Monohybrid Cross

Gregor Mendel was an Austrian monk who studied inheritance in pea plants. He is often described as the father of modern genetics. He studied seven different characteristics of pea plants. We still use his knowledge today to work out genetic crosses.

Monohybrid Cross

A monohybrid cross looks at the inheritance of a single characteristic to determine the possible genotypes and phenotypes of the offspring.

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We can use a Punnett square to show the possible combination of alleles that can result at fertilization.

Punnett Squares

Genotypes of male gametes

Genotypes of female gametes

Possible allele combinations

If R represents the dominant allele for round seed shapes, and r represents the recessive allele for wrinkled seed shape. What is the ratio of round: wrinkled in the offspring?

Monohybrid Cross

The dwarf phenotype has disappeared in the F1 generation. What would happen if the F1 generation cross pollinated?

Second Cross

Tall

Tall

Tt

Tt

F2 Phenotype

Ratio

T

t

T

t

TT

Tt

Tt

tt

Tall

Dwarf

3 Tall : 1 Dwarf

Monohybrid Cross

The ratios we predict may not always be achieved.

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Why not?

Family Trees

• In a family tree, males are represented by squares, females by circles.
• Parents are connected by a horizontal line.
• Brothers and sisters are linked by branches.
• Parents are linked to offspring by vertical lines.

Starter:

On your whiteboard:

Write down as many genetic disorders as you can think of

Pick a genetic disease and research the following:

• What is the disease?
• What effect does the disease have?
• How does it impact the individuals life?  Would it impact others around them?
• How many people does it affect?
• Is there a treatment/cure?
• What is already being done?
• What else could be done to help those suffering from the disease?

Monohybrid Cross

What would happen if we crossed a homozygous tall pea plant with a homozygous dwarf plant?

Tall

Dwarf

TT

tt

T

T

t

t

Tt

Tt

Tt

Tt

Tall

Key Word Check!

1 Heterozygous

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2 Homozygous

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3 Allele

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4 Phenotype

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5 Genptype

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6 Recessive

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7 Dominant

A-The characteristics displayed by an individual

B-When the individual has two copies of the same allele

C-A gene that is always masked by the dominant version of the allele

D-When the individual when two different alleles of the gene.

E-The genes within an individuals’ genetic make up

F-A gene is always expressed in the characteristic.

G-Different versions of the same gene

Practise Questions

Q1) a) Are the following alleles, heterozygous or homozygous?

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b) What will their phenotype be?

Practise Questions

Q2) If a true breeding male rabbit with brown hair mates with a true breeding female rabbit with white hair, what colour will the offspring have?

Brown=B

White=b

Practise Questions

Q3) If a heterozygous male dog with straight hair breeds with a true breeding female dog with curly hair, what hair will the offspring have?

Curly=c

Straight=C

Practise Questions

Q4) If a homozygous male cat with blue eyes breeds with a heterozygous female cat with green eyes, what colour eyes will the offspring have?

Blue=g

Green=G