Starter: Recall and Review.

Get into pairs, on whiteboards - one person from the pair writes notes on each of the topics below. After 3 minutes swap and add to one another’s notes.

Human Reproductive System

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Plant Reproductive System

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Title: Variation & Inheritance

Unit 2 Key Area 4: Variation & Inheritance

LO: To understand the link between variation, genes and inheritance.

SQA Specification:

-Comparison of discrete variation (single gene inheritance) and continuous variation (polygenic inheritance).

-Understanding of genetic terms: gene; allele; phenotype; genotype; dominant; recessive; homozygous; heterozygous and P, F1 and F2.

-Monohybrid crosses from parental generation through to F2 generation.

- Reasons why predicted phenotype ratios among offspring are not always achieved.

Starter: Discuss if you look like any member of your family? Who and what features? Why do you think that is?

Variation and inheritance

Learning intentions

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To learn about variation, genes and inheritance.

Success Criteria

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I can describe two different type of variation.

I can know the difference between a gene and an allele.

I know the difference between genotype and phenotype.

I can use the following terms to describe inherited characteristics - dominant, recessive, homozygous, heterzygous.

I can complete a punnet square and use it to make predictions about offspring.

I can apply my knowledge to past paper questions.

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

Different Types of Variation

A characteristic is controlled by one gene or more than one gene (polygenic).

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This leads to different types of variation.

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• Discrete variation
• Continuous variation

Discrete Variation

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

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• Characteristics determined by the

inheritance of a single gene.

Memory tool!

DIScrete variation = DIStinct groups

Discrete Variation

Tongue roller or non-tongue roller.

Eye colour

Earlobes attached or not.

Continuous Variation

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

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• Characteristics determined by the inheritance of many genes (polygenic)

Continuous Variation

Height

Tail Length

Hand Span

SQA Specification:

-Comparison of discrete variation (single gene inheritance) and continuous variation (polygenic inheritance).

-Understanding of genetic terms: gene; allele; phenotype; genotype; dominant; recessive; homozygous; heterozygous and P, F1 and F2.

-Monohybrid crosses from parental generation through to F2 generation.

- Reasons why predicted phenotype ratios among offspring are not always achieved.

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.

What is the difference between a bar graph and a histogram?

Read the following sentences. Decide if they are correct. If they are incorrect what is the correct answer?

1. Eye colour is an example of continuous data.
2. Traits which are controlled by a single gene will be shown as discrete data.
3. Hand span is an example of a trait which is controlled by a single gene.
4. Polygenic traits are controlled by more than one gene.
5. Polygenic traits are shown as discrete data.

discrete

continuous data.

more than one gene (polygenic)

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.

Investigating Variation

2020 Q16

2019 Q12

Variation and inheritance

Learning intentions

​

To learn about variation, genes and inheritance.

Success Criteria

​

I can describe two different type of variation.

I can know the difference between a gene and an allele.

I know the difference between genotype and phenotype.

I can use the following terms to describe inherited characteristics - dominant, recessive, homozygous, heterzygous.

I can complete a punnet square and use it to make predictions about offspring.

I can apply my knowledge to past paper questions.

Starter

1. Give an example of a type of continuous variation.
2. What type of variation is controlled by a single gene?
3. Where does your DNA come from?

Variation and inheritance

Learning intentions

​

To learn about variation, genes and inheritance.

Success Criteria

​

I can describe two different type of variation.

I can know the difference between a gene and an allele.

I know the difference between genotype and phenotype.

I can use the following terms to describe inherited characteristics - dominant, recessive, homozygous, heterzygous.

I can complete a punnet square and use it to make predictions about offspring.

I can apply my knowledge to past paper questions.

Inheritance

SQA Specification:

-Comparison of discrete variation (single gene inheritance) and continuous variation (polygenic inheritance).

-Understanding of genetic terms: gene; allele; phenotype; genotype; dominant; recessive; homozygous; heterozygous and P, F1 and F2.

-Monohybrid crosses from parental generation through to F2 generation.

- Reasons why predicted phenotype ratios among offspring are not always achieved.

Inheritance

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

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

Dominant or Recessive

Alleles can be described as either dominant or recessive.

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Dominant Alleles – always shows up in the appearance 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 lowercase letter, e.g. b.

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Dominant and recessive

What colour eyes does each individual have?

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

Which combinations are homozygous or heterozygous?

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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• Genotype is the combination of alleles an organism possesses for a particular trait.

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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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1. CC
2. Cc
3. cc

both dominant = curly hair

Both different (but one is dominant) = curly hair

both recessive = straight hair

Which individuals are homozygous and which are heterozygous?

The unit of heredity that controls a characteristic.

Different forms of a gene

The characteristics that are observed.

The combination of genes that is possessed by an organism.

The allele that is expressed (seen) 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.

Variation and inheritance

Learning intentions

​

To learn about variation, genes and inheritance.

Success Criteria

​

I can describe two different type of variation.

I can know the difference between a gene and an allele.

I know the difference between genotype and phenotype.

I can use the following terms to describe inherited characteristics - dominant, recessive, homozygous, heterzygous.

I can complete a punnet square and use it to make predictions about offspring.

I can apply my knowledge to past paper questions.

Practise!

Black coat

Heterozygous

Homozygous

bb

a

b

c

d

More Practise!

• Grain colour (purple dominant vs yellow recessive) P=purple; p=yellow
• Tongue rolling (roller dominant vs non-roller recessive) R=roller; r=non-roller

Purple grain

Purple grain

yellow grain

roller

roller

Non- roller

a

b

c

d

e

f

1. The allele that is expressed in the phenotype.

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• When an organism possesses two identical alleles.

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• The unit of heredity that controls a characteristic.

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• The combination of genes that is possessed by an organism.

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• When an organism possesses two different alleles.

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• The physical attributes that are observed.

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

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• Different forms of a gene

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Dominant

Homozygous

Gene

Genotype

Heterozygous

Phenotype

Recessive

Allele

Inheritance key word bingo

Sperm

Egg

Diploid

Haploid

Allele

Homozygous

Heterozygous

Dominant

Recessive

Ovary

Gene Phenotype�Genotype Stigma

Anther

Pollen

Ovule Oviduct

Sperm duct Testes

Starter - Match the words and definitions

1. Gene
2. Allele
3. Phenotype
4. Genotype
5. Dominant
6. Recessive
7. Homozygous
8. Heterozygous

1. When an organism possesses 2 of the same allele
2. Different forms of a gene
3. The allele that is only observed in the phenotype if homozygous
4. The unit of hereditary information that controls a characteristic
5. When an organism possesses 2 different alleles
6. The physical attributes that are observed
7. The combination of alleles that are possessed
8. The allele that is expressed in the phenotype

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Variation and inheritance

Learning intentions

​

To learn about variation, genes and inheritance.

Success Criteria

​

I can describe two different type of variation.

I can know the difference between a gene and an allele.

I know the difference between genotype and phenotype.

I can use the following terms to describe inherited characteristics - dominant, recessive, homozygous, heterzygous.

I can complete a punnet square and use it to make predictions about offspring.

I can apply my knowledge to past paper questions.

SQA Specification:

-Comparison of discrete variation (single gene inheritance) and continuous variation (polygenic inheritance).

-Understanding of genetic terms: gene; allele; phenotype; genotype; dominant; recessive; homozygous; heterozygous and P, F1 and F2.

-Monohybrid crosses from parental generation through to F2 generation.

- Reasons why predicted phenotype ratios among offspring are not always achieved.

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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1. A plant which is tall.
2. A dwarf plant
3. A plant which has both alleles the same and is tall

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• Two heterozygous plants reproduce, will their offspring be tall or short?

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.

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

Mendell and The Pea

Monohybrid Cross

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

We 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

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

P1 (parent) Phenotype

P1 Genotype

F1 Genotype

F1 Phenotype

Tall

Dwarf

TT

tt

T

T

t

t

Tt

Tt

Tt

Tt

Tall

Monohybrid Cross

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

Second Cross

P2 Phenotype

P2 Genotype

F2 Genotype

F2 Phenotype

Tall

Tall

Tt

Tt

F2 Phenotype

Ratio

T

t

T

t

TT

Tt

Tt

tt

Tall

Dwarf

3 Tall : 1 Dwarf

SQA Specification:

-Comparison of discrete variation (single gene inheritance) and continuous variation (polygenic inheritance).

-Understanding of genetic terms: gene; allele; phenotype; genotype; dominant; recessive; homozygous; heterozygous and P, F1 and F2.

-Monohybrid crosses from parental generation through to F2 generation.

- Reasons why predicted phenotype ratios among offspring are not always achieved.

Variation and inheritance

Learning intentions

​

To learn about variation, genes and inheritance.

Success Criteria

​

I can describe two different type of variation.

I can know the difference between a gene and an allele.

I know the difference between genotype and phenotype.

I can use the following terms to describe inherited characteristics - dominant, recessive, homozygous, heterzygous.

I can complete a punnet square and use it to make predictions about offspring.

I can apply my knowledge to past paper questions.

Starter

Brown hair (B) is dominant over red hair(b).

1. Draw a punnett square to show how 2 brown haired parents can have a baby with red hair
2. What would the genotype of the baby be?
3. What would the genotypes of the parents be?
4. What would be the chances of them having a baby with red hair?
5. Would the baby be homozygous or heterozygous?

Reasons why predicted phenotype ratios among offspring are not always achieved.

The ratios we predict may not always be achieved.

Why not?

Because fertilisation is a random process. This means that the chances of a particular combination are the same each time it happens.

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.

This is the Parental generation or P

This is the first filial generation or F1

This is the second filial generation or F2.

Practice Questions

1. Which two people are found in the P generation?
2. Which individuals are in the F1 generation?
3. Which individuals suffer from the disease?

Albinism

In humans, albinism is a recessive trait. The disorder causes a lack of pigment in the skin and hair, making an albino appear very pale with white hair and pale blue eyes.

1. a) Given the following genotypes, describe the phenotypes (normal or albino)

AA = __________________________� Aa = _________________________� aa = __________________________

In the family tree/pedigree chart:

b) How many offspring are in the F1 generation? �

�c) How many people have albinism?

d) Add information to the pedigree to show the phenotype and possible genotypes of each individual.

Variation and inheritance

Learning intentions

​

To learn about variation, genes and inheritance.

Success Criteria

​

I can describe two different type of variation.

I can know the difference between a gene and an allele.

I know the difference between genotype and phenotype.

I can use the following terms to describe inherited characteristics - dominant, recessive, homozygous, heterzygous.

I can complete a punnet square and use it to make predictions about offspring.

I can apply my knowledge to past paper questions.

Make a key word Fortune teller

How to fold: https://www.youtube.com/watch?v=IVmX-LFuv18

Create a revision fortune teller for the key words we have learned today

1. Choose four of the 12 key words to write on the outside flaps of the fortune teller e.g. gene, allele, etc.
2. In the next layer, write the remaining eight words, one to each of the triangles.
3. The final things to add are questions.
4. Under each of the inner flaps of the fortune teller, you need to write a definition and a keyword
5. For instance, if the word on the flap was “heterozygous", the definition might be “two different alleles“

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SQA Specification:

-Comparison of discrete variation (single gene inheritance) and continuous variation (polygenic inheritance).

-Understanding of genetic terms: gene; allele; phenotype; genotype; dominant; recessive; homozygous; heterozygous and P, F1 and F2.

-Monohybrid crosses from parental generation through to F2 generation.

- Reasons why predicted phenotype ratios among offspring are not always achieved.