Starter

Write down everything you know about genetics

Unit 3- Sustainability and Interdependence

Inbreeding

Starter:

• Define the term ‘cultivar’
• Define the terms ‘homozygous’ and ‘heterozygous’
• Explain the process of selective breeding
• Why do you think breeding closely related individuals could be harmful?

Learning Intention:

• Explain what is meant by “true breeding”
• Work the inheritance of a gene using a Punnet square.

N5 Revision: Variation and Inheritance

Inbreeding

Learning intentions:

To revise the key words and terminology from N5 Variation and inheritance

To learn about the implications of inbreeding

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Success Criteria:

I can state and use correctly the key words from N5 variation and inheritance

I can complete a punnet square

I can know the negative implications of inbreeding for crops

I can explain why naturally inbreeding species no longer suffer from inbreeding depression.

Variation in a population can be defined as either:

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• Continuous (varying from extreme to another) e.g.

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• Discrete (divides members of a species on to two or more groups) e.g.

Single gene inheritance

An inherited characteristic may show discrete variation if it can be used to divide up the members of a species into distinct groups e.g. seed colour

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• Discrete variation is usually controlled by a small number of genes.

• the environment has little or no effect.

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• This type of variation can be shown on a bar graph

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Discrete Variation

• Alleles are different forms of a gene
• A characteristic that shows discrete variation is normally controlled by alleles of a single gene.
• The alleles can either be dominant or recessive.

Inheritance

Individuals have two alleles for each gene. Dominant alleles are given a capital letter, recessive alleles a small letter.

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If organisms have the same alleles for a gene they are said to be homozygous. They can be homozygous dominant (RR) or homozygous recessive (rr).

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Organisms with different alleles are said to be heterozygous (Rr) for that characteristic.

More revision

White Mouse (bb)

White Mouse (bb)

White Mouse (bb)

White Mouse (bb)

White Mouse (bb)

Black Mouse (BB)

Black Mouse (BB)

Black Mouse (BB)

Black Mouse (BB)

Black Mouse (BB)

X

X

X

X

True Breeding

A true breeding organisms is always homozygous, therefore the alleles are known.

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• A monohybrid (single gene) cross examines only one difference in an inherited characteristic (e.g. round v wrinkled).

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• True breeding parents (homozygous) are bred.

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• The F1 generation are all heterozygous.

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• When the F1 generation are crossed the offspring show a 3:1 phenotypic ratio and a 1:2:1 genotypic ratio

Monohybrid crosses

Black Mouse (BB)

White Mouse (bb)

Black Mouse (Bb)

Black Mouse (Bb)

Black Mouse (BB)

Black Mouse (Bb)

Black Mouse (Bb)

White Mouse (bb)

X

X

Single gene (monohybrid) inheritance

3 Black Mice : 1 white mouse

P

F1

F2

Draw monohybrid crosses for the F1 & F2 generation for the following examples:

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1. Peas - RR (round) x rr (wrinkled)

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2. People – homozygous dominant brown hair x homozygous recessive blonde hair

Examples

• An inherited characteristic that shows continuous variation varies among the members of the species in a smooth, continuous manner. It does not fall into distinct groups.

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• The polygenic inheritance is controlled by a variety of genes. The greater the number of genes involved the more intermediate phenotypes that will be produced.

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• Polygenic traits are influenced by the environment (adequate sunshine and rainfall)

Polygenic Inheritance

https://dashboard.blooket.com/set/620284f5e1b3ecffe7378826

Inbreeding

Learning intentions:

To revise the key words and terminology from N5 Variation and inheritance

To learn about the implications of inbreeding

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Success Criteria:

I can state and use correctly the key words from N5 variation and inheritance

I can complete a punnet square

I can state the negative implications of inbreeding for crops

I can explain why naturally inbreeding species no longer suffer from inbreeding depression.

LI:

• State the meaning of inbreeding
• Describe the effects on inbreeding: elimination of heterozygotes and inbreeding depression

Selecting and breeding

The aim of breeding programmes is to select the desired gene from one parent and combine it with a different desired gene from another. The result being offspring with the desired genes from both parents (superior offspring).

Breeding Programmes

Inbreeding involves the fusion of two gametes from close relatives.

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It ensures each generation receives the alleles for the desired characteristic.

Inbreeding

When selective breeding is used, strains are formed by inbreeding - mating of genetically similar individuals. Self-pollinating plants are natural inbreeders.

Inbreeding naturally occurs in some self-pollinating plant species

Effects of Inbreeding

Effects of Inbreeding

The Vadoma tribe of Zimbabwe have Ectrodactyly (two toed feet). This mutation is more common due to inbreeding.

Methemoglobinemia

https://www.youtube.com/watch?v=n0lZWnG14-E

Inbreeding can cause harmful mutations

Starter

• What is inbreeding?
• What does it mean to be heterozygous?
• Why might this be beneficial?

Effects of Inbreeding

Inbreeding ensures that the members of each generation of a selectively bred strain receive alleles for the desired characteristic. But can also lead to:

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The cross below shows what can happen to a variety of wheat when inbreeding occurs. There is a chance that a combination of two recessive deleterious (harmful) alleles (aa) will be produced.

Loss of heterozygosity

P

F1

F2

F3

Aa (selfed)

AA

Aa

Aa

aa

Heterozygosity

100%

50%

25%

12.5%

AA AA AA AA

AA Aa Aa aa

AA Aa Aa aa

aa aa aa aa

4AA 4AA 4AA 4AA

4aa 4aa 4aa 4aa

4AA

AA

2Aa

aa

AA

2Aa

aa

4aa

4AA

AA

2Aa

aa

AA

2Aa

aa

4aa

Loss of heterozygosity

Loss of heterozygosity

Continuous inbreeding leads to a loss of heterozygosity (Aa) and development of homozygosity (AA & aa).

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As each generation is formed, strains show a higher degree of homozygosity = little genetic diversity, increased chance of harmful genetic combinations.

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If an organisms which is not used to inbreeding (outbreeder) is forced to inbreed inbreeding depression can occur.

Inbreeding depression in maize

Inbreeding Depression

Inbreeding Depression

The accumulation of homozygous alleles can cause the expression of deleterious (harmful) recessive alleles = inbreeding depression.

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Eventually this can lead to a decline in vigour (hardiness, strength, stamina), size and fertility and yield of the plant or animal.

Breeders try to prevent this by using parent plants which are homozygous for the desired trait but heterozygous for other traits.

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Self-pollinating plants are naturally inbreeding and less susceptible to inbreeding depression due to the elimination of deleterious alleles by natural selection.

Summarise Inbreeding in 4-5 bullet points

• Why does inbreeding take place?
• What are the negative effects of inbreeding?
• How are these negative effects overcome?
• What about organisms that are naturally inbreeding?

Inbreeding

• Animals/plants are inbred until till the population breeds true (all show in their phenotype) the desired characteristic.
• Negative effects - loss of heterozygosity and inbreeding depression = lack of vigour, size, fertility.
• The negative effects can be counteracted by breeding with parents that are homozygous for the desired trait and heterozygous for other traits.
• Naturally inbreeding organisms have eliminated deleterious alleles due to natural selection.

Inbreeding

Learning intentions:

To revise the key words and terminology from N5 Variation and inheritance

To learn about the implications of inbreeding

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Success Criteria:

I can state and use correctly the key words from N5 variation and inheritance

I can complete a punnet square

I can know the negative implications of inbreeding for crops

I can explain why naturally inbreeding species no longer suffer from inbreeding depression.

Questions:

1) Distinguish between the terms:

A) Inbreeding and outbreeding

B) Homozygous and heterozygous.

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2) Describe if each statement is true/false. If false, correct it.

A) Self-pollinating plants are naturally inbreeding.

B) Continuous inbreeding results in loss of homozygosity.

C) Cross-pollinating plants and animals are natural outbreeders.

D) During inbreeding selected members of a species are bred for several generations until they breed true.

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Q3) a) why are self pollinating plants less susceptible to inbreeding depression?

b) what can be done to avoid inbreeding depression when carrying out repeated inbreeding on species that are natural outbreeders?

Questions:

1) Distinguish between the terms:

A) Inbreeding and outbreeding

Inbreeding involves the fusion of two gametes from close relatives.

Outbreeding involves the fusion of two gametes from unrelated individuals

B) Homozygous and heterozygous.

Homozygous - organisms have the same alleles for a gene e.g. RR or rr

Heterozygous - Organisms with different alleles e.g. Rr

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2) Describe if each statement is true/false. If false, correct it.

A) Self-pollinating plants are naturally inbreeding.

B) Continuous inbreeding results in loss of homozygosity heterozygosity

C) Cross-pollinating plants and animals are natural outbreeders.

D) During inbreeding selected members of a species are bred for several generations until they breed true.

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Q3) a) why are self pollinating plants less susceptible to inbreeding depression? due to the elimination of deleterious alleles by natural selection.

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b) what can be done to avoid inbreeding depression when carrying out repeated inbreeding on species that are natural outbreeders? Farmers choose parents which are homozygous for the desired trait but are genetically diverse in other ways.

Inbreeding Research - Group task

1) Domestic dogs

Purebred dogs were inbred for desired characteristics like herding, fetching, and tracking skills. Unfortunately, health problems also resulted like hip, elbow, heart, and eye problems

2) The Florida Panther

Hunting and habitat loss have reduced its numbers to 70 individuals confined to South Florida. So few panthers remain that they are now inbred, which has caused health problems like heart defects and abnormal sperm. These defects make it even harder for them to survive.

3) Thoroughbred Horses

Thoroughbred horses were selectively bred (inbred) for speed. Some Thoroughbreds have skeletal defects, which can lead to broken bones. They also have reproductive problems.

4) The Hapsburg Royal Family of Europe

The Hapsburg family ruled Austria and Spain as well as many other European countries between the 15-18^th centuries. In order to keep “pure” bloodlines and seal alliances for increased power, the Hapsburgs inter-married one another frequently. Marriages between first cousins and uncles and nieces were fairly common. One result of this inbreeding is the “Hapsburg Jaw” where the lower jaw grows longer than the upper jaw making for an extended chin.

5) Maple Syrup Urine Disease

The Amish communities had very small founding populations, which led to genes for this disorder to be more common in today’s population. This circumstance results in the high rate of Maple Syrup Urine Disease in today’s population. This disease can cause seizures, comas, and death, if left untreated.

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Create slides to explain your case study to the rest of the class. Include references to loss of heterozygosity and definitions of True breeding, Inbreeding, Inbreeding Depression.

You should now be able to…

New words: plot, outbreeding, inbreeding, inbreeding depression, deleterious

• State the difference between outbreeding and inbreeding.
• Explain inbreeding depression and how it can be avoided
• Define hybrid vigour

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