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Junior Certificate Science Junior Certificate Science BiologyBiology

Inheritance and SelectionInheritance and Selection

Theresa Lowry-LehnenTheresa Lowry-LehnenRGN, BSc (Hon’s) Specialist Clinical Practitioner (Nursing), Dip Counselling, RGN, BSc (Hon’s) Specialist Clinical Practitioner (Nursing), Dip Counselling,

Dip Adv Psychotherapy, BSc (Hon’s) Clinical Science, PGCE (QTS), H. Dip. Ed, Dip Adv Psychotherapy, BSc (Hon’s) Clinical Science, PGCE (QTS), H. Dip. Ed, MEd, MEd,

Emotional Intelligence MHS AccreditedEmotional Intelligence MHS Accredited

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VariationVariation“Variation” is the name given to differences between individuals of the SAME species.

Variation is due to GENETIC or ENVIRONMENTAL causes. For example, consider identical twins:

1) Ways in which Tom and James are the same (caused by genes):

2) Ways in which Tom and James are different (caused by environment):

12/04/23Where is this information Where is this information stored?stored?

Section of a chromosome:

Genes for eye colour

Genes for hair

colour

Genes for blood group:

Different species have different numbers of chromosomes. Humans have 46 (23 pairs) in every cell.

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Sexual ReproductionSexual Reproduction

The human egg and sperm cell (“GAMETES”) contain 23 chromosomes each.

When fertilisation happens the gametes fuse together to make a single cell called a ZYGOTE. The zygote has 46 chromosomes (23 pairs).

12/04/23Sexual vs. Asexual Sexual vs. Asexual reproductionreproduction

Sexual reproduction:•2 parents are needed

•Offspring will have “pairs” of chromosomes

•This will cause genetic variation

Asexual reproduction:•Only 1 parent needed

•Offspring are genetically identical to parent (“clones”)

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MitosisMitosis

Each daughter cell has the same number of chromosomes and

genetic information as the parent.

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MeiosisMeiosis

Each daughter cell has half the number of

chromosomes of the parent.

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Mitosis vs. MeiosisMitosis vs. MeiosisMitosis:

1. Used for growth and repair of cells

2. Used in asexual reproduction

3. Cells with identical number of chromosomes and genetic information are produced

Meiosis:

1. Used to produce gametes for sexual reproduction

2. Each daughter cell has half the number of chromosomes of the parent

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FertilityFertilityThe events that happen in a female body during the

menstrual cycle are triggered by hormones (chemical messengers). Artificial hormones can be used to:

In normal circumstances natural hormones are responsible for releasing the egg and for thickening the lining of the womb. These hormones are produced by the pituitary gland in the brain and in the ovaries.

1) Stimulate the release of eggs (fertility treatment)

2) Inhibit the release of eggs (contraceptive pills)

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FertilityFertility3 hormones are involved in the menstrual cycle: oestrogen, LH and FSH. Here’s how:

Step 3: LH stimulates the release of the mature egg in the middle of the menstrual cycle

Artificial fertility:

1) To INCREASE fertility FSH is given to stimulate maturation of eggs.

2) To DECREASE fertility oestrogen is given (“The Pill”) to inhibit FSH production stopping eggs from maturing.

Step 1: FSH produced by the pituitary gland causes both an egg to mature and the ovaries to start producing oestrogen

Step 2: The rising levels of oestrogen cause the pituitary gland to stop producing FSH and produce LH instead

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Key wordsKey wordsGamete

Zygote

Allele

Dominant

Recessive

Homozygous

Heterozygous

•This allele determines the development of a characteristic

•This is formed when an egg is fertilised by a sperm

•This allele will determine a characteristic only if there are no dominant ones

•This word refers to a pair of chromosomes being made of two different alleles of a gene

•An egg or a sperm are called this

•This word refers to a pair of chromosomes being made of two of the same alleles of a gene

•An alternative form of a gene

12/04/23Genes, Chromosomes and Genes, Chromosomes and DNADNA

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Some facts:

- Made up of paired bases

- Contain instructions on what a cell does, how the organism should work etc

- The instructions are in the form of a code

- The code is made up from the four bases that hold the strands together

- The bases represent the order in which amino acids are assembled to make proteins

- Each group of 3 bases represents one amino acid

- There are only about 20 amino acids

How genes workHow genes work

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Boy or Girl?Boy or Girl?

X Y X

XX XYGirl Boy

“Allele”

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Father

Mother

Son

Daughter

Boy or Girl?Boy or Girl?

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Eye colourEye colour

In eye colour the brown eye allele is dominant, so we call it B, and the blue eye is recessive, so we call it b:

bbBB Bb

Homozygous brown-eyed

parent

Heterozygous brown-eyed

parent

Blue-eyed parent

What would the offspring have?

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Eye colourEye colourExample 1: A homozygous brown-eyed parent and a

blue-eyed parent:

Example 2: 2 heterozygous brown-

eyed parents

BB bbX Bb BbXParents:

Gametes:

Offspring: Bb Bb BbBb BB Bb bbbB

B B bb B bB b

(FOIL)

All offspring have brown eyes

25% chance of blue eyes

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Eye colourEye colour

Example 3: A heterozygous brown-eyed father and a blue-eyed mother:

Bb

Bb Bb bbbb

bb

b bB b

Equal (50%) chance of being either brown eyed or blue eyed.

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B b

b

b

Another methodAnother method

Example 3: A heterozygous brown-eyed father and a blue-eyed mother:

B b

b Bb bb

b Bb bb

Father

Mother

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Example questionsExample questions

1) In mice, white fur is dominant. What type of offspring would you expect from a cross between a heterozygous individual and one with grey fur? Explain your answer with a genetic diagram.

2) A homozygous long-tailed cat is crossed with a homozygous short-tailed cat and produces a litter of 9 long-tailed kittens. Show the probable offspring which would be produced if two of these kittens were mated and describe the characteristics of the offspring (hint: work out the kitten’s genotype first).

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Inherited diseasesInherited diseases1) Cystic fibrosis (1 in 2000)– a disease that causes thick and sticky mucus to coat the lungs, gut and pancreas. It’s caused by recessive alleles:

2) Huntingdon's disease (1 in 20,000)– a disease of the nervous system that causes shaking and eventually dementia. It’s caused by a dominant allele:

3) Sickle cell anaemia – a disease that alters the shape of red blood cells, thereby reducing their oxygen capacity, causing weakness and anaemia. It’s caused by recessive alleles:

Ff FfX

Cc ccX

Ss SsX

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MutationsMutationsMutations are changes in the structure of the DNA molecule. They can be passed on to daughter cells through cell division. They will result in the wrong proteins being produced.

Mutations can be caused by:

- Ionising radiation (UV, X-rays etc)

- Radioactive substances

- Certain chemicals

Effects:

- Mostly harmful

- Causes death or abnormality in reproductive cells

- Causes cancer in body cells

- Some CAN be neutral or even beneficial (e.g. the peppered moth)

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Modern GeneticsModern Genetics

My name is Gregor Mendel. I am the father of modern genetics because of

the work I did on pea plants in 1865…

Take two plants; one which is pure-bred for tallness and one pure-bred for shortness, and cross them:

X

Mendel’s experiment:

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Modern GeneticsModern Genetics

All the plants produced were tall.

Now cross two of these plants…

3 out of every 4 plants were tall, leading Mendel to hypothesise that “for every characteristic there must be two determiners”

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ClonesClonesPlants can reproduce ASEXUALLY. The offspring are genetically ________ to the parent plant and are called _________. Two examples:

1) This spider plant has grown a rooting side branch (“stolon”) which will eventually become __________.

2) A gardener has taken cuttings of this plant (which probably has good characteristics) and is growing them in a ____ atmosphere until the ____ develop.

Words – clones, damp, independent, roots, identical

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CloningCloning1) Cloning plants:

2) Cloning sheep:

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Selective breedingSelective breeding

I raise cows. Each type of cow is good at a certain job. The Friesian cow

produces large quantities of milk, the Jersey cow

produces very nice milk and the Hereford cow produces lot of beef.

If, for example, I want lots of milk I would only breed Friesian cows with each other – this is SELECTIVE

BREEDING.

Friesian

Jersey

Hereford

12/04/23Selective breeding vs. Selective breeding vs. CloningCloningAdvantages Disadvantages

Cloning

Selective breeding

12/04/23Selective breeding vs. Selective breeding vs. CloningCloningAdvantages Disadvantages

Cloning

1) Allows large numbers of organisms with good characteristics to be produced

2) Very efficient

1) Causes reduced numbers of alleles

2) Loss of variation could harm survival chances if the environment changes

Selective breeding

1) Produced organisms with favoured characteristics

2) Very efficient and economically viable

1) Causes reduced numbers of alleles

2) Loss of variation could harm survival chances if the environment changes

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Genetic ModificationGenetic Modification

Possible uses of genetic modification of organisms:

-Improving crop yield

-Improving resistance to pesticides

-Extend shelf-life

-Manufacture a certain chemical (e.g. insulin)

-Convenience

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Genetic engineeringGenetic engineering

Insulin is a hormone produced by the pancreas to help control blood sugar levels. Diabetics can’t produce enough insulin and often need to inject it.

Insulin can be made by genetic engineering:

12/04/23Genetic engineering - Genetic engineering - InsulinInsulin

Step 1: Using RESTRICTION ENZYMES “cut out” the part of the human chromosome that is responsible for producing insulin.

Step 2: Using another restriction enzyme cut open a ring of bacterial DNA (a “plasmid”). Other enzymes are then used to insert the piece of human DNA into the plasmid.

Step 3: Place the plasmid into a bacterium which will start to divide rapidly. As it divides it will replicate the plasmid and make millions of them, each with the instruction to produce insulin. Commercial quantities of insulin can then be produced.

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EvolutionEvolution

Charles Darwin (1809-1882)

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EvolutionEvolutionEvolution is the slow, continual

change of organisms over a very long time. All living things on the Earth

have developed from the first simple life forms that arrived 3,000,000,000

years ago.

One of the effects of evolution is that species will become better adapted to their environment. If these species don’t adapt they may become extinct due to being unable to deal with any of these factors…

1) Increased competition

2) Changes in the environment

3) New diseases

4) New predators

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EvolutionEvolutionMy key observations:1) All living things produce more

offspring than survive to adulthood

2) In spite of this, population sizes remain roughly constant

3) Variation exists among species4) Characteristics can be passed on

from one generation to the next.

These observations led me to the conclusion that species evolve over a along period of time by a mechanism called “Natural Selection”. The main evidence for this is from fossil records.

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Natural SelectionNatural Selection1) Each species shows variation:

2) There is competition within each species for food, living space, water, mates etc

4) These survivors will pass on their better genes to their offspring who will also show this beneficial variation.

Get off my land

Gutted!

Yum

3) The “better adapted” members of these species are more likely to survive – “Survival of the Fittest”

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A smaller example…A smaller example…Consider the four steps of natural selection in the example of some bacteria that has become resistant to penicillin:

1) Variation – some strains of bacteria are resistant and some aren’t.

2) Competition – The non-resistant bacteria are killed by the penicillin.

3) Survival of the fittest – the resistant bacteria survive.

4) Passing on of genes – the resistant bacteria reproduce and pass on their adaptations to their offspring.

Bacteria

Penicillin