standard grade inheritance

INHERITANCE…

This unit consists of 3 sub-topics…

VARIATION

WHAT IS INHERITANCE

GENETICS AND SOCIETY

SUB-TOPIC A… VARIATION.

WHAT IS A SPECIES ?

A Group of organisms which are very similar

AND Are able to produce

fertile offspring

The species is made up of different VARIETIES (breeds,ie Dogs )

All these are same species!Broccoli, kale, Cabbage, Sprouts

Cauliflower,are all members of the same species ! (Brassica Olearea)

Lemurs of Madagascar

Amazonian Frogs

Can you think of some more examples ? Write them down !!

…Interbreeding

Members of very different species cannot breed and produce offspring

For example,Dogs and Giraffes

…BUT (There’s always a ‘but’ in Biology) Sometimes the

members of two very similar species CAN interbreed.

HOWEVERAny offspring are

always STERILE

Eg. A Horse and a Donkey

…Make mine a MULE

What does ‘sterile’ mean ?

Try this one…

If a Horse…

Mates with a.. Zebra.

What is the result called ?

Can they have any babies ?

It’s a Zebrorse !!

So a species is ?

A group of organisms which can..

Interbreed AND……

Give birth to _________________

Fertile offspring

Write down some examples of SPECIES with their VARIETIES

VariationVariation can come about for two reasons:

1. Some features can be inherited. That means that you get them from your parents

2. Other features are affected by the environment.

3. Lots of features are a combination of both

Examples?

Environmental or Inherited?

How does variation come about?Sexual reproduction

Genetic information exchanged by

Characteristics

These are features you exhibit physically

( your looks)

Example: Eye colour

Traits

The different versions of a characteristic

Example: blue, green, and brown eyes

Why aren’t fruits from the same plant identical ?

What about this wheat grown in the same field from the same parent plants ?

Why does one organism look different to another ?

1. Do the members of this family have any similar features ?

2. Are the members different in any ways ?

3. What reasons can you think of to explain these differences ?

Inherited differences. These are due to

genes or the bits of message we get from a parents sperm and egg.

In plants the genes are in the pollen and ovule.

The genes are found in the nucleus of plant and animal cells.

Nucleus

Inherited Differences in Humans.

Genes control the characteristics that develop.

1/2 the instructions come from the father and 1/2 come from the mother.

The new individual is genetically unique.

So why are Identical twins not identical ? Twins have

identical genes in their bodies…….

Yet they do not have identical characteristics.

What do we find?

Height shows a continuous variation – there is a range of values with most people roughly in the middle

Eye colour, hair colour etc show a discontinuous variation – there are distinct groups but some are more common

Eye colour in 9K

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blue green hazel brown grey black

Frequency

Discontinuous variation

•Cut and dried characteristics there are no in-betweens.

•Always caused by genes.

•Examples :- Natural hair colour, blood groups.

Discontinuous variation

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Number of pupils

Tongue rollers Non -Tongue rollers

Graph to show number of girls who can roll their tongues.

Series1

Continuous Variation

•Gradual or not so clear-cut variation

•Bell shaped graph

•The classes are artificial and have been decided upon by us to make it easier to draw a graph.

•May be caused by genes or environment or both.

•Examples :- weight, leaf length, height, skin colour.

Continuous variation.

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Number of students

6.5-7.0 7.0-7.5 7.5-8.0 8.0-8.5 8.5-9.0Length of index finger

Graph to show the length of girls index fingers in the class.

Class results

Inherited, environmental or both?

Example Cause Example Cause

Sex I Weight B

Height B Dyed blonde hair

E

Strength B Beard ICut on face

E Intelligence

B

Got a bad cold

E Blood group

I

Eye colour

I

Question 1 What is the term for an animal

that cannot breed A – Disappointed B – Fertile C – Sterile D – Hostile

Question 2

What do you get if you cross a horse with a donkey

A – Liger B - Zebrorse C – Binturong D - Mule

Question 3

Which of the following is an example of discontinuous variation

A – Finger print B - Height C – Weight D – Hand span

Question 4

What is an example of continuous variation

A – Tongue rolling B - Weight C – Finger print D – Blood group

Question 5

Which of the following is a group of living things that can interbreed to produce fertile offspring?

A - community B – population C – genus D - species

Question 6

Which of the following is a block graph of a characteristic showing continuous variation where the entire range of the characteristic is divided into smaller groups for convenience

A – Hysterectomy

B – Histogram

C – Hysterical

D – Bar chart

Question 7

Which of the following is a bell-shaped curve of a characteristic showing continuous variation where most individuals fall into the centre of the range?

A – Skewed distribution

B – Abnormal distribution

C – Normal distribution

D – Asymmetrical distribution

Question 8

What is the name of an animal resulting from a cross between a lion and a tiger

A – Tigron

B – Tigger

C – Puma

D – Sabre-toothed mouse

Now check your learning outcomes sheet.Make sure you have marked off ALL the boxes.Ask your teacher to go over any points you do not understand

SUB TOPIC B – WHAT IS INHERITANCE ?

Inheritance

Occurs when traits are passed down from parent to child.

These are things like eye colour, skin colour and hair colour.

They are inherited.

IDENTIFYING PHENOTYPES

– A description of the APPEARANCE of an organism

– A characteristic can have several phenotypes

Eg.A Daffodil can have yellow,white or orange flower colour

Patterns of Inheritance

The way in which inherited characteristics are passed on from parents to their offspring was first studied by an Austrian monk called Gregor Mendel.

He worked out patterns of inheritance by doing breeding experiments using pea plants

Genetics-’Monkey’ business

Modern genetics had its beginnings in an abbey garden, where a monk named Gregor Mendel documented a particular mechanism of inheritance.

He discovered the basic principles of heredity by breeding garden peas in carefully planned experiments.

His approach to science had been influenced at the University of Vienna by one of his professors: the physicist Doppler.

Mendel’s work...

In order to study inheritance, Mendel chose to use peas, probably as they are available in many varieties.

The use of plants also allowed strict control over the mating.

He chose to study only characters that varied in an ‘either-or’ rather than a ‘more-or-less’ manner.

Genetic crosses... To cross 2

varieties of pea plants, Mendel used an artist’s brush.

He transferred pollen from a true breeding white flower to the carpel of a true breeding purple flower.

Tracking heritable characteristics Mendel tracked

heritable characters for 3 generations.

When F1 hybrids were allowed to self-pollinate a 3:1 ratio of the 2 varieties occurred in the F2 generation.

Mendel’s law of segregation By carrying out these

monohybrid crosses, Mendel determined that their must be 2 forms of a gene for each character and that these segregate during gamete production.

Mendel discovered this c.1860.

DNA was not discovered until 1953.

Mendel’s impact

Mendel’s theories of inheritance, first discovered in garden peas, are equally valid for figs, flies, fish, birds and human beings.

Mendel’s impact endures, not only on genetics, but on all of science, as a case study of the power of hypothesis/deductive thinking.

Symbols and terminology... The symbol for parents is... The symbol for the offspring in the

first generation is... The symbol for the offspring of the

second generation is... The phenotype found most

frequently found through the generations is called the...

The less common phenotype is called

the...

Crosses involving only one characteristic are called MONOHYBRID CROSSES

p

f1

f2

DominantRecessive

TRUE BREEDING

If an organism is crossed with a member of the same strain

AND Offspring are

exactly the same kind

The organism is said to be TRUE BREEDINGThis means that offspring of true-breeding

white Guinea pigs are ALWAYS white

Monohybrid inheritance of coat colour in mice

Various coat colours are found amongst mice.Two of these are black fur and brown fur.

If a mouse has black fur, in this exerciseits phenotype will be represented:

If a mouse has brown fur, in this exercise its phenotype will be represented:

Consider the following cross.

true-breeding true-breeding black mouse x black mouse

Parents

F1 ?

Do you think the F1 will be all black offspring ? Do you think the F1 will be all brown offspring ? Do you think the F1 will be some black and some brown ?

1..You are right.

true-breeding true-breeding black mouse x black mouseParents

F1 all black offspring

A true-breeding black mouse crossedwith another true-breeding black mousecan only produce more black mice.

2 and 3…You are wrong.

true-breeding true-breeding black mouse x black mouse

Parents

F1

all black offspring

A true-breeding black mouse crossed with another true-breeding black mouse cannot produce brown mice,only black mice.


true-breeding true-breeding brown mouse x brown mouse

Parents

F1?

1.Do you think the F1 will be all black offspring 2.Do you think the F1 will be all brown offspring 3.Do you think the F1 will be some black and some brown

2…You are right.


Parents

F1

all brown offspring

A true-breeding brown mouse crossedwith another true-breeding brown mouse can only produce more brown mice.



Parents

F1all brown offspring

A true-breeding brown mouse crossed with another true-breeding brown mouse cannot produce black mice, only brown mice.


true-breeding true-breeding black mouse x brown mouseParents

F1 ?1.Do you think the F1 will be all black offspring 2.Do you think the F1 will be all brown offspring 3.Do you think the F1 will be some black and some brown

1…You are right.

true-breeding true-breeding black mouse x brown mouseParents

F1all black offspring

The genetic information for black coat colourmasks the genetic information for brown coat colour.The black colour is dominant and the brown colour is recessive.


true-breeding true-breeding black mouse x brown mouse

Parents

F1all black offspring

The genetic informationfor black coat colour that comes from oneparent dominates andmasks the genetic information for brown coat colour that comesfrom the other parent.So all the F1 mice inthis cross are black.

How is this information carried then ? On thread-like

structures called CHROMOSOMES

Found in the______________Of every cell Two matching sets of

23 arranged in pairs46 in total (in Humans)A picture of them is

called a KARYOTYPE

nucleus

..So what’s the difference between Males and Female chromosomes then ?

..SEX CHROMOSOMES

There are TWO X and Y They are the

23rd pair Have a look to

see who has what XX XY

Have a look at the next slide.Identify the gender of the four individuals from their Karyotypes

Meiosis

Cell division – ‘reduction division’ (different from Mitosis)Production of sex cells called gametes containing HALF the normal number of chromosomes (HAPLOID)

Why do we need Meiosis?

Meiosis is necessary to halve the number of chromosomes going into the sex cells

Why halve the chromosomes in gametes?

At fertilisation the male and female sex cells will provide ½ of the chromosomes each – so the offspring inherits characteristics from BOTH parents

When a sperm and egg cell(Gametes) fuse together, they produce this. The fullchromosome number is restored (46 or

DIPLOID)

We use this word to describe cells which contain the full

complement of genetic material. In humans this would be

46 chromosomes (23 pairs)

Division of a cell to produce 2 daughter cells which each has the same

number and kind of chromosomes as the mother cell

Type of reproduction that involves fusion of gametes containing the HAPLOID

(HALF) number of chromosomes.

Why is this important ?

X YX X

X X YX

XX XY XX XY

female male female male

Parents

Sex cells

Offspring

50% of the offspring should be male and 50% should be female, eg a ratio of 1:1.

female male

Determination of gender:

Genes Bits of information passed down from parent to child.Carried on the Chromosomes which are made of DNA

Each Gene has two forms called ALLELES one from each parent

The set of genes an organism possesses is called its GENOTYPE

Gene control of characteristics All characteristics are controlled

by a minimum of 2 genes.

These genes give the characteristic a different of presenting itself.

Different genes that control the same feature are called ALLELES

EYE COLOUR

Possible alleles – blue , brown, green, hazel etc (each colour needs its own gene)

It is possible to have pairs of different alleles, alleles are usually given a letter

REMEMBER…Genotype and phenotype Genotype is the letter or term

used to describe the allele of an individual gene or pair of genes

Phenotype – is how the gene (or pair) shows itself, how it appears.

Dominance and recessive- ness

Some alleles for a feature are able to mask the influence of other (weaker) gene when they are paired

Stronger gene is DOMINANT and is represented by a capital letter e.g. H

The masked gene is RESSESIVE shown as lower case of the same letter e.g. h

Gene diagram – Flower colour

Genotype of alleles- R = red flower

r = yellow flower

All genes occur in pairs – so 2 alleles affect a characteristic – possible combinations are;

genotype RR Rr rrPhenotype RED RED YELLOW


Male female

RR rr

parent

gamete R R r r

Offspring genotype Rr RrRrRr

Phenotype All red


Male female

Rr Rr

parent

gamete R r R r

Offspring genotype RR RrRrrr

PhenotypeRed yellow red red 3 red : 1 yellow


Male female

Rr rr

parent

gamete R r r r

Offspring genotype Rr Rrrrrr

PhenotypeRed yellow yellow red

Red 50% yellow 50%

Punnett Square

Another method of showing crosses

Gamete genotypes are inserted

Parent genotypes are inserted B=black b=white

Bb male black

bb white female

B b

b

b

What are the crosses

Bb bb

Bb bb

2 white and 2 black offspring

50:50 chance with these parents

Ok… Lets look at it again

Alleles… Usually represented by letters. T –Capital form

is considered a dominant allele

t – Lower-case form is considered a recessive allele

TT – shows the dominant phenotype

Tt or tT – is also dominant

tt - shows the recessive phenotype

Punnett Square..if T is the allele for being ‘Tall’

Uses mum and dad’s GENOTYPES to determine the possible traits of their offspring.

4 offspring each with the genotype Tt

Tt Tt

Tt Tt

T T

t

t

What is the phenotype of the 4 offspring ?

Monohybrid inheritanceLet the allele for round seeds be: R (dominant

allele)Let the allele for wrinkled seeds be: r (recessive allele)

Parents phenotype round seeds x wrinkled seedsgenotype RR rr

Gametes

F1 generation

R R r r

F1 phenotypes 100% plants producing round seeds

F1 genotypes 100% heterozygotes Rr

gametes R Rr Rr Rrr Rr Rr

gametes

F1 cross

Parents phenotype round seeds x round seeds genotype Rr Rr

Gametes

F2 generation

R r rR

Phenotype 75% plants producing round seeds

25% plants producing wrinkled seeds

Genotype 25% RR 50% Rr 25% rr

Ratio 3:1 Round seeds: wrinkled seeds

gametesgametes R rR RR Rrr Rr rr

Does the observed ratio match the theoretical ratio?

The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled

Mendel’s observed ratio was 2.96:1 The discrepancy is due to statistical error The observed ratio is very rarely the

same as the expected ratio The larger the sample the more nearly

the results approximate to the theoretical ratio

Harry Potter and the recessive allele

How Are Wizards Made?


Being a wizard or a muggle is all decided by genetics

All humans including wizards receive one allele from each parent


The allele for wizarding

ability is m

Wizards have the alleles mm

How Are Wizards Made?The allele for Muggleness is M

Muggles have the alleles Mm or

MM

M is dominant to m so you can only be a wizard if you have no M allele

The Malfoys

Lucius Malfoy (mm)

Narcissa Malfoy (mm)

Draco Malfoy( )

The Malfoys are a ‘pure blood’ family

All their ancestors are wizards so they must have the alleles mm

mm

Lily Potter (mm)

James Potter (mm)

Harry Potter (WW)

Both Harry’s parents had magical ability so they must both have been mm

They passed these alleles on to Harry

The Potters

mm

The Weasleys are pure blood wizards so they all have the alleles mm

Hermione is a powerful witch so she must be mm

Both her parents are muggles so they must be Mm so they can give her a m allele each

Mm Mm

mm

Tom Riddle is a ‘half blood’.

His mother was a witch (mm) and his father was a muggle

His father must have had the alleles Mm so he could give him the other m allele

mm Mm

mm

Filch is a ‘squib’

Both his parents are mm so he should be too because he can’t get an M allele from either parent but he can’t do any magic

This means he has a mutation so his wizarding powers don’t work or the man he thinks is his father isn’t really and his mother had an affair with a muggle!

What wizarding alleles would Ron and Hermione’s children have?

Ron (mm)

Hermione (mm)

Children

( )mm

Ron

m m

Hermione

m

m

Their children could only get the m allele from both parents so they would all be wizards

mm mm

mm mm

What wizarding alleles would Ginny and Dudley’s children

have? If Dudley is Mm

Ginny mm

Dudley Mm

Children

WW or mMmM mm

Dudley

m M

Ginny

m

m

Half of their children would be likely to get the m allele from both parents so they would be wizards

The other half would be likely to get an M allele from Dudley and would be muggles

m m

m m

m M

m M

What wizarding alleles would Ginny and Dudley’s children have?

If Dudley is MM

Ginny mm

Dudley MM

Children

WMm M

Dudley

M M

Ginnym WM WM

m WM WM

Their children would get the m allele from Ginny and the M allele from Dudley so they would all be muggles

m M m M

m M m M

What wizarding alleles would

You expect Hermione’s

brothers and sisters

to have ?

Mr Granger

m M

Mrs Grange

r

m WW WM

M WM MM

The Granger’s children have a one in four chance of getting m alleles from both parents and having magical ability

They also have a one in four chance of getting M alleles from both parents and being a muggle

They could also get only one m from their mother or father and still be a muggle

m M

m M

m m

M M

Now check your fact sheet.Make sure you have marked off ALL the boxes.Ask your teacher to go over any points you do not understand

SUB-TOPIC C

GENETICS AND SOCIETY

SELECTIVE BREEDING

Look at the difference between these species of dog :

Wild dogs Terriers

Collies Viemerana

What were the differences between the dogs?

•Size

•Colour

•Muscle development

•Length of coat

•Job

•Nature

Where have all these different species come from?

All these species are related to the wolf. But how?

Over thousands of years man has selected characteristics in dogs that are useful…..

•Very small dogs•Used for pets

•Large hunting dogs•Strong & powerful

•Large working dogs•Strong and athletic

Selective Breeding is the gradual improvement of animal and plant

characteristics over time, for man’s benefit.

Select for breeding only those animals or plants with desirable characteristics

This artificial selection of characteristics happens in plants

as well..

In the wild there are various species of corn plant

Good point: Strong stem

Bad point: Small head

Good point: Huge head of grain

Bad point: Drought sensitive

1

2

3

4

Bad point: Small root

Good point: strong roots

Bad point: Small plant

Good point: Disease resistant

Good point: Strong stem

Good point: Huge head of grain

Super CORN!

Good point: Strong roots

Good point: Disease resistant

Look what has happened to the varieties of the corn over last few hundred years.

Look at the variety of plants that have been artificially selected from mustard!

Growing lots of different varieties of wheat…………

……looking for new characteristics.

Things I must know about selective breeding(SB)

is the gradual improvement of organisms characteristics – for humans benefit.

takes hundreds of years

We have lots of SB animals and plants

SB animals & plants produced higher yields:

1. more milk2. more meat3. more fruit

MUTATIONSA mutation is a change

in the structure and amount of an

organism’s genetic material

How can mutations lead to big changes? Accumulation of many small

mutations, each with a small effect

Accumulation of several small mutations, each with a large effect

One large mutation with a large effect

Normal fly head

This is a normal Fly’s head

Antennapedia fly

Here,the legs replace the antennae on the head…a harmful mutation

What about Mutation ?

Spontaneous(very rare !) Increases caused by

environmental factors(‘Mutagens’)

UV light X-rays Benzene, formaldehyde, carbon

tetrachloride,colchicines.

Mutagens and their effects

Ionising radiation – Nuclear radiation, xrays, gamma rays (e.g. medical treatment) associated with development of cancers (e.g. leukaemia, thyroid cancer and skin cancer


Viruses and microorganisms – integrate into human chromosome, upset genes and can trigger cancer


Environmental poisons – Organic solvents such as formaldehyde, tobacco, coal tars, benzene, asbestos, some dyes


Alcohol and diet – High alcohol intake increase the risk of some cancers. Diet high in fat and those containing burned or highly preserved meat

Harmful mutations

Cystic fibrosis and sickle cell anaemia

Dysfunctional proteins Albinism – caused by mutation

in gene of enzyme pathway of melanin

More harmful mutations Bacteria – antibiotic

resistance through mutation, transfer between bacterial species

Super bugs such as MRSA have arisen this way

RNA viruses – such as HIV – mutates it’s protein coat so that the host human is unable to make antibodies quick enough against it

Down’s Syndrome is the most common chromosomal abnormality.

It occurs in 1:800 to 1000 live births.

Look at the following example of a harmful mutation….

Cause

92% to 95% of all causes of Down’s Syndrome are attributable to an extra chromosome 21.

Children with an extra chromosome 21 are born to parents of all ages but greater risk for women 35 years and older.

Intelligence

This varies from severely retarded to low normal intelligence but is generally within the moderate range.

Social Development

May be 2 to 3 years beyond the mental age, especially during early childhood.

Sensory Problems

Strabismus, Myopia ,Hyperopia, excessive tears, head tilt, cataracts.

Physical Disorders

-Respiratory infections.

Leukemia (is 10 to 30 times more frequent). Thyroid dysfunction.

How can we tell if a baby will have Down’s Syndrome ?

..Amniocentesis testing

Fluid is drawn from the womb

It’s Amniotic fluid

It contains cells from the foetus

These can be used to give a ‘Karyotype’Remember…this gives a picture of the

chromosomes of an organism………..

Does this baby have Down’s..?

standard grade inheritance

Lifestyle

variation variation

different species

examples of species

continuous variation

blonde hair b height

similar species

identical genes

b strength e