Biology - Unit 4 - Inheritance, Selection And Speciation

Front 1

What is a gene?

Back 1

A sequence of bases on a DNA molecule that codes for a protein(polypeptide) which results in a characteristic. e.g. the gene for eye colour.

Front 2

What are alleles?

Back 2

One or more alternative versions of the same gene. (Most plants and animals have two alleles of each gene, one from each parent, the order of the bases for each allele is slightly different, which code for different versions of the same characteristic.)

Front 3

What is a genotype?

Back 3

The genetic constitution of an organism. The alleles an organism has i.e. BB Bb bb

Front 4

What is a phenotype?

Back 4

The expression of the genetic constitution an its interaction with the environment. (an organisms characteristics).

Front 5

What is dominant?

Back 5

An allele whose characteristic appears in the phenotype even when there is only one copy. Dominant alleles are shown by a capital letter. (e.g. the allele for brown eyes is B which is dominant, anyone with the genotype Bb or BB will have brown eyes.)

Front 6

What is recessive?

Back 6

An allele characteristic only occurs in the phenotype, if two copies are present. Recessive alleles are shown by a lower case letter. (e.g. the allele for blue eyes is recessive if a persons genotype is bb then they will have blue eyes.)

Front 7

What is co - dominance?

Back 7

Alleles that are both expressed in the phenotype at the same time. Neither one is recessive or dominant. (e.g. the alleles for haemoglobin)

Front 8

What is the locus?

Back 8

The locus is the fixed position of the gene on a chromosome, alleles of the same gene are found at the same locus on each chromosome in pair.

Front 9

What is a homozygote?

Back 9

An organism which carries two copies of the same allele. e.g. BB OR bb

Front 10

What is a heterozygote?

Back 10

An organism which carries two different alleles e.g. Bb

Front 11

How many alleles do individuals have for one gene?

Back 11

2

Front 12

How many alleles do gametes contain?

Back 12

1

Front 13

Genetic diagrams show what?

Back 13

The phenotypes and genotypes of potential offspring. If two specific individuals are crossed.

Front 14

What is monohybrid inheritance?

Back 14

The inheritance of a single characteristic (gene) controlled by different alleles.

Front 15

What is a punnet square?

Back 15

Is basically another way of showing a genetic diagram.

Front 16

Sickle cell anaemia is an example of what type of alleles?

Back 16

Co - dominant alleles.

Front 17

What does it mean by some characteristics are sex linked?

Back 17

Some characteristics (genes) are specifically carried on the X or Y chromosome.

Front 18

The Y chromosome is smaller than the X chromosome what does this mean?

Back 18

This means that the Y chromosome carries fewer genes, so most genes on the sex chromosomes are only carried on the X chromosome. (called X-linked genes).

Front 19

What sex chromosomes do males and females carry?

Back 19

Males - XY

Females - XX

Front 20

What are the three blood types? - alleles?

Back 20

A B O

Front 21

What to genetic pedigree diagrams show?

Back 21

These show an inherited trait (characteristic) in a group of related individuals.

Front 22

What is a gene pool?

Back 22

Is the complete range of alleles present in a population.

Front 23

What is allele frequency?

Back 23

How often an allele occurs in a population.

Front 24

What does the Hardy- Weinberg principle predict?

Back 24

That the frequencies of alleles in a population won't change from one generation to the next.

Front 25

What certain conditions have to be in place for the Hardy - Weinberg principle to be true.

Back 25

Has to be a large population where there is no immigration or emigrations, mutations or natural selection. There also needs to be random mating all possible genotypes can breed with all others.

Front 26

What can the Hardy - Weinberg equation be used to find out?

Back 26

To estimate the frequency of particular alleles and genotypes within populations.

Front 27

What can the Hardy - Weinberg equation also be used to find out?

Back 27

Whether the hardy - Weinberg principle applies to particular alleles in particular populations.

Front 28

What are the two equations for hardy - Weinberg?

Back 28

p + q = 1

p(2) + 2pq + q(2) = 1

Front 29

p + q = 1 - what can you find out from this equation?

Back 29

The frequency of one allele if you know the frequency of the other.

Front 30

In the p + q = 1 equation what do p and q mean?

Back 30

p = the frequency of the dominant allele

q = the frequency of the recessive allele

Front 31

E.g. If a species of plant only has red or white flowers. Allele R (red) is dominant and allele r (white) is recessive. If the frequency of R = 0.4 what is r? - using hardy - Weinberg first equation.

Back 31

1 - 0.4 = 0.6

Front 32

p(2) + 2pq + q(2) = 1 - what can you figure out from this equation from Hardy - Weinberg?

Back 32

You can figure out the frequency of one genotype, if you know the frequencies of the others.

Front 33

In the equation p(2) + 2pq + q(2) = 1 - what does p(2), 2pq and q(2) mean?

Back 33

p(2) = the frequency of homozygous dominant genotype.

2pq = the frequency of the heterozygous genotype.

q(2) = the frequency of the homozygous recessive genotype.

Front 34

Make sure to practise worked examples of the Hardy - Weinberg equation!

Back 34

PRACTISE!!!

Front 35

What is the process of natural selection?

Back 35

1 - The frequency of an allele within a population changes, this occurs when an allele codes for a characteristic that affects the chance of an organisms survival.

2 - There is different reproductive success within a population, individuals with an allele making them more likely to survive, will reproduce and pass on their genes (incl beneficial one) than an individual with different alleles.

3 - This means a greater proportion of the next generation inherit the beneficial allele.

4 - In turn they will be more likely to pass on their genes.

5 - So the frequency of the beneficial allele increases.

Front 36

What are the two types of natural selection that effect allele frequency in different ways?

Back 36

Stabilising selection and Directional selection.

Front 37

What is Stabilising selection?

Back 37

Where individuals with alleles for characteristics towards the middle of the range are more favoured and more likely to survive and reproduce. This occurs when the environment isn't changing. This reduces the range of possible phenotypes.

Front 38

E.g. what is the advantage of a mammal population having average length fur in a stable climate? - stabilising selection

Back 38

The individuals with fur at extremes have reduces chances of survival, as it would be harder to maintain the right body temp.

Front 39

What is directional selection?

Back 39

Where individuals with alleles for characteristics of an extreme type are favoured and more likely to reproduce. This could be a response to environmental change.

Front 40

E.g. How are cheetahs a good example of directional selection?

Back 40

These are the fastest animals on land and it's likely this characteristic occurred through directional selection. Animals with allele for speed more likely to catch prey.

Front 41

What is speciation?

Back 41

The development of a new species.

Front 42

When does speciation occur?

Back 42

When populations of the same species become reproductively isolated.

Front 43

What is geographical isolation?

Back 43

Where a natural physical barrier divides a population of species, causing some individuals to be separated from the main population.

Front 44

Why do species who have been geographically isolated change?

Back 44

This is due to the two new populations experiencing slightly different conditions. For example a different climate on either side of the physical barrier.

Front 45

What will happen to the different populations when they experience different selective pressures? - from geographical isolation.

Back 45

Different alleles will become more advantageous in different populations. Then directional or stabilizing selection ill occur. Allele frequency will also change as mutations occur independently in each population. Then different phenotypes will occur.

Front 46

What is the climax of two species becoming reproductively isolated?

Back 46

The different populations would have changed for much due to mutations and advantageous alleles and will not be able to reproduce with members of the other population to produce fertile offspring. They have then become reproductively isolated. Then will be separate species.

Front 47

Lake Malawi in East Africa contains around 400 different species of cichlids which are small,

brightly coloured fish. All these species have evolved from a common ancestor.

(a) Describe one way in which scientists could find out whether cichlids from two different

populations belong to the same species.

Back 47

breed together;

if fertile offspring, then same species;

Front 48

Lake Malawi in East Africa contains around 400 different species of cichlids which are small,

brightly coloured fish. All these species have evolved from a common ancestor.

During the last 700 000 years there have been long periods when the water level was

much lower and Lake Malawi split up into many smaller lakes. Explain how speciation of

the cichlids may have occurred following the formation of separate, smaller lakes.

Back 48

isolation of two populations;

variation already present due to mutations;

different environmental conditions / selection pressures;

selection of different features and hence different alleles;

different frequency of alleles;

separate gene pools / no interbreeding;

Front 49

What is meant by a sex-linked gene?

Back 49

gene located on X / Y/ one sex chromosome;

Front 50

How do multiple alleles of a gene arise?

Back 50

mutations;

which are different/at different positions in the gene;

Front 51

In an investigation, the tolerance to copper ions of the grass Agrostis tenuis was determined.

Samples were taken of plants growing in waste from a copper mine and from nearby areas just

outside the mine. The mean copper tolerance of plants from the mine waste was found to be

four times higher than that of plants in the surrounding area.

(a) Explain how natural selection could produce a copper-tolerant population in the mine

waste.

Back 51

variation present in (original population);

(copper) tolerant individuals more likely to survive;

(these reproduce and) pass on genes (to next generation/offspring);

more/increase (in frequency) of copper tolerance alleles/genes;

Front 52

James Bay is a large ocean bay in northern Canada. It was formed by the melting of

glaciers. One species of lemming inhabits the eastern side of James Bay and another

species of lemming inhabits the western side. Before the glaciers melted there was only

one species of lemming present. Explain how two species of lemming evolved from the

original species.

Back 52

geographical isolation of populations;

variation present in population(s);

different environmental conditions;

different selection pressures/different phenotypes selected;

change in genetic constitution of populations/gene pools/allele

frequency; (two populations) so unable (to breed) to produce

fertile offspring;

Front 53

PRACTISE GENETIC CROSSES! and GENETIC DIAGRAMS!

Front 54

Colour blindness is controlled by a gene on the X chromosome. The allele for colour

blindness, Xb, is recessive to the allele for normal colour vision, XB . The gene controlling the

presence of a white streak in the hair is not sex linked, with the allele for the presence of a white

streak, H, being dominant to the allele for the absence of a white streak, h.

(a) Explain why colour blindness is more common in men than in women.

Back 54

males are XY and females XX / males have one X chromosome and

females two X chromosomes;

males only have one allele (of the gene) present / recessive allele

always expressed;

colour blindness is masked in heterozygote / female needs 2 recessive

alleles to be colour blind;

Front 55

Give two assumptions that must be made when using the Hardy-Weinberg equation.

Back 55

No selective advantage / All genotypes equally fertile;

Large population;

Random mating; (IGNORE ‘random fertilisation’)

No mutation;

No emigration/immigration;

Front 56

What does the Hardy–Weinberg principle predict?

Back 56

The frequency/proportion of alleles (of a particular gene);

Will stay constant from one generation to the next/over

generations/no genetic change over time;

Providing no mutation/no selection/population large/population

genetically isolated/mating at random/no migration;

Front 57

Explain what is meant by the term phenotype.

Back 57

The physical characteristic displayed in an organism due to its genes and environment.