A2 Biology Inheritance And Evolution

Front 1

Define Genotype

Back 1

The genetic constitution of an organism (for a particular gene this refers to alleles present)

Front 2

Define Phenotype

Back 2

The Appearance of a Characteristic due to the Expression of the Genotype and its Interaction with the Environment

Front 3

Define Dominant and Recessive alleles

Back 3

Dominant: Always expressed in the Phenotype

Recessive: Only Expressed in the Phenotype when Homozygous Recessive

Front 4

Define Codominant Alleles

Back 4

Where both Alleles are expressed in the Phenotype, with Both Contributing

Front 5

Define a Locus

Back 5

The position of a gene on a chromosome

Front 6

Why do gametes contain only one allele from each homologous chromosomes of the parent?

Back 6

Meiosis. In Meiosis the Homologous Chromosomes of each pair come together and then separate into separate gametes which each contain only one of the original pair of alleles.

Front 7

What is Monohybrid Inheritance?

Back 7

Inheritance of one particular characteristic

Front 8

What is a Test Cross?

Back 8

Crossing organism A (Dominant Phenotype) with organism B (Homozygous Recessive) to determine the Genotype of A

Front 9

Why might there be a difference between the expected and observed ratios in a cross?

Back 9

Small Sample Size- Sampling error is greater.

Random Fusion of Gametes- Random Chance

Selection Bias against a Particular Phenotype- Results in fewer of some phenotype.

Front 10

What would a Chi-Squared test be used for in genetics?

Back 10

Comparing the Goodness of Fit between expected ratios and observed phenotypic ratios.

Sees if there is a statistical difference.

Front 11

Define Multiple Alleles

Back 11

Where there are more than two alleles for a particular gene

Front 12

What are the alleles for blood groups?

Back 12

IA IB and IO

(Small letters in superscript not Subscript)

Front 13

Why do recessive sex linked traits most often occur in males?

Back 13

There is no other allele on the Y chromosome so the recessive allele is always expressed.

Front 14

What evidence in a pedigree chart can show that an allele is Recessive?

Back 14

2 Unaffected Parents who have an Affected Child as the parents must be heterozygous and pass on recessive allele carriers (mother heterozygous if sex linked)

Front 15

What evidence in a pedigree chart can show that an allele is Dominant?

Back 15

2 Affected parents who have an Unaffected child as the Parents must be heterozygous and pass on recessive unaffected allele

Front 16

What evidence in a pedigree chart can show that an allele is Not Sex Linked when known to be Recessive?

Back 16

2 Unaffected Parents who have an Affected Daughter.

As the father would pass on his dominant allele on X chromosome and daughters would be unaffected.

Front 17

What evidence in a pedigree chart can show that an allele is Not Sex Linked when known to be Dominant?

Back 17

2 Affected Parents who have an Unaffected Daughter.

As the father would pass on his dominant affected allele on the X chromosome and daughters would be affected.

Front 18

Define Dihybrid Inheritance

Back 18

The inheritance of two different characteristics, each controlled by a different gene.

Front 19

What is the ratio for dihybrid inheritance of two heterozygous fully organisms

Back 19

9:3:3:1

Front 20

What are Autosomal Linked Genes and what do they result in?

Back 20

Genes present on the Same Chromosomes at Different Loci which are usually inherited together.

This results in no independent assortment, so fewer genetic combinations in the gametes.

This leads to a reduced variety of gametes and so a reduced variety of offspring.

Front 21

Define Sex-Linked Genes and Autosomal Linked Genes

Back 21

Sex: Gene carried on only one type of sex chromosome, usually X

Autosomal: Genes present on the same autosomal chromosome which have close loci. Usually Inherited Together

Front 22

What is the ratio for crossing of two Autosomal Linked Genes

Back 22

3:1

3 Is dominant 1 is Recessive

Front 23

Why does crossing Autosomal Linked Genes not always result in a direct 3:1 ratio?

Back 23

Some Crossing Over occurs during Meiosis which results in separation of alleles and new combinations of alleles e.g Ab and aB.

Front 24

What is Epistasis?

Back 24

When two or more genes contribute to a phenotype.

Often due to metabolic pathways dependent on different enzymes working in sequence.

Front 25

Give the definition of Species and Population.

Back 25

Species: Individuals which can breed together to produce fertile offspring.

Population: A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed

Front 26

Give the definition of Gene Pool and Allelic Frequency

Back 26

Gene Pool: All the Alleles of all the genes of all the individuals in a population at any one time

Allelic Frequency: the Number of times an allele of a particular gene occurs within the gene pool

Front 27

What is the Hardy Weinberg Principle?

Back 27

A mathematical model which predicts that the allele frequencies in a population will not change from generation to generation.

It also gives a method for calculating frequencies of alleles and genotypes in a population.

Front 28

What are the Conditions Required for Hardy Weinberg Principle to apply?

Back 28

Population Large and Isolated (no flow of alleles in or out)

Mating in population is random

No Mutations of Genes Occur

No Selection (All alleles just as likely)

Front 29

What are the formulae for Hardy Weinberg Principle?

Back 29

p + q = 1, 100% of population

p=frequency of dominant allele.

q=frequency of recessive allele

p^2 + 2pq + q^2 = 1, 100% of population

p^2=frequency of homozyhous dominant genotype

2pq= frequency of heterozygous genotype

q^2=frequency of homozyhous recessive genotype

Front 30

What two types of factors lead to variation between individuals in a species?

Back 30

Genetic and Environmental factors.

Front 31

Give 4 Genetic Factors which cause variation and name which one is the primary source of variation.

Back 31

1. Gene Mutations: Changes in the Base Sequence of DNA resulting in production of different polypeptides
2. Crossing Over: Exchange of alleles between the chromosomes of a homologous pair result in new combinations of alleles.
3. Independent Segregation of Chromosomes: In first meiotic division the separation of two members of each homologous pair occurs independently of the separation of other homologous pairs
4. Random Fertilisation: Gametes fuse randomly

Mutation is primary source.

Front 32

Give three features of Characteristics mainly influenced by genetic factors

Back 32

1. Controlled by 1 or 2 genes

2. Expressed as distinct phenotypes with no intermediates

3. Represented as distinct groups on a bar chart or pie graph

Front 33

Give three features of Characteristics mainly influenced by environmental factors

Back 33

1. Controlled by many genes

2. Have no separate phenotypes, have a range of intermediates between two extremes

3. Produce a curve of normal distribution when plotted on a graph

Front 34

Give some examples of Selection Pressures

Back 34

Biotic Factors (from living things) such as Predation, Disease and Competition.

Abiotic Factors such as Sunlight, Water and Temperature

Front 35

Outline the Process of Natural Selection

Back 35

• Selection is due to environmental conditions favouring particular phenotypes
• Variation is present in a population due to Mutations and Meiosis.
• A change in the environment results in organisms with a particular phenotype being better adapted to this environment surviving and reproducing more than those that are less adapted.
• This is known as differential survival and differential reproductive success
• Organisms with Alleles for selected phenotypes will have a greater chance of surviving and reproducing to pass on their alleles
• Frequency of the favourable alleles in the gene pool increases as does the frequency of the phenotype.
• This continues from generation to generation as selection continues. This is known as Natural Selection

Front 36

Name and define the two types of speciation we need to know

Back 36

Allopatric Speciation: Speciation where the groups are separated by geographic isolation

Sympatric Speciation: Speciation where the groups are not geographically isolated but have become reproductively isolated.

Front 37

How does Allopatric Speciation occur?

Back 37

• Variation exists within the population due to mutations and Meiosis.
• Geographical Isolation splits the population into two or more separate groups due to a physical barrier.
• Groups are Reproductively Isolated with no gene flow between the gene pools of the separated populations.
• Different Selection Pressures operate in the different environments resulting in different phenotypes being selected for.
• Organisms with selected phenotypes survive and breed passing on their advantageous alleles.
• The frequency of different selected alleles and their phenotype increases, so allelic frequencies in the separate populations change.
• Different Mutations also occur independently in each population.
• Over a long period of time, allelic frequencies change so much in the separate gene pools that different species develop.

Front 38

How does Sympatric Speciation occur?

Back 38

• Random Mutations occur within a population that could lead to one group of organisms not reproducing with another of the same species in the same habitat.
• This reproductively isolates the two populations.
• There is no gene flow between the gene pools of the two populations.
• Allelic frequencies change as mutations occur independently in the isolated populations.
• Over a long period of time, allelic frequencies change so much in the separate gene pools that different species develop.