Paper 2B Part 2 Flashcards
Define genepool
all the alleles of all the genes of all the individuals in a population at a given time at a given time
What is natural selection?
the process by which organisms that are better adapted to their environment tend to survive and breed at the expense of those less well adapted.
Phenotypic variation is a result of:
- Genetic factors 2. Environmental factors
Why does genetic variation occur?
- Meiosis 2. Sexual reproduction 3. Main factor – MutationsAll can result in selection occuring
What is the hardy weinberg principle?
A mathematical equation used to calculate the frequencies of the alleles of a gene in a population
The hardy weinberg principle is a ______ analysis
statitical
What does the hardy weinberg principle established what?
- Establishes the frequency of the dominant and recessive alleles- Establishes the frequency of carriers (heterozygotes) in a population
The total frequency of alleles for a gene in a gene pool with only one dominant and recessive alleles will =
1 (100%)
In the equation p+q = 1, what do p and q represent?
Dominant allele = pRecessive allele = q
The frequency that A combines with A in the zygote is
p x p = p2
The frequency that a combines with a in the zygote is
q x q = q2
The frequency that A combines with a in the zygote is
p x q = pq
The frequency that a combines with A in the zygote is
q x p = qp
P2 + 2pq + q2 =
1
What is p2?
the frequency/ number of individuals in that population that are homozygous dominant (AA)
What is 2pq?
the frequency/number of individuals that are heterozygous (Aa or aA)
What is q2?
the frequency / number of individuals in that population that are homozygous recessive (aa)
The Hardy Weinberg formulae is based on the principle that:
The proportion of dominant and recessive alleles of any gene in a population remains from one generation to the next
Key conditions of The Hardy Weinberg formulae ?
- No new mutations arise- The population is isolated (no gene flow / flow of alleles into or out of the population)- There is no selection bias- Population studied is large- Mating is random
Why are the conditions in the hardy Weinberg principle important?
- No new mutations arise – no introduction of new alleles- The population is isolated (no gene flow / flow of alleles into or out of the population) – movement encourages interbreeding which reduces genetic differences between populations- There is no selection bias – natural selection = advantageous alleles favoured- Population studied is large – prevents the effects of random events affecting allele frequencies or changes due to chance- Mating is random – prevents the selection of particular alleles, selective breeding would alter allele frequencies
Null Hypothesis:
.There will be no significant difference between two sets of data
Alternative Hypothesis:
.There will be a significant difference between two sets of data
Statistical Testing –
a mechanism for making quantitative decisions about a process or processes
Chi-squared test used for?
comparing observed and expected values
What is the level of probability?
The level of probability that you can accept or reject your null hypothesis (significant or due to chance)
What does you calculated chi squared value tell you?
Calculate a chi squared valueCompare your calculated value with a critical valueAt a 0.05 level of probability95% confidence the difference is significant5% probability it is due to chance
Degrees of Freedom, what are they with example
.The number of variables that are free to change.Calculated by number of categories (n) – 1.Example: 3 categories – 1 = degrees of freedom is 2
How to analyse chi-squared results
.Conduct your statistical test = calculated chi squared value .Compare calculated chi squared and critical values.If your Chi squared value is higher than the critical value at 0.05 probability, reject the null hypothesis and the results are not due to chance.If your value is LESS, ACCEPT null hypothesis.If your value is GREATER, REJECT null hypothesis.
What does Harry Robinson remind us?
Harry Robinson - HR - Higher Reject, for the chi test
What are the steps to a statistical analysis?
- Formulate a Null Hypothesis 2. Select the appropriate statistical test3. Carry out the calculation 4. Determine the degrees of freedom5. Compare your calculated value to the critical value calculated at 0.056. Compare the calculated value with the critical value: a) Higher than the critical value = difference is not due to chance = reject the null hypothesis b) Lower than the critical value = difference is likely due to chance = accept the null hypothesis
What does a chi-squared test allow us to do?
.Identify significant differences between observed and expected results.Measure the degree of deviation between them.Determine if differences present between data sets (2+) are significant or due to chance
When can we use the chi-squared test?
.Data is categorical Phenotypes i.e. eye colour, gender, location.The portion of numbers expected in each category is known.The number in each category is greater than 5
Chi-squared test formula
Chi-squared = Sum ( (observed result – expected result)^2 / expected result)
What does the funny E mean?
sum of
For the chi-squared test, what is ‘o’?
observed result
For the chi-squared test, what is ‘E’?
Excepted result
What does Chi Squared test allow us to do?
.Identify significant differences between observed and expected results.Measure the degree of deviation between them.Determine if differences present between data sets (2+) are significant or due to chance.
What conditions must apply for the chi-square test?
.Data is categorical (e.g. Phenotypes i.e. eye colour, gender or location).The portion of numbers expected in each category is known.The number in each category is greater than 5
Chi squared test formula and meaning
χ^2=∑((O-E)^2/E)Σ Sum ofO Observed resultE Expected result
Step by step chi squared test
- Formulate a Null Hypothesis 2. Select the appropriate statistical test3. Carry out the calculation 4. Determine the degrees of freedom (n-1)5. Compare your calculated value to the critical value calculated at 0.056. Compare the calculated value with the critical value: 1. Higher than the critical value = difference is not due to chance = reject the null hypothesis2. Lower than the critical value = difference is likely due to chance = accept the null hypothesis
Statistical Analysis Steps
- Formulate a Null Hypothesis 2. Select the appropriate statistical test3. Carry out the calculation 4. Determine the degrees of freedom5. Compare your calculated value to the critical value calculated at 0.056. Compare the calculated value with the critical value: a) Higher than the critical value = difference is not due to chance = reject the null hypothesis b) Lower than the critical value = difference is likely due to chance = accept the null hypothesis
What is the HardyWeinberg Principle
The Hardy-Weinberg principle is a mathematical equation used to calculate the frequencies of the alleles of a gene in a population.Classed as a statistical analysis- Established the frequency of the dominant and recessive alleles- Established the frequency of carriers (heterozygotes) in a population
What principle is hardy-weinberg based on?
The proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next
What conditions is the hardy weinberg princple based on? Why are these important?
- No new mutations arise, so no introduction of new alleles- The population is isolated, so no movement which encourages interbreeding which would reduce genetic differences between populations- There is no selection bias, natural selection = advantageous alleles favoured- Population studied is large, prevents the effects of random events affecting allele frequencies or changes due to chance- Mating is random, prevents the selection of particular alleles – selection breeding would alter allele frequencies
Explain each part of the hardyweinberg principle
p = dominant alleleq = recessive allelep2 + 2pq + q2 = 1p2 is frequency of individuals that are homozygous dominant (AA)2pq is frequency of individuals that are heterozygous (Aa or aA)q2 is the frequency of individuals that are homozygous recessive (aa)1 = all the alleles present must add up to 1 or 100%
Define Gene
A segment of a nucleic acid that carries the code for a particular polypeptide or fRNA
Define locus
The location of a specific gene on a chromosome
Define amino acid
Monomers which make up proteins, coded for by 3 nucleotides
Define triplet
3 bases code for 1 amino acid
Define genetic code
The sequence of bases on mRNA which codes for amino acids
Define degenerate code
Base combinations that lead to the same amino acid
Define non-overlapping
Each of the amino acids that are coded for are distinct from the bases of adjacent amino acid codes
Define universal
The same in all living organisms and cells
Define exons
A part of DNA which codes
Define introns
A part of DNA which doesn’t code
Define chromosomes
Structures found inside the nucleus which hold genetic information
Define chromatid
One of the two strands of a chromosome, held together by the centromere, after DNA replication, before division
Define histones
Proteins found in the nucleus of eukaryotes which DNA coils around
Define allele
A version of a gene
What are the rules for calculating inheritance?
- Choose a letter to represent the trait you are investigating (B for blue eyes)- Choose letters that are different lower case and capitals (Gg not Ww)- Capital = dominant, lower case = recessive- Label parents and their phenotypes (parent 1 = brown eyes)- Label gametes the parents produce and circle them- Draw a Punnett square- Label the gender of each parent- Always write the dominant allele first- Work out the cross- State the phenotypes- Calculate the ration
What is a monohybrid cross?
a cross in which the alleles of only one gene are involved- Inheritance of a single gene- Used to determine the dominance relationship between two alleles- The cross begins with the parental (P1 or P) generation
What is always the expected ration when heterozygotes are crossed?
03:01
In diploid organisms, characteristics are determined by alleles that occur in ____
pairs
Only one of each pair of alleles can be present in a single _____ in diploid organisms
gamete
What do dihybrid crosses do?
- Consider the inheritance of two characteristics at the same time- Shows how two characteristics, determined by 2 different genes, located on different chromosomes, are inherited
How did Mendel use Peas to investigate bihybrid inheritance?
Pea plants varied in two ways:1. Seed colour2. Seed shapeYellow and round = dominantGreen and wrinkled = recessiveSo there were 4 possible combinations:1. R and Y2. R and G3. W and Y4. W and GOr by genotype1. RY2. Ry3. rY4. ry1 and 4 are homozygous, dominant and recessive respectivelyHe bread these two to produce a plant with 100% chance of RrYy (heterozygous for both characteristics, so all round and yellow), Mendel then crossed these two overThat means there was a ratio of RY:Ry:rY:ry of 9:3:3:1
what is Mendel’s Law of Independent Assortment –
Each member of a pair of allels may combaine randomlu with either of another pair
The gene for colour and gene for shape are on ________ chromosomes
different
WHat is codominance?
When both alleles are expressed in the phenotype- Neither allele is dominant nor recessive, they are both equally dominant
Explain how snapdragons are an example of codominant alleles
- One allele codes for an enzyme that catalyzes the synthesis of a red pigment in flowers- The other allele code for an altered version of the enzyme that doesn’t produce the red pigment – flowers remain white1. Homozygous for allele 1 – pigment produced – red flowers2. Homozygous for allele 2 – no enzyme activity so no pigment – white flowers3. Heterozygous – single functioning allele so only produces enough pigment to make the flowers pink
Rules of codominant writing
We can’t use upper and lower case letters as this implies dominant/recessive- We use different letters insteado R = redo W = white- Letters should be superscript to the letter that represents the gene in question:o C = colour
What are mutiple alleles with example
- Multiple alleles have more than two alternate forms of a single gene, located at the same loci of homologous chromosomes- Polygenetic traits (eye colour) are determined by several genes at different gene loci- Multiple alleles are involved in the determination of a single train by codominance- E.g.o Human blood groupso 3 alleles associated with he immunoglobulin gene (gene I)o Gene I dictates the presence of a certain antigen on the cell surface of red blood cells
The allele is I^A, what is the antigen produced, possible genotypes, blood group, and diagram?
A IAIA and IAIOAcheck notes
The allele is I^B, what is the antigen produced, possible genotypes, blood group, and diagram?
B IBIB, IBIO BCheck notes
The allele is I^O, what is the antigen produced, possible genotypes, blood group, and diagram?
Neither IOIO OCheck notes
The allele is I^A I^B, what is the antigen produced, possible genotypes, blood group, and diagram?
A and BIAIBABCheck notes
- For red blood cells, there are 3 alleles, but only 2 can be present in an individual, why?
- This is because there are only two homologous chromosomes, so only 2 gene loci
- IA and IB are codominant- IO is recessive to both- This gives rise to ___ possible blood groups
4
Which are the blood groups, and which is the most common?
A, B, AB, OO is the most common – 48%
If you have which antigen, your blood is positive?
Rhesus (Rh) D antigen
Receiving blood from the wrong group can be life threatening, why? How can this be counteracted?
- The antibodies will attack the cells- BUT- As group O red blood cells have no antigens, it can safely be given to any other group
Explain the antibodies associated with each red blood cell type
- A antigens on the red blood cells with anti-B antibodies in the plasma- B antigens with anti-A bodies in the plasma- O antigens but both anti-A and anti-B antibodies in the plasma- Both A and B antigens so no antibodies
What is the difference between chromosomes and chromatids?
• Before replication, one chromosome is composed of one DNA molecule• Following replication, each chromosome is composed of two identical DNA molecules (i.e. DNA replication increases the amount of DNA but does not increase the number of chromosomes)• The two identical copies – each forming one half of the replicated chromosome – are called chromatids• During the later stages of cell division, these chromatids separate longitudinally to become individual chromosomes
Desxribe the human Karyotype
- 46 chromosomes- 23 pairs- 22 of the 23pairs have homoglous partners which are identical- 23rd pair are sex chromosomes (X and Y)
Which of XX, and XY is male and femal?
XY – maleXX – female
What is the ratio of offspring for reproduction of males and females? (in terms of x and y chromosomes)
Offspring – 2x XX, 2x XYPhenotype – 2x male, 2x femaleRatio – 1:1
- Genes found on either X or Y are _______
sex-linked
Which is longer, x or y?
X
Some genes found on x do not have a _______ on Y?
Homologous equivalent
- Recessive characteristics found on those people will be more frequent in men, why?
This is because they have no homologous series on Y that could carry the dominant allele
What is hemophillia?
- X-linked genetic disorder (defective gene on X)- Blood does not clot correctly- Leads to excess bleeding following a cut or persistent internal bleeding- Fatal if not treatedFatalities have selectively reduced the gene in the population to approximately 1 in 20,000
Why is hemophillia rare in females?
- Have two x chromosomes- Hemophiliac females used to die at the onset of puberty
Is hemophilia recessive or dominant?
Recessive
What does the recessive hemophilia allele code for?
codes for an alternative sequence which results in a faulty protein
What do pedigree charts allow us to do?
- Allow us to trace inheritance of sex-linked characteristics
What are the main methods of identification?
Using a second, separate gene on the plasmid that is easily identifiable – 1. Resistant to an antibiotic2. Make a fluorescent protein3. Produce an enzyme whose action can be identified
Explain autosomal linkages
When 2 or more genes are carried on the same autosome = autosomal linked• All linked genes stay together during meiosis• This means they will pass into the gamete together• Meaning they will pass into the offspring together• They do not follow Mendel’s Law of Independent Assortment as each allele is not free to mix with either allele from another pair
Predict the genotypes of offspring of GgNn and GgNn if GN and gn are autosomal linked
GGNNGgNnGgNnggnn
Which genetic cross has 3:1 ratio?
monohybrid two heterozygous
Which genetic cross has 9:3:3:1 ratio?
dihybrid two heterozygous
Which genetic cross has 1:1:1:1 ratio?
blood group (heterozygous A and B) or sex linkage (carrier female and normal male)
Which genetic cross has 1:2:1 ratio?
Codominant heterozygous
What does epi mean?
upon/over
What is epistasis?
- Epistasis describes a condition whereby one gene controls the expression of another gene- Or- When an allele of one gene affects or masks the expression of another in the phenotype
Ratio for crossing over AaBb and AaBb where a dominant B means A works and a recessive bb means A doesnt work
09:04:03
Explaination of epistemic genes
- The expression of gene B affects the expression of gene A- bb = no melanin/white- If there is no melanin then gene A cannot be expressed- This means AA, Aa, and aa, will all produce white fur if bb is present- If B is present in the genotype, melanin is produced- If A and B are produced then melanin and banded are produced, so agouti- If B is found with aa, then melanin I produced but bands are not, black
How does epistemic genes affect biochemical oathways
- Some genes act in sequence by coding for specific enzymes in a pathway- Dominant alleles code for the functional form of the enzyme- Recessive homozygotes would disrupt the pathway- The presence of one non-functional gene will affect the other as failure to express one gene will result in no pigment being made
