[Y2] Genetics, Population, Evolution, and Ecosystems Flashcards
What is a genotype?
The genetic constitution of an organism.
It describes all the alleles that an organism has.
What is a phenotype
The observable or biochemical characteristics of an organism.
What is a gene?
A length of DNA, that is a sequence of nucleotide bases that normally code for a particular polypeptide.
What is a locus?
The position of a gene on a particular DNA molecule.
What is an allele?
One of the different forms of a gene.
How can an organism have two different alleles?
(Heterozygous)
If the organisms is diploid, and therefore has homologous chromosomes, it would have two loci that each carry one allele.
What is codominance?
When two alleles both contribute to the phenotype.
What is the case when an organism is said to have ‘multiple alleles’ for a character?
(give an example of this)
When its genes has more than two allelic forms.
e.g. blood group
What is the difference between a mutation and a modification?
Mutation is a change to the genotype due to a change in DNA whereas a modification is any change to the phenotype.
Mutations may be inherited by future genrations whilst modifiactions are not usually inherited.
What is the first filial?
The F1 generation with pure-breed parents.
What is the law of segregation?
In diploid organisms, characteristics are determined by alleles that occur in pairs. Only one of each pair of allels can present in a single gamete.
What is the ratio of phenotypes during an F2 generation cross?
Dominant phenotype : Recessive phenotype
3: 1
Why dont we see exact ratios when carrying out genetic crosses?
We see discrepencies due to statistical errors.
This is because each cross is independent of each other.
(when Mendel did his crosses the closest to the 3:1 ration were the crosses with the largest data set)
What is dihybrid inheritance?
When two characteristics conrtilled by two different genes located on different chromosomes are inherited.
What characteristics did Mendel look into?
- Seed shape.
- Seed colour.
Why can you get four different gametes from a dihybrid cross?
Because the gene for one characteristics and the gene for the other are on seperate chromosomes.
And they can combine with anyone of of eachother as chromosomes arrange themselves at random on the equator during meiosis.
Fertilisation is also random so any one gamete can be crossed with another.
Describe the generation’s theortetical phenotypes from a two pure breed parent genration to an F2 generation.
ROUND/wrinkled
YELLOW/green
Pure breed :
100% round yellow, round AND 100% wrinkeld green.
F1:
100% round yellow (dominant features) (but this wont be all be homozygous)
F2: 9 : 3 : 3 : 1 9 = round / yellow 3 = round / green 3 = wrinkled / yellow 1 = wrinkled / green
What is Mendel’s law of independant assortment?
Each member of a pair of alleles may combine randomly with either of another pair.
What is codominance?
When both alleles are expressed in the phenotype.
What is ‘multiple alleles’?
Where there are more than two alleles, of which only two may be present at the loci of an idividual’s homologous chromosome.
What plant displays codominance?
Describe how codominace works in their petel pigementation?
Snapdragon plants.
If homozygous for first allele, both alleles code for the enzyme, and hence the pigment, production. These plants are red.
If homozygous for the other allele, no enzyme and hence no pigment is produced. These plants are white.
If heterozygous, their single allele for the functional enzyme produce just sufficient red pigment to produce pink flowers.
How would you represent codminance when drawing a punnet square?
- Different letter for characteristics that are codominant (e.g R for red, W for white).
- These letters should be superscript over a common letter (like C for colour).
So Cᴿ for red and Cᵂ for white.
(pink would be CᴿCᵂ).
What would happen in a cross between individuals of blood group O and blood group AB?
Rather than producing individuals of either of the parental blood groups, you get individials of the other two groups (A and B).
What would happen in a cross between an individual of blood group A (heterozygous) and blood group B (heterogzygous)?
You have indivuals of all blood groups. 25% A (Iᴬ i) 25% B (Iᴮ i) 25% AB (Iᴬ Iᴮ) 25% O (i i)
In humans the sex-chromosomes are X and Y.
What does this mean?
- As females have two X chromosomes, all the gametes are the same in that they contain a single X chromosome.
- As males have once X chromosome and one Y, the produce two different types of gametes - half have an X and half a Y.
Why may some ressesive characteristics appear more frequently in (human) males?
- The X chromome is longer thant the Y.
- For most of the X chromosome there is no equivilant homologous portion.
- Characteristics that are ressesive on the non-homologous portion of the X chromosome (in males as only males have a non-homologous portion) will apear more frequently in males.
- This is because there is no homolous portion on the Y, that might have had the dominant allele had it been X.
What chart can be used to trace the inheritane of a sex linked gene?
A pedigree chart.
What is the standart notation of a pedegee chart?
Males = square.
Females = circle.
Shading within either shape = the presence of a character.
What does linked mean in the context of genes?
Two genes that occur on the same chromosome.
What is an autosome?
Any chromosome that is not a sex chromosome.
What is autosomal linkage?
The situaltion where two or more genes are carried on the same autosome (and so are inherited together).
How many possible gametes are there (providing no crossing over) are there for two different characteristics (in heterozygous parents) that are autosomally linked?
2
would be four if it wasnt autosomally linked
When does epistasis arise?
When the allele of one gene affects or masks the expression of another in the pheotype.
What is a null hypothesis?
- A hypothesis used to examine the reults of scientific investigations.
- Is based on the assumption that there will be no statistically significant difference between sets of observations.
- Any difference is due to chance alone.
What criteria must be met in order to carry out a chi-squared test?
- The sample size must be relatively large (over 20).
- The data must fall into discrete categories.
- Only raw counts and not percentages, rates etc can be used.
- It is used to compare experimental results with theoretical ones, like genetic crosses with expected Mendelian ratios.
What is the formula for the Chi-squared statistical test?
Chi squared = sum of ([obverved numbers - expected number]²) / expected numbers
χ² = Σ [(O-E)²/E]
What is a degree of freedom within a chi-squared test?
The number of catageoires minus 1
What are the possible conclusion of a chi-squared test, and what must be met (if p = 0.05)?
If the probibility of the deviation is due is 0.05 or more, the deviation is said to be not significant, and you would accept the null hypthesis.
If the deviation is less than 0.05, the deviation is said to be significant, so some factor other than chance is affecting the reults and the null hyothesis must be rejected.
What is a population?
A group or organisms of the same specied that occupies a particular space at a particular time and that can potentially interbreed.
What is a gene pool?
All the alleles of all the genes of all the individuals in a population at a given time.
What is the allelic frequnecy?
The number of times an allele occurs within the gene pool.
What is the hardy-weinberg principle?
An equation that calculates the frequency of the alleles of a particular gene in a population.
What conditions must be met to be able to use the hardy-weinberg principle?
- No mutation arise
- The population is isolated (there is no flow of alleles into or out of the population.
- There is no selection (all alleles are equally likely to be passed to the next generation).
- The population is large.
- Mating within the population is random.
What are the hardy-weinberg equations?
p = probibility of allele 'A' q = probiblity of allele 'a'
So,
- p + q = 1
p² = probiblity of homozygous dominant. 2pq = probibility of heterozygous dominant. q² = probibility of homozygous recessive.
So,
- p² + 2pq + q² = 1
Why might genetic differences within a (sexually reproducing) population arise?
- Mutations: These may or may not be passed on to the next generation but is still the main source of variation.
- Meiosis: This produces new combinations of alleles before they are passed into the gametes, and so they are all different.
- Random fertilisation of gametes: This produces new allelic combinations and the offspring are therefore different from parents. Which gametes fuse are also random, adding to the variety.
What type of variation do environmental factors not influence as much?
Variation that is largely the result of genetic factors that fit organisms into few distinct forms which no intermediate types.
What are some environmental influences?
- Climate conditions (e.g. temp, rainfall, and sunlight)
- Soil conditions
- pH
- food availability.
What causes variation?
The combined effects of genetic differences and environmental influences.
Why is it difficult to draw conclusions about the causes of variation in any particular case?
As it is hard to distinguish between the effects of the many genetic and environmental influences that combine to produce differenced between individuals.
What is selection pressure?
The environmental factors that limit the population of a species.
Give examples of selection pressures?
- Predation
- Disease
- Competition.
What is a gene pool?
The total number of all the alleles of all the genes of all the individuals within a particular population at a given time.
