Chapter 7- Genetics, populations, evolution and ecosystems Flashcards
Define genotype
A genotype is all of the alleles that an organism carries on its chromosomes
Define phenotype
A phenotype is observable characteristics on an organism which result as a result of the genotype as well as environmental factors
Define homozygous
A pair of homologous chromosomes carrying the same alleles for a single gene, e.g ee and EE
Define heterozygous
A pair of homologous chromosomes carrying 2 different alleles for a single gene, e.g Ee
Define recessive allele
An allele that is only expressed if no dominant allele is present
Define dominant allele
An allele that will always be expressed in the phenotype
Define co-dominant
When both alleles are equally dominant and expressed in the phenotype
Define sex-linkage
A gene whose locus is on the X chromosme
Define autosomal linkage
This is when one gene modifies or masks the expression of a different gene at a different locus
Define monohybrid
Monohybrid is the genetic inheritance cross of a charactersitic determined by one gene
Define dihybrid
The genetic inheritance cross for characteristics determined by 2 genes
Define gene pool
A gene pool is all the alleles of all the genes within a population at one time
What is a population
A population is all the individuals of one species in one area at one time
What is an allele frequency
It is the proportion of an allele within the gene pool
Is the Hardy wengberg principle of inheritance accurate
The mathematic model makes assumption which impedes the accuracy
It assumes that there will be no change in the allele frequency between generations, so it’s not perfectly accurate
The assumptions are:
- No migration to introduce or remove alleles from the population
-No mutations to create new alleles
- No selection favouring particular alleles
-Mating is random (no interbreeding)
- The population is large
There will not be a natural population that meets these assumptions, but the model is still useful to gain estimates of allele frequency
What are three types of selection
- Stabilising
-Directional
-Disruptive
What is the chi-squared test
The chi-squared test is a statistical test that determines whether or not there is a significant difference between the observed and expected results
- When a difference is not significant, any differences that are observed can be said to be due to chance alone
- When a difference is significant, this suggests the presence of a factor that is being accounted for
How can you calculate chi-squared
- Obtain the expected and observed
- Calculate the difference between each sets of results
- Square each difference
-It is irrelevant whether the difference is positive or negative - Divide each squared difference by the expected value
- Add the resulting values to get a sum of these answers to obtain the chi-squared value.
How can you analyse the chi-squared value
To work out what the chi-squared value means, we need to compare the chi-squared value to a critical value
- The critical value is read from a table of critical values and depends on the probability level used and the degrees of freedom
(Biologists generally use a probability level of 0.05% or 5%)
- This means that there is only a 5% probability that the difference between expected and observed is due to chance
What if the chi-squared value is greater than or equal to the critical value
If the chi-squared value is greater than or equal to the critical value, then there is a significant difference between observed and expected, therefore:
- A factor other than chance is causing the difference
- The null hypothesis can be rejected
What if the chi-squared value is lower the critical value
If the chi-squared value is smaller than the critical value, the there is no significant difference between observed and expected results
- Therefore:
- Any differences are due to chance
- The null hypothesis is accepted
Define species
A group of organisms that can breed together to produce fertile offspring
How many chromosomes does a human have
46
How many pairs of chromosomes does a human have
23
