Phenotypic ratios Flashcards
Why are the ratios not fully correct?
Actual numbers vary because process is random.
Larger sample number = closer to expected ratio
What is autosomal linkage?
2 genes on same non-sex chromosome.
Inherited as one unit
Closer two genes are, less likely for crossing over to occur.
What does recombinant offspring refer to?
Different combinations of alleles than either parent.
Closer alleles are on the gene = fewer recombinant offspring produced.
What does recombinant frequency refer to?
Measure of amount of crossing over that happened in meiosis.
number of recombinant offspring/total number of offspring
What can the recombination frequency suggest?
50% = no linkage + genes on separate chromosomes
> 50% = gene linkage + random process of independent assortment is hindered
Can be used to map genes on a chromosome
What is the chi-squared test?
Measures size of difference between results you actually get and those you expect to get.
Helps determine whether differences in expected + observed results are significant or not
Compare size of differences
+ number of observations
How to calculate chi-squared?
χ2 = ∑(O – E)2/E
χ2= the test statistic
∑= the sum of
0 = observed frequencies
E = expected frequencies
Degrees of freedom = n-1
What does a large chi-squared value suggest?
There is a statistically significant difference between the observed and expected results
Probability differences are due to chance = low.
Other reason for results
What is epistasis?
Interaction of genes at different loci.
Links with continuous variation
What is a form of epistasis?
Gene regulation: regulatory genes control activity of structural genes (lac operon)
What does hypostatic refer to?
A gene that is affected by another gene
What does epistatic refer to?
A gene that affects the expression of another gene
How are genes expressed in a biochemical pathway?
Genes produce enzymes that work in a sequence to create a pigment.
If any gene is not expressed, its corresponding enzyme won’t be made, disrupting the process and preventing pigment production.
If any gene is missing, the necessary intermediate molecules won’t form, stopping the next step in the pathway.
This means the effects of these genes won’t be visible.
What is dominant epistasis?
Occurs when a dominant allele results in a gene having an affect on another.
Genes in a sequence would be effectively ‘masked’
What is recessive epistasis?
When recessive allele of one gene hides the expression of all alleles of another gene.
