Genotype And Phenotype/ Linkage Flashcards
What are the 3 dominance relationships between genotypes and phenotypes
Complete- where 1 allele clearly dominant and so offspring is replica of that allele/phenotype
Incomplete - where F1 offsprings don’t resemble either of parents (the dominance of the alleles not enough
Codominant - where both alleles are dominant to eachother and expressed in F1 phenotype
How is blood group A B O an example of codominance
There are 3 alleles for blood group
IO is recessive to IA and IB
IA and IB if present together are dominant and the blood group is AB
What is pleiotrophy
Where some genes or alleles can affect many characteristics at once
Eg in Manx cats the ML allele can disrupt spinal development (no tail) and another characteristic is its lethal, causing death if present twice
An epistatic gene is able to modify or mask phenotype as another genes expression is masked
What is the gene masked called
Hypostatic gene
What is penetrance as a principle
Sometimes a genotype doesn’t always show the same phenotype
Penetrance is how many members with a particular genotype (alleles) show the expected phenotype
Give an example of penetrance of the brca 1 gene
Brca is present in both men and women causing cancer, however the mutation is more likely to cause phenotype of cancer in men than women
What is it called when some disorders show different signs and symptoms in different people?
Variable expressivity
How is polydactyly an example of both incomplete penetrance and expressive variability
Incomplete penetrance- children with phenotype more likely to get it than parents with same genotype
Expressive variability - because it can affect either toes or hands
What else can affect penetrance and expressivity
Other genes or the environment
How are thermosensitve alleles an example of how environment affects expression
The alleles might not work depending on temperature
What is complementation analysis
Screening through mutants with same phenotype to see how many genes involved
What is complementation in a complementation analysis
When there are 2 genes involved in a phenotype/disorder and the offspring inherits them they don’t express the phenotype(not a mutant) - complementary genes
What is a complementation group
A set of mutations on the same chromosomal locus (same gene)
This does not cause complementation when crossed (still mutant)
What alleles need to be present for complementation analysis to work
A recessive allele
How would intragenic complementation affect complementation analysis
It wouldn’t work as complementation would occur even if mutations in 1 gene present
Genes close together on chromosomes, inherited together are called linked (linkage)
How are genes seperated creating non parental genotypes?
Recombination / crossing over
Independent assortment of genes on different chromosomes
How would you follow linkage patterns? 2 ways
You could follow dna via a marker
Or do genetic crosses which would show recombinant in phenotypes (non parents genotypes)
Which generation and genotypes would you use in a test cross to see linkage/ recombination
You would use the F2 generation
1 homozygous recessive for both genes - wwvv - purple eyes and vestigial wings
1 heterozygous for both genes - WwVv - normal and normal
What would the ratio be if genes were unlinked in a cross of both recessive homozygous and heterozygous for both genes
1:1:1:1 ratio
Which combinations are present more if genes are linked after a cross
The parental combinations
So either both normal eyes and wings
Or both mutant characteristic purple eyes and vestigial wings
Why is there non parental genotypes found in crosses of genes are linked
Eg purple eyes but normal wings
There has been recombination happened
So some offspring have purple eyes but normal wings vice versa
How would you calculate the genetic distance between genes such as purple eyes and vestigial wings
Recombination frequency
How do you calculate recombination frequency
Number of recombinant offspring / total offsprings
X 100
= recombination frequency %
What unit is used in a map unit of the genetic distance between genes
cM
Centimorgans are how far on chromosomes genes are
(Depending on recombination frequency)
Why are genetic maps using genetic crosses not colinear to physical maps
Recombination has hot spots - it is not random
This would drive some genes further apart and some genes would still be close if recombination hasn’t occurred
Why is understanding recombination frequency important
Can work out what stimulates recombinations in genes / why areas are prone
Understanding linkage is important to track mutations
