Genetics, Genome Structure and Organisation, and Gene Function Flashcards
How many characters are changing in a monohybrid cross?
One
How many characters are changing in a dihybrid cross?
Two
What does a monohybrid cross demonstrate?
Allelic segregation
What does a dihybrid cross demonstrate?
Independent assortment of alleles
What is the probability relationship between each assortment in independent assortment?
Each assortment is equally probable
What is the phenotype ratio in partial dominance?
1:2:1
What is partial dominance?
When the phenotype is an intermediate between the two alleles
What are the two alleles labelled when there is no clear dominance relationship?
R^1 and R^2
Define co-dominance
When two alleles produce distinct and detectable gene products and distinct and detectable effects on phenotype
How is co-dominance different to partial dominance?
In partial dominance, a mixture of the alleles in the genotype are seen in the phenotype but in co-dominance both alleles in the genotype are seen in the phenotype.
How do multiple alleles occur?
A mutation occurs producing a new allele so one gene exhibits multiple alleles
What is a null mutation?
A mutation that abolishes function
What are recessive lethal alleles?
Null mutations in essential genes that can be tolerated in the heterozygous state but homozygous alleles are embryo lethal
Why are dominant lethal alleles usually lost from the population?
Individuals with dominant lethal alleles die before reproducing
Why might dominant lethal alleles not be lost from the population?
When the phenotype exhibits late onset e.g. Huntington’s
Define epistasis
One gene masks or modifies the expression of another gene
What does gene interaction imply?
More than one protein may be required for the development of a single phenotype
What does the mutation fut1 do?
In relation to blood group: prevents synthesis of complete H substance so A and B antigen production is supressed
Which antibodies do Bombay individuals produce?
Anti-H antigen antibodies
What are Bombay individuals at risk of?
Haemolytic transfusion if they receive blood containing H antigens
What is duplicate recessive epistasis?
When a recessive allele is masking the expression of dominant alleles at two loci
In duplicate recessive epistasis, what would aa do?
Mask any genotype at locus B
In duplicate recessive epistasis, what would bb do?
Mask any genotype at locus A
What is novel phenotype?
A phenotype that is unique in comparison to the parent phenotypes
What are males described as for X-linked genes?
Hemizygous
What is gene drive?
A form of genome editing
What is the aim of forward genetics?
To identify mutations that produce a certain phenotype
Is forward genetics a controlled or random process?
Random; randomly generates mutations hoping that differences are phenotypically observed
What is the aim of reverse genetics?
To identify the phenotype that results from specific mutations
What is the role of gene knock out in reverse genetics?
Confirms that the phenotype is a direct result of the mutation
What are the main 3 advantages of unicellular model organisms?
- Very short reproductive cycles
- Can be grown easily
- Large numbers produced allow rapid identification of rare organisms
Describe the prokaryotic genome
Single, circular chromosome with less junk DNA than eukaryotes making it more efficient
What can add functionality to the prokaryotic genome?
Extra DNA in the form of plasmids
How can reverse genetics be carried out on unicellular organisms?
Using recombinant DNA technology to construct a mutated version of the target gene which can be transformed into E. coli and the phenotype can be analysed
Give 5 advantages of zebrafish as a model organism
- Fast early development
- Many eggs
- Eggs develop outside the mother
- Eggs are transparent
- Can be used for both forward and reverse genetic screens
Give 3 disadvantages of zebrafish as a model organism
- Need to be bred for 2 generations until homozygous offspring are observed
- Requires significant resources
- More licensing needed
Define syntenic
Genes that occur on the same chromosome
What are orthologues?
Homologous genes where a gene diverges after a speciation event but the gene and its main function are conserved
What technique can be used in mice to investigate human gene function and simulate human disease phenotypes?
Gene knockouts (reverse genetics)
Where are embryonic stem cells derived from?
Inner cell mass of the blastocyst
What is the aim of targeted mutagenesis using ESC?
To inactivate genes to investigate their function
