Genetics Flashcards
Define genotype
The genetic makeup - the alleles an organism has
Define phenotype
The observable characteristics
Define locus
Where on the chromosome the alleles are
Define monogenic inheritance
The inheritance of characteristic controlled by a single gene
Define co-dominant alleles
Where neither alleles are dominant or recessive, heterozygous forms a new phenotype
E.g. snapdragons
CRed +CWhite = CPink
Define dihybrid inheritance
How do you work out the offspring’s genotype
The inheritance of two characteristics controlled by different genes
Two monohybrid crosses in one
(You first workout what alleles the gametes of each parent would have) - then make a large punnet square
Define sex linkage
Any gene that is carried on the X or Y chromosome
In which sex are recessive conditions more likely to be expressed
Males as there is no dominant allele on the X
What are the two sex linked disorders
Haemophilia
Colour blindness
What are autosome chromosomes
Any chromosome that is not a sex chromosome
What does it mean when chromosomes are linked
Two genes are on the same chromosome
- no effect on one another
- just in the same location
Why does linkage of autosomal genes decrease the possible number of allele combinations
Because the genes are linked so independently assorted into the same gamete - assuming they weren’t separated by crossing over
Define epistasis
When one gene masks or suppresses another gene
Whats a classic example of epistasis
Widows peak - v shaped hair growth.
Describe Recessive epistatic alleles
When one gene is epistatic to another as it can mask the expression of gene 2, specifically if gene 1 is recessive
If the plant doesn’t have the dominant gene, it doesn’t matter if it has the dominant allele for gene 2 as it is not expressed
What happens when the epistatic allele is dominant
Having one copy of it will mask the expression of the other gene
Define gene pool
The sum total of all the genes in a population at any given time
How do you calculate allele frequency
P+q=1
What is the hardy-Weinberg principle
In a stable population with np disturbing factors, the allele frequencies will remain constant from one generation to the next and there will be no evolution
What is the hardy-Weinberg principle expressed as
p^2+ 2pq + q^2 =1
Where p^2= frequency of homozygous dominant
2pq = frequency of heterozygous genotype
q^2 = frequency of homozygous recessive
What factors effect evolution
- mutation
- sexual selection
- gene flow - movement of alleles between populations
- genetic drift - change in allele frequency due to the random nature of mutation
- natural selection
What are the two types of limiting factors for size of a population
- density-dependent factors - dependent on population size and include competition, predation, parasitism and communicable diseases
- density independent factors - affect populations of all sizes in the same way - climate change, natural disasters, seasonal change, and human activities (e.g. deforestation)
What is the founder effect
Extreme example of genetics drift
- small populations can arise due to the establishment of new colonies by a few isolated individuals
What is directional selection
Occurs when there is a change in the environment
Normal (most common) phenotype is no longer the most advantageous
Less common organisms are positively selected
What is disruptive selection
The extremes are selected for and the norm is selected against
What is speciation
The formation of new species through evolution
What are the events leading to speciation
Members of a population become isolated and no longer interbreed with rest of population
Alleles within the groups continue to undergo random mutations
Accumulation of mutations and changes in allele frequencies over many generations eventually lead too large changes in phenotype
What is allopatric speciation
What happens when some members of a population are separated from the rest of the group by a physical barrier - geographical isolation
What is sympathetic speciation
Occurs within populations that share the same habitat
When members of two different species interbreed and form fertile offspring
What are prezygotic reproductive barriers
Barriers that prevent fertilisation and formation of a zygote
What are postzygotic reproductive barriers
Often produced as a result of hybridisation, reduce the viability or reproductive potential of offspring
What are the problems caused by inbreeding
Decrease genetic biodiversity
Limits populations ability to adapt to changes in environment
Likely to have recessive alleles - cause of many genetic disorders e.g. cystic fibrosis
What is chlorosis
A genetic condition in plants that cause the leaves to look yellow/ pale
Because cells are not producing a sufficient amount of chlorophyll
What are the causes of chlorosis
Lack of light
Mineral deficiencies
Virus infection
Define codominance
When two different alleles occur for a gene - both are equally dominant, both alleles are expressed in the phenotype
E.g. colour of snapdragon flowers
One red allele + one white allele = pink phenotype
What is stabilising selection
Occurs when environmental conditions stay the same. Individuals closest to the mean are favoured, any new characteristics are selected against.
Result in low diversity
What is meant by a genetic bottleneck
Where a catastrophic event dramatically reduces the size of a population
Thereby decreasing the variety of alleles in the gene pool and causing large changes in allele frequencies
Explain how the automated sequencing machine orders DNA fragments from the PCR reaction
Electrophoresis
Negatively charged DNA moves towards the positive electrode (anode)
Smaller fragments move faster
Outline the role of the polymerase chain reaction (PCR) in sequencing a genome
To amplify/ make copies of DNA
With a range of different lengths
Outline the role of electrophoresis in sequencing a genome
To put DNA pieces in size order too read base sequence/ order of bases
Outline the role of expladigestion of DNA by restriction enzymes in sequencing a genome
To cut genome into smaller fragments
Suggest why a genome has to be fragmented before sequencing
To big/ very large
Increase accuracy
Divide job over time - split between labs
