Genetics, Populations, Evolutions & Ecosystems Flashcards
What is a genotype?
The genetic constitution of an organism
What is the definition of a phenotype?
The expression of the genotype and its interaction with the environment (Set of characteristics an organism has depends on genotype + environment)
What is an allele?
Alternative forms of the same gene
What is a gene?
A length of DNA which codes for a particular protein occupying a specific locus on a chromosome
What is a locus?
The position of a gene on a chromosome
What is Multiple alleles?
This is when one gene has more than 2 possible alleles
In a diploid organism, how many alleles does each genotype have?
2, one from the female and one from the male at fertilisation
What does it mean for an allele to be dominant?
It will be expressed in the phenotype, 1 present for expression – represented as an uppercase letter
What does it mean for an allele to be recessive?
It won’t be expressed in the phenotype, so 2 copies present for expression – lowercase letter
What are Co dominant alleles?
This is when alleles are equally dominant and equally expressed in the phenotype
What are genetic diagrams used for?
To predict the genotypes and phenotypes off the offspring produced if the parents are bred
When are monohybrid crosses used?
When considering the inheritance of one characteristic
What are test crosses used for?
To determine an unknown genotype
How would you conduct the test to find an unknown genotype and explain the results?
Cross the unknown with a homozygous recessive individual
- If all offspring have dominant phenotype, the unknown genotype is homozygous dominant
- If half of the offspring have the recessive phenotype, the unknown genotype is heterozygous
What is a dihybrid cross?
This is the inheritance of 2 characteristics
What is Autosomal Linkage?
This is the inheritance of genes that are located at different loci on the same chromosome. The genes are on autosomes (not sex chromosomes).
What process can occur during autosomal linkage?
As the genes are on the same chromosome, crossing over can occur when the homologous chromosomes are in a bivalent
The closer the 2 genes are to each other…(autosomal linkage)
The less likely crossing over is to occur
What is the chiasma?
The point where crossing over occurs
What are the additional phenotypes that appear due to crossing over called?
Recombinants
What is Sex Linkage
This refers to genes found on the sex chromosomes
What 2 chromosomes do females have?
XX
What 2 chromosomes do males have?
XY
Explain the difference between X and Y?
Y is considered genetically empty and usually the genes are on the X chromosome in humans
Why are males more likely to show recessive phenotypes?
This is because males only have 1 X chromosome, so they only require one copy of the recessive allele for expression. Females have 2 X chromosomes, so must inherit 2 recessive alleles to be affected and is less likely to happen
What is a carrier?
A person carrying an allele which is not expressed in the phenotype but can be passed on to the offspring
What is Epistasis?
This is when one gene affects or alters the expression of another
What is recessive Epistasis?
2 copies required to mask expression of hypostatic gene
What is Dominant Epitasis?
Expression of dominant allele (1 or 2) of epistatic gene masks expression of hypostatic gene
What does the term gene pool mean?
The total number of genes of every individual in an interbreeding population
What does allele frequency mean?
How often an allele occurs within a population
What is the Hardy Weinberg Principle?
Mathematical model which predicts allele frequencies will not change from gen to gen meaning there will be no genetic change in the population over time
What assumptions are the hardy Weinberg principle based of?
- Mating is random
- No natural selection takes place
- No mutations
- No gene flow / genetic drift
- Population is large
When is the equation used?
When one gene with 2 alleles, one dominant and one recessive is being considered
What is the formula of the H.W.P
p2 + 2pq + q2 = 1 p = freq of dominant allele q = freq of recessive allele 2pq = freq of heterozygote p2 = freq of homozygous dominant q2 = freq of homozygous recessive
REMEMBER = p + q = 1
What is evolution?
This is when the frequency of alleles changes in a population from 1 gen to the next
What are the 2 factors that affect / cause allele frequency to change?
- Natural Selection
- Genetic Drift
What is Natural Selection?
‘Survival of the fittest’, individuals with alleles that give them a selective advantage reproduce more than others in the population, increasing the frequency of the favourable allele.
What is genetic drift?
This is the effect of a few individuals that, by chance, fail to reproduce or have more offspring than others…thus changing the allele frequency in the next generation. This has a more pronounced effect in small populations
What are the 3 types of selection?
- Directional
- Stabilising
- Disruptive
What is directional selection?
Occurs in a changing environment
- One extreme in a range of the phenotype is at a selective advantage
- Over time this feature becomes more common and the unfavourable characteristic becomes rare
- Mode changes/standard deviation reduces
- Antibiotic resistance in bacteria, peppered moth
What is stabilising selection?
- Occurs in an unchanging environment
- Selection is against individuals at both extremes of the characteristic
- Mode stays the same / standard deviation reduces
- Birth weight in humans
What is disruptive selection?
- Occurs when the individuals with both extremes of the phenotype are selected for, those in the middle of the range are selected against
- Banded snail, where pale and dark are more likely to survive than those with an intermediate colour
What is speciation?
This is the development of new species from pre-existing ones by natural selection
What are the 2 types of Selection?
- Allopatric
- Sympatric
Explain the process of speciation?
- Reproductive isolation of part of the population from the rest of it
- So part of the population is unable to interbreed with the rest of the population…no gene flow between the isolated groups
- Over time the gene pools of the two groups will accumulate differences, as natural selection (and genetic drift) operates on the 2 separate parts of the population.
- Eventually a point may be reached when the 2 parts of the population cannot interbreed to produce fertile offspring… a new species has formed from a pre-existing one.
Explain the process of Natural Selection?
1) Genetic Variation in the population due to random mutations which produce new alleles of a gene
2) Selective pressure – due to competition, predation and disease
3) Differential survival + reproduction – individuals best suited = more likely to survive = reproduce and pass on favourable alleles to next generation
4) Evolutionary change – the gene pool of the population changes from one gen to the enxt; frequency will increase over time of favourable alleles
