A2 Biology Unit 4 Flashcards - Inheritance and selection

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What is a Genotype?
Genetic make-up of an organism eg. dominant or recessive alleles
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What is a Phenotype?
Observed characteristics of an organism
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Apart from genes what can affect an organism's appearance?
The enviroment - eg; scars
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What is a gene?
A section of DNA that is a sequence of nucleotide bases
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What is an allele?
One of the different forms of genes that code for characteristics
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What are the three geneotypes shown in a pair of chromosomes?
Homozygous dominant, homozygous recessive and heterozygous
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What's it called when 2 allele both contribute to the phenotype?
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Explain how co-dominance can be shown in plant flowers
Either the two colours will be mixed together (eg. red and white to create pink flowers) or both colours will be shown
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What is 'Monohybrid inheritance?'
Inheritance of a single gene
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Give an example of monohybrid inheritance with peas
Peas are either yellow or green however if only green peas are bred with green peas then only green peas will be produced
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What is it called when one characteristic is constantly bred for generations?
Pure breeding
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Which chromosome are sex-linked diseases most commonly carried on?
X chromosome
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Why are sex-linked diseases more common in males?
As they only have 1 X chromosomes so only need the diseased gene on this one whereas females need the gene on both X chromosomes
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What is 'multiple alleles?'
Where there are more than 2 alleles of which only 2 may be present
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What is allele frequency?
The amount of times an allele occurs within a gene pool
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What is a gene pool?
All the alleles of all the genes of all the individuals in a population
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What equation is used to find out allele frequency?
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What conditions must be present for Hardy Weinberg to work?
No mutations, population isolated, no selection, large population, mating within population is random
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What are the 2 equations for Hardy Weingberg?
p+q= 1 and p2+2pq+q2= 1
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What is selection?
Process that allows best-adapted individuals in a population to survive and pass on favoured alleles
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What are the two types of selection?
Directional and Stabilising
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What is 'Directional Selection?'
When conditions change (eg; enviroment) characteristics are favoured that can fit into this change and survive
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What is 'Stabilising Selection?'
If enviromental conditions stay the same, the individuals with phenotypes closest to the mean survive
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What is 'Speciation?'
The evolution of a new species from existing species
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When does speciation occur?
When a species is seperated
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Explain how speciation can occur
If a species is seperated then they can no longer interbreed, they also will have to deal with different enviromental conditions so will evolve by selection differently
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When during speciation are the species now called 2 different species?
When they can longer interbreed and produce fertile offspring
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Other cards in this set

Card 2


What is a Phenotype?


Observed characteristics of an organism

Card 3


Apart from genes what can affect an organism's appearance?


Preview of the front of card 3

Card 4


What is a gene?


Preview of the front of card 4

Card 5


What is an allele?


Preview of the front of card 5
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