Inheritance and Evolution Flashcards
(40 cards)
Define Genotype
the genetic constitution of an organism
Define Phenotype
the appearance of a characteristic due to expression of the genotype and its interaction with the environment
What are Alleles
different forms of the same gene
what is a dominant allele
an allele that is always expressed in the phenotype
what is a recessive allele
an allele that is only expressed when the genotype is homozygous recessive (two of them are present)
what are Co-Dominant alleles
where both alleles are expressed in the phenotype
what does sex linkage mean
where the gene is carried on only one type of sex chromosome (usually the X chromosome)
how would you prove an allele is recessive from a pedigree chart
- 2 unaffected parents who have an affected child
- this means that the parents must be heterozygous and carriers
how would you prove a recessive allele is not sex linked from a pedigree chart
- 2 unaffected parents produce an affected daughter
- the father wouldn’t be able to pass on a recessive allele if he was unaffected
how would you prove an allele is dominant from a pedigree chart
- 2 affected parents produce unaffected children
- both parents must be heterozygous and pass on their recessive alleles
how would you prove a dominant allele is not sex linked from a pedigree chart
- 2 affected parents produce an unaffected daughter
- the father wouldn’t be able to pass on a recessive allele so all the daughters would be affected
how would you prove a recessive allele is sex linked from a pedigree chart
- the phenotype is more commonly/only seen in males
- the males are more likely to inherit the trait as they only need to inherit one allele (females would have to inherit two)
why might the observed and expected ratios of the phenotypes of offsprings be different?
- the sample size is small therefore there is a greater sampling error
- random fusion of gametes during fertilisation
- epistasis
- linked genes (sex or autosomal)
when is a chi squared test used?
- used when we have categoric data and to compare the observed and expected ratios of the phenotypes of offspring
what are autosomal chromosomes
the non-sex chromosomes
what are autosomal linked genes
- genes that are present in the same chromosome at different loci
describe why autosomal linked genes leads to a much higher proportion of certain phenotypes than others?
- autosomal linked genes are more likely to be inherited together as there is no independent assortment and therefore fewer genetic combinations of alleles
- there will be a lower proportion of other phenotypes due to the rare occurrence of crossing over producing recombinant alleles
what is Epistasis?
- when the allele of one gene affects or masks the expression of another gene at another locus
Describe Allopatric Speciation
- Variation due to mutation gives rise to different alleles within a species
- species split into different groups due to geographical isolation
- no gene flow between different groups
- different selection pressures select different advantageous alleles
- organisms with advantageous alleles more likely to survive, reproduce and pass on the alleles increasing frequency of allele in population
- over period of time gene pools become so different that the different populations cannot interbreed to produce fertile offspring
Define Sympatric Speciation
- Variation due mutation gives rise to different alleles within a species
- these species are not geographically isolated but instead reproductively isolated due to different mating seasons or different courtship behaviour
- no gene flow between different groups and therefore different allelic frequencies
- over period of time gene pools become so different that the different populations cannot interbreed to produce fertile offspring
Describe Genetic Drift
- by chance, the allele of a particular gene is passed on to the offspring more often than other alleles of the same gene
- frequency of this allele increases over time
What type of population does Genetic Drift have the most impact on and why?
- a small population
- less genetic variation and therefore, a lower ability to adapt to changing conditions.
what conditions need to be upheld for the Hardy-Weinberg principle to be reliable?
- the population is large and isolated
- mating within the population is random
- no mutations of the gene occur
- there is no selection (all alleles are likely to be passed on to the next generation)
what is the HW equation for frequency of alleles
p + q = 1.0
- p = frequency of dominant allele
- q = frequency of recessive allele
