D3.2 - genetics: definitions and variation (5j) Flashcards
what is the pattern of inheritance common to all eukaryotes with a sexual life cycle?
- production of haploid gametes in parents and their fusion to form a diploid zygote
- a diploid cell has 2 copies of each autosomal gene, because it inherits one of each autosomal chromosome from each parent
what is a gene?
a gene is a heritable factor that consists of a length of DNA and which influences a specific characteristic
what is a gene pool?
a gene pool is all the genes and their different alleles present in a population
what is an allele?
an allele is a specific form of a gene with a slight difference in the base sequence compared with another allele for the same gene
how are new alleles formed?
new alleles are formed by mutation
why is there a difference in the number of alleles that occur in a gene pool compared with the number that and individual inherits?
single -nucleotide polymorphisms form multiple alleles, which occur in genomes within a population and therefore occur in a gene pool
- there is a different allele for each SNP combination that occurs with in a gene
- however, an individual will only inherit one or two different alleles
- this is because an allele is present at a particular locus on one type of chromosome
- individuals inherit one type of each chromosome from 3ach of their parents
what is a genotype?
a genotype is the combination of alleles inherited by an organism
what is the difference between homozygous and heterozygous genotypes?
homozygous genotype - have 2 of the same alleles
heterozygous genotype - have 2 of the different alleles
what is a phenotype?
a phenotype is the observable traits of an organism resulting from genotype and environmental factors
what are the 3 causes of human traits?
- genotype
- environmental factors
- combination of genotype and environmental factors
what are some examples of how the genotype can cause human traits?
- eye colour
- blood group
- hair colour at root
- natural shape of earlobe
what are some examples of how the interaction of genotype and the environment can cause human traits?
- tattoos
- scars
- languages spoken
what are some examples of how environmental factors can cause human traits?
- height
- weight
- skin colour
- sporting achievement
what is phenotype plasticity?
the capacity to develop traits suited to the environment experienced by an organism, by varying patterns of gene expression
what is the mode of action of phenotype plasticity?
not due to change in genotype
what is the permanence of phenotype plasticity?
changes in traits may be reversible during the lifetime of an organism
what are continuous variables?
- no discrete categories
- many possible phenotypes
what are discrete variables?
- distinct categories
- few possible phenotype
what are the effects of the environment on continuous and discrete variables?
continuous - strongly influenced by environment
discrete - unaffected by the environment
how are genes involved in continuous and discrete variables?
continuous - controlled by multiple genes (polygenic)
discrete - controlled by 1 or few genes
what are the causes of continuous variation?
polygenic inheritance and environmental factors
what is polygenic inheritance?
when 2 or more genes influence the expression of one trait
why is there variation in human skin colour?
- skin colour is impacted by polygenic inheritance and environmental factors
- 4 genes contribute to human skin colour, each of which has alleles that deposit different amounts of melanin into the skin
- there are many possible combinations of alleles present in an individual.
- the additive effects of the four genes mean there are many possible amounts of melanin that may be deposited into a person’s skin through genetic factors
- however, people’s skin colour and changes due to sun exposure, which causes more melanin to be deposited and therefore a darkening of the shin; the greater the sun exposure, the more melanin is added
outline the causes of variation in one example of continuous variation in humans.
- one example of continous variation in humans is height or skin colour.
- with continous variation, any level of phenotype is possible.
- polygenic inheritance is the combined effect of more than I gene on a trait.
- there are additive effects on the trait of alleles on multiple genes.
- environmental factors can also cause continuous variation, such as sunlight affecting skin colour.
