Patterns of inheritance Flashcards
what is continuous variation
when individuals in a population vary within a range, no distinct categories examples include height, fur length
what is discontinuous variation
two or more distinct categories, no intermediates, blood group
what do you call inherited characteristics that show continuous variation and are usually controlled my by many genes
polygenic
what do you call inherited characteristics that show discontinuous variation and are usually controlled by one gene
monogenic
what causes genetic variation in phenotypes, give examples
genotype
environment- diet in animals, etiolation (plants grow abnormally long due to lack of light)
how does sexual reproduction cause genetic variation
meiosis makes gametes with a unique assortment of alleles through crossing over and independent assortment
what is a gene
a sequence of bases that codes for a protein
what is an allele
different version of a gene
what is a genotype
the alleles it has
what is a phenotype
the characteristics alleles produce
what does homozygous mean
two copies of the same allele
what is meant by the term codominant allele
when alleles are both expressed in th phenotype because neither one is recessive, for example horses hair can be a mixture of white and coloured hairs
what is a carrier
a person carrying an allele which is not expressed in the phenotype but can be passed onto offspring
what is dihybrid inheritance
the the inheritance of two characteristics which are controlled by different genes
what chromosomes do women have
XX
what chromosomes do men have
XY
what does characteristics being sex linked mean?
some characteristics are sex linked meaning that the alleles that code for them are on the sex chromosome
what is an autosome
a gene that is not a sex gene
what ratio do you expect in a dihybrid cross
9:3:3:1
what is epistasis
when the allele of one gene masks the expression of the alleles of the other genes
what ratio would you expect in a recessive epistatic cross
9:3:4
what ratio would you expect in a dominant epistatic cross
12:3:1
label the chi squared equation
O= observed result
E= expected result
£= the sum of
define the term gene pool
the complete range of alleles in a population
what is stabilising selection
when an environment is stable and individuals with characteristics towards the middle of the range are more likely o survive, reduced the range of phenotypes
what is directional selection
when there is a change in the environment and individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce
what is genetic drift
individuals in a species show variation in their genotype
by chance the allele for one genotype are passed onto the offspring more often than others
so frequency of that allele increases
it can then lead to evolution by chance
does genetic drift affect larger or smaller population sizes and why
smaller as In smaller populations chance has more effect
what is genetic bottleneck
when an event like a natural disaster causes a big reduction in a population size leading to a reduction in gene pool
what is the founder effect
what happens when just a few organisms from a population start a new population and there are only a small number of alleles in the initial gene pool
what is the Hardy-Weinberg principle and what assumptions must be made
mathematical model which reprints that the frequencies of alleles in a population won’t change from one generation to the next
has to be a large population
no immigration/emmigration
no mutations
random mating
label the allele frequency equation
p= frequency of dominant allele
q= frequency of recessive allele
label the genotype frequency equation
p2= frequency of homozygous dominant genotype
2pq= frequency of heterozygous genotype
q2= frequency of homozygous recessive genotype
what are some examples of artificial selection
bread wheat- high wheat yield, higher tolerance of cols, uniform stalk heights, short stalks
dairy cattle- high milk yield, long lactation, large udders
resistance to mastitis
calm temperament
what are the problems with artificial selection
reduces gene pool
less chance of resistance to new disease
health problems for certain organisms
what is allopatric speciation
when populations become reproductively isolated through a combination of geographic isolation and natural selection
define the term species
a group of organisms with similar characteristics tat can reproduce to give fertile offspring
what is sympatric speciation
speciation without geographical isolation and from random mutation
how dos reproductive isolation occur
seasonal chnages
mechanical changes like genitalia
behavioural changes- different courting rituals
