Patterns of Inheritence Flashcards
define phenotype
expression of an organisms genetic constitution combined with interaction with the environment
how can meiosis bring about genetic variation
random assortment of chromosomes during line up
crossing over in prophase 1
how does random fertilisation bring about genetic variation
gametes are haploid cells (only contain half DNA)
every gamete contains different DNA same two individuals can produce genetically different offspring
define monogenic inheritance
one phenotypic characteristic is controlled by a single gene
define dihybrid inheritance
two phenotypic characteristics controlled by two different genes present on two different chromosomes at the same time
what is meant by sex linkage
an allele is located on the sex chromosome-its expression depends on sex of the individual
what is meant by multiple alleles
a gene that has more than two alleles
what is meant by codominant alleles
two dominant alleles that both contribute to phenotype
either blend of characteristics or characteristics appearing together
what is meant by autosomal linkage
two or more genes located on the same chromosome
only one homologous pair needed for all four alleles to be present
for genes not linked, two homologous pairs needed
what is meant by epistasis
when two non linked genes interact
one gene masks or suppresses the other gene
what is the chi squared test
a statistical test to find out whether difference between observed and expected data is due to chance
how is a chi squared test performed
formula results in a number which is compared with critical value (for corresponding degrees of freedom)
if number greater than or equal to critical value-no significant difference and due to chance
how can the number of genes coding for a characteristic influence variation
discontinuous variation-characteristic determined by one gene
continuous variation-characteristic determined by more than one gene
what is stabilising selection
occurs when environmental conditions stay the same
Individuals closest to mean are favoured and new characteristics selected against
results in low diversity
what is directional selection
when environmental conditions change
individuals with phenotypes suited for conditions will survive and pass on genes
mean of population will move towards these characteristics
what is genetic drift
change in populations allele frequency
occurs due to chance not selective pressures
what is meant by genetic bottle neck
catastrophic event dramatically reduces size of population
decreases variety of alleles in gene pool
causes large change in allele frequency
what is meant by the founder effect
a small number of individuals become isolated forming a new population with limited gene pool
allele frequencies not reflective of original population
what is the hardy weinberg principle
allows us to estimate frequency of alleles in population
explain the hardy Weinberg equation for calculating allele frequency
frequencies of each allele must add up to 1
p+q=1
p=frequency of dominant allele
q=frequency of recessive allele
explain the hardy Weinberg equation for calculating genotype frequency
p2+2pq+q2=1
p2=frequency of homozygous dominant
2pq=frequency of heterozygous
q2=frequency of homozygous recessive
define speciation
when a population is split and isolated there are different selective pressures
if the genetic makeup changes to the extent they can no longer interbreed-become separate species
what is meant by allopatric speciation
speciation resulting from physical barrier
environments are different so different alleles favoured
what is meant by sympatric speciation
speciation resulting from non physical barrier
any changes in anatomy or behaviour may affect breeding
what is artificial selection
humans choose particular organisms to breed together to produce a desired characteristic in the offspring
why is it important to keep a resource of genetic material when selective breeding
allows traits that were accidentally bred out to be reintroduced
revert back to a point before any negative traits introduced
what ethical issues surround artificial selection
anatomical changes in animals
higher susceptibility to disease
