Mutations and Gene Pools Flashcards
mutation
a change in a gene or chromosome leading to a new characteristic in an organism
mutagen
an environmental agent that increases the rate of mutation
population
a group of organisms of the same species living together in a particular place and particular time
lethal recessive
recessive alleles that, inherited in the homozygous condition, result int he death of the embryo, foetus or child
monosomy
where an individual has only one copy of a chromosome instead of two
trisomy
where an individual has three copies of a chromosome instead of two
genome
the compelte set of genetic material in a cell; an organisms’ complete set of DNA
random assortment
the random separation of maternal and paternal chromosomes during the first division of meiosis
crossing over
the interchange of the parts of the chromatids of a homologus pair of chromosomes during the first stage of meiosis
non-disjunction
when one or more chromosomes fails to separate during meiosis
random fertilisation
the ability of any one sperm to fertilise any available egg
natural selection
the process by which a species becomes better adapted to its environment; those individuals with favourable characteristics have survived an advantage and so pass on those characteristics on to subsequent generations
random genetic drift
the occurrence of characteristics in a population as a result of chance rather than natural selection; occurs only in small populations aka Sewall Wright effect
founder effect
the type of genetic drift that occurs when a new population is formed by a small number of individuals; the small size of the sample can cause marked deviations in allele frequencies from the original population
gene flow
the transfer of alleles from one population to another through migration
geographical barriers
a feature in the landscape that prevents populations from interbreeding; includes oceans, mountain ranges, large lake systems, deserts and expansive ice sheets
sociocultural barriers
barriers to interbreeding that are due to social and cultural factors
special creation
the belief that God created all species
evolution
the gradual change in the characteristics of a species
variation
the differences that exist between individuals or populations of a species
survival of the fittest
the principle whereby organisms with favourable characteristics survive; but organisms with unfavourable characteristics die before they have a chance to reproduce
speciation
the process of new species developing
Tay-Sach’s disease
a genetic disorder caused by a missing enzyme that results in fatty substances accumulating in the nervous system
thalassemia
an inherited disease caused by a recessive allele, in which anaemia results from defects in the formation of harmoglobin
sickle-cell anaemia
an inherited disease causing early death; results from the inheritance of two alleles for sickle-cell anaemia
what is the difference between a gene mutation and chromosomal mutation?
a gene mutation occurs within a small amount of contained base pairs, whereas a chromosome mutation involves all or part of a chromosome, and affects more than one gene
give two examples of a chromosomal mutation
Down syndrome (trisomy 21) and cri-du-chat (missing part of chromosome 5)
give two examples of a gene mutation
cystic fibrosis, albinism, Duchenne form of muscular dystrophy
give 5 examples of a mutagen
mustard gas, high temperatures, x-rays, radiation from radioactive waste, UV light, cosmic rays
what sorts of factors affect the gene pool?
chance events - mutation that alters the expression of a gene
natural means - changes to environment
natural selection (survival of the fittest)
random genetic drift
migration
genetic diseases
geographical barriers
give an example of a place where the founder effect has occurred?
Finland: a small gruop of individuals settled there around 2000 years ago and the population has remained relatively isolated with very little immigration
how does migration affect allele frequencies? Give an example
if migrants bring aleles that are not already in the population, the frequencies for the alleles of that gene would be altered. eg China –> majority of people aer Rh positive but Europeans introduced the Rh allele into the Chinese population
how do geographical and sociocultural factors influence allele frequencies of a gene pool?
geographical barriers (mountain ranges, large lake systems, expansive ice sheets, deserts) prevent species on either side from interbreeding sociocultural barriers (different languages, cultures, religions, economic background, education, social position) --> people of different groups tended not to associate with each other
what are the main principles of evolution?
- there is variation of characteristics within an individual
- more offspring are produced than can possibly survive to maturity
- struggle for existence due to excessive birth rates and limited resources
- survival of the fittest
- favourable characteristics (have survival value) are passed on to other generations
- the proportion of alleles that produce favourable characteristics gradually increases
describe two examples of natural selection in humans
body stature: short-bodied, long-limbed Africans; long-bodied, short-limbed Inuit
what is the difference between trisomy and monosomy?
trisomy: extra copy of a chromosome
monosomy: one chromosome is missing
how can mutations affect the proportion of certain alleles in gene pools?
the frequency of mutations would gradually decrease as the people with the mutation die before they reach reproductive age and pass on the genes to the next generation
how do new variations occur in a population?
through fertilisation and meiosis
what is a selectively advantageous mutation?
a mutation that enhances the species’ chances of survival
how could isolation lead to selection and speciation?
prevents the interbreeding of species in different areas. different alleles are favoured in different environments
occurs when two populations are separated for long enough, and adapt to their environmental conditions, interbreeding would no longer be possible
