10 — genetics and evolution Flashcards
outline how reproductive isolation can occur in an animal population (3)
- can be sympathetic or allopathic
- temporal isolation by members of difference populations reproducing at different times
- behavioural isolation by difference in courtship behaviours
- geographic isolation by a population being separated by natural barriers to contact
outline the process of speciation (4)
- speciation is the splitting of a species into 2 species
- productive isolation/ lack of interbreeding
- isolation due to geography/ reproductive behaviour/ reproductive timing
- gene pools separated
- differences in traits cause gene pools to change/ diverge
- speciation changes accumulating over long periods
list two causes of variation within a gene pool (2)
- sexual reproduction/ random fertilisation/ meiosis
- mutation
describe how variation contributes to evolution by natural selection (3)
- variation is different phenotypes/ differences between individuals in a population/ species
- struggle for survival
- some individuals have advantageous characteristics have greater chance of survival
- favourable alleles passed on to next generation
outline what is required for speciation to occur (3)
- divided species/ gene pool
- reproductive isolation
- may be due to temporal/ behavioural/ geographic isolation
- different natural selection
starting from the concept of gene pool, explain briefly now populations of early vertebrates could have evolved into different groups (3)
- gene pool is all genes/ all alleles
- geographic/ temporal/ behavioural isolation
- speciation if populations are reproductively isolated
- in different environments there are different selection pressures
- allele frequencies change
starting from the concept of gene pool, explain briefly how populations of early vertebrates could have evolved into different groups (3)
- gene pool is all genes/ all alleles
- geographic/ temporal/ behavioural isolation
- speciation/ gene pool split if populations are reproductively isolated
- in different environments there are different selection pressures/ opportunities
- allele frequencies change
define the term polygenic inheritance (1)
- character affected by two or more genes
outline, with examples, different types of inheritance that produce non-Mendelian ratios (4)
- some traits may involve many genes
- linked genes on the same chromosome
- small numbers of recombinant phenotypes due to crossing over between linked genes
- codominance of specific alleles
- sex linked effects
- environmental influence on inheritance
explain the cause of sickle cell anaemia and how this disease affects humans (8)
- caused by a single nucleotide
- mutation of a gene of a subunit of hemoglobin
- mRNA copies the mutation of DNA and substitutes an amino acid in hemoglobin
- glutamic acid is substituted by valine
- sickle cell anemia involves distorted hemoglobin protein
causes sickling of red blood cells - block capillaries
- sickled red blood cells cannot carry enough oxygen for the body
- homozygous state causes severe anaemia
- heterozygous state only affected at high altitude
- heterozygous state provides protection against malaria parasite
explain how observation of the fossil record provides evidence for evolution (4)
- fossils show the types of organisms that lived in the past
- fossils can provide direct or indirect evident left in layers of rocks
- fossils can be dated by radioisotope dating of the rocks that hold them
- the sequence in which fossils appear matches the sequence in which species evolved
- sequences of fossils show progressive change over time
- increase in complexity of structures over time
- other extinct group in the fossil record suggest that organisms change over time
outline how experiments into inheritance can be performed using fruit flies and what has been discovered by carrying out such experiments (4)
- cross fruit flies with a certain trait with females of another characteristic
- analyse offspring of the cross
- dihybrid crosses
- discovered sec linkage
- ratios are different for males and females
- discovery of non mendelian ratios
- autosomal linkage
- fruit flies useful in inheritance experiments due to short life cycle
describe the methods used in cladistics and how evidence gained from this research can be utilised (7)
- study DNA of the same gene is different species
- study the amino acid sequence of the same protein in different species
- deduce which organisms are part of a clade
- use similarities and differences in sequence to construct a clad organ
- clad organ shows the most probable sequence of divergence of a clade
- deduce evolutionary origins
- numbers of base differences help deduce time since precise diverged
- deduce closeness of relationships according to similarities in bases
- used to help classify groups of organisms
- shows how closely humans are related to other primates
- has caused changes to classification of the figwort family
- distinguishing between homologous and analogous structures led to mistakes in classification
outline the changes to chromosomes that occur during prophase in the first division of meiosis (4)
- pairing of homologous chromosomes form bivalents
crossing over - exchange of DNA between chromatids
- new combination of alleles generated
- condensation of chromatids
- formation of a chiasma where crossing over occurred
explain the effects that the environment can have on DNA in living organisms (4)
mutation
- environment can cause mutation
- mutations are base sequence changes
- radiation can cause mutations
- mutagenic chemicals can cause mutations
epigenetics
- environment can cause changes to gene expression
- methylation in DNA changed in response to environmental factors
- methylation inhibits gene transcription
- body temperature can affect gene expression
