Chapter 20

  • Created by: Kaiya1000
  • Created on: 16-04-18 12:13
how does variation arise
frommutations or changes to the genetic code which are randomand constantle taking place
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what is chlorosis
when leaves do not produce the large quantities of cholorphyl they are meant to so leaveslook pale and the lack of chlorophyll reduces photosynthesis
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is chlorosis a mutation
no it is not a change in coding its a change in the phenotype due to environmental factors
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what factors cause chlorosis
lack of light- chlorphyl production is turned off /mineral deficiencies - lack of iron/magnesium as iron is a cofactor that helpes make chorophyll//virus infections- interfering with metabolisim of cells and cannot support the synthesis of chorophyl
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Is body mass geneticor environmental
it is determined by acombination of the two extreme cases is usually environmental (quality or food /lackjof food)/ sometimes obesity is due to genetics where the depositation of fat is altered
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Hiow is genetic diversity created
the combination of different alleles you recieve fromyour parents influences characteristics the combination its the random fusion of gametes atfertilisation that results in genetic variation
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what is the genotype
combination of alleles an organism inherits
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what is the phenotype
observable characteristics of an organism
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what are modifications
changes the environment makesto apersons phenotype
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dominant allele
version of the gene that will always be expressed if present
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recessive allele
only expressed if two copies of the allele are opresentin
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two identical alleles for a characteristic- homozygous dominant/recessive
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two different allels for a characteristic so allele for dominat phenotype expressed
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Continuos variation
characteristic that takes any value within a range caused by genetic ,environmental controlled by polygenes some examples are heigh
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Discontinous variation
a characteristic that can only appear in discrete values it is mostly genetic and controlled by omnly one/two genes some exasmple sare blood grouo
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What is monogenic inheritance
the ineritance of a single gene
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what is a genetic cross used for
to show how genes are passed on from one generation to the next
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How do you perform a genetic cross
1.state phenotypes 2. state genotypes with assigned letters 3. state gametes circle the letters 4. punnet square 5. state proportion of each genotype 6. state phenotype for all possible genotypes
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explain a homozygous genetic cross
organisms with homozygous alleles for gene are pure breeding individuals so you study when they cross
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explain a heterozygous genetic cross
two heterozygous offspring from 1st gen cross the offspring is the 2nd gen
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what is codominance
two different allels occur for gene both dominant so both allels are expressed in phenotype
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can some genes have multiple alleles
yes some have more than two versions for example blood groups however only two alleles can be present
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what does se linkage refer to?
characteristics that are determined by genes on sex chromosomes are known as this - as y chromosome is smaller it has only one copy of some genes
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An example of a sex linked disorder
haemophilia - blood clots slowly due to absence of protein clotting factor - if male inherits recessive allele for haemophilia on x they will not have a dominat on the y so will get disorder- females being heterozygous for haemophilia are carriers
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What is dihybrid ineritance
inheritance of two genes with different characteristics that can involve two + alleles for example yellow/gree pea or wirnkled/round
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what is dihybrid inheritances f2 gen expected ratio
the expected ratio of f 2 gen is 9:3:3
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how can the ratio of offspring produced differ
1. fertilisation of gametes is random chance events can skew ratio
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What is linkage
genes are located on the same chromosome
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what is autosomal linkage
when genes that are linked are found on one of the other pairs of chromosomes
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What is recombinant offspring
having different combinations of alleles than parents
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how do you measure recombination frequency
number of recombinant offsppring / total number of offspring
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what do the results mean
frequency of 50 % indicates no linkage with genes on separate chromosomes less than 50% there is linkage but independent assortment was hindered
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what does the chi squared test show
the observed ratio will be different to the expected ratio you need to know hetther the differences are due to chance or the differences are significant / so its a statistical test measuring the difference between observed and expected result to chec
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what is the formula
x2 = Z [ (O - E)2 / E ]
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how to you work out the degrees of freedom
catorgories - 1
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what do the results indicate
if calculate value is greater than critical value the null hypothesis is acceppted there is no significant difference
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what is epistasis ?
interaction of genes at different loci many genes interact this way
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what s the difference between epistatic and hypostatic
ep= gene that affects expression of another gene hyp= gene affected by another gene
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what are the two types of episatic genes
dominant and recessive
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What is evolution
the change in inherited characteristics of a group of organisms over time due to changes in the frequency of alleles in a population
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what is a gene pool
sum of total genes in a population
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Allele frequency
the relative frequency of an allele in a population which is not linked to whether it codes for dominant/reccessive characteristic
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Card 2


what is chlorosis


when leaves do not produce the large quantities of cholorphyl they are meant to so leaveslook pale and the lack of chlorophyll reduces photosynthesis

Card 3


is chlorosis a mutation


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Card 4


what factors cause chlorosis


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Card 5


Is body mass geneticor environmental


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