Chapter 20 Patterns of Inheritance & Variation Flashcards
What is ‘chlorosis’?
A condition plants suffer from…
- leaves = pale/ yellow
- cells not producing normal amount of chlorophyll pigment
- reduces ability to make food by photosynthesis
What factors cause chlorosis? (3)
ENVIRONMENTAL factors
(1) Lack of light
- absence of light - plants turn off chlorophyll production - conserving resources
- only occurs where plant doesn’t get light
(2) Mineral deficiencies
- minerals (iron / magnesium) needed for production of chlorophyll
(3) Virus infections
- virus interferes w/ the metabolism of cells
- yellowing = cannot support synthesis of chlorophyll
What is genetic variation caused by?
versions of genes you inherit
- combination of alleles determined by sexual reproduction
(meiosis) - forming gametes
(random fusion of gametes)
Define ‘genotype’.
combination of alleles an organism inherits - genetic make-up
What is a dominant allele?
version of the gene which will always be expressed if present in an organism
- (showing) individual can have 1 OR 2, you can’t tell from phenotype
What is a recessive allele?
only expressed if 2 copies of allele are present
- you know their genotype - they must have 2 is they are presenting
Define ‘phenotype’.
observable characteristics of an organism
What is homozygous?
2 identical alleles for a characteristic
- can be homozygous recessive (rr)
- can be homozygous dominant (RR)
What is heterozygous?
2 different alleles for a characteristic
- always DOMINANT is expressed
Variation divided into 2 groups??
CONTINUOUS
- extremes and everything between (can take any value)
- many genes involved (poly)
DISCONTINUOUS
- distinct groups
- one/ two genes involved
What is monogenetic inheritance?
the inheritance of 1 gene
- genetic cross diagram
What is codominance?
occurs when 2 diff alleles occur for a gene
- both equally dominant!!
- both expressed in phenotype
Sex-linkage??
X chromosome - large - have many genes (not involved in sexual development)
- sex linked = genes (found on sex chromosomes) which determine characteristics
What is dihybrid inheritance?
the inheritance of 2 genes (can be on diff homologous chromosomes - m/f)
- dihybrid cross 9:3:3:1
What is autosomal linkage?
when genes which are linked are found on 1 of the other pairs of chromosomes.
(NOT sex-linkage)
Linked genes??
Inherited as 1 unit
- no independent assortment - during meiosis
- unless allele serrated by chiasmata
What are recombinant offspring?
have diff combo of alleles than either parent
Chi squared
statistical test
- measures size of diff
- between expected and observed results
- helps determine whether the diff is significant
- by comparing size of diff and no. of observations
- used to test the null hypothesis
What is the null hypothesis in Chi squared tests?
- there is no significant diff between expected and observed
- any diff is due to chance
What do Chi squared test values tell us?
used to find the probability of the diff being due to chance alone
What is epistasis?
interactions of genes at diff loci
What is dominant epistasis?
When the dominant allele is results in a gene having an effect on another gene.
What factors affect evolution?? (5)
(1) mutation
- new alleles produced - genetic variation
(2) sexual selection
- leads to allele coding for characteristics
(3) gene flow
- movement of alleles between populations
(4) genetic drift
- occurs in small populations
- mutation
(5) natural selection
What do population genetics investigate?
allele frequencies within populations - how they change over time
Example of selection pressures?
- changes in environment
- presence of new diseases
- prey
- competitors
- human influence/ interference
What are the 2 types of limiting factors?
(1) density-dependent factors
- dependent on pop size
- competition, predation, prey, communicable disease
(2) density-independent factors
- affect all pop of any size
- climate change, natural disasters, seasonal change, human activities
What is the founder effect?
small pop arise due to establishment of new colonies by a few isolated individuals
- leads to founder effect (extreme example of genetic drift)
Types of selection (3)??
(1) Stabilising selection
(2) Directional selection
(3) Disruptive selection - diversifying
Types of speciation?
(1) allopatric
- separation due to physical barrier
- geographically isolated
(2) sympatric
- 2 organisms of diff species interbreed = fertile offspring
- more likely to happen in plants
- hybrid formed
- diff no of chromosomes
- reproductively isolates hybrid organism
