6.1.2 - Patterns of Inheritance Flashcards
What is continuous variation?
a characteristic that can take any value in a range
- polygenic (under the control of multiple genes)
- affected by genetics and environment
eg. skin colour, leaf surface area
What is discontinuous variation?
a character that can only appear in discrete categories
- under the control of one gene
- affected by genes
eg. blood group, pea shape
What is chlorosis?
a plant condition when plant cells don’t produce the normal amount of chlorophyll, causing the leaves to become pale/yellow
-caused by lack of light, mineral deficiencies and viral infections
What is a gene?
a section of DNA found at a locus that controls a particular characteristic
-codes for a protein
What is an allele?
a form of a particular gene
What is monogenic inheritance?
the inheritance of a characteristic on a single gene
What is multiple alleles?
more than two forms of a gene
What is dihybrid inheritance?
the inheritance of two different characteristics caused by two different genes simultaneously
How can you tell if an individual bred is homozygous or heterozygous?
by breeding with a homozygous recessive individual
-if their offspring is homozygous recessive, the individual is heterozygous
What is codominance?
when two alleles are equally expressed in the phenotype
What is sickle cell anaemia?
- an example of codominance
- mutation where β chains of haemoglobin are affected
- amino acid in position 6 is changed from (soluble) glutamic acid to (insoluble) valine
- when oxygenated, the β chain becomes more soluble and crystalline, making the red blood cell less flexible and sickle shapes
- red blood cells therefore get stuck in capillaries
- is caused by codominant alleles
What chromosomes do male humans have?
XY
What chromosomes do female humans have?
XX
What is sex linkage?
genes carried on the sex chromosomes which control a specific characteristic
-only alleles on X chromosome expressed
What is haemophilia?
A sex-linked genetic disorder where blood clots very slowly due to the absence of a protein blood-clotting factor
-males have it (females can be carriers when heterozygous -is very rare for them to be homozygous haemophilic)
Why are males not heterozygous for sex-linked characteristics?
they only have 1 allele but you need to have 2 alleles to be heterozygous
What is (autosomal) linkage?
genes found close to eachother on the same chromosome which are not separated during crossing over in prophase 1
-causes unusual ratio like 5:1:1:5 when a ratio of 1:1:1:1 is expected
What causes a ratio of 5:1:1:5 in the offspring to be produced?
autosomal linkage
What are recombinant offspring?
offspring with different combinations of alleles to either parent (due to autosomal linkage)
recombination frequency =
no. recombinant offspring
_____________________
total no. of offspring
>50% = no linkage (genes on separate chromosomes) <50% = linkage
What is epistasis?
the interactions between different genes at different loci
eg. gene regulation (like LAC operon)
What is a locus?
a position of a gene on a chromosome
What are the types of epistasis?
- antagonistic epistasis (recessive and dominant epistasis)
- complementary epistasis
What is antagonistic epistasis?
epistasis where genes work against eachother
-dominant or recessive
What is an epistatic allele?
allele on first locus which causes the affect
What is a hypostatic allele?
allele at second locus which is affected (by epistatic allele) that stops the protein synthesis of the allele
How can the hypostatic allele stop protein synthesis of the allele?
produces a…
- repressor protein which binds to allele and stops transcription
- enzyme breaks down mRNA
- protein binds to mRNA and prevents it binding to the ribosome
- protein binds to ribosome so that mRNA can’t
What is the ratio of offspring produced by recessive epistasis?
9:4:3
What causes a ratio of 9:4:3 in the offspring to be produced?
recessive epistasis
What is the ratio of offspring produced by dominant epistasis?
12:3:1
What causes a ratio of 12:3:1 in the offspring to be produced?
dominant epistasis
What is complementary epistasis?
epistasis where genes work together
What is the ratio of offspring produced by complementary epistasis?
9:7
What causes a ratio of 9:7 in the offspring to be produced?
complementary epistasis
What is the chi-squared test used for?
to determine (the significance of) the difference between observed and expected results
What must you have in order to use the chi-squared test?
- 20+ individuals in sample
- discrete categories
- raw data (aka not percentage values)
What factors can affect the evolution of a species?
- stabilising selection
- directional selection
- genetic drift
- genetic bottleneck
- founder effect
What is stabilising selection?
natural selection favouring average phenotypes
-extreme phenotypes are selected against
What is directional selection?
natural selection which favours one extreme phenotype
What is genetic drift?
random change of allele frequency
-particularly in small populations
What is genetic bottleneck?
when large numbers of a population die, leading to a reduced gene pool and therefore a lower genetic biodiversity in the population
-particularly in small populations
What is the founder effect?
when a few individuals of a species colonise a new area, leading to a reduced genetic variation in the offspring
-rare alleles can become more common
What does the Hardy-Weinberg principle state?
In a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next and there will be no evolution.
What assumptions are made when using the Hardy-Weinberg principle’s equations?
- population is large
- mating is random
- no selection occurs (no selection pressures)
- no mutations, migration or genetic drift occurs
What does p stand for in p+q = 1 (in Hardy-Weinberg’s principle’s equations)?
dominant allele frequency
What does q stand for in p+q = 1 (in Hardy-Weinberg’s principle’s equations)?
recessive allele frequency
What does p^2 stand for in p^2 +2pq +q^2 (in Hardy-Weinberg’s principle’s equations)?
homozygous dominant genotype frequency
What does q^2 stand for in p^2 +2pq +q^2 (in Hardy-Weinberg’s principle’s equations)?
homozygous recessive genotype frequency
What does 2pq stand for in p^2 +2pq +q^2 (in Hardy-Weinberg’s principle’s equations)?
heterozygous dominant genotype frequency
What is a species according to the biological species concept?
a group of organisms that can interbreed to produce fertile offspring
eg. all dogs
What is speciation?
the formation of a new species
Why does speciation occur?
- populations become isolated from eachother (no gene flow)
- random mutations (produces different alleles may be selected for)
- changes in allele frequencies over many generations (populations change so much they no longer breed)
What are the two types of speciation?
- allopatric speciation
- sympatric speciation
What is allopatric speciation?
speciation that occurs as a result of geographical isolation
- most common form
- diff environments in diff locations select for diff alleles
eg. galapagos finches
Name an example of allopatric speciation
Galapagos finches
What is sympatric speciation?
speciation that occurs as a result of reproductive isolation
- two organisms of diff species interbreed to produce fertile offspring
- organisms continue to share same habitat
- common in plants, rare in animals
What is artificial selection?
selective breeding of organisms involving humans selecting desired characteristics (aka phenotypes) and interbreeding them to produce desired offspring
Name some examples of selective breeding in plants
- disease resistant plants in food crops
- increased crop yield
- plants with drought resistance
- plants that produce better tasting/larger fruits
- plants with larger flowers
Name some examples of selective breeding in animals
- cows, sheep, etc bred for higher yield of milk or meat (large udders, muscular, fertile, etc)
- chickens bred to lay large eggs
- domestic dogs bred to have a gentle nature or desirable appearance
- horses bred to have desirable appearance and/or fast pace
Why is it important to maintain a resource of genetic material for use in selective breeding?
ensures gene pool doesn’t become too small (which would reduce variation and make species more vulnerable to disease or climate change)
What ethical considerations are there surrounding the use of artificial selection?
- inbreeding reduces gene pool so increases chance of harmful genetic defects being inherited and organisms being vulnerable to disease
- intensive artificial processes have resulted in damaging conditions/diseases like breathing difficulties in pugs
