Chapter 20 Inheritance Flashcards
What is your genotype? What is your phenotype?
Genotype- combination of alleles an organism inherits for a characteristic
Phenotype- observable characteristics of an organism
What is a dominant allele? What is a recessive allele?
Dominant- always expressed in the phenotype if in the genotype
Recessive- only expressed in the phenotype if both copies of the allele are inherited
What is discontinuous variation and what causes it?
Variation that falls into distinct categories, controlled by usually 1 gene, and not affected by the environment normally
E.g blood type, eye colour
What is continuous variation and what causes it?
Variation that falls in a range with extreme values at each end, controlled by multiple genes and affected by the environment
E.g Height, weight
Shown as a bell curv
What creates genetic variation?
Independent assortments of chromosomes during meiosis, metaphase, resulting in each gamete being genetically unique
Crossing over of non-sister chromatids during prophase and the formation of chiasmata, recombinant genes
Mutations
Chance- which of the gametes will fuse together
What is chlorosis and etiolation?
Chlorosis- an inability to produce enough chlorophyll, due to environmental factors e.g insufficient minerals
Etiolation- lack of light causes causes extension of stem, but no increase in leaves, very tall thin plants
What is monogenic inheritance and how do you perform a cross?
Looking at one gene, where one allele is dominant and another recessive
Punnet square, gametes in each side
G g
G GG Gg
G GG Gg
What is co dominance? What is the result?
When two alleles of a gene are equally dominant so both are expressed in the phenotype
This normally means a mixed result
E.g red and white both dominant
Red and white protein made, so overall a pink colour seen
How do you perform genetic crosses with codominance?
Put the characteristic first letter is caps
The allele is in subscript
e.g genotype= C^W C^R
How is blood type inherited?
3 alleles- IA IB and Io
A and B codominant, result in AB blood type
Io recessive, only O is both alleles are O
Determines which type of antigen on blood cells
What are sex-linked diseases? Why do disease proportions change depending on gender in these cases? Give an example
Alleles which are responsible are found on the sex chromosomes
If on the Y chromosome only, only affects males
If on the X chromosome but recessive, in males, only 1 recessive is needed as not on the Y,
No dominant to cancel it out, so disease more common
e.g Haemophilia
What is a dihybrid cross?
A genetic cross used to show the inheritance of two different characteristics, could be on different pairs of homologous chromosomes so either linked or not linked
Outline the genetic crosses for YyRr x YyRr (two heterozygous for both characteristics)?
Gametes- take all combinations
YR Yr yR yr YR Yr yR yr
Put letters together when writing them out- first count how many have a capital of both
Then see how many left have 1 capital of each
Then how many with no capitals
What are linked genes? How does it affect inheritance?
Genes which are found on the same chromosome so are inherited together unless there is crossing over
Likely not predicted, instead group your dominant alleles and your recessive alleles keep these gametes together
Any weird outputs are likely the products of crossing over
It is difficult to say which is which, but the phenotypic ratio from the predicted cross is wrong
What is the autosome? What is autosomal linkage?
Autosome- non-sex chromosomes
Autosomal linkage- 2 linked genes found on the same autosomal chromosomes
What is the formula for recombinant frequency? What does this mean in terms of linkage?
Recombinant frequency= (n of recombinant offspring (1 dominant and 1 recessive either way round) / (total alleles in offspring)
If greater than 50%, no linkage
The closed the genes are on the chromosomes, the lower the chance of crossing over
What is the chi squared formula and how do you interpret the results? What is the degrees of freedom calculation?
Chi squared= the sum of (((o-e)^2)/e)
If Chi squared > d of freedom, we reject Ho, less than a 5% probability that these results are due to chance
D of freedom= n of categories - 1
There is not a SIGNIFICANT DIFFERENCE between the observed and expected ratio
What is epistasis? Give an example
When the expression of one gene is effected by another, masked by the other
E.g if the first allele doesn’t protein A
But the second allele should make protein B from A as it has the genes
So it looks like A and B isn’t there, but B could be, but masked by A
What is antagonistic epistasis? What is complementary epistasis?
Presence of a gene inhibits another
Presence of a gene encourages expression of another
What is the hypostatic gene? What is the epistasis gene?
Hypostatic- the gene that is being controlled by another
Epistastic- the gene which is controlling the other
What is recessive and dominant antagonistic epistasis?
Recessive- when two alleles needed to inhibit expression of another
Dominant- only one allele needed to inhibit the expression of another
What is genetic diversity? What is allele frequency?
Genetic diversity- the genetic differences between individuals within a population
Allele frequency- how often an allele occurs within a population
What is directional selection and give an example?
Individuals of certain characteristics favoured in one direction
E.g if climate becomes colder, longer hair furred individuals favoured, shifts to the right
What is stabilising selection? Give an example
Average individuals favoured
E.g if the habitat conditions have been stable for a long time, no benefit to being in either extreme
What are genetic bottlenecks?
Many alleles lost when a change in environment killed a large number of the population
New population descended from the few surviving members, so limited gene pool
What is the founder effect?
A few migrate away and become isolated from the population
As only made of a few individuals, they have a reduced gene pool, with allele frequencies that differ to the main population
If mutations occur in one population but not the other, this increases the difference further
Some alleles are lost
What is genetic drift? What is the gene pool?
Some characteristics are passed on by chance rather than due to factors that affect an individuals survival
Gene pool- all the alleles of all genes in all individuals in a population in a given time
What the assumptions for the Hardy-Weinberg equation?
No selection
No migration
Random mating
No mutations
Large population
How do you use the Hardy-Weinberg equation?
P is dominant Q is recessive
If looking at only appearance of the allele (homozygous or heterozygous ) use p + q= 1
If looking combination e.g only heterozygous, using p2 + 2pq + q2 = 1
Rearrange where necessary
What is speciation? What are types of speciation?
Formation of a new species through the process of evolution
Allopatric- due members being separated by a physical barrier
Sympatric- within the same habitat so either behavioural or plants
What is the process allopatric speciation?
Geographical isolation of some members of the species, resulting in reproductive isolation
Founder effect: the allele frequency of the founding members may not be representative of the original population e.g if a recessive allele present in these founders, could become more common.
Mutations occur in only one side of the population. If advantageous and able to help cope with selection pressures, the frequency of this allele increases, as the organism will be successful, reproduce, and pass on the allele
No gene flow between populations
Differing selection pressures mean successful characteristics in one population not the same as the other
Over time and many generations, the allele frequencies in each population are too different to enable breeding and the production of fertile offspring, and so two new species
What is sympatric speciation and give an example?
Speciation within the same habitat
E.g plants
As long as even number of chromosomes are in the diploid cell, fertile offspring are formed, but may not be able to reproduce with the original species as differing chromosomes
What is artificial selection?
Selective breeding
Same as natural selection but a leader choosing what characteristics are advantageous rather than for survival, changing allele frequency
What are some ethical considerations for selective breeding?
Increased docility means they cannot return to the wild
Live stock more leans so easy ret and need to be housed as cold
Low gene pool increases risk of diseases especially inherited disease
Changing colours means a loss of camouflage
What are gene banks?
Samples of DNA being stored
E.g as seeds, sperm, eggs
Used to increase genetic diversity
What must occur for a new breed of species to form?
A mutation enabling new characteristics to develop
Selection pressure to make this characteristic desirable and defining
How would genes being autosomally linked alter the predicted ratio of 9:3:3:1?
Closer to the parents ratio
e.g if both parents heterozygous, increased proportion of heterozygous individuals
If performing a sex-linked allele genetic cross, how do you display the alleles?
X^br
Y
Even if codominant, importance of X/Y as the base
Why will the observed ratio not exactly match the predicted ratio?
Random chance of which gametes fertilised so likely not exact
How can you determine if a gene is sex-linked from a pattern of inheritance? What else can be determined?
If only one gender has it or its more frequent in one gender, likely sex-linked
Recessive if two parents can produce a child with it
If on the X chromosome, more likely in males if recessive as no other X dominant to cancel it out. If dominant, likely more female sufferers
If only in males, likely on the Y chromosome
Why might a different ratio from 9:3:3:1 occur?
Epistasis, meaning not always expressed in the phenotype even if present
The genes are autosomally linked, meaning they are inherited together as on the same chromosome, so same as the parents
Any small numbers are the result of crossing over in meiosis
No independent assortment
Why might of use of antibiotics be dangerous?
Presence of antibiotics acts as a selection pressure
Genetic variation within the bacteria, only some contain the allele for antibiotic resistance so survive, whilst the others die
Surviving bacteria advantageous, lowered competition, so successful and replicate, passing on alleles for antibiotic resistance to offspring
Allele frequency within the new population increases, if pathogenic, cannot be killed when used to combat disease
Why is genetic drift more importance in small populations?
In small populations, one individual’s alleles have a greater proportional impact upon the whole population
So more likely that when this individual is lost, the allele is also lost
How does stabilising selection affect a certain characteristic (6) ?
Pre existing variation from mutations, crossing over in meiosis and independent assortment, nature of sexual reproduction
Overproduction of offspring
Those at either extremes of the characteristic will die out as unable to survive e.g unable to eat fruit, without reproducing
Alleles of these organisms will be phased out
Average characteristic organisms more successful, able to survive and reproduce
Alleles for their characteristic size passed on, and over time and generations, this allele frequency increases
Use data to illustrate from graphs
What conditions are needed for speciation to occur, not including a geographical barrier and reproductive isolation?
Mutations
Different selection pressures to other locations
Time
Why is it important to keep a range of wild population of crops ?
Artificial selection- lowers gene pool of plants, so more susceptible to changes in the environment
Provide a source of genetic material, alleles for useful characteristics
Can be bred with crops to introduce characteristics
Unknown future demands, could be new disease, changing climate, so alleles not currently desirable may be required for the species to survive
