Patterns of inheritance and variation chp 20 Flashcards
what is an example of a condition in plants that can be brought about via environment and genotype
chlorosis
What are some environmental factors that can cause chlorosis in plants
- lack of light (plants will turn off chlorophyll production reserve resources)
- mineral deficiencies (lack or iron of Mg, they are needed in chlorophyll production)
- virus infections (they can interfere with metabolism of cells and so cannot produce pigment)
what is the difference between alleles and genes within a species
all individuals within a species have the same genes but not necessarily the same alleles of these genes
what influences an individuals phenotype
the individuals mixture of alleles an organism inherits from its parents
what determines the combination of alleles within an organism
by sexual reproduction involving meiosis, the random fusion of gametes at fertilisation
how many alleles are inherited by an individual for most genes
- 2
- one from each parent
what is meant by genotype
- the combination of alleles an organism inherits for a certain characteristic
what is meant by phenotype
the observable characteristics of an organism
what is meant by modifications in respect to phenotype
changes to a organisms phenotype caused by the environment not there genes
what is meant by a dominant allele
- a version of the gene that will always be expressed if present in an organism
- an individual showing the dominant characteristic could be homo- or hetro-zygous
what is meant by a recessive allele
- will only be expressed if 2 copies of the alleles are present in an organism
- an individual has a recessive phenotype, they will have a homozygous genotype
what are all the different terms that can be used to describe the genotype of an organism
- homozygous dominant
- homozygous recessive
- heterozygous (no need for dominant or recessive as will also be dominant)
what is meant by continuous variation
- a characteristic that can take any value within a range
- example is height or weight
what is meant by discontinous variation
- a characteristic that can only appear in specific values
- examples include blood group
how many genes are involved with continuous variation
- polygenic
^controlled by a number of genes
how many genes are involved with discontinous variation
- 1 or 2 genes
what is meant by monogenic inheritance
- the kind of inheritance whereby a trait is determined by the expression of a single gene or allele, not by several genes as in polygenic inheritance.
what are the steps to properly analyse a genetic cross diagram
- 1) state phenotype of both parents
- 2)state genotype of both parents. e.g Aa, A = dominant allele, a = recessive allele
- 3)state gamete of each parent.
- 4)use punnet square to show results of gamete
- 5)state ratio/percentage/fraction of each genotype produced
- 6) state the phenotype that would arise from each genotype
what is meant by true or pure breeding individual
- there genotype is homozygous
what would be the product of breeding homozygous dominant and homozygous recessive individuals
- all offspring heterozygous
- offspring demonstrate the dominant allele phenotype
what is meant by F1 generation
the first generation of offspring produced by a set of parents
what is meant by codominance in reference to alleles
phenomenon in which two alleles are expressed to an equally dominant degree within an organism
what is an example of where codominance occurs within plants
- the colour of snapdragon flowers
- there is an allele that codes for red flowers and an allele than codes for white flowers, when mixed they can create pink flowers
how can codominance result in 3 different phenotypes in snapdragon flowers
- 1)red flowers - plant is homozygous for the allele coding for the production of red pigment
- 2)white flowers - plant is homozygous for the allele coding for no pigment
- 3)pink flowers - plant is heterozygous, single allele present which codes for red pigmentation produces enough pigment to produce pink flowers
how are codominant alleles represented
- a letter is chosen to represent gene
- secondary letter then shown as superscript of gene letter. e.g. C^w for white flowers and C^r for red flowers
what is an example of something in humans that is determined by genes with multiple alleles
- blood group
how many pairs of chromosomes do humans have
- 23 pairs
- 46 individual chromosomes
what is the 23rd pair of chromosomes within males and females
- males - XY
- females - XX
what is meant if a gene is described as sex linked
- characteristics determined by genes carried on the sex chromosomes (X & Y, not really Y)
why are males more susceptible to recessive conditions
- Y chromosome is smaller than the X (doesnt contain all genes that X has)
- there are genes in the X chromosome that males have only 1 copy of,
- they only need one recessive allele to gain the recessive condition
- females have to inherit 2 recessive alleles to gain it which is much rarer
what is an example of a sex-linked genetic disorder
- Haemophilia (recessive condition)
- ^blood is slow to clot due to low level of clotting factors
what is meant by dihybrid inheritance
- the inheritance of 2 characteristics that are controlled by different genes at different loci
what is the expected ratio for the F2 generation of dihybrid inheritance
9:3:3:1
what can affect the ratio of actual offspring produced
- fertilisation of gametes is random (more prominent in smaller sample sizes)
- genes being studied are linked genes, if no crossing over occurs the alleles for the 2 characteristics will always be inherited together
what is the formula for the chi-squared test
what does each thing represent
what does the chi-squared test measure
- measures the side of the difference between the results you actually get and those you expected (helps determine whether differences are significant or not)
what do P values mean
- p values = probability it was down to chance
- smaller values means strong evidence (smaller value of chance)
- larger values mean weak evidence (bigger value for chance)
- if p value if greater than 0.5 results are likely to be down to chance and so must accept null hypothesis
whats the formula for degree of freedom
DF= number of variables in experiment - 1
what is meant by a critical value
the minimum value of a statistical test that gives a 5% probabilty its down to chance so the null hypo can be rejected
what is epistasis
when the expression of one gene is controlled by the inheritance of alleles of another gene at a different loci
what is a hypostatic gene
a gene that is affected by another gene
what is recessive epistasis
when the inheritance of recessive alleles causes the hypostatic gene to be masked
what is dominant epistasis
when the inheritance of dominant alleles causes the hypostatic gene to be masked
how could the epistatic gene actually cause the hypostatic gene to be masked
is the epistatic gene coded for an enzyme that modifies a precursor molecule so that the next enzyme in the pathway will not form complexes
what do 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 is the hardy-weinberg equation
p^2 + 2pq + q^2
define gene pool
sum of total of all genes in a population at any given time
define allele frequency
relative frequency of a particular allele in a population
what factors affect evolution
mutation
sexual selection
gene flow
genetic drift
natural selection
what are limiting factors
density-dependent factors
density-independent factors
what are density-dependent factors
give examples
depend on pop size
e.g.
competition, predation, parasitism, communicable disease
what are density-independent factors
affect pops the same no matter of size
e.g
climate change, natural disasters, season changes
what is stabalising selection
extreme characteristics slected against and modal value selected for increase frequency of alleles coding for this
what is directional selection
one of the extreme phenotypes is selected for and alleles coding for this become more frequent
occurs after change in environment
what is disruptive selection
extremes are selected for, increase the allele frequncy that code for these, reducing ‘average’ allele frequency
define speciation
formation of new species via process of evolution
what events occur that lead to speciation
pops become isolated and no-longer interbreed (no gene flow)
random mutation accumilate
due to random mutations populations can no longer interbreed to make fertile kids
what is allopatric speciation
populations become isolated via geogrphical barrier
what is sympatric speciation
2 species in the same habitat interbreed to form fertile offspring that cannot form fertile offspring with either species and is a new species
what is meantby the wild type
the allele coding for the most common charactersitic
what is pre and post zygotic sympatric speciation
prevents species coming together to form zygote is pre
zygote is infertile is post
