6.1.2 patterns of inheritance Flashcards
what is an individuals phenotype the result of
6.1.1(a)
An individual’s phenotype is a result of its genotype and its environment
which genetic factors can contribute to phenotypic variation
6.1.1(a)
Genetic variation caused by mutations those which are expressed in the phenotype contribute to phenotypic variation
which changes do not contribute to phenotypic variation
6.1.1(a)
Silent mutations do not contribute to the phenotype
what are mutations caused by
6.1.1(a)
mutagenic agents for example
UV light
X-rays
what other genetic factors can influence phenotype
6.1.1(a)
chromosomal mutations
what is deletion
6.1.1(a)
part of the chromosome is lost
what is inversion
6.1.1(a)
section of chromosome breaks off then is re-inserted into the opposite direction
what is translocation
6.1.1(a)
section of the chromosome breaks off then is re-inserted on a different chromosome
what is duplication
6.1.1(a)
part of a chromosome occurs twice
what is non-disjunction
6.1.1(a)
one pair of chromosome fails to separate so the gamete and zygote has an extra chromosome
how is genetic variation caused by sexual reproduction
6.1.1(a)
· Crossing over of non-sister chromatids during prophase I of meiosis -> double-stranded breaks in anaphase I, leading to new allele combinations on chromosomes
· Independent assortment of homologous chromosomes during metaphase I of meiosis
· Independent assortment of sister chromatids during metaphase II of meiosis
· Random fusion of gametes at fertilisation
how other type of variation is there that can impact phenotype
6.1.1(a)
variation caused by environmental factors alone
eg-losing a limb in a car accident
what is epigenetics
6.1.1(a)
when environmental conditions can affect the expression of some genes
what is a example of phenotypic variation caused by the genetics
6.1.1(a)
Lactose intolerance in infants is caused by mutations in the LCT gene. The LCT gene codes for lactase.
A mutation in the LCT gene will cause a change to the shape of lactase. This mutation is observed in infant phenotypes as an impaired ability to digest lactose in breast milk or formula
what is a example of phenotypic variation caused by the environment
6.1.2(a)
chlorosis is a yellowing of leaf tissue due to a lack of chlorophyll leaf expression however there are some environmental causes
eg-damaged roots, nutrient deficiancies, lack of light
what does monogenetic inheritance show
6.1.2(b)
inheritance of a single gene with 2 alleles
what does dihybrid inhertance show
6.1.2(b)
inhertaince of 2 genes
what is codominance
6.1.2(b)
when both alleles are expressed at the same time
what are autosomal chromosomes
6.1.2(b)
chromosomes that are not sex linked
what are linked genes
6.1.2(b)
when two chromosomes are physically close together
is crossing over between linked genes likely or unlikely
unlikely
what is a dihybrid cross and what is the ratio we are expecting
6.1.2(b)
between two hetrozygous (RrYy)
the expected ratio is 9:3:3:1
what is sex linkage
when genes are located on the x chromosome
-men are more likely to inherit sex linked chromosomes as they only have one X chromosome
how can we see if two genes are linked
use recombinant frequency
(recominants/ total offspring) X 100
small recombiannt frequency means more closely linked genes
what is epistasis
when one genes affect the expression of another gene
what is recessive epistasis
when the prescene of a recessive allele prevents the expression of another allele at a second locus
9:4:3
what is dominant epistasis
when the prescence of a domiannt allele at one locus prevents the expression of another allele at a second locus
what is the null hypothesis for the chi squared test
6.1.2(c)
The null hypothesis for a chi-squared test is that there is no significant difference between the observed frequencies and the expected frequencies. This is what we are trying to disprove when we carry out a chi-squared test.
look in booklet at chi-squared equation
6.1.2(c)
How do you work out expected results
in booklet
once you have a chi-squared value what do you need to determine
6.1.2(c)
Once you have a chi-squared value, you need to determine whether it is statistically significant.
0.05 significance level
6.1.2(c)
how do you determine if the chi-squared value is significantly significant
6.1.2(c)
To determine whether the chi-squared value is statistically significant, we need to compare it to a critical value. We read this from a critical values table
how do you determine which critical values to pick
6.1.2(c)
To determine which critical value to pick, you need to calculate the degrees of freedom for the chi-squared test you have done
how do you determine degrees of freedom for a chi-squared test
6.1.2(c)
Degrees of freedom for a chi-squared test = number of categories – 1.
when do you accept your null hypothesis
6.1.2(c)
accept null hypothesis if critical value is bigger than calculated
observed results were not significantly different from excpected results
what is variation within a species called
6.1.2(d)
Variation within a species is called intraspecific variation
what is variation between distinct species called
6.1.2(d)
Variation between distinct species is called interspecific variation
what is continuous variation
6.1.2(d)
occurs when many genes contribute to the phenotype (polygenic)
usually the environment contributes to the phenotype too
how is continuous variation represented
6.1.2(d)
continuous variation is represented on a histogram
what does a histogram show
6.1.2(d)
Continuous variation is plotted on a histogram, which shows a normal distribution. This is a distribution of frequency that is symmetrical around the mean.
what is discontinuous variation
6.1.2(d)
usually controlled by 1 or a small amount of genes
environment has little or no impact
how is discontinous variation represented
6.1.2(d)
on a bar chart as it leads to categoric data
what does natural selection cause
6.1.2(e)
Natural selection can cause a change in allele frequencies, with fitness-increasing alleles becoming more common in the population.
what is fitness
6.1.2(e)
Fitness is a measure of reproductive success: how many offspring an organism leaves in the next generation, relative to others in the group.
what does natural selection take the form of
6.1.2(e)
Natural selection on polygenic, continuous traits may take the form of stabilising selection, directional selection, or disruptive selection
what is stabilising selection
6.1.2(e)
average (middle) phenotype is selected for so the individuals with extreme phenotypes will be selected against. Overtime the individuals with extreme phenotypes will be selected against. Overtime the frequency of extreme phenotypes and the alleles that caused them will decrease
what is directional selection
6.1.2(e)
one extreme is selected for the other is selected against. The alleles for the extreme with higher fitness increase in frequency in the population
what is disruptive selection
6.1.2(e)
the two extremes are selected for they have a reproductive advantage. The alleles causing the middling phenotype will decrease in frequency in the population
what is genetic drift
6.1.2(e)
random change/loss in allele frequencies to due chance
what may genetic drift result in
6.1.2(e)
fixation-the loss of all but one allele for a certain gene. That allele has a 100% frequency and the rest have a 0% frequency
what population size does genetic drift occur in
6.1.2(e)
all sizes but its stronger in smaller populations
in which populations is fixation more likely
6.1.2(e)
small popualations
what is genetic bottleneck
6.1.2(e)
event that drastically reduces the size of the population allele frequency decreases in the population with certain alleles being lost completely
The smaller population will be more susceptible to the effects of genetic drift until number return to normal
what is the founder effect
6.1.2(e)
some individuals break off from the orginal population. Those individuals wont represent the genetic biodiversity of the original population as some alleles may be lost
what is the gene pool
6.1.2(f)
The total number of all the alelles present in a population at one time
what are some factors favouring the stability of the gene pool and if these conditions are fulfilled what happens
6.1.2(f)
-no mutation
-no natural selection
-the population being large
-no gene flow (no individuals emigrating/ immigrating)
-random mating
if these conditions are met then proportion of alleles will stay constant over generations.
what occurs if all the factors favoring stability are fufilled
6.1.2(f)
the ratio of alleles for genes can be calculated using the hardy-weinberg principle
what does P represent
6.1.2(f)
frequency of dominant allele
what does Q represent
6.1.2(F)
frequency of recessive allele
what are the 2 hard weinberg equations
6.1.2(f)
P + Q=1
P^2 + 2PQ + Q^2=1
What do you use p^2 to calculate
6.1.2(f)
frequency of homozygous dominant genotype
what can you use 2PQ to calculate
6.1.2(f)
frequency of heterozygous genotype
what can you use q^2 to calculate
6.1.2(f)
frequency of homozygous recessive genotype
what are the 3 factors that cause speciation (formation of a new species)
6.1.2(g)
-isolation
-mutation
-natural selection
what is allopatric speciation
6.1.2(g)
when new species arise due to isolation of a population by geographical barriers
within isolated population mutations can occur
selection pressure will be different in different habitats
the alleles with highest fitness will be selected leading to different traits evolving overtime
evetually leading to a new species as they wont breed to produce fertile offspring
what is sympatric speciation
6.1.2(g)
takes place with no geographical barrier
a population of habitats live in the same location they are separated into 2 different species with 2 different niches
how does selective breeding occur
6.1.2(h)
-humans apply a selection pressure
-individuals with a desirable phenotype are chosen to interbreed
-some of the alleles for the desirable phenotype are passed onto offspring
-offspring with the most desirable phenotype are chosen to interbreed
-this is repeated for many generations
what occurs over many generations
6.1.2(h)
-alleles that are desirable to humans increase in frequency
-alleles that are less desirable may completely disappear overtime
in artificial natural selection why is it important to maintain a resource of genetic material
6.1.2(h)
so you have individuals that are close to the original wild type so gene pool does not become too small
what is an example of a plant that has been heavily inbred in the past and the desirable traits
6.1.2(h)
maize-
-resistance to pest
-higher yield
-good growth in poor conditions
how has inbredding depression in maize plants occured in the past
6.1.2(h)
-increases the chance of harmful recessive allels being combined in an individual and being expressed in the phenotype
-leads to decreased growth and vulnerability
how can a farmer prevent inbreeding depression
6.12(h)
outbreeding with wild plants
2 ethical issues in regards to artifical natural selection
6.1.2(h)
-higher chance of developing harmful genetic defects due to reduced gene pool
-organisms may be vulnerable to new diseases (less chance of resistant allele being present in offspring)
how have dogs suffered because of natural selection
6.1.2(h)
bullfogs have breathing problems because of shortened snouts
large dogs such as great danes suffer from hip dysplasia
