6.2 Patterns Of Inheritance Flashcards
How can genetic diversity be measured
by looking at the number of polymorphic genes
Phenotype
visible characteristics of an organism e.g. blue eye vs green eye.
What is phenotype a combo of
environment + genetics = could include diet in animals.
What’s etiolation and what’s the effect of it
different environmental conditions (presence or absence of light) can influence if they have a strong or weak stem = in etiolation they always have a weak stem. also affects the colour in plants as well genetics.
Chlorosis
when the leaves produce insufficient chlorophyll due to mineral deficiencies e.g. iron
Genotype
genetic makeup of an organism (combination of alleles)
What can lead to genetic variation.
Meiosis, random fusion of gametes
What do mutagens do
Increase rate of gene mutation
What categories can mutagens be split into
physical (x rays, uv light, gamma rays), chemical (tar, free radicals, nitrous acid) and biological agents (viruses)
Types of chromosome mutation
Deletion
Inversion
Translocation
Duplication
Non disjunction
Deletion
- part of a chromosome is lost/deleted
Inversion
- Section of a chromosome breaks up, turns 180 degrees then joins together again
What’s the problem w inversion
even though u still have the same content the genes can be far away from the regulatory sequences
Translocation
- piece of chromosome breaks up and gets attached to another chromosome
- This effects the expression of genes
Duplication
- when a piece of chromosome becomes duplicated = double amount you need
- Causes over expression which can be dangerous
Non disjunction
- one pair of chromosomes failed to separate during meiosis and it can lead to gametes w extra chromosomes
Subtypes of non disjunction
Aneuploidy, polyploidy
Aneuploidy
chromosome number is not an exact multiple of the haploid number for that organism
Polyploidy
fusion of gametes results in an abnormal chromosome number = more than 2 sets of chromosomes
Effect of environment
can cause genetic variation but they don’t get passed on e.g. hair colour, piercings
Effects of a mutation on a protein
- could code for proteins that could be harmful, advantageous or neutral
Ways genetic variation occurs in meiosis:
- crossing over in prophase 1
- Independent assortment of chromosomes in metaphase 1
- Independent assortment of chromatids in metaphase 2
- Choice of gamete at the end is random - random fertilisation
Monogenic inheritance
- phenotypes or traits that are controlled by one gene e.g. cystic fibrosis is only caused by one gene
Study ab Monogenic inheritance
- Mendel did experiment on peas looking at ones w diff traits and saw what happened
Homologous chromosomes
every chromosome except x and y= same size, same shape, same gene at same loci
Genetic diagram for Monogenic inheritance
First one = pure breeding = two homozygous parents = produces first generation
F1 = first generation breeding = should be 2 heterozygous parents
ALWAYS WRITE A KEY. E.g. T = tall stem and t = short stem
Punnett square for Monogenic inheritance
expected ratio for cross f1s in a mono hybrid inheritance
3:1
Dihybrid inheritance
2 gene locis that get inherited together
expected ration for cross f1s in a dihybrid inheritance
9:3:3:1
Genetic diagram for Dihybrid inheritance
Multiple alleles
- When a gene has multipley alleles e.g. blue, green, red, brown eye
Codominance
2 alleles are dominant and come up in the phenotype together
Heretic diagram showing Codominance
A and B blood groups = dominant
O = recessive
Girls and guys sex chromosome?
- girls have XX and guys have XY
Which sex chromosome carries more genes + why
- Letter x is slightly longer than y so X chromosome carries more genes that aren’t present on the Y chromosome
Effect of X chromosome being slightly longer
- Any recessive trait linked to the X chromosome means guys are more at risk of getting it because they only need one of the recessive allele for it to be present
Why can females be symptomless carriers of recessive x linked disease
- In XX, a recessive x linked disease, females can be symptomless carriers. But male’s XY combination means that they can’t be carriers, they only have one X
Example of X linked disease + effect on males
- Haemophilia is a blood disorder where the blood can’t clot properly. The gene for blood clotting is carried on the X chromosome and males are more likely to get it because they only have one X. Same with colourblindness
X chromosome becomes randomly inactivated. Why?
- In every single XX combo nucleus, one X chromosome becomes randomly inactivated to avoid over expression. This means even if we’re carriers, some girls can still have the bad allele inactivated and the good one present
What does the hardy Weinberg principle do
predicts proportion of dominant + recessive alleles in a population
Hardy Weinberg principle equation
Criteria for hardy Weinberg principle
- has to be a large population size so any sampling error is valid
- Mating within the population should be random
- No selective advantage for any genotype = no selection = alleles are all equally likely to appear in every member of the population
- No mutation, migration or genetic drift
Autosome
chromosome that isn’t a sex chromosome. Genes that are ‘linked’
Which chromosomes are autosomal
Everything except the set chromosome (last chromosome of the 23)
Autosomal linkage
When the two genes are present on the same autosomal chromosome
Why is autosomal linkage not affected by independent assortment
- On separate loci of the same autosomal chromosome there are genes which are linked (stuck together) so they aren’t affected by independent assortment
Why might autosomal linkage cause deviation from 9:3:3:1 ratio
If crossing over doesn’t happen, 2 genes on the same chromosome are often inherited together
Effect of gene loci on inheritance in autosomal linkage
closer the gene loci are, the more likely they are to be inherited together
Epistasis
- when the expression of one gene affects the other. One gene loci can either promote or inhibit the expression of another loci
2 types of Epistasis
Recessive and dominant
Recessive Epistasis
if the first gene is in a recessive format (rr) no matter what’s on the second gene, the second gene won’t be expressed
Name of first and second gene in recessive epistasis
- second gene = hypostatic gene
- First gene = epistatic gene
Link between first and second gene in recessive Epistasis
- The first gene is epistatic to those on the second gene (hypostatic gene)
Example of recessive Epistasis
- Usually somethign that happens w pigments and colours = first gene usually codes for an enzyme that produces pigment. If the first gene isn’t producing the enzyme for pigment bc it’s recessive then the second gene for pigment won’t be expressed
Recessive Epistasis ratio
9:3:4
Dominant Epistasis
if the first gene is in a dominant format then the second gene is not expressed
Dominant Epistasis ratio
12:3:1
Complementary fashion
when the epistatic and hypostatic gene work with eachother. If one doesn’t work they’re both impacted
Chi squared test criteria
- data has to be in categories and not continuous
- Strong biological theory to use to predict expected values
- The sample size has to be large
- The data only contains raw counts (complete numbers)
- There should be no 0s in the count
Null hypothesis
no statistically significant difference between what you observed and what you expected
Chi squared equation
How to do chi squared after doing the equation
- go to statistical table and look at the degrees of freedom (number of categories - 1) and look at the data at 0.05 and see if the result is statistically significant.
What happens if chi squared calculated vakue is smaller than critical value?
- The calculated value of chi squared is smaller than the critical value at p=0.05 therefore accept the null hypothesis as the difference isn’t statically significant
Discontinuous variation
put into specific categories = often monogenic = less influenced by the environment
Continuous variation
has a range = often affected by multiple genes (polygenic) = influenced by the environment aswell
Natural selection
- concept of survival of the fittest = in every population there’s various alleles due to mutations
Why does natural selection occur
- selection pressure initates selection
Why are some members of a species more fitted for survival than others?
- Some alleles are better adapted to the environment than others and those that are better adapted are more likely to survive, reproduce and pass on the advantageous allele
- Over time the allele frequency of that specific allele will change
Stabilising selection
- when the environment favours the intermediate type (average individual) (middle value)
Directional selection
- when the environment begins to favour in a specific direction (specific type of individual)
Disruptive selection
- when the extremes are favoured rather than the intermediate
Genetic diversity
genetic differences between individuals within a population
Allele frequency
how often a particular allele occurs within a population
Effect of population size on genetic drift
- The smaller the population, the more likely they are to be effected by selection pressure + have a genetic drift
Why do selection pressures often occur
Bc of natural disasters
Genetic bottleneck
sharp reduction in size, leading to a loss of genetic diversity.
caused by various factors such as natural disasters, habitat destruction, or human activities.
population rebounds from the bottleneck = still have reduced genetic variation.
may increase its susceptibility to diseases or other threats.
What can genetic bottleneck lead to
low genetic diversity bc modern population descended from few survivors
Gene pool
complete range of alleles in a population
Genetic drift definition
characteristics are passed on by chance rather than due to factors that affect the individuals ability to survive
Founder effect
when you have an original population but the original population migrate and create a new population in which their alleles will not be different
Allele frequency
How often an allele appears in a population
How are allele frequency and evolution relation
Evolution is the change in the frequency of an allele in a population over time
Explain why variation is needed for evolution to take place
Individuals vary, some are better adapted to selection pressures than others, survive, reproduce and pass on alleles
Explain why founder effect can lead to an increased incidence of genetic disease
Allele frequency’s higher than original population
Ig one of these alleles represents a genetic disorder = increased incidence in the population
Speciation
the splitting of a genetically similar population into two or more populations that undergo genetic differentiation and eventually reproductive isolation, leading to the evolution of two or more new species.
Allopatric speciation AKA….
Geographical isolation
Sympatric speciation AKA…
Reproductive isolation
Allopatric speciation
same species go to two different areas due to a geographical barrier between them = no longer able to meet and reproduce = eventually leads to reproductive isolation.
Sympatric speciation
forming 2 different species but they are still in the same habitat = no geographical barrier but reproductive isolation eventually happens due to being in diff areas e.g. forest and beach of same island but no barrier between
Why can two organisms no longer reproduce to produce fertile offspring
no. Of chromosomes may change, courtship behaviours, genital differences
Conditions for speciation to occur
- mutations, natural selection, selection pressure
Why can reproductive isolation occur
seasonal changes (different flowering/mating seasons),
mechanical changes (changes in genitalia prevent successful mating)
behavioural changes (different courtship rituals develop)
Artificial selection
- humans pick the desired phenotypes + interbreed them
What can artificial selection be done w
Farming, plants
Problem of artificial selection (depression)
can lead to inbreeding depression = the more you breed siblings together the higher the chance of the recessive alleles becoming more common
Problem of artificial selection (vigour)
Hybrid vigour = process of crossing individuals of 2 different varieties to increase the chance of heterozygous combination
Gene banks
how you store different genes e.g. in form of seeds, as crops, frozen embryos
Problem w gene banks (diversity)
decreases genetic diversity = in the future if a disease can wipe one of them away it would kill everyone
Problem w gene banks (disease)
inbreeding can cause new diseases
Problem w gene banks (domestication)
if you domesticate animals it decreases their chance of defending themselves = unable to cope in the wild
Ethical considerations for artificial selection
Domesticated animals more docile = less able to defend themselves
Livestock animals more lean = less fat so in colder weather need to be housed
Inbreeding = more susceptible to disease
Colour of coats = loss of camouflage
Evidence to support theory of evolution by natural selection
DNA because:
- Found in all organisms + some sequences highly conserved
- Can compare dna between species
