Chapter 20: Patterns of Variation and Inheritance Flashcards
What is chlorosis and what are the causes?
- Leaves look pale yellow due to cells not producing enough chlorophyll.
Causes:
- Lack of light.
- Mineral deficiencies.
- Viral infections.
Define genotype.
- Alleles that code for a characteristic.
Define phenotype.
- The physical characteristics.
State difference between homozygous + heterozygous genotype.
- Homozygous = two identical alleles for a characteristic.
- Heterozygous = two different alleles for a characteristic where the dominant allele will be expressed.
Define monogenic inheritance.
- Characteristic inherited on a single gene.
Describe codominance.
- Two different alleles occur for a gene –> both equally dominant.
- Both expressed on phenotype of organism if present.
Name an example of a sex linked disease and state the genotypes for males + females.
- Haemophilia.
- X^h Y= infected male
- X^H Y = normal male
- X^H X^H = normal female
- X^H X^h = carrier female.
- X^h X^h = infected female.
Define dihybrid inheritance.
- Inheritance of two characteristics controlled by different genes.
Name an example of dihybrid inheritance + state genotypes.
- Peas.
- Y = allele coding for yellow seeds.
- y = allele coding for green seeds.
- R = allele coding for round seeds.
- r = allele coding for wrinkled seeds.
- F2 generation –> ratio of 9:3:3:1 for yellow rounded:yellow wrinkled:green rounded: green wrinkled.
Why is actual ratio of offspring in F2 gen for peas different to expected 9:3:3:1 ratio.
- Random fertilisation of gametes.
- Genes being studied are on same chromosomes –> linked genes –> inherited together if no crossing over occurs.
- New allele combinations created.
- Sample size too low.
Define linkage.
- Genes that code for different characteristics are present at different gene loci on same chromosome.
Define recombinant offspring.
- Different combination of alleles than each parent.
What does the chi-squared test measure?
- The difference between the expected results and the observed results.
- Tests the null hypothesis.
- Small chi-squared < critical value at 5% –> little difference between observed + expected –> differences due to chance.
- Large chi-squared > critical value at 5% –> reject H0 –> significant difference between observed + expected.
Define epistasis.
- Interaction of genes at different loci.
- Multi-step interaction.
What is a hypostatic gene?
- Gene that is affected by another gene.
What is an epistatic gene?
- Gene that affects the expression of another gene.
- Masks expression –> lack of substrate available to bind to active site of next enzyme in pathway –> less enzyme produced.
What are the conditions required for the Hardy-Weinberg Principle to be valid.
- No mutations –> constant allele frequency.
- Isolated pop.
- Random mating within pop.
- Large pop.
- Characteristic being studied is not sex linked.
- No selection pressures of any type.
What are the factors affecting evolution.
- Mutation
- Sexual selection = increase in allele frequency of alleles that increase reproductive success.
- Gene flow.
- Genetic drift in small pops.
- Natural selection.
Outline stabilising selection.
- Increase in frequency of normal (positive) alleles –> selected for.
- Decrease in frequency of extreme (negative) alleles –> selected against.
Outline directional (natural) selection.
- Change in environment –> normal allele no longer most advantageous.
- Extreme allele becomes more advantageous + is selected for.
- Leads to evolution.
Outline disruptive selection.
- Extremes selected for and norms selected against.
Outline the process of allopatric speciation.
- Geographical isolation to separate gene pools –> no interbreeding between pops.
- Variation due to mutation.
- Natural selection –> different selection pressures –> those with most advantageous alleles survive + reproduce passing advantageous alleles to offspring.
- Increase in allele frequency of advantageous allele + decrease in disadvantageous allele.
- Repeats over many generations.
Outline sympatric speciation.
- Geographical isolation not needed for reproductive isolation.
- Random mating leads to reproductive isolation.
Post-zygotic barrier:
- After fertilisation –> reduces reproductive viability of offspring –> hybridisation –> infertile offspring.
Prezygotic barrier:
- Prevent fertilisation + formation of zygote.
- E.g. geographical isolation, anatomical, seasonal and behavioural changes.
- Rare because organisms are exposed to same selection pressures.
Outline steps of artificial selection/selective breeding.
- Select organisms with desired traits.
- Breed them.
- Monitor offspring + select those who exhibit the desired characteristic.
- Interbreed to offspring.
- Repeat for many generations.
Issues with selective breeding.
- Reduces gene pool.
- Inbreeding.
- Reduced genetic diversity.
- Loss of potentially useful alleles.
- Increased susceptibility to disease.
Issues with inbreeding.
- Many genetic disorders are caused by recessive alleles.
- Decreased genetic diversity + gene pool.
- Large GD –> recessive alleles masked –> heterozygous individuals.
- More closely related individuals same homozygous alleles.
- More likely to get genetic disorders + increased susceptibility to disease.
