Section 7: Genetics, populations, evoloution, and ecosystems Flashcards
Define genotype and phenotype
genotype is the alleles that an organism has
phenotype is the observable characteristics
What is homozygous and heterozygous
Homozygous is when the allele on each chromosomes are the same
Heterozygous is when two alleles are different
What is it called when two alleles both contribute to a phenotype
codominant
What is monohybrid inheritance
the inheritance of a single gene with one trait
What is the difference between monohybrid and dihybrid inheritance
- Monohybrid inheritance:
• Involves the inheritance of one trait controlled by a single gene with two alleles (e.g., flower color).
• Example: Crossing a pea plant with purple flowers (Pp) with one having white flowers (pp).- Dihybrid inheritance:
• Involves the inheritance of two traits controlled by two different genes, each with two alleles (e.g., seed color and seed shape).
• Example: Crossing a plant with yellow round seeds (YyRr) with one having green wrinkled seeds (yyrr).
- Dihybrid inheritance:
What is Mendels law of independent assortment
Each member of the a pair of alleles may combine randomly with either of another pair of
the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.
What are the sex chromosomes of females and males in humans
Females XX chromosomes
Males XY chromosomes
What are non-sex-linked chromosomes called
autosomes
What is autosomal linkage and what does it presume?
When two or more genes are carried on the same autosome
assuming there is no crossing over and don’t segregate.
What is it called when an allele of one gene affects or masks the expression of another in the phenotype
Epistasis
What is epistasis
when an allele of one gene affects or masks the expression of another in the phenotype
If my critical value at p=0.05 is greater than my calculated value of chi-squared is the data significant?
This means there is no significant difference between the observed and expected data. In this case, you accept the null hypothesis and conclude that any differences are likely due to chance.
How do you calculate degrees of freedom
Number of classes minus 1
What are the conditions for the hardy-weinberg principles
no mutations arise
population is isolated
no selection
population is large
mating is random
What are the equations of the hardy weinberg principles
p + q = 1
p2 + q2 + 2pq = 1
Let the probability of allele A = p
and the probability of allele a = q
Define the term allelic frequency
Number of times an allele occurs in a gene pool
State what the hardy-weinberg principle predicts
The proportion of dominant and recessive alleles in a gene pool remains the same from one generation to the next
Genetic variation arises as a result of:
Mutations
Meiosis
Random fertilisation of gametes
State how genetic variation is increases in asexually reproducing organisms
mutation only
State four factors that lead to differential survival and reproduction
predation
competition
disease
natural disasters
What are the three types of selection
stabilising selection - eliminate extremes
directional selection - one extreme favoured
disruptive selection - extremes favoured
What is speciation
the evolution of new species from existing ones
Distinguish allopatric and sympatric speciation
• Allopatric speciation: Occurs when populations are geographically isolated, preventing gene flow and leading to the formation of new species.
• Sympatric speciation: Happens within the same geographic area, often due to reproductive barriers like behavioral differences, polyploidy, or ecological niche specialization.
Explain how isolation can lead to the formation of new species ( 5 marks )
- Populations become isolated (e.g., geographically or reproductively).
- No gene flow occurs between the isolated populations.
- Each population experiences different selection pressures.
- Beneficial mutations arise, and natural selection increases the frequency of advantageous alleles.
- Over time, genetic differences accumulate, and the populations can no longer interbreed to produce fertile offspring, forming new species.
Define the term “ecosystem”. (2 marks)
- An ecosystem is a community of living organisms (biotic) and their interactions with the non-living (abiotic) environment.
- It involves the flow of energy and cycling of nutrients.
Explain the difference between biotic and abiotic factors in an ecosystem. (2 marks)
- Biotic factors are the living components, such as predators or competition.
- Abiotic factors are the non-living components, such as temperature, light, and pH
What is meant by the term “carrying capacity”? (2 marks)
- The maximum stable population size that an environment can support.
- It is determined by factors like food availability, space, and abiotic conditions.
Describe how a population size is regulated by negative feedback. (3 marks)
- If population size exceeds carrying capacity, resources become limited, leading to competition and increased death rates.
- If population size falls below carrying capacity, resources become more abundant, increasing reproduction rates.
- This maintains population size around the carrying capacity.
Explain the role of pioneer species in primary succession. (3 marks)
- Pioneer species colonize bare or inhospitable environments.
- They change abiotic factors, such as improving soil quality by adding organic matter.
- This makes conditions suitable for other species, leading to ecological succession.
How does interspecific competition differ from intraspecific competition? (2 marks)
- Interspecific competition occurs between individuals of different species competing for the same resources.
- Intraspecific competition occurs between individuals of the same species competing for resources.
Explain how mark-release-recapture is used to estimate population size. (4 marks)
- Capture a sample of the population, mark them, and release them back.
- Allow time for the marked individuals to mix with the population.
- Recapture a second sample and count how many are marked.
- Use the formula: (Number marked in 1st sample × Total in 2nd sample) ÷ Number marked in 2nd sample.
What is conservation, and why is it important? (3 marks)
- Conservation is the management of ecosystems to maintain biodiversity.
- It ensures the survival of species and their genetic diversity.
- It provides ecosystem services, like air and water purification, and resources for humans.
Describe the difference between primary and secondary succession. (3 marks)
- Primary succession begins on newly formed or bare land with no soil (e.g., volcanic rock).
- Secondary succession occurs on land where soil is present but vegetation has been removed (e.g., after a fire).
- Secondary succession is faster because soil and seeds are already present.
What is a dihybrid cross? (2 marks)
- A genetic cross involving two traits controlled by two different genes.
- Example: Crossing pea plants for seed color (yellow/green) and seed shape (round/wrinkled).
What is the difference between dominant and recessive alleles? (2 marks)
- A dominant allele is expressed in the phenotype even if only one copy is present.
- A recessive allele is only expressed in the phenotype if both alleles are recessive.
Explain why males are more likely than females to show recessive sex-linked traits. (3 marks)
- Males have one X and one Y chromosome.
- Recessive alleles on the X chromosome are expressed as there is no equivalent allele on the Y chromosome.
- Females have two X chromosomes, so a dominant allele on one X can mask the recessive allele on the other.
Describe the purpose of a test cross and how it is carried out. (3 marks)
- Used to determine the genotype of an individual showing a dominant phenotype.
- Cross the individual with one that is homozygous recessive.
- Analyze the offspring phenotypes: a 1:1 ratio indicates heterozygosity.
Explain how codominance affects the phenotypes of offspring. (3 marks)
- In codominance, both alleles are expressed in the phenotype.
- Heterozygotes show a combination of both alleles.
- Example: In blood groups, IAIB results in the AB phenotype.
What is epistasis, and how does it affect phenotypic ratios? (4 marks)
- Epistasis is when one gene affects the expression of another gene.
- It can modify Mendelian ratios.
- For example, in dihybrid inheritance, the ratio may change from 9:3:3:1 to 9:4:3 due to epistasis.
- One gene may mask or suppress the other gene.
State the Hardy-Weinberg equation and explain what each term represents. (3 marks)
- Equation: p^2 + 2pq + q^2 = 1 .
- p^2 : Frequency of homozygous dominant individuals.
- 2pq : Frequency of heterozygous individuals.
- q^2 : Frequency of homozygous recessive individuals.
What is genetic drift, and in which populations does it have a greater effect? (3 marks)
- Genetic drift is the random change in allele frequencies in a population over time.
- It has a greater effect in small populations.
- Alleles can be lost or fixed by chance more easily in smaller populations.
Explain how natural selection leads to evolution. (5 marks)
- Variation exists in a population due to mutations.
- Some individuals have advantageous alleles.
- These individuals are more likely to survive and reproduce.
- They pass on their advantageous alleles to their offspring.
- Over generations, the frequency of the advantageous allele increases in the population.
Describe how you could estimate the number of plants in a field
Place two tape measures at 90 degrees to each other to create grids
Obtain random coordinates
count number of plants in each coordinate
Large sample (10+) and calculate a mean
Area of the field multiplied by mean number of plants in each quadrant
If i multiply Xmm by 1000 what unit have i converted the value X to
Um
cant find symbol
How would i convert Xcm into um
multiply by 10,000
km -> m -> mm -> um -> nm
what would i multiply each one by to convert the units
x 1000
Suggest factors that result in phenotypic diversity
Habitat differences
Gene mutations
