Section 7: Genetics, populations, evoloution, and ecosystems

Question 1

Define genotype and phenotype

Answer 1

genotype is the alleles that an organism has
phenotype is the observable characteristics

Question 2

What is homozygous and heterozygous

Answer 2

Homozygous is when the allele on each chromosomes are the same
Heterozygous is when two alleles are different

Question 3

What is it called when two alleles both contribute to a phenotype

Answer 3

codominant

Question 4

What is monohybrid inheritance

Answer 4

the inheritance of a single gene with one trait

Question 5

What is the difference between monohybrid and dihybrid inheritance

Answer 5

1. 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).
   
   2. 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).

Question 6

What is Mendels law of independent assortment

Answer 6

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.

Question 7

What are the sex chromosomes of females and males in humans

Answer 7

Females XX chromosomes
Males XY chromosomes

Question 8

What are non-sex-linked chromosomes called

Answer 8

autosomes

Question 9

What is autosomal linkage and what does it presume?

Answer 9

When two or more genes are carried on the same autosome
assuming there is no crossing over and don’t segregate.

Question 10

What is it called when an allele of one gene affects or masks the expression of another in the phenotype

Answer 10

Epistasis

Question 11

What is epistasis

Answer 11

when an allele of one gene affects or masks the expression of another in the phenotype

Question 12

If my critical value at p=0.05 is greater than my calculated value of chi-squared is the data significant?

Answer 12

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.

Question 13

How do you calculate degrees of freedom

Answer 13

Number of classes minus 1

Question 14

What are the conditions for the hardy-weinberg principles

Answer 14

no mutations arise
population is isolated
no selection
population is large
mating is random

Question 15

What are the equations of the hardy weinberg principles

Answer 15

p + q = 1
p2 + q2 + 2pq = 1
Let the probability of allele A = p
and the probability of allele a = q

Question 16

Define the term allelic frequency

Answer 16

Number of times an allele occurs in a gene pool

Question 17

State what the hardy-weinberg principle predicts

Answer 17

The proportion of dominant and recessive alleles in a gene pool remains the same from one generation to the next

Question 18

Genetic variation arises as a result of:

Answer 18

Mutations
Meiosis
Random fertilisation of gametes

Question 19

State how genetic variation is increases in asexually reproducing organisms

Answer 19

mutation only

Question 20

State four factors that lead to differential survival and reproduction

Answer 20

predation
competition
disease
natural disasters

Question 21

What are the three types of selection

Answer 21

stabilising selection - eliminate extremes
directional selection - one extreme favoured
disruptive selection - extremes favoured

Question 22

What is speciation

Answer 22

the evolution of new species from existing ones

Question 23

Distinguish allopatric and sympatric speciation

Answer 23

• 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.

Question 24

Explain how isolation can lead to the formation of new species ( 5 marks )

Answer 24

1. Populations become isolated (e.g., geographically or reproductively).
   
   2. No gene flow occurs between the isolated populations.
   3. Each population experiences different selection pressures.
   4. Beneficial mutations arise, and natural selection increases the frequency of advantageous alleles.
   5. Over time, genetic differences accumulate, and the populations can no longer interbreed to produce fertile offspring, forming new species.

Question 25

Define the term “ecosystem”. (2 marks)

Answer 25

1. An ecosystem is a community of living organisms (biotic) and their interactions with the non-living (abiotic) environment.
   
   2. It involves the flow of energy and cycling of nutrients.

Question 26

Explain the difference between biotic and abiotic factors in an ecosystem. (2 marks)

Answer 26

1. Biotic factors are the living components, such as predators or competition.
   
   2. Abiotic factors are the non-living components, such as temperature, light, and pH

Question 27

What is meant by the term “carrying capacity”? (2 marks)

Answer 27

1. The maximum stable population size that an environment can support.
   
   2. It is determined by factors like food availability, space, and abiotic conditions.

Question 28

Describe how a population size is regulated by negative feedback. (3 marks)

Answer 28

1. If population size exceeds carrying capacity, resources become limited, leading to competition and increased death rates.
   
   2. If population size falls below carrying capacity, resources become more abundant, increasing reproduction rates.
   3. This maintains population size around the carrying capacity.

Question 29

Explain the role of pioneer species in primary succession. (3 marks)

Answer 29

1. Pioneer species colonize bare or inhospitable environments.
   
   2. They change abiotic factors, such as improving soil quality by adding organic matter.
   3. This makes conditions suitable for other species, leading to ecological succession.

Question 30

How does interspecific competition differ from intraspecific competition? (2 marks)

Answer 30

1. Interspecific competition occurs between individuals of different species competing for the same resources.
   
   2. Intraspecific competition occurs between individuals of the same species competing for resources.

Question 31

Explain how mark-release-recapture is used to estimate population size. (4 marks)

Answer 31

1. Capture a sample of the population, mark them, and release them back.
   
   2. Allow time for the marked individuals to mix with the population.
   3. Recapture a second sample and count how many are marked.
   4. Use the formula: (Number marked in 1st sample × Total in 2nd sample) ÷ Number marked in 2nd sample.

Question 32

What is conservation, and why is it important? (3 marks)

Answer 32

1. Conservation is the management of ecosystems to maintain biodiversity.
   
   2. It ensures the survival of species and their genetic diversity.
   3. It provides ecosystem services, like air and water purification, and resources for humans.

Question 33

Describe the difference between primary and secondary succession. (3 marks)

Answer 33

1. Primary succession begins on newly formed or bare land with no soil (e.g., volcanic rock).
   
   2. Secondary succession occurs on land where soil is present but vegetation has been removed (e.g., after a fire).
   3. Secondary succession is faster because soil and seeds are already present.

Question 34

What is a dihybrid cross? (2 marks)

Answer 34

1. A genetic cross involving two traits controlled by two different genes.
   
   2. Example: Crossing pea plants for seed color (yellow/green) and seed shape (round/wrinkled).

Question 35

What is the difference between dominant and recessive alleles? (2 marks)

Answer 35

1. A dominant allele is expressed in the phenotype even if only one copy is present.
   
   2. A recessive allele is only expressed in the phenotype if both alleles are recessive.

Question 36

Explain why males are more likely than females to show recessive sex-linked traits. (3 marks)

Answer 36

1. Males have one X and one Y chromosome.
   
   2. Recessive alleles on the X chromosome are expressed as there is no equivalent allele on the Y chromosome.
   3. Females have two X chromosomes, so a dominant allele on one X can mask the recessive allele on the other.

Question 37

Describe the purpose of a test cross and how it is carried out. (3 marks)

Answer 37

1. Used to determine the genotype of an individual showing a dominant phenotype.
   
   2. Cross the individual with one that is homozygous recessive.
   3. Analyze the offspring phenotypes: a 1:1 ratio indicates heterozygosity.

Question 38

Explain how codominance affects the phenotypes of offspring. (3 marks)

Answer 38

1. In codominance, both alleles are expressed in the phenotype.
   
   2. Heterozygotes show a combination of both alleles.
   3. Example: In blood groups, IAIB results in the AB phenotype.

Question 39

What is epistasis, and how does it affect phenotypic ratios? (4 marks)

Answer 39

1. Epistasis is when one gene affects the expression of another gene.
   
   2. It can modify Mendelian ratios.
   3. For example, in dihybrid inheritance, the ratio may change from 9:3:3:1 to 9:4:3 due to epistasis.
   4. One gene may mask or suppress the other gene.

Question 40

State the Hardy-Weinberg equation and explain what each term represents. (3 marks)

Answer 40

1. Equation: p^2 + 2pq + q^2 = 1 .
   
   2. p^2 : Frequency of homozygous dominant individuals.
   3. 2pq : Frequency of heterozygous individuals.
   4. q^2 : Frequency of homozygous recessive individuals.

Question 41

What is genetic drift, and in which populations does it have a greater effect? (3 marks)

Answer 41

1. Genetic drift is the random change in allele frequencies in a population over time.
   
   2. It has a greater effect in small populations.
   3. Alleles can be lost or fixed by chance more easily in smaller populations.

Question 42

Explain how natural selection leads to evolution. (5 marks)

Answer 42

1. Variation exists in a population due to mutations.
   
   2. Some individuals have advantageous alleles.
   3. These individuals are more likely to survive and reproduce.
   4. They pass on their advantageous alleles to their offspring.
   5. Over generations, the frequency of the advantageous allele increases in the population.