Reproductive Strategies and Genetic Diversity (Unit 2)
Reproductive Strategies: Sexual vs Asexual Reproduction
Sexual reproduction
Involves mixing genetic information from two parents to produce offspring with new genetic combinations.
Increases genetic diversity among offspring.
via meiosis, which allows for the random assortment of chromosomes and the potential for genetic recombination. This process leads to greater variability in traits, enhancing the adaptability of populations to changing environments.
Asexual reproduction
Involves a single parent producing offspring that are genetically similar (clones) to the parent.
No genetic recombination; typically less diversity.
via mitosis, which allows for rapid population growth and the ability to thrive in stable environments, as these offspring are well adapted to their parent’s surroundings.
Genetic Diversity: Why it matters
Genetic diversity is the raw material for natural selection, the mechanism of evolution (Darwin).
Genetic diversity (n.) is defined as genomic differences between individuals within a population.
Observation 1: There is phenotypic variation between members of a species.
Observation 2: Offspring tend to look like their parents.
Observation 3: Individuals produce more offspring than needed to replace themselves.
Observation 4: Some offspring don’t survive to reach sexual maturity.
Inference A: Individuals whose traits give them a greater chance to survive and reproduce leave more offspring than other individuals.
Fitness (n.): The quality of a trait that confers an individual an increased chance of survival or reproduction.
Inference B: The unequal chance of reproduction will lead to the accumulation of favourable (fit) traits in the population over generations.
Theory summary: How sexual reproduction creates genetic diversity
The great advantage of sexual reproduction is that it creates genetic diversity in a population. There are a number of ways in which it does this.
1. Mixing of genetic information between two parents.
2. Random mating within the population.
3. The independent assortment of non-homologous chromosomes at Metaphase I in meiosis.
4. Crossing over and recombination at Prophase I in meiosis.
More on sexual reproduction: Additional advantages
1. Mixing of genetic information between two parents.
2. Random mating within the population.
3. The independent assortment of non-homologous chromosomes at Metaphase I in meiosis.
4. Crossing over and recombination at Prophase I in meiosis.
Advantages of sexual reproduction (summary)
The independent assortment of non-homologous chromosomes at Metaphase I in meiosis.
Crossing over and recombination at Prophase I in meiosis.
1. Mixing of genetic information between two parents.
2. Random mating within the population.
3. The independent assortment of non-homologous chromosomes at Metaphase I in meiosis.
4. Crossing over and recombination at Prophase I in meiosis.
Disadvantages of sexual reproduction
1. Time and energy.
2. Inefficiency.
3. Dependence on vectors (e.g., disease agents or other carriers).
4. Risk to life.
Asexual reproduction: overview
Image/description notes: Asexual reproduction is depicted; advantages & disadvantages are covered.
Advantages of asexual reproduction:
Rapid population growth.
Efficient (no need to look for a mate).
Doesn’t rely on a vector.
Every member of a species can reproduce.
Disadvantage:
Doesn’t increase genetic variation.
Practice questions and key answers
Multiple choice activity: Genetic diversity is important in a species because:
A. it makes the species more interesting.
B. it increases the chance that individuals will all look the same.
C. it ensures the greatest number of individuals will survive.
D. it is necessary for evolution to take place.
E. I don’t know.
Answer: D
Multiple choice – Response: Genetic diversity is important in a species because:
A. it makes the species more interesting.
B. it increases the chance that individuals will all look the same.
C. it ensures the greatest number of individuals will survive.
D. it is necessary for evolution to take place.
E. I don’t know.
Answer: D
Compared to asexual reproduction, sexual reproduction has the advantage of:
A. being faster.
B. being more efficient.
C. promoting more genetic diversity.
D. being safer.
E. I don’t know.
Answer: C
Genetic variation in asexually reproducing species occurs as a result of:
A. mutation.
B. crossing over.
C. independent assortment of non-homologous chromosomes.
D. random mating.
E. I don’t know.
Answer: A
What we’ve covered and what’s next
Key takeaways:
Genetic variation is necessary for evolution to take place via natural selection.
Sexual reproduction increases the amount of genetic variation in a species, but it has some significant disadvantages.
Asexual reproduction has many advantages for a species, but its disadvantage is reduced genetic variation, since variation only comes from mutation.
Link: These ideas illustrate the relationship between diversity and inheritance; reproductive strategy significantly impacts diversity.
What’s coming next: Reproductive cloning! Bringing it all together.
Practical implications and connections
Genetic diversity influences how populations adapt to changing environments and resist disease.
Reproductive strategies are important in agriculture and conservation for managing diversity and stability.
Understanding the balance between diversity and uniformity helps in predicting evolutionary trajectories and in planning breeding programs.
Key definitions and concepts (glossary)
Genetic diversity: Genomic differences between individuals within a population.
Fitness: The quality of a trait that confers an individual an increased chance of survival or reproduction.
Natural selection: The process by which heritable traits that confer a survival or reproductive advantage become more common in a population over generations.
Reproductive cloning: A topic indicated as upcoming in the course material.