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Biology IB HL - 5.2 Natural Selection Part 2

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This deck covers key concepts related to natural selection, including genetic variation, meiosis, and adaptations, as outlined in the Biology IB HL curriculum.

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What will offspring with recombinant chromosomes have?

Offspring with recombinant chromosomes will have unique gene combinations that are not present in either parent
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Key Terms

Term
Definition
What will offspring with recombinant chromosomes have?
Offspring with recombinant chromosomes will have unique gene combinations that are not present in either parent
What is random in meiosis?
When homologous chromosomes line up in metaphase I, their orientation towards the opposing poles is random
What is independent assortment?
The orientation of each bivalent occurs independently, meaning different combinations of maternal / paternal chromosomes can be inherited when bivalen...
What is the total number of combinations that can occur in gametes?
The total number of combinations that can occur in gametes is 2n – where n = haploid number of chromosomes
How many different gametes can humans produce?
Humans have 46 chromosomes (n = 23) and thus can produce 8,388,608 different gametes (223) by random orientation
How many different gametes can humans produce WITH crossing over?
If crossing over also occurs, the number of different gamete combinations becomes immeasurable
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Biology IB HL - 5.2 Natural Selection Part 2
TermDefinition
What will offspring with recombinant chromosomes have?
Offspring with recombinant chromosomes will have unique gene combinations that are not present in either parent
What is random in meiosis?
When homologous chromosomes line up in metaphase I, their orientation towards the opposing poles is random
What is independent assortment?
The orientation of each bivalent occurs independently, meaning different combinations of maternal / paternal chromosomes can be inherited when bivalents separate in anaphase I
What is the total number of combinations that can occur in gametes?
The total number of combinations that can occur in gametes is 2n – where n = haploid number of chromosomes
How many different gametes can humans produce?
Humans have 46 chromosomes (n = 23) and thus can produce 8,388,608 different gametes (223) by random orientation
How many different gametes can humans produce WITH crossing over?
If crossing over also occurs, the number of different gamete combinations becomes immeasurable
What does the fusion of two haploid gametes result in?
The fusion of two haploid gametes results in the formation of a diploid zygote
What can a zygote do to form an embryo?
This zygote can then divide by mitosis and differentiate to form a developing embryo
How does random fertilisation occur?
As meiosis results in genetically distinct gametes, random fertilisation by egg and sperm will always generate different zygotes
Due to random fertilisation what does offspring show?
This means that individual offspring will typically show variation despite shared parentage
How are random twins formed?
Identical twins are formed after fertilisation, by the complete fission of the zygote into two separate cell masses
What is the Malthusian dilemma?
The Malthusian dilemma was proposed by English clergyman Thomas Malthus who identified that populations multiply geometrically (i.e. exponential progression), while food resources only increase arithmetically (i.e. linear progression)
What is the simplified form of the Malthusian dilemma?
In other words, species tend to produce more offspring than the environment can sustainably support
How is competition therefore created?
If left to follow course, a stable population will inevitably outgrow its resource base, leading to competition for survival
How will the population grow with an abundance of resources?
When there is an abundance of resources, a population will grow according to its biotic potential (exponential J-curve)
What happens when more offspring are produced?
With more offspring, there are less resources available to other members of the population (environmental resistance)
What can too many offspring lead to?
This will lead to a struggle for survival and an increase in the mortality rate (causing population growth to slow and plateau)
What is the Malthusian dilemma key to?
This concept is central to Darwin’s understanding of ‘survival of the fittest’ – any trait that is beneficial for competitive survival will be more likely to be passed on to offspring according to natural selection
What are adaptations?
Adaptations are features of organisms that aid their survival by allowing them to be better suited to their environment
What are 5 categories for adaptations?
structural; behavioural; physiological; biochemical; developmental
What are structural adaptations?
Structural: Physical differences in biological structure (e.g. neck length of a giraffe)
What are behavioural adaptations?
Differences in patterns of activity (e.g. opossums feigning death when threatened)
What are physiological adaptations?
Variations in detection and response by vital organs (e.g. homeothermy, colour perception)
What are biochemical adaptations?
Differences in molecular composition of cells and enzyme functions (e.g. blood groups, lactose tolerance)
What are developmental adaptations?
Variable changes that occur across the life span of an organism (e.g. patterns of ageing / senescence)