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Summary Grade 12 IEB Life Sciences/Biology Notes - Speciation R75,00
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Summary Grade 12 IEB Life Sciences/Biology Notes - Speciation

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Covers the entire section on Speciation Includes notes from the textbook, as well as additional class, video and research information, diagrams and practice questions. Applicable to all IEB Grade 12s. Written by a 90% < student.

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  • Strand 4 - evolution (speciation)
  • December 10, 2020
  • 14
  • 2020/2021
  • Summary

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Speciation
Biological species = a group of organisms that closely resemble each other and are able to
Biological species = breed among themselves, but not with any other species, and produce
Biological species = viable offspring.

Population = a group of individuals of the same species occupying a particular habitat at a
Population = particular time.

Natural selection only operates on variation in inherited characteristics.
There must be some genetic variation within a population, which can influence the nature of the
offspring, so that environmental conditions can selected the best adapted individuals.

Causes of variations
1. Sexual reproduction
1. a. Meiosis
1. a .- The random arrangement of homologous chromosomes on the equator
1. a .- Crossing-over when bivalents from
1. b. Chance fertilization
1. b .= During fertilization the genetic material from the female and male gametes recombines.
1. b .= There is no choosing of which male gametes will fuse with which female gamete.
1. c. Random mating
2. .c = Every female game, with her particular genotype, has equal chance to be fertilized by
2. c. = every male gamete, with his particular genotype in the population.
2. Germ-line mutations
2. Any sudden alteration in the genetic makeup of an organisms.
2. - Changes in the base sequences
2. - Whole chromosomes may be deleted or duplicated, and even the entire chromosomal
2. - compliment can multiply in a process called polyploidy.

A small percentage of mutations, in the case of evolution beneficial ones, result in a change in
the phenotypes. If the change results in organisms adapting better to new or unfavourable
conditions, they will survive and breed more successfully than the rest of the population.
This is natural selection as nature has selected the better adapted to survive and breed.
In time the whole population will have the new genotype and a new species will have been
formed i.e. evolution has taken place.

Variation in populations due to mutations
- The different beak forms of the Galapagos finches
- The colour of the white lions
- Resistance of bacteria to antibiotics

, Inbreeding
= mating of genetically closely relates individuals

In nature inbreeding in a population:
- Leads to a loss of genetic diversity, which in nature will prevent evolution
- Results in homozygosity, which can increase the chances of offspring being affected by
- recessive or harmful traits thus increasing the chances of genetic disorders.
- Known as inbreeding depression
- Example in animals: They will have a lower birth weight, do not reproduce so successfully and
- have less resistance to disease, predation and environmental stress.
- Example in plants: They will produce less seeds, seed germination is poor and their resistance
Example in plants: to stress is less.

Humans use inbreeding to try and establish a new and desirable trait or to continue particular
characteristics in an animal or plant group.
However, it often leads to loss of vigour and poor survival as the offspring can become
homozygous for a higher proportion of undesirable recessive genes.

Inbreeding in humans
= The mating of clos relatives, such as mother to son.
It is sometimes referred to as incest, there are taboos against it in many society and in most
countries it is against the law.

Negative effects:
- Close relatives are much more likely to carry the same mutation for a recessive genetic
- disease. They would therefore be genetic carriers or have the abnormality.
- If the parents are related, it increases the chances of the offspring receiving a harmful
- recessive allele from each parent.

Risks of being homozygous for a genetic abnormality:
The closer the relationship, the greater the risk of harmful recessive alleles being homozygous in
the offspring and thus expressed.

Example: Royal families and haemophilia
Example: Jewish populations and Tay Sachs disease

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