iGCSE Biology Section 3 lesson 5

Reproduction and Inheritance Content Section 3 Reproduction and Inheritance Reproduction - Flowering plants - Humans b) Inheritance

Lesson 5 Content b) Inheritance b) Inheritance 3.21 understand that the sex of a person is controlled by one pair of chromosomes, XX in a female and XY in a male 3.22 describe the determination of the sex of offspring at fertilisation, using a genetic diagram 3.23 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes 3.24 understand that mitosis occurs during growth, repair, cloning and asexual reproduction 3.25 understand that division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes 3.26 understand that random fertilisation produces genetic variation of offspring 3.27 know that in human cells the diploid number of chromosomes is 46 and the haploid number is 23 3.28 understand that variation within a species can be genetic, environmental, or a combination of both 3.29 understand that mutation is a rare, random change in genetic material that can be inherited 3.30 describe the process of evolution by means of natural selection 3.31 understand that many mutations are harmful but some are neutral and a few are beneficial 3.32 understand that resistance to antibiotics can increase in bacterial populations, and appreciate how such an increase can lead to infections being difficult to control 3.33 understand that the incidence of mutations can be increased by exposure to ionising radiation (for example gamma rays, X-rays and ultraviolet rays) and some chemical mutagens (for example chemicals in tobacco).

“describe the process of evolution by means of natural selection”

In 1859 Charles Darwin published ‘The Origin of Species by Natural Selection’.

In 1859 Charles Darwin published ‘The Origin of Species by Natural Selection’. As a 22 year old, Darwin joined the crew of HMS Beagle as a naturalist

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Alfred Russel Wallace

Observations and Conclusions

Observations and Conclusions 1. Organisms produce many offspring There must be a struggle for survival and competition for food, water, and a place to live.

Observations and Conclusions 1. Organisms produce many offspring There must be a struggle for survival and competition for food, water, and a place to live. 2. The size of a population of one species in nature tends to remain constant Some organisms are better adapted to survive in their environment. So they breed and produce offspring.

Observations and Conclusions 1. Organisms produce many offspring There must be a struggle for survival and competition for food, water, and a place to live. 2. The size of a population of one species in nature tends to remain constant Some organisms are better adapted to survive in their environment. So they breed and produce offspring. 3. Members of a species vary The offspring inherit the characteristics of the organisms best fitted for survival. So an improved form is evolved by natural selection.

Evolution by Natural Selection 4 key points to remember

Evolution by Natural Selection 4 key points to remember 1. Individuals within a population show variation (i.e. differences due to their genes)

Evolution by Natural Selection 4 key points to remember 2. There is competition between individuals for food and mates, etc., and also predation and disease. This keeps the population sizes constant in spite of production of many offspring i.e. there is a ‘struggle for survival’ and many individuals die.

Evolution by Natural Selection 4 key points to remember 3. Individuals which are better adapted to the environment are more likely to survive, breed successfully and produce offspring. This is termed ‘survival of the fittest’.

Evolution by Natural Selection 4 key points to remember 4. These ‘survivors’ will therefore pass on their genes to their offspring, resulting in an improved organism being evolved through natural selection.

Bacteria resistant to penicillin Evolution in Action Bacteria resistant to penicillin

Bacteria resistant to penicillin Evolution in Action Penicillin is an antibiotic – it kills or slows down the growth of bacteria. Bacteria resistant to penicillin

Bacteria resistant to penicillin Evolution in Action Penicillin is an antibiotic – it kills or slows down the growth of bacteria. Mutations have arisen amongst certain strains of bacteria that have resulted in penicillin resistance. Bacteria resistant to penicillin

Bacteria resistant to penicillin Evolution in Action VARIATION Bacteria mutated. Some were resistant to the antibiotic penicillin. Others were not. Bacteria resistant to penicillin

Bacteria resistant to penicillin Evolution in Action VARIATION Bacteria mutated. Some were resistant to the antibiotic penicillin. Others were not. COMPETITION The non-resistant bacteria were more likely to be killed by the penicillin. Bacteria resistant to penicillin

Bacteria resistant to penicillin Evolution in Action BEST ADAPTED The penicillin-resistant bacteria survived and reproduced more often. Bacteria resistant to penicillin

Bacteria resistant to penicillin Evolution in Action BEST ADAPTED The penicillin-resistant bacteria survived and reproduced more often. PASS ON THEIR GENES More bacteria are becoming resistant to penicillin. This is a major health issue. Bacteria resistant to penicillin

Evolution in Action Varieties Selection by Result Other examples: Gazelles, fast and slow Lions Only the fastest survive to produce offspring Peppered moth, light and dark forms Birds, selecting the least camouflaged Light forms in unpolluted areas, dark in smoky cities Rats – some killed by warfarin, others resistant Warfarin used by farmers New variety of warfarin –resistant rats. Rabbits – resistant to or killed by myxomatosis Virus introduced by farmers New myxomatosis – resistant population

Natural selection by evolution End of Section 3 Lesson 5 In this lesson we have covered: Natural selection by evolution