What is selective breeding?

Choosing the individuals with the most useful characteristics as parents and repeating this over many generations so the characteristic becomes common.

Explain why a selectively bred crop is at greater risk from a new disease.

The plants are genetically very similar, so if one has no resistance none of them do and the whole crop can be lost.

What is inbreeding and why can it cause health problems?

Breeding closely related individuals together; it increases the chance of two recessive alleles for a harmful condition being inherited by the same offspring.

OCR GCSE Combined Science Biology J250

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides Enzyme action, and investigating enzymes Cellular respiration as an exothermic process Aerobic and anaerobic respiration compared Synthesis and breakdown of carbohydrates, proteins and lipids Photosynthesis: producers and the process Photosynthesis as endothermic, and investigating it Limiting factors in photosynthesis

Community Level Systems

Topic overview Cycling materials, and the role of microorganisms The carbon and water cycles, and decomposition Levels of organisation, and abiotic and biotic factors Interdependence, competition, mutualism and parasitism

Genes, Inheritance and Selection

Topic overview Genetic terms, and the genome Genome, environment and mutations Haploid, diploid and meiosis Single gene inheritance and Punnett squares Sex determination and characteristics controlled by many genes Variation within a population, and classification Natural selection and evolution Evidence for evolution from fossils and antibiotic resistance

Global Challenges

Topic overview Field investigations, and human impact on ecosystems Maintaining biodiversity, monitoring conservation and ecotourism Selective breeding and genetic engineering Health, disease, and types of disease Interactions between diseases, and how they spread Reducing the spread of disease, and named examples White blood cells, antibodies and platelets Non-specific defences and the immune system Vaccines, medicines and aseptic technique Developing new medicines, and non-communicable disease Treating cardiovascular disease, and lifestyle factors Cancer, and the use of stem cells in medicine Gene technology in medicine, and the human genome

Organism Level Systems

Topic overview The nervous system and coordinated responses The reflex arc Hormones and the endocrine glands Hormones in reproduction and the menstrual cycle Methods of contraception Homeostasis and control systems in the body Insulin and the control of blood glucose Type 1 and type 2 diabetes

Scaling Up

Topic overview Diffusion, osmosis and active transport Mitosis, the cell cycle and cell differentiation Stem cells in animals and meristems in plants Surface area to volume ratio and exchange surfaces The circulatory system, the heart and blood vessels Red blood cells and plasma Root hair cells, transpiration and translocation Xylem and phloem Factors affecting water uptake, and the potometer

Global Challenges

Selective breeding and genetic engineering

3 things to know
Paper 2 (Biology)

Overview

What selective breeding is and how it improves wheat and dairy cattle, why it reduces genetic variation and raises disease risk, inbreeding and its health problems, the economic and ethical arguments, what genetic engineering and a genetically modified organism are, why a bacterial gene works in a plant, insect-resistant maize, beta-carotene rice and bacterial insulin, and the benefits, risks and objections of modified crops.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Describe how a farmer would use selective breeding to produce wheat with a greater grain yield.

Key term

Give two characteristics a dairy farmer would select for in cattle.

Key term

Explain why selective breeding reduces genetic variation in a population.

Questions from this subtopic

Each one with the model answer underneath.

1
What is selective breeding?
Model answer
Choosing the individuals with the most useful characteristics as parents and repeating this over many generations so the characteristic becomes common.
2
Describe how a farmer would use selective breeding to produce wheat with a greater grain yield.
Model answer
The highest-yielding plants are chosen and bred together, the best of their offspring are bred together, and this is repeated over many generations.
3
Give two characteristics a dairy farmer would select for in cattle.
Model answer
A high yield of milk and a calm temperament that makes the animals easy to handle.
4
Explain why selective breeding reduces genetic variation in a population.
Model answer
Only a few similar individuals are used as parents each generation, so the range of alleles present in the population falls.
5
Explain why a selectively bred crop is at greater risk from a new disease.
Model answer
The plants are genetically very similar, so if one has no resistance none of them do and the whole crop can be lost.
6
What is inbreeding and why can it cause health problems?
Model answer
Breeding closely related individuals together; it increases the chance of two recessive alleles for a harmful condition being inherited by the same offspring.

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Cell Level Systems

Community Level Systems

Genes, Inheritance and Selection

Global Challenges

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Algae and .

phytoplanktonfungianimals

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AA diet high in sugar and fat leads to obesity.

BBody cells then respond poorly to insulin.

CBlood glucose concentration cannot be controlled.

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Homozygous means carrying two identical alleles of a gene.

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