8J Genes Flashcards
Identify two resources that organisms compete for.
Food, water, space, mates, light (plants only)
Define variation
Difference between individuals
What is evolution?
A gradual change over time
Why do organisms produce more offspring that is needed?
To increase the chance that some of them will survive
What do we mean by the “fittest” organism will survive?
The best adapted organism will survive
What animal did Darwin study when developing the theory of natural selection?
Galapagos finches
What was different about these animals?
Beak shape and size
Why were their differences important to Darwin’s theory?
Different beaks were better adapted to eat the different food available on different islands
Define biodiversity
The variety of living things within an ecosystem
State two ways we measure biodiversity
Number of different species, differences between individuals of same species
Why do humans rely on plants?
Plants take in CO2 and produce O2, for food for us and the animals we eat, for medicines
Why is a reduction in biodiversity bad for humans?
Less likely that we had all of the resources that we depend upon
What is interdependence?
All organisms in a habitat rely on each other
Why are food chains more stable in high biodiversity ecosystems?
Removal of one species is less likely to have a massive impact on the rest of the food web.
What do we mean by the term “endangered species”?
When there are few individuals left of a species
Define extinct
When a species has died out and there are no more left
What is a mass extinction?
The extinction of many species all at once
When was the last mass extinction?
65 million years ago
State two natural causes of extinction.
Climatic heating and cooling, changes in sea level, asteroid impacts, disease
State two ways that human activities cause extinction.
Hunting, habitat destruction, introduction of invasive species, over-exploitation of wildlife
What is a gene bank?
A collection of seeds, sperm, eggs, embryos, blood and cuttings to preserve the genetic material of endangered plants of animals
Why is the Northern white rhino described as extinct, even though there are two individuals still alive?
Both are females so cannot reproduce
What did scientists use to create a cloned Pyrenean ibex?
A frozen sample of tissue and a Spanish Ibex
In which part of the cell is an organism’s genetic material found?
Nucleus
What does DNA stand for?
Deoxyribonucleic acid
How many pairs of chromosomes do humans have?
23 pairs (46 chromosomes in total)
What is a gene?
Short sections of DNA that code for proteins
What shape is DNA?
Double helix
What are the base pairs?
A and T, C and G
Why is detergent added to the ground up fruit?
To break down the cell and nucleus membrane, to release the DNA
What is used to separate DNA from a solution?
Ethanol – DNA is insoluble in ethanol so will form a separate layer
Name the four scientists who discovered the structure of DNA.
Watson, Crick, Franklin, Wilkins
When was the structure of DNA discovered?
1950s
How was X-ray crystallography used to discover the structure of DNA?
It was used to photograph the double helix shape of DNA
What did Erwin Chargaff contribute to the discovery of the structure of DNA?
Found out that DNA was made of base pairs – A, T, C and G
How was the final model of DNA created?
Franklin’s x-ray photograph and Chargaff’s base pairs were used to build a model
Why were only three scientists awarded a Nobel Prize for their discovery?
Franklin died before the prize was awarded
Why did these four scientists have to collaborate to discover the structure of DNA?
They each contributed something different to the discovery
What is the Human Genome Project?
A project to discover the exact sequence of base pairs in every gene in every chromosome in a human cell
What is a gamete?
Sex cell, e.g. a sperm or egg
Why do gametes have half a set of chromosomes?
So that when they join they have a full set
How is a karyotype prepared?
Chromosomes are separated from the cell and spread out on a microscope slide
Why is there variation amongst the offspring of two parents?
The alleles in each sperm or egg are completely random
What is trisomy?
When three chromosomes are inherited instead of a pair
What are the effects of trisomy 21?
Down’s syndrome
Give an example of a genetic disorder not caused by trisomy.
Sickle cell anaemia, cystic fibrosis
What is a carrier?
Someone who carries the allele for a disease but does not have the disease itself. They can pass it on to their children
What is an inherited characteristic?
Characteristics that are inherited from parents through the genes
Give an example of a human inherited characteristic.
Eye colour, blood type, freckles
How many chromosomes does each parent pass on to their offspring?
Half a full set, e.g. 23 for humans
Why do siblings look similar, but not identical?
They share some characteristics from each parent
What happens to produce identical twins?
A fertilised egg splits to produce two foetuses
Define what an embryo is.
An early stage of development of an animal, a small ball of cells
Why are identical twins never exactly the same?
Environmental factors affect their appearance
How are non-identical twins produced?
Two eggs, released at the same time, are fertilised by separate sperm
Why do we use models of inheritance?
To predict the likelihood of inheriting certain genes
What is an allele?
Different forms of the same gene
Why is the brown fur allele described as dominant?
It is always expressed even if there is only one copy of the brown allele
Why is the white fur allele described as recessive?
It is only expressed if both alleles are for white fur
Why is it not possible to know the alleles of a brown mouse?
It may have two brown alleles, or one brown and one white allele
How many possible combinations of alleles are there?
Three
For the Punnett square above, what are the chances the mouse will be brown?
¾ or 75%
Why is it more likely that a mouse will be brown than white?
Brown is the dominant allele, only one needs to be inherited to be expressed
