Biology (Combined Science) - Paper 2 - Inheritance, Variation and Evolution

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Asexual reproduction involves...
...only one parent, no fusion of gametes/sex cells (so, no mixing of genetic information), the production of genetically identical offspring (clones) and mitosis.
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What is sexual reproduction?
The fusion of male and female gametes. (e.g. sperm and egg cells in animals and pollen and egg cells in flowering plants)
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Sexual reproduction involves...
...a mix of genetic information and thus produces variation within offspring.
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By what process do gametes (sex cells) form?
Meiosis
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When a cell divides by meiosis...
...copies of the genetic information are made, the cell divides twice to form 4 gametes (each with a single set of chromosomes) and all gametes are genetically different.
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Stages of meiosis...
Begins with a cell with two pairs of chromosomes (known as a diploid cell). Each chromosome replicates itself. The chromosomes part company and move to opposite poles of the cell. The cell divides for the first time. (continues on next card...)
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continued...
The copies now separate and the second cell division takes place. Ends with four haploid cells (gametes - single set of chromosomes), each with half the number of chromosomes of the parent cell.
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Why is meiosis important?
It halves the number of chromosomes in the gametes, meaning that, during fertilisation, the full number of chromosomes is restored.
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How many chromosomes does a human gamete have?
23 (unpaired)
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How many chromosomes does a fertilised human egg cell have?
46 (23 pairs) - half from the mother (egg) and half from the father (sperm).
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What is DNA?
Deoxyribonucleic Acid - The chemical that makes up the genetic material in the nucleus of a cell.
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What is DNA contained in?
Structures called chromosomes.
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What is a gene?
A small section of DNA on a chromosome.
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Genes code for...
...particular sequences of amino acids, to make a specific protein.
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What is an organism's genome?
The entire genetic material of that organism.
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What uses have come from the study of the human genome?
Doctors can search for genes linked to different types of disorders, scientists can better understand the cause of inherited disorders an dhow to treat them and scientists can also investigate how humans may have changed over time.
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What are alleles?
Different forms of the same gene.
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How many alleles does an individual have for each gene?
Two - One from the mother and one from the father
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What is the genotype?
The combination of alleles present in a gene. (e.g. bb)
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What is the phenotype?
How the alleles are expressed (i.e. which characteristic appears) (e.g. bb = blue eyes)
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Alleles can be either...
...dominant or recessive.
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What is a dominant allele?
One that will show a characteristic if inherited by 1 or both parents.
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What is a recessive allele?
One that only shows a characteristic if inherited from both parents.
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What does it mean if a person is homozygous for a particular gene?
The two alleles present for that gene are the same (e.g. bb, BB). A person can be homozygous dominant (BB) or homozygous recessive (bb).
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What does it mean if a person id heterozygous for a particular gene?
The two alleles present for that gene are different (e.g. Bb).
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What is monohybrid inheritance?
Most genes are controlled by several genes working together. Monohybrid inheritance is when only one gene is involved.
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What can be used to predict the out come of a monohybrid cross?
A Punnet Square
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What is polydactyly?
A genetic disorder that results in babies being born with six fingers or toes. It is a very rare condition.
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Is the gene that causes polydactyly dominant or recessive?
Dominant
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What is cystic fibrosis (CF)?
A genetic disorder that causes excessive mucus to be produced in the lungs.
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Why is this excessive mucus a problem?
It often gets infected by bacteria and requires frequent treatment with antibiotics. The mucus also inhibits efficient gas exchange in the lungs meaning that a person's ability to exercise is affected. People with CF have a reduced life expectancy.
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Is the gene that causes CF dominant or recessive?
Recessive
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What are CF carriers?
People that are heterozygous for the CF gene (Cc), meaning that they don't have the disorder (because it's recessive) yet they can still pass it on to their children.
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What are sex chromosomes?
The pair or chromosomes in the human body that carry the genes that determine sex.
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What are the female sex chromosomes?
** - They are identical. They are known as X chromosomes. All eggs carry X chromosomes.
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What are the male sex chromosomes?
XY - The Y chromosome is much shorter. A Y chromosome can only be inherited from the father. Half of the sperm carry X chromosomes and half carry Y chromosomes.
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If a sperm carrying an X chromosome fertilises the egg...
...a girl is produced.
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If a sperm carrying a Y chromosome fertilises the egg...
...a boy is produced.
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What is variation?
Differences in the characteristics of individuals in a population.
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Variation may be due to differences in...
...the genes that individuals have inherited (genetics), the conditions in which individuals have developed (environment) or a combination of both genetic and environmental causes.
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When can new alleles be created?
As a result of a mutation.
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What is evolution?
The gradual change in the inherited characteristics of a population over time.
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What may be caused by evolution?
The formation of new species.
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Who proposed the theory of natural selection?
Charles Darwin
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The theory of natural selection states that...
...all species have evolved from simple life forms that developed more than 3 billion years ago.
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When are new species formed?
When two populations of one species become so different that they can no longer interbreed to produce fertile offspring.
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What are the 5 steps of natural selection?
Mutation - A change in the DNA of an organism leads to variation between individuals of a species. | Variation - Differences between individuals. | Competition - Individuals compete for limited resources. | (continues on next card...)
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continued...
Survival of the Fittest - Individuals who have beneficial genes do well, survive and breed. Those without are less likely to do so, and so their genes are lost. | Evolution - The species slowly changes overtime to be better suited to the environment.
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Where can we find evidence of evolution?
In fossils.
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What are fossils?
The remains of organisms from hundreds of thousands of years ago that are found in rocks.
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Why do scientists use fossils?
To study how organisms have gradually changed over long periods of time.
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In what ways may fossils be formed?
From the hard parts of animals that do not decay easily, from the parts of organisms that have not decayed, because one or more of the conditions needed for decay was absent (e.g. in a peat bog), (continues on next card...)
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continued...
...when parts of an organism are replaced by other materials as they decay or as preserved traces of organisms, e.g. footprints, burrows and foot pathways.
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What is the problem with using fossils to study evolution?
There are gaps in the fossil record due to many early forms of life being soft-bodied, meaning that they have left very few traces behind and due to the few traces there were often being destroyed by geological activity.
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What is selective breeding/artificial selection?
The process by which humans breed plants and animals with particular, desirable genetic characteristics.
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What types of desirable characteristics may be selected to breed?
disease resistance in food crops, production of better quality/more milk or meat in some animals, a gentle nature in domestic dogs and large or unusual flowers.
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What steps are involved in selective breeding?
Choose parents that best show the desired characteristic. Breed them with one another. From the offspring, again, choose those with the desired characteristics and breed. Continue over many generations.
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What problem is caused by selective breeding?
It can lead to inbreeding, meaning some breeds are particularly prone to diseases or inherited defects.
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What is genetic engineering?
The changing of the characteristics of an organism by introducing a gene from another organism.
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Describe the process of genetic engineering...
Locate the desired gene from the chromosome. A specific enzyme is used to extract/isolate the gene. Plasmids are removed from bacterial cells. The DNA of the plasmids is cut open with a specific enzyme. (continues on next card...)
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continued...
...The isolated gene is inserted into each plasmid. (The plasmids act as a vector, used to transfer the DNA from one organism to another.) Bacterial cells are made to take up the genetically modified plasmids. (continues on next card...)
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...(Bacterial cells that successfully take up the plasmids are described as being transformed. The bacterial cells are host cells for the plasmids.) The bacteria then replicate themselves.
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What happens if the genes are inserted into the cells of animals or plants at the egg/embryo stage?
All cells in the organism will get the new gene.
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Some plant crops have been genetically engineered to...
...be resistant to diseases, insects or herbicide attack and to produced bigger, better fruits.
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What are crops that have been modified in this way called?
Genetically Modified crops (GM crops)
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What are the ethical issues surrounding GM crops?
Some people are concerned about the possible long-term effects on populations of wild flowers and insects and on human health (if consumed).
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Fungi/Bacterial cells have been genetically modified to produce useful substances, such as...
...human insulin to treat type 1 diabetes.
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What can genetic modification be used for in the future?
To cure and prevent some inherited diseases in humans.
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What is classification?
The arrangement of animals and plants into groups according to their observed similarities.
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Who developed the main classification system?
Carl Linnaeus
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Linnaeus classified living things into...
Kingdom - Phylum - Class - Order - Family - Genus - Species
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How are organisms named?
Using the binomial system. (They have two parts of their Latin name - The first part is their genus and the second is their species.)
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Why were new models of classification proposed?
Microscopes, so scientists learnt more about cells and biochemical processes became better understood.
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How were scientists able to develop the three-domain system?
From genetic studies.
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Who developed the three domain system?
Carl Woese
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What domains are organisms divided into in the three-domain system?
Archaea (primitive bacteria, usually living in extreme environments), Bacteria (true bacteria) and Eukaryota (including protists, fungi, plants and animals).
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What is meant by the term 'extinct'?
When no members of a species remain alive.
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What is meant by the term 'mass extinction'?
A large number of extinctions occurring at the same time.
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Extinction may be caused by...
...changes to the environment over long periods of time, new predators in an area, new diseases, new and more successful competitors or a single catastrophic event, e.g. a massive volcanic eruption or a collision with an asteroid.
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What are evolutionary trees?
A method used by scientists to show how they think organisms are related.
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What data is used when constructing evolutionary trees?
Current classification data for living organisms and fossil data for extinct organisms.
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Other cards in this set

Card 2

Front

What is sexual reproduction?

Back

The fusion of male and female gametes. (e.g. sperm and egg cells in animals and pollen and egg cells in flowering plants)

Card 3

Front

Sexual reproduction involves...

Back

Preview of the front of card 3

Card 4

Front

By what process do gametes (sex cells) form?

Back

Preview of the front of card 4

Card 5

Front

When a cell divides by meiosis...

Back

Preview of the front of card 5
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