Inheritance, variation and evolution Flashcards
How many chromosomes does a human cell content
23 pairs of chromosomes in the nucleus
How many chromosomes does a human sperm and egg cell both contain
23 single chromosomes
How can cells divide
By mitosis (In mitosis one so is copied into 2 identical daughter cells)
Name 2 gametes
Sperm cell and Egg cell
How are gametes made
By cell division (Meiosis)
Unlike mitosis what does meiosis produce
Non-identical cells (every sperm cell and every egg cell are different)
meiosis takes place in flowering plants (Pollen and egg cells)
What do animals and flowering plants carry out
Sexual reproduction
What does sexual reproduction involves
Fusion of male and female gametes
Mixing of genetic information (DNA) the offspring receives genetic information from both the male and female parents
What does fusion mean
Joining together (Fertilization)
What’s the difference between sexual and asexual reproduction
Asexual reproduction involves one parent but sexual involves two people
What does asexual reproduction not involve
Gametes this means meiosis will not take place
Asexual reproduction are all genetically identical What do scientists called this
Clones (Mitosis=2 identical cells)
Where does meiosis take place
In reproductive organs
Cells in the reproductive organs divide by meiosis to form what
Gametes
How do gametes join
By fertilization to restore the number of chromosomes
Meiosis takes place in the reproductive organs what is this for men and women
In men it’s the testes
In females it’s the ovaries
Explain the stages of meiosis
In the first stage of meiosis all of the chromosomes are copied (in pairs) then the cell divides into 2 and both of these cells divide one more time forming the gametes (In the gametes the chromosomes are single) 
At the start of meiosis chromosomes are in pairs but at the end of meiosis the chromosomes are gametes that are single what does this mean
Meiosis has halved the number of chromosomes
From one original so what does meiosis produce
4 gametes and each are genetically different from each other (each gamete has different alleles)
In sexual reproduction gametes from the male and female join together what is this called
Fertilization
What happens after fertilization
The new cell divide by mitosis (producing a clump of identical cells=Embryo) and the number of cells increase as the embryo as it develops cells differentiate forming different cell types (ex. Mussels)
What does DNA consist of
2 strands and each strand is a polymer (each strand is made by joining together lots of smaller molecules)
The DNA is a polymer made up of two strands what does it form
A double helix
The DNA is contained instructions what is this called
Chromosomes
What is a gene
A gene is a small section of DNA on a chromosome
The genetic material in the nucleus of a cell is composed of a chemical what is this called
DNA
How are proteins made
By joining together amino acids
What does each gene encode for
A specific sequence of amino acids to make a specific protein
What is the genome
The genome is the entire genetic material of an organism (it makes up humans)
How can scientists use the information about the whole human genome in the future
To make medicine
Understanding the human genes will help us to search for genes that are linked to diseases give some examples
The risk of developing cancer or Alzheimer’s disease
What does understanding the human genome help us with
Understanding and treat inherited disorders example. cystic fibrosis
Research about the risk of developing cancer or Alzheimer’s disease
We can use it to trace human migration patterns from the past (Helping people discover their ancestry)
What are alleles
Alleles are versions of a gene
How many pairs of chromosomes control the characteristics of a human
22 pairs control characteristics but one of the pairs carries the gene that determines the sex
What does the genotype of a person tell us
That alleles are present
What is cystic fibrosis
A disorder of the cell membranes
How is cystic fibrosis controlled
By a single gene which has two alleles
How can you tell when a person has cystic fibrosis
When the person has to have 2 copies of the defective allele (has to have inherited a defective allele from both of the parents)
This means that a person with 1 defective allele and 1 normal allele doesn’t have cystic fibrosis
What do you call a person who has 1 defective allele and 1 normal allele
They are a carrier of cystic fibrosis allele
How is cystic fibrosis caused
It’s caused by a recessive allele 
How is polydactyly caused
By a dominant allele
What is polydactyly
Having extra fingers or toes
Name one solution to discovering inherited disorders
Embryo screening
what’s the use of embryo screening
Embryos are tested to see if they have the alleles of inherited disorder then Embryos which don’t have the defective alleles are then implanted into the woman which can then develop into healthy offspring 
What are the issues to embryo screening
It is expensive and the money could be spent elsewhere in the health service
A large number of embryos are created by only a small number are implanted this means that some are destroyed and some people think that it’s unethical
In the future scientists might be able to correct faulty alleles and use this to treat inherited disorders. What is this called
Gene therapy
What does a family tree show
It only shows phenotypes and NOT genotypes
What type of sex chromosomes does a male have
XY
What type of sex chromosomes does a female have
XX
What is variation
The differences in the characteristics of individuals in a population
What are mutations?
They are random changes to DNA that take place all the time and most mutations have no effect on the phenotype
What are the three main causes of variation
The genes they have inherited (genetic causes)
The conditions in which they develop (Environmental causes)
A combination of genes and the environment
Give example’s of a genetic variation
Hair color and eye color
Give some examples of environment variation
The color of flowers depends on the pH of soil
language of humans
Give some examples of a combination of variations caused by genes and the environment
Height in humans (Genetics and enough calcium for bones to develop)
How can a new phenotype be beneficial if the environment changes
A mutation can help survive and become resistant to viruses causing new phenotypes
What is the theory of evolution by natural selection
All species of living things have evolved from the simple life forms that developed more than 3 billion years ago (eg. Single cells)
What happens if 2 populations of 1 species becomes so different in phenotype
They can no longer interbreed to produce fertile offspring meaning they have formed 2 new species
Define evolution
The change in the inherited characteristics of a population over time through a process of natural selection
Explain gene therapy
Genetic modification is being explored as a way to treat inherited disorders in humans
What are the steps of genetic engineering
Identify the gene wanted to transfer (Could be human, plant, or animal genes)
Use enzymes to isolate the gene
Transfer the gene into a small circle of DNA called a plasmid
Plasmids originally came from bacteria and are very useful for transferring DNA from one organism to another in addition you could also use a virus
Then the desired gene is transferred into the cells of the targeted organism and this is always done at the early stages

Where did plasmids originally come from 
Bacteria
What is a vector
When the plasmid or virus transfers the DNA from one organism to another
What are fossils
The remains of organisms from millions of years ago which are found in rocks
When does extinction occur
When there are no remaining individuals of a species is still alive
Name 3 ways how fossils form
Fossils can form when parts of organisms have not decayed this happens when the conditions needed for decay are absence (eg. If the temperature is too cold, If there’s not enough oxygen or water).
Fossils can form even if an organism decays; If parts of the organism are slowly replaced by minerals during the decay process.
Fossils can be preserved traces of organisms for example animals can leave foot prints or burrows and plants can leave preserves spaces
What do fossils show
A huge number of species that have become extinct
4 ways how species can become extinct
From catastrophic events for example an asteroid colliding with the Earth
Environmental changes
A new disease or a new predator could kill all of the individuals of a species
when there is lack of food or water
How can bacteria evolve
Bacteria can evolve rapidly because they produce at a fast rate (every 30min)
What’s the use of antibiotics
To kill bacteria
Name one antibiotic
Penicillin
In what ways are antibiotics used
For medicine
For farming to prevent animals from developing bacterial disease
Name one common strain of antibiotic resistant bacteria 
MRSA
Describe how antibiotic resistance happens
Mutations of bacterial pathogen’s produce new strains some strains might be resistance to antibiotics and so are not killed.
they survive and reproduce so the population of the resistance strains rises
What happens when mutations of bacterial pathogen’s produce new strain
The resistant strain will then spread because people are not immune to it and there is no effective treatment
How can you reduce the rate of development of antibiotic resistant strains
Doctors should not prescribe antibiotics and appropriately (eg. Should not be prescribed to virus)
patients should complete their course of antibiotics so all the bacteria are killed and non-survive to mutate and form resistant strains
restrict the use of antibiotics in farming
The development of new antibiotics is expensive and takes a long time and what is it unlikely of
As the new antibiotic resistant bacteria emerge all the time it is unlikely to keep up with the new resistant strains 
Who was the three domain system developed by
Carl woese 
In the three domain system what are the organisms divided into
Archaea
bacteria
eukaryotes (Protists, Fungi, plants and animals)
What is evolutionary trees
A method used by scientists to show how they believe organisms are related
How did evidence of the internal structures become more developed
the improvements in microscopes and the understanding of biochemical processes processed new models of classification were proposed
Traditional living things have been classified into groups depending on the structure and characteristics in a system who is the system developed by
Carl Linnaeus
What did Linneus classify living things into
Kingdom
Phylum
Class
Order
Family
Genus
Species
How are organisms named
By the binomial system of genus and species
What do scientists use current classification data for
For living organisms and fossil data for extinct organisms
What is the binomial name 
The genus + species = the name
