6. Cell Division & DNA Flashcards
Why does mitosis take place?
- growth
* replace damaged cells
What has to happen before mitosis?
The chromosomes replicate
How many divisions are there in mitosis?
1
Are the cells haploid or diploid in mitosis?
Diploid (in mammals)
How many new cells are produced in mitosis?
2
Are the new cells identical or different in mitosis?
Identical
What does diploid mean?
Has a full set of chromosomes
What does haploid mean?
Half the number or chromosomes
What can meiosis also be referred to as?
Reduction division
Where does meiosis only happen?
In the cells of the reproductive organs
What does meiosis produce?
Gametes
Where are gametes produced in animals?
Ovaries and testes
Where are gametes produced in plants?
Ovule and anther
How many chromosomes do the gametes produced in meiosis have?
Half the number of the parent cell (humans - 23 chromosomes instead of 23 pairs of chromosomes)
How many copies of each chromosome do gametes have? Why?
One so when they fuse the zygote has the normal amount of chromosomes
Are gametes diploid or haploid?
Haploid
Are zygotes diploid or haploid?
Diploid
What happens to the zygote formed at fertilisation?
Divides by mitosis to produce more cells that differentiate as embryo develops
How does meiosis turn one cell into four new cells in humans?
- diploid cell in ovaries or testes (46 chromosomes)
- chromosomes replicate (still 46 chromosomes)
- pairs of chromosomes line up at equator, thicken and spindles attach
- chromosome pairs separate into two new cells and a nucleus reforms
- spindles attach to the (2) duplicates of chromosomes and duplicates are pulled apart into separate cells
- four new cells have formed (23 chromosomes)
How does meiosis turn one cell into four new cells in general?
- diploid cell
- chromosomes replicate
- pairs of chromosomes line up at equator, thicken and spindles attach
- chromosome pairs separate into two new cells and a nucleus reforms
- spindles attach to the (2) duplicates of chromosomes and duplicates are pulled apart into separate cells
- four new cells have formed
How many chromosomes are in a human cell produced by mitosis?
46
How many chromosomes are in a human cell produced by meiosis?
23
What are the two gametes produced by humans?
egg and sperm
How do mitosis and meiosis differ in terms of the number of daughter cells produced?
Mitosis produces two daughter cells whereas meiosis produces four daughter cells
How do mitosis and meiosis differ in terms of the number of cell divisions that occur?
In mitosis one cell division occurs whereas in meiosis two occur
How do mitosis and meiosis differ in terms of the nature of the cells they produce?
Mitosis produces genetically identical cells whereas meiosis produces cells that are all genetically different
How do mitosis and meiosis differ in terms of when it occurs?
Mitosis occurs during growth and asexual production whereas meiosis occurs during sexual reproduction
How do mitosis and meiosis differ in terms of the number of chromosomes that are passed on to their daughter cells?
In mitosis one copy of each chromosome goes to each of the new daughter cells, whereas in meiosis only half of the chromosomes go to each of the new daughter cells
How do mitosis and meiosis differ in terms of what other names they can be called by?
Mitosis is otherwise known as copying division whereas meiosis is otherwise known as reduction division
Why is important that the four daughter cells produced in meiosis contain half the number of chromosomes?
- to restore the original chromosome number when they get fertilised
- to prevent the doubling of the chromosome number
What is the difference between mitosis and meiosis?
- in mitosis two daughter cells are produced; in meiosis four are produced
- in mitosis there is one cell division; in meiosis there are two
- mitosis produces genetically identical cells; meiosis does not
- mitosis occurs during asexual production; meiosis occurs during sexual production
- in mitosis one copy of each chromosome goes to each of the new daughter cells; in meiosis only half of the chromosomes go to each of the daughter cells
How do asexual and sexual reproduction differ in terms of how many parents are involved?
Asexual needs one parent whereas sexual involves the mixing of genetic information from two organisms
How do asexual and sexual reproduction differ in terms of fertilisation?
In asexual there is no fusion of gametes wheres in sexual gametes fuse
How do asexual and sexual reproduction differ in terms of their offspring?
In asexual offspring are genetically identical to that parent whereas in sexual offspring are genetically different from either parent
How do asexual and sexual reproduction differ in terms of genetic variation?
In asexual variation is caused by random mutations whereas in sexual offspring are genetically different from their parents
How many daughter cells are produced in mitosis?
2
How many daughter cells are produced in meiosis?
4
How many cell divisions occur in mitosis?
1
How many cell divisions occur in meiosis?
2
When does mitosis occur?
During growth and asexual reproduction
When does meiosis occur?
In the formation of gametes during sexual reproduction
What can mitosis also be referred to as?
Copying division
What can meiosis also be referred to as?
Reduction division
How many parents are involved in asexual reproduction?
1
How many parents are involved in sexual reproduction?
2
What process allows asexual reproduction to occur?
Mitosis
How is genetic variation caused during asexual reproduction?
Random mutations
Examples of asexual reproduction?
- strawberry runners
- potato runners
- starfish
What are the female gametes in animals?
Egg cells (ova)
What are the male gametes in animals?
Sperm
Where are female gametes produced in animals?
Ovaries
Where are male gametes produced in animals?
Testes
What are the female gametes in plants?
Egg cell nucleus
What are the male gametes in plants?
Pollen grain nucleus
Where are the female gametes produced in plants?
Ovary of carpel
Where are the male gametes produced in plants?
Anther of stamen
What is the form of asexual reproduction in bacteria?
Binary fission
Advantages of sexual reproduction?
Variation in the offspring increases the chances of survival if circumstances change
Why does genetic variation increase chance of survival?
If circumstances change some individuals will survive the chance due to having different characteristics
Disadvantages of sexual reproduction?
- slow
* finding a mate takes time and energy
Advantages of asexual reproduction?
- only needs to be one parent so no energy or time is wasted finding a mate
- large numbers of clones are produced when conditions are favourable
Disadvantages of asexual reproduction?
Vulnerable to extinction due to lack of variation - could easily catch disease
Which organisms can reproduce sexually and asexually depending on their circumstances?
- mosquitoes (malaria)
- fungus (releasing spores)
- plants that produce seeds sexually but reproduce sexually
How does malaria reproduce sexually and asexually?
The parasite reproduces sexually when it’s in the mosquito and asexually when it’s in the human host
How does fungus reproduce sexually and asexually?
- asexually-produced spores form fungi that are genetically identical to the parent fungus
- sexually-produced spores introduce variation and are often produced in response to a change in the environment
How do plant species reproduce sexually and asexually?
- produce their seeds sexually
* reproduce asexually e.g. daffodil bulbs - new bulbs divide off main bulb but each bulb grows into new identical plant
Where does the asexual reproduction of malaria take place?
In the human liver and red blood cells
Where does sexual reproduction of malaria take place?
In the mosquito, triggered by the lower body temperature
How does sexual reproduction of malaria occur?
- in mosquitoes, triggered by lower body temperature
- in 20 minutes the sexual forms develop and burst out of the RBCs and fuse to form a zygote
- meiosis then occurs to form new asexual parasites
- these go to infect human hosts
What chemical are chromosomes made of?
DNA
What is genetic information carried on?
Chromosomes
What is a section of DNA called?
A gene
What does DNA stand for?
Deoxyribonucleic acid
What is all the genetic material in a cell composed of?
DNA
What is DNA?
A polymer of nucleotides, made up of two stands forming a double helix
Where is DNA found in?
Chromosomes
What does a nucleotide consist of?
A common sugar and phosphate group with one of 4 different bases attached to the sugar
What are the four bases that DNA contains?
A, T, C and G
How many bases is the code for an amino acid?
3
What does three bases code for?
An amino acid
What does the order of bases control?
The order in which amino acids are assembled to produce a protein
Where are the genes controlling a certain characteristic located on a pair of chromosomes?
They are in the same location on each chromosome
What is the shape of a DNA molecule?
A double helix
What is a nucleotide?
A monomer which makes up DNA
What is complimentary base pairing?
When each base in a DNA strand links to a base on the opposite strand in the helix
What does A pair with?
T
What does T pair with?
A
What does G pair with?
C
What does C pair with?
G
What does each gene code for?
A particular sequence of amino acids which are put together to make proteins
How many amino acids are there?
20
How are proteins made?
Amino acids are put together in many different orders
How long is a gene?
Hundred or thousands of bases long
What is the genome of an organism?
The entire genetic material of that organism
Why does A and always pair with T and C with G?
- bonds won’t form in the correct way
* physical size - bases are different lengths so there could be a bulge on the DNA if bases too long
What has the study of the human genome allowed for?
- the search for genes being linked to different types of disease
- the understanding and treatment of inherited disorders
- tracing human migration patterns from the past
How does protein synthesis occur?
- the code from DNA is copied to form a messenger molecule
- this leaves the nucleus and moves to a ribosome
- carrier molecules bring the code for specific amino acids to the ribosome and attach to the messenger molecules in the order determined by the sequence of bases
- the amino acids are joined together in the correct order to form the protein
What happens after a chain of amino acids has been assembled during protein synthesis?
It folds into a unique shape which allows the protein to perform its task
What allows a protein to do its job?
It’s structure
Examples of proteins?
- hair protein (keratin)
- hormones
- collagen
- enzymes
Who discovered the structure of DNA?
Rosalind Franklin
What is a mutation?
A random change in an organism’s DNA
When do mutations occur?
All the time
What is often the cause of mutations?
A mistake in the copying of DNA before a cell divides
What arise due to mutation?
New forms of genes
How can the chance of mutation be increased?
Exposure to some chemicals and radiation
How can a mutation change the protein synthesised from that gene?
- one of the amino acids may be substituted for another
- this may change the intermolecular forces between the amino acids so the protein may change shape
- it may lose function
What do non-coding parts of DNA do?
Switch genes on and off
What happens if there is a mutation to the non-coding areas of DNA?
It may affect how genes are expressed
What are the different forms of a gene called?
Alleles
How many alleles do gametes have?
1
How many alleles do cells in an organism have, apart from gametes?
2 - 1 on each chromosome of a pair
Why do we have two alleles in each cell?
We inherit half from our mother and half from our father
What can an allele be?
- dominant
* recessive
What is a gamete?
A male or female sex cell
What is a gene?
A length of DNA found on a chromosome that carries the instructions needed to make a protein
What is a dominant allele?
An allele that is always expressed in the phenotype
How is the dominant allele represented?
By a capital letter
What does it mean when an organism is homozygous?
It has two alleles for a particular gene that are the same
What is a genotype?
The alleles present for a particular gene in an organism (the letters)
What is a chromosome?
A thread-like structure in the cell nucleus, made of a molecule of DNA, which carries genes
What is an allele?
One of the different forms of a particular gene
What is a recessive allele?
An allele that is only expressed in the phenotype if two copies are present
How is the recessive allele represented?
a lowercase letter
What does it mean when an organism is heterozygous?
It has two alleles for a particular gene that are different
What is a phenotype?
The characteristic that is shown or expressed
What do genetic diagrams show?
How certain characteristics are inherited
What did Gregor Mendel experiment on?
Peas
What was the pattern regarding sample size and the Mendelian ratio?
The bigger the sample size of peas, the closer to the Mendelian ratio
Were Mendel’s results reproducible?
Yes
What type of allele is polydactyly caused by?
Dominant
What type of allele is cystic fibrosis caused?
Recessive
What is polydactyly?
Having extra fingers or toes
What is cystic fibrosis?
A cell membrane disorder
Will the parent with the defective polydactyly allele also have it? Why?
Yes because the allele is dominant
What is the purpose of embryo screening?
To detect inherited genetic disorders in embryos
What are the two types of embryo screening?
- pre-implantation genetic diagnosis (PGD)
* chorionic villus sampling (CVS)
What happens in pre-implantation genetic diagnosis?
- during IVF, a cell is removed from the embryo and its genes analysed
- only embryos with ‘healthy’ alleles are implanted into the uterus
- embryos with ‘faulty’ alleles are destroyed
What happens in chorionic villus sampling?
- sample of cells taken from placenta at 10-13 weeks and genes analysed
- if the embryo has an inherited disorder, the parents can decide whether or not to terminate the pregnancy
Arguments for embryo screening?
- helps to stop people suffering from inherited disorders
- treating disorders costs government so could reduce healthcare costs
- during IVF most embryos are destroyed anyway
- if an inherited disorder is diagnosed through CVS, the parents don’t have to terminate the baby
Arguments against embryo screening?
- there may come a point where everyone wants to screen their babies to pick the most ‘desirable’
- implies that people with genetic disorders are ‘undesirable’ - could create predjudice
- after PGD rejected embryos are destroyed - unethical
- risk that CVS could cause miscarriage
- expensive
How many pairs of chromosomes are in every human body cell?
23
What do the 23rd pair of chromosomes control?
The sex of a person
What sex chromosomes do males have?
X and Y, XY
What does the Y chromosome cause?
Male characteristics
What sex chromosomes do females have?
Two X chromosomes, XX
What does the XX chromosome cause?
Female characteristics
Which organisms did Mendel study?
Peas
What type of peas did Mendel cross in the first generation?
Round peas and wrinkled peas (RR and rr)
What type of peas did Mendel cross in the second generation?
Round peas and round peas
What did Mendel call what we now know to be genes?
Hereditary units
Why wasn’t Mendel’s theory first accepted by other scientists?
They didn’t know about genes, chromosomes or DNA
What are species?
A group of organisms that are able to interbreed to produce fertile offspring
What is variation?
The difference in the characteristics of individuals in a population
What can variation be caused by?
- genetic causes
- environmental causes
- a combination
Where do variants in a population arise from?
Mutations
How often do mutations occur?
All the time however very rarely will it lead to a new phenotype
What happens if a new phenotype is suited to an environmental change?
It can lead to a relatively rapid change in species
What is evolution?
A change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species
What does the theory of evolution by natural selection state?
All species have evolved from simple life forms that first developed more than three billion years ago
What happens if two populations of one species become so different in phenotype?
They can no longer interbreed to produce fertile offspring and have formed two new species
When do two populations of one species become two different species?
When they become so different in phenotype that they can no longer interbreed to produce fertile offspring
When does extinction occur?
When there are no remaining individuals of a species alive
What are the causes of extinction?
- environmental changes
- new predator
- new disease
- competition
What is the order of the general outline you need to use in a natural selection exam question?
- variation
- caused by mutation
- which variation has an advantage and why
- survive and breed
- pass on advantageous genes to next generation
What was Lamarck’s theory of evolution?
- evolution of animals was caused by the inheritance of acquired characteristics
- based on the idea that changes occur in an organism throughout it’s lifetime
What was Darwin’s theory of evolution?
- individual organisms within a species show a wide range of variation for a characteristic
- individuals with characteristics most suited to the environment are more likely to survive
- characteristics that have enabled these individuals to survive are passed on
Why was the theory of evolution by natural selection only gradually accepted?
- the theory challenged the idea that God made life
- insufficient evidence to convince many scientists
- mechanism of inheritance was not known until 50 years after the theory was published
What does Darwin’s theory not include?
Ideas of genes/DNA
Why do people have different ideas about how life began on earth?
- religion
- evidence - some theories have more than others
- status of scientist
- culture
What are the conflicting theories of how life began on earth?
- Darwin’s theory of natural selection
- Lamarck’s theory of acquired characteristics
- creationism
- theory of intelligent design
Why are there conflicting theories about how life on earth began?
Lack of evidence
How do fossils produce evidence that species today have evolved from simpler organisms?
- they are remains of organisms that lived a long time ago
- they show changes over time
- they have similar feature to present day species
What are fossils?
The remains of organisms from many years ago
How can fossils be formed?
- from parts of organisms that have not decayed because one or more of the conditions needed to decay are absent
- when parts of an organism are replaced by other materials as they decay
- as preserved traces of organisms, such as footprints
Example of fossils forming due to one or more of the conditions needed for decay being absent?
Insects in amber lacking oxygen for decay
What does early forms of life being soft-bodied mean for our understanding?
They have few traces behind
What are some sources of evidence for evolution?
- fossils
* antibiotic resistance
How does antibiotic resistance provide evidence for evolution?
- bacteria evolve rapidly as they reproduce at a fast rate
- bacteria can develop antibiotic resistance in a process of natural selection
- mutations of bacterial pathogens produce new antibiotic resistant strains and the pathogens of the non-resistant strain are killed
- population of resistant strain increases and spread
Why do new species arise?
- isolation - two populations of a species becoming separated
- genetic variation
- natural selection
- speciation
What is speciation?
When populations become so different that successful interbreeding is no longer possible
What is selective breeding?
A process used by humans to produce different breeds of animals or varieties of plants
How is selective breeding executed?
- choosing parents with the desired characteristics from a mixed population
- breeding these together
- from the offspring, breed those with the desired characteristics
Some examples of how selective breeding can be useful?
- disease resistance in crops
- animals which produce more meat/milk
- domestic dogs with a gentle nature
- large or unusual flowers
What is inbreeding?
- when future generations of selectively bred organisms share very similar genes
- some diseases will be more dangerous as all the organisms would be affected
- also there is increased risk of genetic diseases caused by recessive genes
- also some genes would be lost, making more difficult to produce new varieties in the future
What are some of the limitations of selective breeding?
Inbreeding:
- more prone to disease
- increased risk of genetic diseases
- smaller gene pool
What is genetic engineering?
A process which involves modifying the genome of an organism by introducing a gene from another organism
What are the additional small pieces of genetic material in bacterial cells?
Plasmids
What does the vector do in genetic engineering?
It is used to insert the gene into the required cells
What is the vector usually during genetic engineering?
A bacterial plasmid or a virus
Example of genetic engineering?
Gene for making human growth hormone inserted into sheep - so they will produce the hormone in their milk
What are some current applications for plant genetic modification?
- disease and pest resistant plants
- keeping fruit and vegetables fresher for longer
- plants that have increased nutritional benefits
- producing soy with higher levels of anti-cancer proteins naturally found
Advantages of genetic engineering?
- treating diseases
* more efficient food production
Disadvantages of genetic engineering?
- long term effects e.g. changing genes could pass on problems to future generations
- same with GM crops (changing genes may get into general circulation)
Ethical issues of genetic engineering?
- not a natural process and interfering with nature
* altering organisms for human gain seen to be against God’s will
What is cloning?
When an identical copy of an organism is made
What process is usually involved in cloning?
Mitosis (binary fission in bacteria)
What are the four ways of cloning organisms?
- cuttings
- tissue culture
- embryo transplants
- adult cell cloning
Advantages of using cuttings to clone plants?
They reproduce quickly and is quicker than tissue culture
How is tissue culture used to clone plants? (process)
- small tissue sample taken from parent plant and grown in agar with nutrients and hormones to form tissue
- tiny identical plants are formed and then grown on
What is an important condition that needs to be used when cloning cells using tissue culture?
The agar needs to be sterile so you don’t have bacteria contaminating it
Advantages of using tissue culture to clone plants?
- plants can be made very quickly
- in very little space
- all year round
How are embryo transplants used to clone animals? (process)
- each embryo is divided into individual cells and each cell grows into an embryo in the lab
- embryos are transferred to host mothers
- identical cloned calves are born
In embryo transplants, what embryo is used initially?
From particular cattle e.g. a prized bull semen with a prized cow egg
In embryo transplants, how does each cell grow into an embryo?
By mitosis
In embryo transplants, who are the cloned organisms identical to?
Each other, but not the mothers that gave birth to them
Advantages of embryo transplants to clone animals?
Produces hundreds of ideal offspring
How is adult cell cloning used to clone animals? (process)
- nucleus removed from unfertilised egg cell and nucleus from adult body cell is inserted into egg cell
- electric shock stimulates egg cell to divide to form embryo
- inserted into womb of an adult female
Benefits of cloning?
- lots of ideal offspring quickly produced with ideal characteristics
- could help preserve endangered species
- lead to a greater understanding of development of the embryo and age-related disorders
Concerns of cloning?
- cloned animals may not be as healthy as normal ones
- reduced gene pool
- may lead to cloning of humans
What is the disadvantage if there is a reduced gene pool?
Fewer alleles available if there is an environmental change so if a new disease appeared, all might be wiped out
What is classification?
When organisms are put into groups depending of their structure and characteristics
What system did Carl Linnaeus develop?
The binomial system
Who developed the binomial system?
Carl Linnaeus
What did Linnaeus classify living things into?
- kingdom
- phylum
- class
- order
- family
- genus
- species
What is the mnemonic to remember the binomial system?
King prawn curry or fat greasy sausages
What is the mnemonic to remember the binomial system? (and what they stand for!)
- king - kingdom
- prawn - phylum
- curry - class
- or - order
- fat - family
- greasy - genus
- sausages - species
What is the kingdom of humans?
Animalia
What is the phylum of humans?
Chordata
What is the class of humans?
Mammalia
What is the order of humans?
Primale
What is the family of humans?
Hominidae
What is the genus of humans?
Homo
What is the species of humans?
sapien
What is the largest group in the binomial system?
Kingdom
What is the newer model of classification?
The ‘three domain system’
Who was the ‘three domain system’ developed by?
Carl Woese
Why were new models of classification proposed?
Evidence of internal structures became more developed due to improvements in microscopes
What are organisms divided into in the three domain system?
- archaea
- bacteria
- eukaryota
What are archaea?
Primitive bacteria usually living in extreme environments
What do eukaryota include?
Protists, fungi, plants and animals
What are the six kingdoms that organisms are classified into?
- archaebacteria
- eubacteria
- protista
- fungi
- plantae
- animalia
What method is used to show how sciensts believe organisms are related?
Evolutionary trees
What do evolutionary trees do?
Show how scientists believe organisms are related
What do evolutionary trees use?
Current classification data for organisms and fossil data
What is the importance of the binomial system for scientists around the world?
So all scientists use the same genus/species names so avoid confusion
