DNA & Reproduction- Biology Paper 2 Flashcards
What is DNA?
A polymer made up of lots of nucleotides
What does each nucleotide consist of ?
one sugar molecule, one phosphate molecule, one base
What forms a ‘backbone’ to the DNA strands?
the sugar and phosphate molecule
What are the 4 different bases?
Adenine, Thymine, Cytosine, Guanine
Which bases pair with which?
Adenine with Thymine, and Guanine with Cytosine
What does complementary base pairing decide?
Which base pairs with which base
What does a sequence of 3 bases make?
One amino acid
Where are proteins made ?
In the ribosomes
What do the ribosomes use to make proteins?
The code in the DNA
What does mRNA do?
carries a copy of the protein code between the DNA and the ribosome
Give 2 functions of proteins
Enzymes, which act as biological catalysts and hormones, which carry messages around the body
What is a mutation?
A ransom change in an organism’s DNA, which can sometimes be inhereted
What can cause DNA mutations?
ionising radiation and chemical mutagens - such as tar from cigarette smoke
What do mutations do?
Change the sequence of DNA bases in a gene and this can lead to changes in the protein that it codes for
What are the different types of DNA mutation?
Insertions, Deletions and substitutions
What is an insertion mutation?
Where a new base is inserted into the DNA base sequence where it shouldn’t be. This can change the amino acid that the base codes for
What is a deletion mutation?
When a random base is deleted from the DNA base sequence .This has knock on effects down the sequence
What are substitution mutations?
Where a ransom base in the DNA base sequence is changed to a different base
How many chromosomes do gametes have?
23
What is a gamete?
a sperm or egg cell
What is sexual reproduction?
where male and female gametes fuse. The genetic material becomes mixed because there are 2 different parents
How does asexual reproduction occur?
By mitosis
How many parents are there in asexual reproduction?
one
In asexual reproduction, why are the offspring genetically identical to the parent?
Because there’s only one parent and so genetic information is not mixed
What is meiosis?
Meiosis is the type of cell division that produces gametes
What are the steps of meiosis?
- Genetic material is replicated
- Chromosomes are pulled apart
- Cell divides 2 more times
- 4 non- Identical daughter cells are produced, each with 23 chromosomes
Where in the body does meiosis happen?
In the reproductive organs
What process does asexual reproduction use?
Mitosis
What is produced when male and female gametes fuse?
A zygote
What are the advantages of sexual reproduction?
- Produces variation in the offspring
- The species can adapt to new environments due to variation, which gives them a survival advantage
- A disease is less likely to affect all the individuals in a population
- Humans can speed up natural selection through selective breeding, which can increase food production
What are the disadvantages of sexual reproduction?
- time and energy are needed to find a mate
- it is not possible for an isolated individual
What are the advantages of asexual reproduction?
- the population can increase rapidly when the conditions are favourable
- only one parent is needed
- it is more time and energy efficient as you don’t need a mate
- it is faster than sexual reproduction
What are the disadvantages of asexual reproduction?
- it does not lead to variation in a population
- the species may only be suited to one habitat
- disease may affect all the individuals in a population
How does the parasite carried by mosquitoes reproduce when it’s in the mosquito?
Sexually
How does the parasite carried by mosquitoes reproduce when it’s in the human body?
Asexually
How do fungus reproduce?
Both sexually and asexually
How do strawberries reproduce asexually?
Strawberry plants produce ‘runners’. These are stems that grow horizontally on the surface of the soil away from a plant. At various points along the runner, a new strawberry plant forms that is identical to the original plant.
How do bulbs reproduce asexually?
New bulbs can form from the main bulb and grow into a new identical plant
How do plants sexually reproduce?
Plants use sexual reproduction to produce seeds
What are chromosomes?
long threads of DNA, which are made up of many genes.
What are genes?
mall section of DNA in a chromosome. Each gene codes for a particular sequence of amino acids in order to make a specific protein. It is the unit of heredity, and may be copied and passed on to the next generation.
What is a genome?
the entire genetic material of an organism
What does understanding the human genome allow us to do?
- search for genes linked to different types of disease
- understand inherited disorders and their treatment
- trace human migration patterns from the past
do all parts of the DNA code for proteins?
Not all parts of the DNA code for proteins, there is a coding and non-coding part of DNA, which can switch genes on and off, so variations in these areas may affect gene expression, and if the correct protein is synthesised or not.
What is a punnet sqaure?
A type of genetic diagram, which shows the probability of any offspring inheriting certain genes
What are alleles?
Different versions of a gene
How many alleles to gametes have?
One
How many alleles do most cells have?
2
What do genes do?
Determine your characteristics
What is homozygous?
Where two alleles for the characteristic are identical
What is heterozygous?
alleles are both different for the same characteristic
What is a dominant allele?
an allele is always expressed, even if only one copy is present
What is a recessive allele?
an allele that is only expressed if the individual has two copies
How is a dominant allele represented?
by a capital letter, for example, A
How is a recessive allele represented?
by a lower case letter, for example
What is a genotype?
the collection of alleles that determine an organism’s characteristics
What is a phenotype?
The visible characteristics of an organism which occur as a result of its genes.
Characteristics that are determined by a single gene can be studied using what?
A monohybrid cross
What are inherited disorders?
Disorders that are caused by a faulty allele, which can be passed on to an individuals offspring
What are 2 inherited disorders?
Cystic fibrosis and polydactyly
What is cystic fibrosis?
an inherited disorder of cell membranes that mainly affects the lungs and digestive system. They can become clogged with lots of thick, sticky mucus as too much is produced.
What allele causes cystic fibrosis?
A faulty recessive allele on chromosome 7, carried by about 1 in 25 people
What are people with only one copy of the cystic fibrosis allele called?
Carriers
What must happen for a child to have cystic fibrosis?
Both parents must be either carriers or have the disorder themselves
What is the chance of a child getting cystic fibrosis if both of their parents are carriers?
1 in 4
Will a person who is homozygous (ff) with the recessive allele develop cystic fibrosis?
Yes
What will happen to someone who is a heterozygous(Ff) in terms of cystic fibrosis?
they will be a carrier of the recessive allele, but will not develop cystic fibrosis and have no symptoms.
Will someone who is homozygous with a dominant allele (FF) develop cystic fibrosis?
no, because you need 2 faulty alleles to develop the condition
What is Polydactyly?
an inherited condition in which a person has extra fingers or toes.
What is Polydactyl caused by?
a dominant allele of a gene. This means it can be passed on by just one allele from one parent if they have the disorder.
Will someone who is homozygous (PP) or heterozygous (Pp) for the dominant allele develop polydactyly?
Yes
What is the probability of the offspring having polydactyly?
50%
Do offspring need to carry just one dominant allele from their parents to inherit the polydactyl condition?
Yes
Are there any carriers for polydactyl?
No because it is caused by a dominant allele
What is a family tree?
A diagram that shows how a characteristic of a group of related people is developed
What is embryonic screening?
A way of detecting inherited disorders in embryos
What methods are in place for embryonic screening?
Pre-implantation genetic diagnosis and Chorionic villus sampling
What did Mendel notice?
That characteristics in plants were passed on from one generation to the next. His research became the foundation of modern genetics
From Mendel’s research on pea plants, what 3 conclusions did Mendel come to about heredity in plants?
1) Characteristics in plants are determined by ‘‘hereditary units’’
2) Hereditary units are passed on to offspring unchanged from both parents, one unity from each parent.
3) Hereditary units can be dominant or recessive- if an individual has both the dominant and recessive unit for a characteristic, the dominant characteristic will be expressed.
What is gene theory?
The idea that genes are the units of inheritance
What did Mendel do with pea plants?
He crossed the pea plants of different heights - a tall pea plant and a dwarf pea plant. The offspring produced were all tall pea plants. He then bred 2 of these tall pea plants together. The resulting offspring consisted of 3 tall pea plants and one dwarf pea plants
What are the 2 types of variation?
Genetic variation and environmental variation
What is variation?
differences between individuals because of differing DNA
What are some examples of environmental variation?
Sun tans, yellow leaves, scars, accent
What are examples of both genetic and environmental variation?
Height, intelligence, health
Who came up with the theory of evolution?
Charles Darwin
What is evolution?
The idea that all of today’s species have evolved from simple life forms that first started to develop over 3 billion years ago
What is natural selection?
The natural process whereby the best-adapted individuals survive longer, have more offspring and thereby spread their characteristics. Sometimes referred to as ‘survival of the fittest’
What is a phenotype?
The visible characteristics of an organism which occur as a result of its genes.
How does natural selection work?
1) Individuals within a species show wide variation in their characteristics because of the mix of genetic variants present in the population
2) Some genetic variants give rise to characteristics that are better suited to the environment. Organisms with these characteristics have a better chance of survival and so are more likely to breed successfully
3) So, the genetic variants that are responsible for the useful characteristics are more likely to be passed on to the next generation
What is speciation?
When a population of the same species change enough to become reproductively isolated- this means that they can’t interbreed to produce fertile offspring
What is extinction?
When no living individuals of a species remain
What are the reasons for a species becoming extinct?
- the environment changing too quickly
- a new predator killing the species
- a new disease killing the species
- the species being unable to compete with another new species for food
- a catastrophic event that kill the species
What was Lamarck’s hypothesis about evolution?
That if an organism used a characteristic a lot, then it would become more developed during its lifetime and the organism’s offspring would inherit the characteristic.
What is selective breeding?
Where humans artificially select the plants or animals that are going to breed so that genes for particular characteristics remain in the population. Basically, organisms are selectively bred to develop features that are useful or attractive
What is selective breeding also known as?
Artificial selection
What is the process of selective breeding?
1) From your existing stock, select the ones which have the characteristics you’re after
2) Breed them with each other
3) Select the best offspring and breed them together.
4) Continue this process over several generations and the desirable trait will get stronger. Eventually, all the offspring will have the characteristic
How can selective breeding help agriculture?
It can be used to improve yield
What is the gene pool?
The number of different alleles in a population
What are the disadvantages of inbreeding?
health problems can be caused because there’s more of a chance of organisms inheriting harmful genetic defects, new diseases can be deadly because there’s no genetic variation
What is genetic engineering?
transferring a gene responsible for a desired characteristic from one organism’s genome into another organism so that it also has the desired characteristic
What is the process of genetic engineering?
1) A useful gene is isolated(cut) from one organism’s genome using enzymes and is inserted into a vector.
2) When the vector is introduced to the target organism, the useful gene is inserted into its cells
What is an example of genetic engineering in use?
GM crops that have had their genes modified to improve the quality and size of their fruit
What are the advantages of genetically modified crops?
- yield can be increased
- foods can be made with increased nutrients
What are the disadvantages of genetically modified crops?
- biodiversity may decrease
- may not be good for human health
- transplanted genes may get out into the natural environment
What is cloning?
Making a genetically identical copy of an organism/asexual reproduction
What 2 ways are used to clone plants?
Using tissue culture and using cuttings
How can animal clones be produced?
Using embryo transplants
What is adult cell cloning?
Taking an unfertilised egg and removing its nucleus. The nucleus is then removed from an adult body and is inserted into the ‘empty’ egg cell. The egg cell is then stimulated by an electric shock to make it divide like a normal embryo. The embryo is then inserted into the uterus when it has grown enough
What are the advantages of cloning?
- you can quickly get a lot of ‘ideal’ offspring with known characteristics
- the study of animal clones could lead to a greater understanding of the development of the embryo
- cloning could be used to help preserve endangered species
What are the disadvantages of cloning?
- cloning reduces the gene pool
- cloned animals may not be as health as normal ones
- if human cloning was to occur, there may be many unsuccessful attempts
What are fossils?
the remains of organisms from many years ago, which are found in rocks
Which ways do fossils form?
- From gradual replacement by minerals
- From casts and impressions
- From preservation in places where no decay happens
What is isolation?
Where populations of a species are separated. This can lead to speciation
Who was one of the earliest scientists that came up with the idea of speciation?
Alfred Russel Wallace
What increases the spread of antibiotic resistant bacteria?
- Over using anti-biotics
- Not taking antibiotics for the full course
What is antibiotic-resistance?
When bacteria mutate and this allows them to become resistant to antibiotics
What is the Linnaean system?
the classification of organisms according to their characteristics and the structures that make them up
What are the 3 domains of the three-domain system?
Archaea, bacteria, eukaryota
What is the binomial system?
Where every organism is given its own two part Latin name. The first part refers to the genus that the organism belongs to- this gives you information on the organism’s ancestry. The second part refers to the species
What do evolutionary trees show?
How scientists think different species are related to each other. They show common ancestors and relationships between species.
