Inheritance, variation and evolution (B2.6) Flashcards
What is a gene?
A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein.
What is an allele?
Different versions of a gene we have 2 alleles per gene( 1 from each parent)
What is a genotype?
The alleles for a specific characteristic that are present
What is a gamete?
Gametes are sex cells eg sperm and egg cells but are not fused together.
They have 23 chromosomes (one copy of each chromosome called a chromatid)
What is a diploid and a haploid?
A gamete is a haploid as haploids are a single set of chromosomes of 23.
When the two gametes combine, they merge the two sets of chromosome to have 46, which are referred to as diploid. This produces a new cell called a zygote
What is a phenotype?
Observable physical characteristics as a result of genes
What is meant by a dominant allele?
The dominant allele is always expressed and is (B) even if only one copy is present
What is meant by a recessive allele?
The recessive allele needs 2 recessive alleles to be expressed (b)
What is meant by homozygous?
2 of the same alleles( bb= homozygous recessive or BB= homozygous dominant)
What is meant by heterozygous dominant?
Different alleles (Bb)
How many chromosomes do human cells have in their nucleus?
23 pairs (46)
What is sexual reproduction?
What is 2 advantages and 2 disadvantages?
2 parents have sex by mixing 2 sets of genetic information from 2 gametes and the offspring is genetically different
ADV- variation in offspring DIS- slower to reproduce and we need 2 partners.
What is asexual reproduction?
What is 2 advantages and 2 disadvantages?
1 parent makes identical copies of its cells and DNA and the offspring is identical to the parent (no gametes are required)
ADV- quick and no partners DIS- no variation and offspring will inherit diseases
What are the male and female sex organs in plants?
Male= stamen and female= stigma
Describe how sexual reproduction occurs and what type of cell division is used:
The gametes from each parent fuses and forms a zygote. Meiosis occurs
Describe the process of Meiosis
Cells in reproductive organs divide by meiosis to form gametes. Two cell divisions occur and the chromosomes replicate but only 1/2 of each chromosome goes to a new daughter cell. 4 new daughter cells are produced and the daughter cells are genetically different.
Describe the rough process of Mitosis
Only 1 cell division occurs and it produces 2 genetically identical daughter cells. The cell which has 46 will double to 92 and the split into 2 cells each of 46.
The chromosomes replicate which copies all genetic information (as a chromatid) and goes to each new daughter cell.
Why does Mitosis occur?
During growth, repair and asexual reproduction
Why does meiosis occur?
Meiosis only occurs in reproductive cells so the ovaries and testes in humans, to create haploid gametes that will be used in fertilisation
What is a chromatid?
one copy of each chromosome
Describe the organisation of our structure from small to large (8)
Genes, DNA, Chromosomes, Nucleus, Cell, Tissue, Organ , Organism
What is DNA?
Deoxyribonucleic acid. The genetic material in the nucleus of a cell is composed of DNA. DNA is made up of two strands forming a double helix. The DNA is contained in structures called
chromosomes.
What are the sex organs in flowering plants?
pollen and egg cells
What happens after meiosis?
Gametes join at fertilisation to restore the normal number of chromosomes. The new cell divides by mitosis. The number of cells increases and are identical. As the embryo develops cells start to differentiate.
What is a chromosome?
Coiled DNA- Humans have 46 chromosomes arranged in 23 pairs.
What is a genome?
The entire genetic material of an organism
What does the human genome allow us to understand?
We can: search for genes linked to different types of disease
• understanding and treatment of inherited disorders
• use in tracing human migration patterns from the past( allows people to understand their ancestry)
Why could climate change affect asexually reproducing organisms more than sexually reproducing organisms?
If parents are unable to adapt to a certain condition there offspring will also die as the offspring is a clone- whereas in sexual reproduction there is more variation
Who determines the sex of an foetus?
The father
What are the sex chromosomes for a boy and for a girl? What pair of chromosomes code for gender?
Boy= XY and Girl= XX
The last 23rd pair
Describe sex determination
We have 2 sex chromosomes of x and y chromosomes. Males have one of each whereas females have XX chromosomes. This means the male gamete determines the sex of an embryo. So the mother has XX and the father has XY so the baby will be either ( XX,XY,XX,XY- so there’s a 1:1 chance of a boy or a girl)
In the human sex chromosomes, what is the recessive and what is the dominant? Why is it important that the dominant chromosome is DOMINANT?
Male dominant= Y and Female recessive= X
Otherwise the world would only have females
What is an inherited disorder?
These disorders are caused by the inheritance of certain alleles
What is Cystic Fibrosis and the symptoms?
Disorder of cell membranes which affects lungs and causes breathing difficulty as hairs don’t waft mucus up which blocks tubes- symptoms= difficulty breathing and walking
What is the allele and genotype that causes Cystic Fibrosis?
STRICTLY Homozygous recessive allele and the persons genotype is (cc)
What is a carrier?
What is a mutation?
If a person receives only one recessive allele, their one dominant allele means they do not have symptoms of the disorder. However, they are able to pass it to their children. They are called a carrier.
A mutation is a random change in the DNA/gene
What is polydactyly?
Having an extra toe or thumb
What type of allele and genotype causes polydactyly?
1 dominant allele ( PP or Pp)
How can we see (or prevent) if an embryo has genetic disorders?
Screening techniques i.e. IVF, Amniocentesis or Chorionic Villus Sampling
What is Amniocentesis?
Carried out at 15 weeks or so and we take amniotic fluid from foetus and test the fluid for genetic disorders using foetal cells.
What is Chorionic Villus Sampling?
Carried out at 10-12 weeks and we take a sample of the tissue of placenta and test foetal cells
What are the downsides to both embryo testing methods?
Can cause/ increases risk of miscarriage and in case of false result- a healthy pregnancy can be terminated
Describe IVF
Gametes are removed from both parents and are fused outside the body via in vitro ( in a lab). Then the embryo develops via fertilised egg and we test embryo cells for a disorder. Embryos with good alleles are implanted into mother and develop whilst embryos with bad alleles are destroyed
Why do identical twins look identical?
Have the same DNA
What is variation?
Differences in the characteristics of individuals in a population
What are the 3 causes of variation?
1) The alleles that individuals have inherited (genetic causes i.e. hair and eyes)
2) Environment i.e. languages or scars
3) Combination of both genes and environment like: height/weight
Why do genetic variations occur and what do they lead to ?
Due to mutations causing phenotypes to change
Explain the process of genetic variation
The DNA of an organism randomly changes due to a mutation. Therefore the genotype changes sometimes resulting in a change of the phenotypes causing variation
What’s the difference between discontinuous and continuous data?
Discontinuous= specific groups like hair colour/ blood group
Continuous= data with a range i.e. height/weight
What difficulties can arise when testing identical twins?
Hard to control EVERYTHING?
Ethical issues i.e. pressurising or separating twins
What is natural selection?
How species change and adapt so best adapted organisms with desired phenotypes survive/ reproduce whilst other less adapted organisms die
Describe the process of natural selection using rabbits and foxes
Lets say some rabbits have alleles for good sight/hearing and others dont- when a fox is around the rabbits with good eyesight/hearing will run away and survive but the other rabbits with non adapted alleles will die= natural selection
What is evolution?
The change in inherited characteristics of a population through the process of natural selection over a long period of time
What can happen when 2 populations of the same species become VERY different in phenotype?
The 2 populations become 2 separate species and cannot breed successfully with the other population
What is selective breeding (artificial selection)?
When humans choose which organisms to breed to produce offspring with desired characteristics
What is the point of selective breeding in the future?
Next generation will be likely to have desired characteristics
Describe selective breeding (detailed)
1) Organisms show variation in features and humans select organisms with desired characteristics i.e. good nature/ temperament
2) 2 chosen organisms are mated/ bred and offspring is produced.
3) Offspring with good features and bred all over again and again for many generations UNTIL all of the population have these characteristics.
What are some desired features we want in animals?
Good milk yield
Produces lots of meat
Good temperament
Gentle domestic pets
What are some advantages of selective breeding?
Unique/ unusual plants– Genetic manipulation leads to unusual genetic combinations– economic profit— speeds up evolution– better genes/alleles in a population overall
What are some disadvantages of selective breeding?
Reduces variation of phenotypes in a population—
In case of a new change to environment, all animals/ plants share genotypes so none are able to survive–
More inherited diseases
Inbreeding means breeding related animals/plants for a specific look– which can cause inherited defects/diseases
What is genetic engineering?
genes from 1 organisms i.e. humans are cut out and transferred to cells of a different organism i.e. bacteria——– Genetic engineering involves the modification of genetic material of an organism
What is an example of how we have genetically modified bacteria?
People with T1 diabetes cannot produce their own Insulin (a hormone for blood glucose regulation)and must inject themselves with insulin regularly
We have genetically modified bacteria to contain the human insulin gene which means the bacteria reproduce and produce lots of human insulin which we take for T1 diabetes
How can we make GM crops better than regular crops?
Transfer the gene into plants to make GM crops that are bigger( greater yield) or disease resistant or resistant to herbicides
What is gene therapy?
Genetic modification to treat human inherited disorders
Describe the process of genetic engineering
Find the gene you want to transfer
Use enzymes to isolate and cut out gene from the organism
Transfer the gene into vector like: a plasmid or virus
Insert the gene into the cells of the target organism i.e. animal/plant
What is a plasmid?
A small circle of DNA useful for transferring DNA from one organism to another
At what stage of the organism do we transfer the gene?
Early stages of development (i.e. for animals at early embryo stage) to make sure ALL cells receive the transferred gene so that the organism develops with the characteristic we want
What are some advantages of Genetic engineering in agriculture?
Better Growth rates Bigger yield (more food) Disease/Drought resistant Herbicide/ pesticide resistant Mass production of desired genes
What are some concerns of Genetic Engineering?
New science We dont know long term effects Encourages more human engineering Expensive People feel eating GM crops is unsafe Effect on population of flowers/insects
How could genetic engineering be used to cure genetic disorders?
Healthy cells inserted into affected cells and the affected cells begin to work properly so we can alter peoples genes to make sure they dont have the disorder
Why might the government not allow the production of certain GM foods?
- Extinction of the natural food
- They dont know long term effect
What do fossils provide?
Good evidence for evolution
What are fossils?
Remains of organisms from millions of years ago which are found in rocks
What are the 3 ways fossils can form?
1) Parts of an organism have not decayed when conditions for decay are absent i.e. temp= too cold or if there is not enough oxygen
2) When parts of the organism are replaced by minerals during the decay process
3) Preserved traces of organisms i.e. footprints or burrows or plants leaving preserved spaces in area of roots
What do we need for decay to occur?
Oxygen
What conditions can cause fossilisation?
Lack of oxygen, extreme cold temperatures and absence of bacteria
What is an issue about fossils?
Many earlier forms of life were soft bodied so they dont form fossils so we dont have evidence about evolution from the start
Also some fossils have been destroyed due to tectonic hazards i.e. volcanoes
How can fossils give evidence for evolution?
We see how older fossils change and how younger ones developed
What does extinct mean?
When there are no remaining individuals of a species alive
How can species become extinct?
Due to a catastrophic event (i.e. asteroids)
Environmental changes
new disease or predator
If a new species evolves and competes with the old species for food/water
How do fossils form?
Dead bodies of animals buried via mud/sand
Layer of sediment presses down on them
Pressure increases
The pressure leaves the remains to stone or minerals fill in the hole
What is the name of the type of organism that evolves extremely rapidly? Why?
Bacteria— they reproduce at such a fast rate so they evolve rapidly
How did doctors begin to treat bacterial diseases ?
Antibiotics like Penicillin KILL bacteria
How are antibiotics used?
Widely used in medicine and in farming to prevent animals from developing bacterial disease
What has occurred due to the evolution of bacteria?
Certain strains of bacteria are no longer killed by antibiotics so they are “ antibiotic resistant”
Name 1 common strain of antibiotic resistant bacteria
MRSA
How does antibiotic resistance happen?
In any population of an organism- there are genetic variations due to mutations
Some bacterium have a mutation that makes them resistant to antibiotics
We use antibiotics to kill the bacteria without the mutation BUT the antibiotic resistant bacteria still survive
These resistant strains reproduce causing the population of the resistant strain to rise and spread and there is no treatment
How can we reduce the development of antibiotic resistant strains of bacteria?
Doctors mustn’t prescribe antibiotics inappropriately i.e for a virus as this wouldn’t work
Patients must complete their course of antibiotics to make sure ALL bacteria is killed and none can survive to mutate
We must restrict use of antibiotics in farming
Why dont researchers just develop new antibiotics?
Takes a very long time
Very Expensive
New strains emerge all the time so its unlikely we can keep up!
What can we observe from lots of species?
They have similar characteristics in common despite being different species
Who and how have species been classified by?
Traditionally living things have been classified into groups
depending on their structure and characteristics in a system
developed by Carl Linnaeus.
How did Linneaus do this?
Divided all living organisms into 2 kingdoms of “ the animal kingdom” and the “plant kingdom”
He then divided each kingdom into smaller categories
What are the names of linneaus’ classification categories?
Linnaeus classified living things into: kingdom, phylum, class, order,
family, genus and species.
What mmemonic can we use to remember this?
King Phillip came over for good soup
How are organisms named?
Organisms are named by the binomial
system (2 names) of genus and species.
We have a polar bear–
The Family is called Ursidae
The Genus is called Ursus and the species is called Maritimus
What is the binominal name of this organism?
Genus+ species= Ursus Maritimus
What do we base this classification system on?
Characteristics we can see (phenotypes)
What advances have been made since this classification system?
As evidence of internal structures became more developed due to
improvements in microscopes, and the understanding of
biochemical processes progressed, new models of classification
were propose.
We can use microscopes to look at internal structures or analyse DNA
What system do scientists now use?
The 3 domain system developed by Carl Woese.
What is the 3 domain system?
. In this system
organisms are divided into:
• Archaea (primitive bacteria usually living in extreme environments)
• Bacteria (true bacteria i.e in our digestive system)
• Eukaryota (which includes protists like amoeba, fungi, plants and animals)
What are evolutionary trees?
Evolutionary trees are a method used by scientists to show how they believe organisms are related.
What do we need to make an evolutionary tree for living and extinct species?
They use current classification
data for living organisms
Fossil data for extinct organisms= issue as many fossils are incomplete
