1
Q
What is sexual reproduction?
A
- When genetic information from 2 organisms (father and mother) are combined to produce offspring which are genetically different to either parent.
- the mother will produce gametes (reproductive cells) which are egg cells and the fathers gametes will be sperm cells
- the gametes will fuse to produce a zygote
2
Q
What are gametes?
A
- haploid sex cells which contain half (23) the normal amount of chromosomes that a diploid cell would have (46)
3
Q
What happens at fertilisation?
A
- a male gamete fuses with a female gamete to produce a fertilised egg (known as a zygote) which will have a full set of chromosomes.
- this zygote then divides by mitosis, undergoing cell division and developing into an embryo, this embryo inherits characteristics from both the mother and father as it has received a mixture of chromosomes.
4
Q
What is DNA?
A
- The genetic material in the nucleus of a cell is composed of a chemical called DNA.
- DNA is a polymer made up of two strands coiled together, forming a double helix.
- The DNA is contained in structures called chromosomes.
- contains genetic information that creates a code, producing instructions for how human cells operate in order to coordinate and control our bodies.
- the DNA of an organism is its genome, most cells contain a full copy of the organisms genome
5
Q
What is human genome and where is it found?
A
- human genome is the entire genetic material of that organism
- it is found in the nucleus on 46 very long molecules of DNA with each molecule being inside a chromosome
- In humans, the genome consists of 23 pairs of chromosomes located in the cell’s nucleus
6
Q
What are proteins?
A
- proteins are polymers, made by linking different amino acids together in a chain. The order of amino acids are controlled by genes.
7
Q
What is meiosis?
A
- meiosis is a form of cell division which produces four genetically different, haploid sex cells or gametes which contain a single set of 23 chromosomes in the reproductive organs.
8
Q
What are the differences between mitosis and meiosis?
A
- mitosis is a form of cell division which produces two genetically identical, diploid daughter cells, meiosis is a form of cell division which produces four genetically different haploid sex cells or gametes
- Meiosis only produces gametes whilst mitosis can replicate a variety of different cells
- Mitosis takes place all over the body, meiosis only takes place in the sex organs
- Mitosis consists of one stage whereas meiosis consists of two stages
- the end result of mitosis is two genetically identical daughter cells, whereas the end result for meiosis is 4 genetically different daughter cells
- Mitosis produces genetically identical diploid daughter cells for growth and repair. Meiosis produces haploid non-identical sex cells, or gametes for genetic variation within fertilisation
9
Q
What are some similarities between mitosis and meiosis?
A
- Both mitosis and meiosis take place in the cell nuclei
- Both mitosis and meiosis involve cell division
- Both occur in humans and other animals
- They both replicate genetic material
- They both go through Prophase, Interphase, Metaphase, Anaphase and Telophase and Cytokinesis
10
Q
Describe division 1 of meiosis.
A
- Before the cell divides the DNA duplicates, each maternal and paternal chromosome will replicate and the two copies will remain attached, making each chromosome look like an x
- The chromosome x’s will then randomly line up in pairs along the centre of the cell. It’s important to remember that these pairs are completely random and will be different each time. One chromosome in each pair would’ve come from the mother and the other from the father
- These pairs are then pulled apart as the cell has divided so each chromosome in a pair has went to separate cells. This allows the dna in each cell to be different because in the original PAIRS one was maternal the other was paternal
- The two cells now have a mixture of the mother and father’s chromosomes allowing there to be genetic variation
11
Q
Describe division 2 of meiosis.
A
- In the second division the chromosomes line up yet again in the centre of the cell and are pulled apart
- This creates 4 haploid daughter cells/ gametes with a swingle set of chromosomes (23)
- these 4 cells are all genetically different
12
Q
Describe the structure of DNA?
A
- dna is a polymer made from 2 strands, individually they form a helix but when put together they form a double helix
-DNA is a polymer made up of lots of monomers which are known as nucleotides - if a single DNA strand were to be laid out flat and 2d a single strand would have many repeating monomers (nucleotides) and when joined up with the second strand the bases in the nucleotides would connect and then a double helix shape would be formed.
- to form a chain/strand of DNA nucleotide will connect via the phosphate of one nucleotide and the sugar of another, this will keep repeating across thousands of nucleotides forming one long chain known as the sugar phosphate backbone which protects a protective outer casing. (Since this is a single strand the bases will be sticking out, when it joins with another strand the complimentary bases will connect and then form the double helix)
13
Q
Describe the structure of nucleotides.
A
- each nucleotide is made up of 1 sugar molecule, 1 phosphate molecule and 1 base
- every nucleotide in the polymer (DNA) will have the same phosphate and sugar but different bases (adenine, thymine, cytosine or guanine)
- to form a polymer, nucleotides will connect via the phosphate of one nucleotide and the sugar of another with bases sticking out, ready to connect to another strand
14
Q
Describe the sugar phosphate backbone.
A
- to form a polymer, nucleotides will connect via the phosphate of one nucleotide and the sugar of another
- the phosphate of one nucleotide will keep bonding to the sugar of another and repeat across thousands of nucleotides to form one long chain known as the sugar phosphate backbone.
- this long chain provides a protective outer casing to the bases in the middle
(The bases that connect to the sugars are are either adenine, thymine, cytosine or guanine)
15
Q
What are the DNA bases and their complimentary pairs, and how are they joined together.
A
- Adenine - thymine
- Cytosine - guanine
- the complimentary base pairs are joined together by weak hydrogen bonds. This is because parts of DNA bases have slight electrical charges, a slightly negatively charged part of one base attracts a slightly positive charged part of another base. This is what creates a weak form of attraction between weak hydrogen bonds.
16
Q
What is a gene and genetic code?
A
- a particular sequence of bases (also sometimes referred to as a small section of dna) that codes for a protein
- when referring to the genetic code it is the sequence of bases that provides a code for what proteins the cell will produce
17
Q
Describe how DNA, bases, amino acids and proteins are linked?
A
- on a dna strand, each group of 3 bases is known as a triplet and it codes for a specific, different amino acid
- this will form a chain of amino acids that will form a protein
- DNA is responsible for determining which amino acids are formed, therefore what proteins the cell produces determines what type of cell it will be. EG. Red blood cells will need a lot of haemoglobin so their dna will code for the specific amino acids that will create haemoglobin
- each protein will be made from a different sequence of amino acids that provides a specific function for the cell
18
Q
How many types of amino acids are there?
A
- there are only 20 amino acids but they can make thousands of combinations therefore a diverse range of proteins
19
Q
What does DNA stand for?
A
Deoxyribonucleic acid
20
Q
How is DNA arranged inside a cell?
A
- since all the DNA in a single cell is altogether a 2m long strand, in order to make it all compact and able to fit inside the cells nucleus, it is separated into 46 sections.
- each of these sections is a very tight coil which is known as a chromosome and each body cell (apart from reproductive cells) will have 46 chromosomes.
21
Q
What are chromosomes?
A
- chromosomes are long, coiled up molecules of DNA found in the nucleus of eukaryotic cells
- each body cell (apart from reproductive cells) contain 23 pairs of these
22
Q
How many TYPES of chromosomes do humans have?
A
- there are actually only 23 types of chromosomes as we have 2 of each type. 23 of them come from the father the other 23 come from the mother.
- since they are the same 23 chromosomes doubled, we just say that we have 23 pairs of chromosomes
23
Q
What is the significance of chromosome 23?
A
- chromosome 23 is different as this is the sex chromosome determining the sex
- there is an X chromosome as well as a Y chromosome
- women will have XX chromosomes and men will have XY chromosomes
24
Q
What chromosomes do women have?
A
XX
25
What chromosomes do men have?
XY
26
Explain how you would extract DNA from fruit cells.
1. Firstly you have to create a solution of water with salt and detergent
2. Mash some strawberries thoroughly and place them in a beaker, along with the solution.
3. Mix well
4. Place the beaker in a water bath and remove after 15 minutes
5. Filter the mixture in order to get the froth and big insoluble bits of cell out, collect the filtrate in a small beaker.
6. Add ice cold ethanol to the filtered mixture so that the DNA will start to come out the solution, as it is not soluble in cold ethanol and must form a stringy white PRECIPITATE that can be lifted out the tube with a glass rod.
27
When extracting DNA from fruit cells, why is salt used in the solution.
- salt will make the dna clump together, helping it to become a precipitate
28
When extracting DNA from fruit cells, why is detergent used in the solution.
- the detergent will break down the cell surface membrane and the membrane around the nucleus, allowing the DNA to be released.
29
When extracting DNA from fruit cells, why is ice cold ethanol used.
- since the DNA is not soluble in ice cold ethanol, this helps the DNA to precipitate (solidify and appear) and form a stringy white precipitate
30
How are our characteristics determined?
- the genes that we inherit determine our characteristics
- genes are a segment of DNA that codes for a specific type of protein, there are often multiple forms of the same protein, therefore there is a different genetic code for each protein, these different codes are known as ALLELES.
- some characteristics can be controlled by a single gene but most characteristics are caused by several genes interacting.
31
What are alleles?
- alleles are different versions of the same genes
- eg. Genes for the same characteristic like eye colour can contain slightly different instructions that create variation eg. Brown or blue.
32
How many types of alleles do we have in our body?
- you have 2 version (alleles) of every gene in your body, one on each chromosome in a pair from the mother and father, there are only 23 types of chromosomes but you get two of each of these from the mother and father leaving you with 46.
- these two alleles could either be HETEROZYGOUS or HOMOZYGOUS
- the alleles could also be DOMINANT or recessive
33
What does homozygous mean?
- if an organism has two alleles for a particular gene and they are the same, then it’s homozygous
34
What does heterozygous mean?
- if an organism has two alleles for a particular gene that are different, it is heterozygous.
35
What is a dominant allele?
- represented with a capital letter and they overrule recessive alleles
- to display a dominant characteristic it must be DD or Dd
36
What is a recessive allele?
- represented with a lowercase letter, becomes overruled by a dominant allele
- to show a recessive characteristic it must be dd
37
What is the genotype?
- the collection of alleles you have
38
What is the phenotype?
- physical characteristics you get from the genotype
39
What is mono hybrid inheritance?
- the inheritance of a single characteristic
40
What is the purpose of a mono hybrid cross diagram?
- mono hybrid cross diagrams are able to show the possible combination of alleles when two organisms produce offspring allowing us know the possible genotype but also estimate the phenotype the offspring’s will have
- with this, we are able to create ratios and probabilities of specific phenotypes.
41
What is the purpose of a punnet square?
- mono hybrid inheritance can be shown in a punnet square.
- it separates the alleles and then and then cross-merges them to show the 4 possible outcomes of the offspring’s genotype
- with this you can predict the phenotype and create ratios and probabilities.
42
What is cystic fibrosis?
- a disease caused by a recessive allele
- people with CF have problems with their lungs and digestive system becoming clogged with thick, sticky mucus
- if someone were to inherit 2 recessive cystic fibrosis alleles they would have the disease
- if someone were to have a dominant allele along with the recessive CF allele they would not have the disease but they would still be a carrier
43
How can genetic diagrams determine sex?
- genetic diagrams can show how sex is determined in humans
- among the 23 pairs chromosomes, the 23rd pair are the sex chromosomes labelled XX (female) or XY (male)
- you could put these pairs of alleles in a genetic diagram to determine the possibility of genotypes in the offspring
- it will always be a 50\50 chance of getting a boy or girl.
44
What is a family pedigree?
- a family pedigree is a family tree of genetic disorders that diagrams how genotypes are inherited in families
- it can also show mono hybrid inheritance
45
Describe how a family pedigree would be portrayed with cystic fibrosis.
- a family pedigree can detail who in the family tree does not have the disease, has the disease or is just a carrier.
- if there was a carrier in the family, and they produced offspring with another carrier, the baby would have a 55% chance of being a carrier, 25% of having the disease and another 25% of not having it at all (worked out via punnet square)
46
What is the human genome project?
- a project in which thousands of scientists around the world collaborated on to try and find every single human gene
- the project started in 1990 and a completed map of of the human genome, including over 20,500 genes was completed in 2003
- the projects aims to figure out what each of them do
- it has helped to identify about 1800 genes related to disease which has had large benefits for medicine
47
How has the human genome project helped to predict and prevent diseases?
- since many common diseases like cancers and heart diseases are caused by the interaction of different genes (aswell as lifestyle), if doctors knew what genes could cause these diseases, they could provide induvidually tailored advice on the best diet and lifestyle to avoid possible future diseases that could arise due to genes
- this could also prompt doctors to provide checkups to catch possible diseases in early stages to ensure early treatment
48
How has the human genome project affect testing and treatment for inherited disorder?
- inherited diseases are caused by the presence of faulty diseases in a persons genome
- because of the project, doctors can identify which genes and alleles cause inherited diseases
- once an allele that causes an inherited disease has been identified, people can be tested for it and better treatment could be curated, possible even a cure
49
How has the human genome project benefitted medicine?
- helps us identify what genetic variation an individual has and whether they will react accordingly to a medicine
- it helps to identify which medicines will be best to treat a persons illness since genetic variation (caused by the alleles we have) can affect how we react to medicine.
50
What are some drawbacks of the human genome project?
- creates increased stress- if someone were to find out from an early age that they are susceptible to a life threatening disease, this may cause increased panic
- geneism- people with genetic problems becoming pressure to not having children
- discrimination- discrimination from employers and insurers could make it difficult to get a job or life insurance due to the fact someone may have any genetic likelihood of a disease
51
Explain variation in organisms.
- while different species look very different eg. A dog and a daisy flower, there are also differences in organisms of the same species eg. Dogs are all the same specie yet pugs and Dalmatian’s look drastically different
- these differences between individuals of the same species is known as variation
52
What is continuous variation?
- the data can be any value in a range, there are small degrees of differences for a particular characteristic between individuals
- eg. Height, mass, leave length is not defined by an exact value, there are many inbetween types
- continuous variation graphs produce a smooth bell curve and also (if it is a bar graph) it will have no gaps between the bars to show that the data is continuous, spread out across all values
53
What is discontinuous variation?
- when data can only take on a limited set of values, there are very distinct differences
- eg. Blood type, number of leaves
- these are all have exact values with no inbetweens
- discontinuous variation graphs produce a step like shape and also (if it is a bar graph) there will be slight gaps between the bars showing it is a fixed value
54
What types of phenotypic variation is there?
- genetic- caused by genes
- environmental- caused by the environment the organism lives in
55
What is genetic variation?
- genetic variation is caused by organisms having different alleles leading to differences in their phenotypes
- can be caused by new alleles arising through mutations OR through sexual reproduction which causes genetic variation since it results in alleles being combined in lots of different ways in offspring.
56
How is genetic variation through sexual reproduction caused?
- meiosis creates genetic variation between the gametes produced by an individual, meaning that each gamete carries different alleles
- during fertilisation any of these random gametes could fuse with the counter male or female gamete to form a zygote
- since the two gametes that were fused are completely random, genetic variation is caused between zygotes and they will each have a unique combination of alleles
57
What are some examples of genetic variation in humans?
- eye colour
- blood type
- gender
- ability to roll tongue
58
What is environmental variation?
- the differing conditions that an organism lives in like climate, diet, culture, lifestyle and accidents can affect its characteristics
Eg. In plants those that are grown in sunlight will be greener and flourish rather than those in darkness which will be yellow and weak or in humans accidents may lead to scarring on the body
- these are known as acquired characteristics that an organism gains in its lifetime.
59
What are mutations?
- mutations are changes to the DNA base sequence
- when they occur within a gene, they can result in an allele or a different version of the gene
- a change in the base sequence of the DNA causes the sequence of amino acids to change, therefore the protein formed will be different.
- the altered protein may have a completely different shape and function and even change the individuals characteristics
- or there may be no change and the mutation could be neutral
- these mutations always occur spontaneously, like when DNA is being replicated before mitosis
60
What can cause a higher rate of mutations?
- carcinogens- harmful chemicals found in things like cigarettes
- certain types of radiation- X-rays or gamma rays
- they don’t always cause mutations, just increase the risk of them occurring
61
How are cystic fibrosis and mutations linked?
- mutations can sometimes have a drastic effect eg. It may completely alter a protein so that it can no longer perform its function
- this is what occurs in cystic fibrosis when a mutation causes the protein that regulates the movement of salt and water into and out of cells to stop working properly, leading to the production of a thick sticky mucus in the lungs or digestive tract making breathing and digestion very difficult
62
What is non-coding DNA?
- most mutations happen in non coding DNA which is not apart of any gene so it does not code for any protein
- most non coding DNA doesn’t do much, however some of it is really important as it plays a role in the expression of genes (whether they are turned on or off)
- for example in the nerve cells, the protein that produces haemoglobin can be switched off as it is only needed in the red blood cells, it is not expressed in nerve cells
Biology
flashcards
Decks in class (9)
# Cards
-
CB1- Key Concepts In Biology27
-
CB2- Cells And Control67
-
CB3- Genetics62
-
CB4- Natural Selection And Genetic Modification56
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CB5- Health, Disease And The Development Of Medicines44
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CB6- Plant Structures And Their Functions60
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CB7- Animal Coordination, Control And Homeostasis63
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CB8- Exchange And Transport In Animals47
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CB9- Ecosystems And Material Cycles52
