DNA, GENES AND CHROMOSOMES Flashcards
1
Q
ELABORATE ON DNA IN PROKARYOTES?
A
PROKARYOTES POSSESS A SINGLE, CIRCULAR CHROMOSOMAL DNA MOLECULE. (SOMETIMES REFERRED TO AS A NUCLEOID)
THEY USUALLY HAVE ONE OR MORE PLASMIDS (plasmids are very small circular dna molecules, gene for antibiotic resistance is found in plasmids)
THE DNA WITHIN PROKARYOTIC CELLS is not associated with proteins (histones)
dna aint enclosed in nucleus.
2
Q
chromosomes are made of what? whats chromatin and what are chromosomes and chromatids made from?
A
chromosomes are made of very long, condensed dna molecule assoscitated with proteins (in eukaryotic cells).
the main proteins are the large postively charged globular proteins called histones, their role is to organise and condense the dna tightly so that it fits into the nucleus. (the other proteins are enzymes used in copying + repairing the dna).
the tightly combination of dna and proteins is called chromatin (dna is coiled around histone proteins to make chromatin). - this is what chromatids, and therefore chromosomes are made of.
3
Q
during interphase (S phase) the dna replicates to create what?
A
two identical strands of DNA called chromatids, joined together by a narrow region called the centromere. The two chromatids that make up the double structure of a chromosome are known as ‘sister chromatids’.
4
Q
why is it important for these sister chromatids to be identical? and what it each chromatid made up of?
A
important for them to be identical (same genes) as this is key to cell division, as one chromatid goes into 1 daughter cell, and the other chromatid goes into the other daughter cell, ensuring the daighter cells are genetically identical.
chromatids are made up of one very long condensed dna molecule, which is made up of a series of genes.
5
Q
the dna found in mitochondria and chloroplasts is similar to the dna of prokaryotes in that it is what?
A
short,
circular
and not associated with protein.
6
Q
mitochondrial dna is located _____ and chloroplast dna is located ____
A
mtdna in the matrix of mitochondria, cpDna in the stroma.
7
Q
define gene?
A
A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide (protein) or a functional RNA molecule.
8
Q
give the 3 types of RNA molecules required for protein synthesis.? and how?
A
mRNA - the base sequences on messenger RNA molecules are used by ribosomes to form polypeptide chains
tRNA - amino acids are carried to the ribosome by transfer RNA molecules
rRNA - ribosomal RNA molecules form part of the structure of ribosomes.
9
Q
central dogma of molecular bio is …
A
when one gene codes for one mrna molecule, which codes for one polypeptide.
10
Q
Every chromosome consists of a long DNA molecule that codes for several different proteins
A length of DNA that codes for a single polypeptide or protein is called a gene.
the position of a GENE ON A CHROMOSOME IS ITS WHAT?
A
LOCUS (PLURAL LOCI)
11
Q
Each gene can exist in two or more different forms called alleles. DIFFERENT ALLELES OF A GENE HAVE DIFFERENT WHAT? but share what in common.
A
HAVE SLIGHTLY DIFFERENT SEQUENCES OF NUCLEOTIDE, BUT STILL OCCUPY THE SAME POSITION (LOCUS) ON THE CHROMOSOME.
12
Q
The DNA nucleotide base code found within a gene is a what?
A
three-letter or triplet code.
13
Q
EACH TRIPLET CODE (EACH SEQUENCE OF 3 BASES), CODES FOR WHAT?
A
1 AMINO ACID.
14
Q
THE TRIPLET OF BASES (TRIPLET CODE) ARE KNOWN AS WHAT?
A
CODONS, AND EACH CODON CODES FOR A DIFF AMINO ACID. THERE ARE 20 DIFF AMINO ACIDS.
15
Q
SOME OF THESE TRIPLET OF BASES CODE FOR WHAT?
A
START + STOP SIGNALS. THESE SIGNALS TELL THE CELL WHERE INDIVIDUAL GENES START AND STOP, ENSURING THE CELL READS THE DNA CORRECTLY (CODE IS OVERLAPPING), CAN PRODUCE THE CORRECT SEQUENCES OF AMINO ACIDS, (HENCE THE CORRECT PROTEIN MOLECULE), THAT IT REQUIRES TO FUNCTION PROPERLY.
16
Q
THERE ARE 4 BASES, HENCE HOW MUCH DIFFERENT TRIPLET CODES POSSIBLE.
A
64 (4^3).
17
Q
there are only 20 amino acids present, hence what occurs to the rest of the 44 triplet codes (codons), hence the code is said to be what?
the genetic code is universal meaning what?
A
these multiple codons code for the same amino acid, hence the code is said to be degenerate (many triplet codes coding for the same amino acid).
meaning that almost every organism uses the same code (there are a few rare and minor exceptions). meaning the same codons code for the same amino acids in all living things.
18
Q
the genome (complete set of genes), within eukaryotic cells, contain many non-coding sections of dna, these dont code for what? non coding dna can be found where
A
amino acids.
non coding dna can be found in 2 places:
between genes, as non-coding multiple repeats, since they contain the same base sequences repeated multiple times.
within genes, as introns, (the coding exons can be separated by one or more introns).
19
Q
define genome?
A
complete set of genes present in a cell.
20
Q
define proteome?
A
full range of proteins that a cell is able to produce.
21
Q
which is larger proteome or genome of an organism? and why?
A
proteome is usually larger. this is due to the large amount of post-translational modification of proteins (in the golgi apparatus).
22
Q
processes like _____ and ______ increases the number of proteins to be produced?
A
alternative splicing and post-trsnslational modification of proteins.
23
Q
compare mrna to trna in structure?
A
Features of mRNA:
Single-stranded, linear molecule.
Contains a base sequence complementary to a DNA sequence.
Contains codons, which are sets of three bases that code for an amino acid.
Small enough to leave the nucleus.
Features of tRNA:
Single-stranded molecule folded into a clover-leaf shape.
Uses hydrogen bonds between complementary base pairs to hold it in shape.
Contains a specific sequence of three bases at one end, known as the anticodon which is complementary to a specifc codon on mrna molecules and hence bind together.
Contains an amino acid binding site at the opposite end.
24
Q
give the 2 stages of protein synthesis?
A
transcription and translation
25
what occurs in transcription and tranlsation?
Transcribtion - dna is transcribed and an mrna molecule is produced.
translation - mrna is translated and an amino acid sequence is produced.
26
explain the process of trancription?
the dna in the nucleus of a cell unwinds and unzips via hydrogen bonds breaking between completementary base pairs, by the enyme dna helicase.
leaving the 2 strands in dna separated. one of these strands act as a template and the other that is not transcribed is known as the non-template strand/non-transcribed strand
complementary base pairing happens, where freely activated RNA nucleotides join together to the unpaired bases on the template strand (via hydrogen bonding), forming pre-mrna, which is catalysed by RNA polymerase. ( that also forms the sugar-phosphate backbone via phosphodiester bonds). (premrna undergoes splicing to remove the introns),
when the gene has been transcibed (when mrna molecule is complete), the h2 bonds between the mrna and dna template strand break and the double stranded dna moleculle re-froms. mrna then leaves the nucleus via a pore in the nuclear envelope.
27
How do mRNA codons and tRNA anticodons relate to the DNA strands in terms of base sequences?
mRNA codons have the same base sequence as the non-transcribed (coding) DNA strand, except Uracil (U) replaces Thymine (T). tRNA anticodons have the same base sequence as the transcribed (template) DNA strand, also with Uracil instead of Thymine.
28
Where can non-coding DNA be found within eukaryotic cells?
Non-coding DNA can be found between genes as non-coding multiple repeats and within genes as introns.
29
During transcription, eukaryotic cells transcribe the whole gene (all introns and exons) to produce pre-mRNA molecules. What happens to pre-mRNA before it exits the nucleus?
Splicing occurs, removing non-coding introns and joining together coding exons, forming mature mRNA.
30
Why does pre-mRNA contain both introns and exons?
Because eukaryotic cells transcribe the whole gene, including both coding (exons) and non-coding (introns) sections.
31
Where does the mature mRNA go after splicing?
It exits the nucleus and joins a ribosome for translation.
32
The exons (coding regions) of genes can be spliced in many different ways to produce different mature mRNA molecules through what? what does this mean?
alternative splicing.This means that a single eukaryotic gene can code for more than one polypeptide chain. (part of the reason why proteome is bigger than the genome.
33
where does translation occur?
in the cytoplasm at the ribosome.
34
explain the process of translation?
occurs in the cytoplasm at the ribosome, where the newly formed mrna molecule leaves the nucleus via a pore in the nuclear envelope, and enters the cytoplasm where it attaches to the ribosome. this mrna strand attached to the ribosome carrise a codon, control/determines the anticodon on the trna molecule. the trna molecules using its amino acid binding site , binds to their specific amino acid and hence moves towards the mrna strand on the ribosome. the anticodon on trna then binds to the codon on mrna. this first binding is known as the start codon. two trna molecules can fit onto the ribosome at any one time, bringing the amino acids they are carying side by side, where a peptide bond is formed between them, that requires energy in the form of atp which is provided by the mitochondria within the cell. this process repeatedly carries on as the ribosome travels along the mrna strand, until a stop codon is reached. this acts as a signal for translation to stop and at this point the amino acid chain coded for by the mrna molecule is complete. the amino acid chen then forms the final polypeptide and is released.
35
what is a codon? and anticodon?
A codon is a sequence of three mRNA bases that codes for a specific amino acid. An anticodon is a sequence of three tRNA bases that are complementary to a codon.
36
the 4 bases in dna/rna have the ability to form 64 codons (triplet bases). we know that 20 are different and the rest of the 44 whillst being different codes can code for the same amino acids making the genetic code degenerate, meaning multiple codons coding for the same amino acid. this means that a change in the genetic code doesnt necessarily mean what?
doesnt necessarily mean that there will be a change in amino acid sequence formed. (eg UGU and UGC both code for the amino acid cysteine).
37
briefly, start codons do what and stop codons do what?
start codon mark the start of the protein and hence intiates the process of translation from the right location.
stop codon causes translation to terminate at the end of the protein and that stop codon actually doesnt code for any amino acids.
38
what does it mean if the genetic code is non-overlapping?
Each base is only read once in the codon (triplet base) it is part of.
39
The number of amino acids in a protein can be calculated using the number of coding nucleotides in the mRNA molecule and vice versa. explain...
When given the number of coding mRNA nucleotides, divide by 3 and minus one (for the stop codon – it is best to state this in your answer too)
When given the number of amino acids, multiply by 3 and add three (for the stop codon)
40
DEFINE A GENE MUTATION?
A GENE MUTATION IS A CHANGE IN THE base SEQUENCE OF chromosomes, resulting in an altered polypeptide forming.
41
MUTATIONS OCCUR IN WHAT WAY?
CONTINUOSOLY/spontaneusoly.
42
MOST MUTATIONS do not alter the polypeptide or only alter it slightly so that WHAT? AND WHY?
THEY DONT ALTER IT OR ALTER IT SLIGHTLY, SO THE STRUCTURE OR FUNCTION (PROTEIN) DOESNT CHANGE. THE REASON FOR WHY IT DOESNT ALTER/ALTERSLIGHTLY IS BECAUSE THE GENETIC CODE IS DEGENERATE.
43
As the DNA base sequence determines the sequence of amino acids that make up a protein, mutations in a gene can sometimes lead to a change in what?
the polypeptide the gene codes for.
44
give the different ways in which a mutation in the dna base sequence can occur
;
Deletion of nucleotides.
substitution of nucleotides.
45
why do not all base substitutions that occur, result in a change in the base sequence coding for amino acids?
due to the degenerate nature of the genetic code, not all base substitutions result in a change in the base sequence coding for amino acids.
46
what is meant by deletion of nucleotides
/
a mutation that occurs when a nucleotide in a dna strand (and hence its base) is randomly deleted from the dna sequence. this deletion results in the change of base sequence and hence changes the amino acid that would have been coded for by the original sequence.
as a result of this, a deletion mutation has a knock-on effect as its changing the groups of 3 bases further on in the dna base sequence., which may dramatically change the amino acid sequence produced from this gene and hence the ability of polypeptide to function.
47
whats the substitution (mutation) of nucleotides?
a mutation that occurs when a single base from a triplet code in the dna base sequence, is randomly substituted and swapped for a different base. this therefore only has an effect on that specific triplet code.
48
unlike a deletion mutation, why doesnt sub mutation have an effect on the entire dna base sequence?
because only single triplet code experiences a change in one of the 3 bases, which hence doesnt have a knock-on effect on the rest of the dna base sequence since the rest of the bases arent affected and dont change. (only change the amino acid for the triplet (a group of three bases) in which the mutation occurs)
49
what are mutagenic agents? and give examples?
Mutagenic agents are environmental factors that increase the mutation rate of cells
Examples include:
High-energy radiation such as UV light
Ionising radiation such as X rays
Toxic chemicals such as peroxides
50
when does non-disjunction occur?
when chromosomes fail to separete during meiosis (this occurs sponataneously)
51
the gametes resulting from non-disjunction may end with what?
The gametes may end up with one extra copy of a particular chromosome or no copies of a particular chromosome
These gametes will have a different number of chromosomes compared to the normal haploid number
If the abnormal gametes take part in fertilization, then a chromosome mutation occurs as the diploid cell will have the incorrect number of chromosomes
52
chromosome mutation involes a change in what?
the number of chromosomes
53
normal chromosome separation during meiosis vs non disjunction in meiosis where chromosomes fail to separate during meiosis.
normal separation means there will be a single copy of chromosome for each gamete whereas when non-disjunction takes place, this means that some gametes can have an extra copy of a chromosome or some gametes can have no copies at all. (some gametes will have more than others)
54
DEFINE MEIOSIS?
cell division WHEN TWO DAUGHTER CELLS ARE PRODUCED AND ARE GENETICALLY DIFFERENT TO EACH OTHER AS WELL AS TO THE PARENT CELL. THIS OCCURS AS A RESULT OF INDEPENDENT ASSORMENT AND CROSSING OVER. there are two nuclear divisions in the process hence 4 genetically different haploid daughter cells (gametes are formed in the end)
55
elaborate on Independent assortment? include the definition, the key idea, etc. (wouldnt take this as serious!)
📌 Definition:
The alleles of two (or more) different genes get sorted into gametes independently of one another.
📌 Key Idea:
The allele a gamete receives for one gene does not influence the allele received for another gene.
📌 Why Does This Happen?
✔️ Random chromosome alignment/arrangement in the middle of the cell during metaphase of meiosis.
✔️ Homologous chromosomes then separate in different combinations, leading to genetic variation in gametes.
📌 Result:
Each gamete can have different combinations of alleles, increasing genetic diversity!
(Independent assortment is the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase I
The different combinations of chromosomes in daughter cells increases genetic variation between gametes
(Each pair can be arranged with either chromosome on top, this is completely random
The orientation of one homologous pair is independent / unaffected by the orientation of any other pair)
56
define haploid and diploid?
haploid - one copy of each chromosome in a cell (n)
diploid - 2 copies of each chromosome in a cell. (2n)
n=number of chromosomes.
57
whats occurs in indepenent segregation and for what reason?
homologous pairs of chromosomes line up in in the equator of the cell, where its random where the paternal and maternal chromosomes line up at which side/end of the equator (they are opposite (ends) to each other).
when these homologous chromosomes separate, a large number of possible combos of chromosomes in the daughter cells are produced, causing daughter cells to be genetically different.
58
WHATS CROSSING OVER?
THIS IS WHEN THE HOMOLOGOUS PAIRS OF CHROMOSOMES LINE UP/ALIGN opposite each other, IN THE EQUATOR OF THE CELL, and the non sister chromatides cross over, become tangled/twist (hence creating tension), hence breaking a section of the chromatids, which can then swap to form a recombinant chromatid (when the broken section of the chromatid recombines with another chromatid), introducing new combos of alleles in the gametes. (genetic variation in gametes)
59
what are gametes?
sex cells (sperm and egg in human) - (pollen and egg in plants)
60
how does meiosis introduce variation?
crossing over
indepedent assortment
61
what expression is used to calc the possible number of diff combos of chromosommes following meiosis, without crossing over?
2^n - where n = the number of homologous chromosome pairs. (haploid number)jjj
62
how does meiosis differ from mitosis?
meiosis produces 4 genetically different haploid gamete cells with half the number of chromosomes as the diploid parent cells.
mitosis produces 2 genetically identical diploid daughter cells with the same number of chromosomes as the parent cells.
63
what happens during meiosis 1?
homologous chromosomes pair line up in the equator, and are separated randomly into 2 new cells. each cell contains either maternal or paternal copy. this is independent segregation. crossing over is rare, but when it takes place, it does the same where non sister chromatids of homolougous chromosomes pairs, cross to form bivalents.
crossing over (exchange at sections of genetic material) occurs at the chiasmata.
cell divides into 2. homologous chromosomes separate randomly. each cell contains either maternal or paternal copy.
64
whats happens during meiosis 2?
independent assortment of sister chromatids which are separated at opposite ends (as spindle fibres attach to the centromeres of the homologous chromosomes, splitting it apart).
each cell divides again producing 4 genetically different haploid daughter cells.
65
Examiner Tips and Tricks
Understanding the difference between chromosomes and chromatids can be difficult. We count chromosomes by the number of centromeres present. So when the 46 chromosomes duplicate during interphase and the amount of DNA in the cell doubles there are still only 46 chromosomes present because there are still only 46 centromeres present. However, there are now 92 chromatids, which are strands of replicated chromosomes.
66
During fertilization any male gamete can fuse with any female gamete to form what?
A ZYGOTE
67
This random fusion of gametes at fertilization creates genetic variation between zygotes, how?
as each will have a unique combo of alleles.
68
when in exams meisosis is shown on diagrams, and u are being asked to identify where meiosis is happening what do u look for?
look for on the diagram where it goes from being a diploid cell (2n) to a haploid (n)
69
How does the chromosome content of a cell change throughout mitotic and meiotic divisions?
Mitosis: Ends with two genetically identical daughter cells, ensuring growth and cell replacement. All body cells (except gametes) contain the full genome.
Meiosis: Ends with four genetically different daughter cells, each with half the parent cell’s genetic material. This promotes genetic variation, reducing the risk of inheriting genetic diseases.
70
Meiosis creates genetic variation between the gametes produced by an individual through ________ and ______________
This means each gamete carries substantially different ______
During fertilization, any male gamete can fuse with any female gamete to form a_______
This random fusion of gametes at fertilization creates genetic variation between zygotes as each will have a _____ _______ __ _______
Zygotes eventually grow and develop into adults
The presence of genetically diverse zygotes contributes to the _____ _______ of a species.
Meiosis creates genetic variation between the gametes produced by an individual through crossing over and independent assortment
This means each gamete carries substantially different alleles
During fertilization, any male gamete can fuse with any female gamete to form a zygote
This random fusion of gametes at fertilization creates genetic variation between zygotes as each will have a unique combination of alleles
Zygotes eventually grow and develop into adults
The presence of genetically diverse zygotes contributes to the genetic diversity of a species.
71
define genetic variation
The small differences in DNA base sequences between individual organisms within a species population.
72
Genetic variation is transferred from one generation to the next and it results in ____ within a species population.
genetic diversity within a species population.
73
define genetic diversity
Genetic diversity is the number of different alleles of genes in a population
74
how does mutation contribute to genetic diversity or the size of the gene pool?
Mutation results in the generation of new alleles hence it contributes to genetic diversity or the size of the gene pool
75
define gene pool?
all the diff alleles of all the genes of all the individuals in a population at any one time.
76
when a mutation results into a new allele being produced, apart from the new allele having the possibiltiy of being advantageous and disadvantageous, there is also a chance that it has no effect on the phenotype. how?
due to the fact that the genetic code might be degenerate.
77
Differences in the alleles possessed by individuals within a population result in ...
differences in phenotypes
78
the individuals with the favoured phenotypes are described as having a higher fitness what does this mean?
The fitness of an organism is defined as its ability to survive and pass on its alleles to offspring
Organisms with higher fitness posses adaptations that make them better suited to their environment
79
compare a population with a large gene pool/high genetic diversity compared to a population with a small gene pool/low genetic diversity ( in terms of adaptation/survival)
a population with a large gene pool or high genetic diversity means that the individuals in it have a strong ability to adapt to change.
a population with a small gene pool or very low genetic diversity means the individuals in it lack that ability to adapt to changes in the environment and are hence more vulnerable to extinction.
80
effect on inbreeding within the same populations?
inbreeding results in low genetic variation, which means species/inidivudals are less likely to surive in the event of any environmental changes.
81
logarithmic scales allows for what?
Logarithmic scales allow for a wide range of values to be displayed on a single graph. (used when dealing with data relating to large numbers of bacteria in a culture)
82
Genetic variation exists within populations due to what?
the diff alleles present.
83
Natural selection can cause the frequency of alleles in a population to what?
change overtime,
84
random mutations can produce new alleles of a gene. many mutations are harmful but under certain environmental conditions the new alleles may benefit their prossessor, leading to what?
increased chance of survival and increased reproductive success.
85
define reproductive success?
the number of offspring an individual produces (per breeding even or in their lifetime).
86
the advantageous allele resulted in natural selection is passed onto the next gen. as a result the new allele will what?
increase in frequency in the population.
87
explain the process of natural selection?
new alleles for a gene are created as a result of a random mutation happening.
if the new alleles increases the likelihood of the individual surviving in that environment, then they are more likely to survive and reproduce.
and hence pass on these advantageous alleles to the next gen.
as a result over many gens, the frequency of this new allele increases in the population.
88
what are the 2 types of selection?
stabilising and directional.
89
whats stabilising selection (elaborate on it)
Stabilising selection is natural selection that keeps allele frequencies relatively constant over generations. This means things stay as they are unless there is a change in the environment.
A classic example of stabilising selection can be seen in human birth weights
Very-low and very-high birth weights are selected against leading to the maintenance of the intermediate/ MODAL birth weights which is the model trait. and the model trait is the selective advantage.
(Stabilising selection selects against the extreme phenotypes (high and low birth weights) and selects for the intermediate/modal phenotypes (medium birth weights))
standard deviation decreases, as individuals with the extreme trait decrease since they are less likely to survive.
90
WHAT DOES IT MEAN IF A TRAIT IS SELECTED AGAINST (IN THE CASE OF HUMAN BIRTH WEIGHTS)?
When a trait is selected against, it means individuals with that trait have a disadvantage in survival or reproduction compared to others. Over time, fewer individuals with that trait pass on their genes, so the trait becomes less common in the population. IN THE CASE OF HUMAN BIRTH WEIGHTS:
Very low and very high birth weights are selected against because babies with these weights have higher risks of death or complications.
Intermediate birth weights are favored because they have the highest survival rate.
91
whats directional selection (elaborate on it)`give the context in antibiotic resistance.
Directional selection is natural selection that produces a gradual change in allele frequencies over several generations
This usually happens when there is a change in environment/selection pressures or a new allele has appeared in the population that is advantageous. IN THE CASE OF ANTIOBIOTIC RESITANCE, WHEN THERE IS CHANGE IN THE ENV, WHICH IS THE INTRODUCTION OF ANTIBIOTICS, THE BACTERIA WHICH HAD THE ALLELES FOR HIGH ANTIBIOTIC RESISTANCE WERE MORE LIKELY TO SURVIVE,BREED AND PASS ON THAT ALLELE FOR ANTIBIOTIC RESITANCE TO THE NEXT GEN. HENCE THAT ANTIOBIOTIC RESISTANCE ALLELE BECOMES MORE AND MORE FREQUENT IN THE POPOULTATION OVER SUBSEQUENT GENERATIONS.
92
what are introns?
sections of dna that do not code for popypeptides. introns are found in eurkaryotic DNA, but not in prokaryotic DNA.
93
what are exons?
sequences of DNA that do code for amino acids.
94
define chromosome mutations and what is it arised/caused by?
mutations which cause the change in the number of chromosomes which can arise spontaneously by chromosome non-disjunction during meiosis
95
define non-disjunction?
when (homologous) chromosomes or chromatids do not split equally dfuring anaphase.
96
in chromosome non-disjunction, changes in the number or structure of chromosomes as we know can arise spontaneously due to chromosome non-disjunction during meiosis.
HOWEVER THIS CAN OCCUR IN 2 FORMS. WHAT ARE THEY? (i.e the 2 types of chromosome number changes)
changes in whole sets of chromosomes can happen which is known as (polyploidy). the change occurs when you have 3 or more sets of chromosomes rather than the usual 2. (meaning for instance if its 3 sets for each chromosome you would get 3 copies, and there are 3 sets hence 23 times 3 =69 total chromosomes). polyploidy mainly occurs in plants.
changes in the number of individual chromosomes (aneuploidy)
97
in polyploidy, WHEN NON DISJUNCTION OCCURS IN MEIOSIS 1 (AS THE SPINDLE FIBRES HAVENT ATTACHED TO THE CHROMOSOME ON ONE SIDE, WHERE IT HAS ATTACHED ON THE OTHER SIDE, HENCE ALL CHROMOSOMES FAIL TO SEPARATE EQUALLY) , what results in the 2 daughter cells and hence what results in the gamete? and whats the result when the diploid gamete(gamete which has 1 more than the normal number of chromosomes) fuses with a haploid gamete (gamete which has the normal number of chromosomes (1))
WHAT RESULTS IN THE 2 DAUGTER CELLS IS THAT ONE DAUGHTER CELL WILL HAVE NO CHROMOSOMES AND THE OTHER DAUGHTER CELLWILL HAVE ALL THE CHROMOSOMES. AS A RESULT OF THIS, IN MEIOSIS 2, 2 OF THE GAMETES WHICH ARE RESULTED FROM THE DAUGHTER CELL CONTAINING ALL THE CHROMOSOMES, WILL BEdiploid (2n) and hence havE 1 more copy of the chromosome, WHEREAS THE OTHER 2 GAMETES RESULTING FROM THE DAUGHTER CELL WITH NO CHROMOSOMES, WILL ALSO HAVE NO CHROMOSOMES, AND HENCE HAVING 1 FEWER CHROMOSOME. (than the normal number (in haploid))
WHEN A DIPLOID GAMETE FUSES WITH A HAPLOID GAMETE, A TRIPLOID GAMETE IS PRODUCED (3N), meaning a gamete which has 3 copies for each chromosome.
REMEMBER ALL OF THIS IS OCCURS UNDER THE FACT THAT NON-DISJUNCTION (I.E THE FAILURE OF THE CHROMOSOMES TO SEPARATE EQUALLY), OCCURS IN MEIOSIS 1. (diff outcome in meiosis 2)
https://merchanttaylorsschools-my.sharepoint.com/:w:/g/personal/tofoma_merchanttaylors_com/EXemmofd5PlAiChZqH9RO8UBkt5ZSPPxz7v-7vivpUWbxA?e=1oTAVS
98
POPYLPLOIDY CAN ALSO OCCUR WHEN NON-DISJUNCTION TAKES PLACE IN MEIOSIS 2 (which takes place in one of the daughter cells), elaborate on number of copies for each chromosome that results in the gametes.
first in meiosis when, the homologus pairs of chromosomes separate equally, resulting in a normal daughter cell where the chromatids are attached to the spindle fibres equally on both side, resulting in 2 normal (n) haploid gametes forming (gamete with copy of each chromosome), (hence normal meiosis 2),
WHEREAS IN MEIOSIS 1, IT RESULTS IN THE OTHER DAUGHTER CELL EXPERIENCING NON-DISJUNCTION, WHERE ONLY SPINDLE FIBRES ATTACHTED TO CHROMOSOME ON ONE SIDE AND NOT ON THE OTHER, HENCE ALL CHROMATIDS FAILY TO SEPARATE EQUALLY, RESULTING IN A GAMETE WITH NO CHROMOSOMES, AND A DIPLOID (2N) GAMETE WITH 2 COPIES PER CHROMOSOME.
https://merchanttaylorsschools-my.sharepoint.com/:w:/g/personal/tofoma_merchanttaylors_com/EXGUZ--N481LkkbYqbORd54BunyK9ut8OjJrMap9MQwS0Q?e=MhGzrC
99
HOW DOES ANEUPLOIDY ARISE. when non disjunction like in polyploidy, occurs in meiosis 1 and occurs in meiosis 2? AND WHATS THE RESULT WHEN AN N+1 GAMETE (HAPLOID GAMETE WITH AN ADDITIONAL CHROMOSOME) FUSES WITH A HAPLOID GAMETE (N).
https://merchanttaylorsschools-my.sharepoint.com/:w:/g/personal/tofoma_merchanttaylors_com/EVS-QtuJGUtGnkitHyXEdjIBg5IEGeMSVV27lBlHRyu0jw?e=6pqYCW
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COMPARE THE OUTCOME OF WHAT FAILS TO SEPARATE, AS WELL AS HOW MANY GAMETES ARE AFFECT, WHEN NON-DISJUNCTION TAKES PLACE IN MEIOSIS 1 VS WHEN IN MEIOSIS 2.
NON DISJUNCTION IN MEIOSIS 1, MEANS THAT THE HOMOLOGOUS PAIRS OF CHROMOSOMES FAIL TO SEPARATE, RESULTING IN ALL 4 GAMETES BEING AFFECT ( TWO (2N) DIPLOID GAMETES, AND 2 WITH NO CHROMOSOMES AT ALL)
NON-DISJUNCTION IN MEIOSIS 2, MEANS THAT THE SISTER CHROMATIDS FAIL TO SEPRATE, RESULING IN 2 GAMETES BEING AFFECTED, AND 2 BEING UNAFFECTED (NORMAL HAPLOID).
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IN ANEUPLOIDY, ON FERITLISATION OF THE N+1 GAMETE (HAPLOID WITH ONE ADDITIONAL CHROMOSOME), WITH A NORMAL HAPLOID (n) gamete, what does the resultant zygote have and what is this an example of?
the resultant zygote will have more or fewer chromosomes than normal in all their body cells. e.g downs syndrome is 3 copies of chromosome 21. (trisomy)
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ASSORTMENT VS SEGREGATION
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KEYYYY
Independent assortment creates a large number of possible combinations of chromosomes in the daughter cells,AND HENCE THE GAMETES PRODUCED, while crossing over results in new combinations of alleles on those chromosomes.
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WHATS NATURAL SELECTION
THE PROCESS THAT LEADS TO EVOLUTION
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natural selection results in species that are better adapted to the environment they live in (it will select for favourable alleles that produce suitable adaptations, and will select against unfavourable alleles). give the types of adaptations that may be found in organisms in an environment?
anatomical: structure/physical feature. like eg, The white fur of a polar bear provides camouflage in the snow so it has less chance of being detected by prey
physiological: Mosquitos produce chemicals that stop the animal’s blood clotting when they bite, so that they can feed more easily
behavioural: The way an organism behaves, like the autumn migration of swallows from the uk to africa to avoid food shortages in the UK winter.
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define species?
two organisms of the same species (population) that are able to reproduce/breed to produce fertile offspring. species must reproduce, and pass on advantageous alleles, for the survival of their species.
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why is courtship behaviour essential?
for successful mating (meaning mating and produce fertile offspring) and for species recognition. this helps a species to survive. TO ENSURE SUCCESSFUL REPRODUCTION ASWELL.
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define courtship behaviour?
sequence of actions which is unique to each species. this is how animals identify members of their own species to reproduce with. (can include a sequence of dance moves, sounds, display of colourful feathers or fighting etc..)
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importance of courtship behaviour in relation to survival of the offspring
the choice fo a strong and healthy mate, means the advatageous alleles are passed on to the next gen, hence the offspring is more likely to also survive, breed and pass on that advatangeous allele and so on....... ensuring the survival of the entire species
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the more similar a courtship sequence carried out by different species, then what? AND WHAT DOES THAT MEAN IN RELATION TO THEIR DNA BASE SEQUENCE IN AN EXAMPLE.
THE MOST CLOSELY RELATED THE SPECIES ARE.
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THE BEHAVIOUR CARRIED OUT BY MEMBERS OF SPECIES IS _________ CODED FOR, MEANING WHAT.
IS GENETICALLY CODED FOR. MEANING THE CLOSER THE SEQUENCE OF BEHAVIOURS IN COURTSHIP RITUALS BETWEEN DIFFERENT SPECIES, MEANS THAT THE MORE CLOSELY RELATED THESE SPECIES ARE. AND SINCE THE BEHAVIOURS ARE GENETICALLY CODED FOR, THIS MEANS THAT THEIR DNA BASE SEQUENCE WOULD BE MORE CLOSELY RELATED.
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DEFINE PHYLOGENTETIC CLASSIFICATION?
PHYLOGENETIC CLASSIFICATION ARRANGES SPECIES INTO GROUPS ACCORDING TO THEIR EVOLUTIONARY ORGINS AND RELATIONSHIPS. (IT TELLS US HOW CLOSELY RELATED SPECIES ARE AND HOW RECENT THEIR SHARED COMMON ANCESTORS ARE).
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WHY ARE HUMANS AND CHIMPANSEES MOST CLOSELY RELATED TO EACH OTHER HERE?
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CLASSIFICATION SYSTEM IS AN EXAMPLE OF WHAT?
A HIERARCHY
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DEFINE A HIERARCHY?
SMALLER GROUPS ARRANGED WITHIN LARGER GROUPS, WITH NO OVERLAP BETWEEN THE GROUPS
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define the binomial system? first name IS THE GENUS, SECOND NAME IS SPECIES
universal way of identifying organisms
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GIVE THE 3 DIFFERENT WAYS TOMEASURE (ITS 3 COMPONENTS) BIODIVERSITY?
SPECIES DIVERSITY - THE NUMBER OF DIFFERENT SPECIES AND THE NUMBER OF INDIVIDUALS OF EACH SPECIES WITHIN IN COMMUNITY.
GENETIC DIVERSITY - THE VARIERTY OF GENES AMONGST ALL THE INDIVIDUALS IN A POPULATION OF ONE SPECIES
ECOSYSTEM DIVERSITY - THE RANGE OF DIFF HABITATS.
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WHATS ONE MEASURE OF SPECIES DIVERSITY AND DEFINE IT?
SPECIES RICHNESS WHICH IS THE NUMBER OF DIFFERENT SPECIES IN A COMMUNITYA
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A DECREASE IN BIODIVERSITY IS A CAUSE FOR CONCERN, AND THIS IS CAUSED BY WHAT?
HUMAN ACTIVITY
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HOW DOES AGRICULTURAL LAND REDUCE BIODIVERSITY? WHAT IMPACT DOES THIS HAVE AND WHAT STIMULATES/CAUSES THIS.
AGRICULTURAL LAND CONTAINS A LOWER VARIETY OF PLANT SPECIES AND THEREFORE A REDUCED A NUMBER OF DIFFERENT SPECIES OF CONSUMERS.
THIS MEANS THAT DIVERSITY IS REDUCED
THIS RESULTS IN A REDUCED NUMBER OF FOOD SOURCES, REDUCED NICHES AND REDUCED HABITATS.
THIS IS CAUSED BY THE USE OF PESTICIDES WHICH KILL NATIVE SPECIES THAT WOULD COMPETE WITH THE CROP PLANTS.
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AGRICULTURAL LAND IS ____
LESS DIVERSE
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FORESTS ARE EXTREMELY DIVERSE BECAUSE THEY PROVIDE WIDE RANGE OF DIFFERENT HABITATS FOR A LARGE NUMBER OF DIFFERENT SPECIES.. HOW DOES DEFORESTATION REDUCE BIODIVERSITY?
DEFORESTATION USUALLY CLEARS FOREST AND REPLACES IT WITH AGRICULTURAL LAND WHICH IS MUCH LESS DIVERSE.
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what AGRICULTURAL PRACTICES REDUCE BIODIVERSITY? AND EXPLAIN HOW FOR EACH.
WOODLAND CLEARANCE (VIA OVER-GRAZING OF LAND) - THIS IS DONE TO INCREASE THE AREA OF FARMLAND. HENCE REDCUES THE NUMBER OF TREES AND SOMETIMES THE NUMBER OF DIFFERENT TREE SPECIES. IT ALSO DESTROYS HABITATS, SO SOME SPECIES COULD LOSE THEIR SHELTER AND FOOD SOURCE.THIS MEANS SPECIES WILL DIE OR WILL BE FORCED TO MIGRATE TO ANOTHER SUITABLE AREA, FURTHER REDUCING BIODIVERSITY.
HEDGEROW REMOVAL - THIS IS ALSO DONE TO INCREASE THE AREA OF FARMLAND BY TURNING LOTS OF SMALL FIELDS INTO FEWER LARGE FIELDS. REDUCING BIODIVERSITY FOR THE SAME REASON AS WOODLANCE CLEARANCE.
PESTICIDES - THESE ARE CHEMICALS THAT KILL ORGANISMS (PESTS) THAT FEED ON CROPS. THIS REDUCES BIODIVERSITY BY DIRECTLY KILLING THE PESTS. AND ANY SPECIES THAT FEED ON THAT PESTS WILL LOSE A FOOD SOURCE, SO THEIR NUMBERS COULD DECREASE AS WELL.
HERBICIDES - THESE ARE CHEMICALS THAT KILL UNWANTED PLANTS (WEEDS). THIS REDUCES PLANTS DIVERSITY AND COULD REDUCE THE NUMBER OF ORGANIMS THAT FEED ON THE WEED.
MONOCULTURE - THIS IS WHEN FARMERS HAVE FIELDS CONTAINING ONLY 1 TYPE OF CROP/PLANT. A SINGLE TYPE OF PLANT REDUCES BIODIVERSITY DIRECTLY AND WILL SUPPORT FEWER ORGANISMS, (EG AS A HABITAT/FOOD SOURCE), WHICH FURTHER REDUCES BIODIVERSITY.
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HOW CAN U TEST/COMPARE THE CLOSENESS/RELATEDNESS OF DIFFERENT SPECIES TO EACH OTHER? (GENETIC DIVERSITY BETWEEN/WITHIN SPECIES)
GENOME SEQUENCING (COMPARING DNA BASE SEQUENCE + COMPARING MRNA BASE SEQUENCE)- entire base sequence of an organisms dna can be determined. the dna bse sequence of one organism can then be compared to the dna base sequence of anither organism to see how closely related dem man are. closely related species will have a higher percentage of similarity in their DNA base order.
COMPARING AMINO ACID SEQUENCE - PROTEINS MADE OF SEQEUNCES OF AMINO ACIDS WHICH ARE MADE UP OF DNA BASE SEQUENCES RELATED ORGANISMS HAVE SIMILAR DNA BASE SEQUENCES AND SO SIMILAR AMINO ACID SEQUENCES IN THEIR PROTEINS.
IMMUNOLOGICAL COMPARISONS - SIMILAR PROTEINS WILL ALSO BIND THE SAME ANTIBODIES. (EG SINCE HUMAN AND CHIMOANZEE ARE CLOSED RELATED, THEY HAVE SIMILAR PROTEINS (SIMILAR SHAPE/STRUCTURE) HENCE WHICH WILL BIND TO A SIMILAR/SAME ANTIBODY.
THE FREQUENCY OF OBERVABLE CHARACTERISTICS
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THE LARGER THE DIVERSITY INDEX, THE WHAT?
THE GREATER THE SPECIES DIVERSITY IN THE HABITAT.
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WHAT ARE THE ADVTANGES AND DISAD OF GIVING THE RESULTS AS A RATIO/% IN EXPERIEMTNS
IT ENABLES COMPARISONS TO BE MADE,
DISAD: THEY DO NOT GIVE ACTUAL NUMBERS SO IT CAN BE DIFFICULT TO JUDGE THE SAMPLE SIZE
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SD VALUES SHOW WHAT?
THE VARIATION AROUND THE MEAN AND HOW SPREAD OUT THE DATA ARE
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PLOTTING DATA USING A LOG SCALE ENABLES ...
A LARGE RANGE OF VALUES TO BE FITTED ON THE GRAPH
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WHY WAS THE DATA MEASURED PER GRAM OF BODY MASS
ENABLES A COMPARISON TO BE MADE, AS ANIMALS DIFFER IN SIZE
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WHY IS DATA COLLECTED RANDOMLY
TO AVOID BIAS
ALLOWS A STATISTICAL TEST TO BE CARRIED OUT
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FORMULA FOR DIVERSITY INDEX?
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DEFINE INTER AND INTRASPECIFIC VARIATION?
INTERSPECIFIC - VARIATION BETWEEN MEMBERS OF DIFF SPECIES
INTRA - VARIATION BETWEEN MEMBERS OF THE SAME SPECIES
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WHAT ARE SOME REASONS WHY WHEN TAKING MEASUREMENTS OF SOME INDIVIDUALS TO INVESTIGATIVE A CERTAIN POPULATION, THOSE MEASUREMENTS OF THOSE INDIVIDUALS ARENT REPRESENTATIVE OF THE ENTIRE POPULATION? AND HENCE HOW DO U PREVENT SAMPLING BIAS? NAD REMOVE CHANCE
SAMPLING BIAS. SELECTION PROCESS MAY BE BIASED
CHANCE.
TO PREVENT SAMPLING BIAS, RANDOM SAMPING IS CARRIED OUT AND IS AS FOLLOWS:
DIVIDE THE STUDY AREA INTO A GRID OF NUMBERED LINES
USE A RANDOM NUMBER GENERATOR TO OBTAIN A SERIES OF COORIDNATES.
TAKE SAMPLES.
TO REMOVE CHANCE:
WE CAN USE A LARGE SAMPLE SIZE
ANALYSIS OF THE DATA COLLECTED.
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