biology Flashcards
1
Q
Friedrich Miescher
A
Discovered nucleic acid in 1869. This helped scientists understand the building blocks of DNA and RNA.
2
Q
Rosalind Franklin
A
Used X-ray crystallography to take photos of the structure of DNA in 1952 These images helped Watson and Crick propose their model for the double helix structure of DNA (1953).
3
Q
Maurice Wilkins
A
Showed Watson and Crick one of Franklin’s x-ray photographs without her permission. 1953.
4
Q
Erwin Chargaff
A
Proposed Chargaff’s rules in 1950.
1. The amount of adenine (A) in DNA is equal to the amount of thymine (T)
2. The amount of guanine (G) is equal to the amount of cytosine (C)
This hinted towards the base pair of the DNA. In 1952 he met Watson and Crick and explained his findings. This helped them discover the structure of DNA.
5
Q
James Watson and Francis Crick
A
Discovered the double helix structure of DNA in 1953 based on the X-ray images taken by Rosalind Franklin, as well as Chargaff’s rules.
6
Q
DNA replication purpose
A
To duplicate the code carried by the DNA. It occurs in preparation for cell division (mitosis or meiosis).
7
Q
DNA replication step 1
A
DNA helicase (enzyme) breaks weak hydrogen bonds to separate two strands of DNA. Once they are separated, the two strands become templates to make new strands.
8
Q
DNA replication step 2
A
The enzyme primase attaches a short sequence of RNA, known as a primer, to show DNA polymerase where to start adding nucleotides.
9
Q
DNA replication step 3
A
Complementary nucleotides are added by the enzyme DNA polymerase. Synthesis of the new daughter strand is in a 5’ to 3’ direction.
10
Q
Complementary base pairs
A
Adenine pairs with thymine, and cytosine pairs with guanine. (A+T, C+G)
11
Q
DNA replication step 4
A
DNA ligase removes and replaces the primers. The
result is two identical DNA molecules that are each
made of one original parent strand and one new
daughter strand. DNA replication is described as
semi-conservative.
12
Q
After DNA replication
A
In eukaryotic organisms, two sister chromatids are now ready for cell division. In prokaryotes, two circular chromosomes are now ready for binary fission.
13
Q
Continuous vs discontinuous synthesis
A
Synthesis is continuous along the leading strand.
Synthesis is discontinuous along the lagging strand.
Primers are attached at short intervals, starting from the replication fork. DNA polymerase synthesises short strands of new DNA called Okazaki fragments. DNA polymerase moves in opposite directions on the two anti-parallel parent strands.
14
Q
Semiconservative
A
DNA replication is semiconservative because one strand is the original/parent strand, and one is new.
15
Q
Evolution
A
The process of cumulative, heritable changes in allele frequencies in a population over a long time (many generations).
16
Q
Chromosome structure
A
DNA tightly coiled around proteins called histones.
17
Q
Why do cells need to divide?
A
They make new cells in order to grow and also to replace old dead cells.
18
Q
Steps in mitosis
A
IPMAT. Interphase, prophase, metaphase, anaphase, telophase.
19
Q
Interphase
A
Interphase is the phase of the cell cycle where a cell prepares for cell division. It is characterized by a high level of metabolic activity, growth, and DNA replication in three stages: G1, S, and G2. During this phase, the cell synthesizes new proteins and organelles, replicates its DNA, and prepares for cell division by ensuring the stability of the genome and the proper division of cells.
20
Q
Prophase
A
Chromosomes condense to become visible under a microscope. Nuclear membrane disintegrates. Centrioles move to opposite poles of the cell.
21
Q
Metaphase
A
Spindle fibres grow and attach to centromeres. Chromosomes line up single file down the middle of the plate.
22
Q
Anaphase
A
Spindle fibres shorten. Sister chromatids get pulled to opposite ends.
23
Q
Telophase
A
Cell elongates and cleavage furrow forms. Two new nuclei are formed.
24
Q
Purpose of mitosis
A
Growth, replacement of cells (repair), asexual reproduction.
25
Haploid
The presence of a single set of chromosomes in an organism's cells.
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Diploid
Referring to two complete sets of chromosomes in an organism's cells, with each parent contributing a chromosome to each pair
27
Mendel's work
In one of Mendel’s experiments, he took a pure-breeding tall pea plant and crossed it with a pure-breeding short pea plant. Pure-breeding plants are ones that, when crossed among themselves, always give rise to offspring that are like the parents. This was one of many experiments conducted by Mendel, leading to the principles of inheritance.
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Mendel's principles of inheritance
The law of segregation, the law of independent assortment, the law of dominance
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The law of segregation
Alternate versions of factors cause variation in inherited characteristics. An organism inherits two factors for each characteristic - one from each parent. Dominant factors will always mask recessive factors. The two factors for each characteristic separate during gamete production
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The law of independent assortment
Factors for different characteristics are sorted independently
31
The law of dominance
An organism with alternate forms of a gene will express the form that is dominant.
32
Homozygous
Possessing two identical alleles of a gene. AA is homozygous dominant and aa is homozygous recessive.
33
Heterozygous
Possessing two different alleles of a gene. e.g Aa. The dominant allele will be expressed.
34
Autosomal trait
A trait which is inherited on an autosome (non sex chromosome) A gene on an autosome is called autosomal.
35
Sex-linked trait
A trait which is inherited on a sex chromosome. A gene on a sex chromosome is called sex linked.
36
Punnett square
A table that displays all the possible offspring genotypes (given the parental alleles) that can be produced at fertilisation. You can determine the likelihood of producing a child with a particular trait using a Punnett square.
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Chromosome
Compacted DNA. DNA wrapped around protein structures called histones
38
Homologous
Chromosomes that contain the same genes and have the same length and shape. However, they may carry different versions of those genes, known as alleles.
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Ova
A mature female reproductive cell which can divide and give rise to an embryo after fertilisation.
40
Sperm
A male reproductive cell.
41
Fertilisation
The union of two gametes. During fertilization, sperm and egg fuse to form a diploid zygote to initiate prenatal development.
42
Zygote
A diploid cell resulting from the fusion of two haploid gametes; a fertilised egg.
43
Mutations
The changing of the structure of a gene, resulting in a variant form that may be transmitted to subsequent generations, caused by the alteration of single base units in DNA
44
Gene
A distinct sequence of nucleotides forming part of a chromosome which codes for a protein. A stored set of instructions for a protein, found on a specific locus on a chromosome.
45
Allele
A different form of the same gene. There are dominant alleles and recessive alleles.
46
Karyotype
The standard graphical form used to display and analyse chromosomes.
47
Locus
The position of a gene, a cluster of genes or even a single nucleotide on a chromosome.
48
Genotype
The genetic composition of an organism for a particular set of alleles (one from each parent) that an organism has for a particular trait.
49
Phenotype
The observable outcome of a gene being expressed.
50
Dominant allele
Always expressed in the phenotype. It masks a recessive allele if paired with one. It has the same effect on the phenotype whether it is paired with the same allele or a different one. Represented by a capital letter.
51
Recessive allele
Only expressed in the phenotype when present with the same allele (homozygous). Masked by a dominant allele. Represented by a lowercase letter.
52
Monohybrid cross
Inheritance of a single autosomal gene. Involves fertilisation between two monohybrids (parents with genotypes consisting of one dominant and one recessive allele). Only one gene is investigated. A monohybrid is an organism that is heterozygous with respect to a single gene. Monohybrids are the offspring from a cross between parents who are both homozygous but for two different alleles.
53
Hybrid
Offspring of parents that differ in genetically determined traits. The parents may be of different species, genera, or (rarely) families.
54
Pedigree
Chart that shows the presence or absence of a trait within a family across generations.
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Forms of inheritance
Autosomal dominant, autosomal recessive, X-linked recessive, X-linked dominant, Y-linked
55
Autosomal dominant
In autosomal dominant inheritance, a single dominant allele is responsible for the occurrence of a phenotype.
Each affected person usually has an affected parent, and the phenotype occurs in every generation.
A single copy of the affected allele is enough to cause the condition. A parent with a single copy of a dominant allele on an autosome (heterozygous) will theoretically pass it on to 50% of the offspring.
If the parent is homozygous for the dominant trait, then 100% of the offspring will be affected.
56
Autosomal recessive
People with only one defective allele in the pair of alleles are called carriers.
These people are most often not affected with the condition. They can pass the abnormal gene on to their children.
The parents of an affected person are always at least carriers of the allele.
A carrier is usually unaffected, because a dominant allele will silence the effects of the recessive allele that causes the condition.
57
X-linked recessive
When a recessive phenotype under investigation is determined by an allele on the X chromosome, it is said to be an X-linked recessive phenotype.
Males who have the recessive allele on their X chromosome will always express the phenotype, because they only have one X chromosome.
Females will only express the phenotype when both X chromosomes have the affected allele.
For a female child to be affected, the father must be affected and the mother must be either affected or a carrier.
A heterozygous female will be a carrier.
58
X-linked dominant
The heterozygous females will always show the phenotype, and any individuals with the phenotype must have a parent with the phenotype.
Males showing the phenotype will not pass the affected allele on to their sons (because they must inherit their father’s Y chromosome), but they will pass it on to all their daughters, who will also show the phenotype. This is because daughters always inherit their father’s X chromosome.
A heterozygous female is expected to pass on the allele to 50% of her offspring, regardless of their sex.
The condition should appear in every generation.
An affected male receives the dominant allele from an affected mother.
59
Y-linked
A trait is carried on the Y chromosome.
Only males are affected.
The most conspicuous phenotype associated with genes on the Y chromosome is male gender.
60
Polygenic inheritance
The inheritance of more than one gene that affects the inheritance of a single characteristic. For one characteristic, two or more genes, and therefore two or more alleles contribute to a phenotype. E.g human height.
61
Polygene
Genes that have a small additive effect on a phenotype, and each gene consists of multiple alleles.
62
Theory of evolution
All organisms have developed from previous organisms and that all living things have a common ancestor in some initial form of primitive life. Developed by Charles Darwin.
63
Natural selection
The process through which populations of living organisms adapt and change due to selection pressures in their environment.
64
Selection pressure
An environmental factor that can be survived by those individuals in a population who possess a beneficial trait, but not others. It can contribute to changes in allele frequency in a population gene pool.
65
Stages/principles of natural selection
Variation; overproduction/limited resources; competition and survival of the fittest; higher reproductive rate; heritability; allele frequency change.
66
Variation
Variation in alleles/traits/phenotypes within a population
due to…
- mutation in alleles
- meiosis/sexual reproduction processes
- processes include crossing over, independent assortment, and random fertilisation, and random mating.
67
Overproduction/limited resources
There are more individuals produced in a population than the environment can support
- environmental resources are limited
- not all individuals can survive to reproduce
68
Competition and survival of the fittest
Various selective pressures result in competition between individuals in a population, meaning the individuals who are more ‘fit’ are better suited to the environment in which it lives
- environmental selection pressures such as food availability, predators and some diseases favour those with more advantageous traits/alleles
- this may lead to competition between individuals in a population
- those with the advantageous trait may outcompete those without the advantageous trait
69
Higher reproductive rate
Those with an advantageous trait/allele/phenotype will be more likely to survive, reproduce, and pass to offspring (heritability)
70
Heritability
Advantageous alleles are passed to offspring (e.g camouflaged colouration)
71
Allele frequency change
Advantageous alleles increase in frequency (allele fixation), disadvantageous alleles decrease in frequency (allele extinction)
72
Mutation (natural selection)
A permanent change in the DNA sequence of an organism’s genome. On a rare occasion, a mutation can be beneficial by creating a new allele for a populations gene pool. This leads to further variation.
73
Consider how Darwin was treated initially and debate why Darwin's theory is considered more compelling than Lamarck's
74
Convergent
Two or more unrelated species live in the same environment, resulting in their characteristics becoming similar/converging.
75
Divergent
One species splits into groups and each group develops different characteristics due to their different environments.
76
Gene pool
The total collection of alleles within a population.
77
Somatic mutations
Mutations that only affect body cells (not sex cells).
78
Causes of mutation
- DNA damage/replication errors
- Environmental factors (e.g. pollution, radiation, chemicals)
- Viruses
79
How do selection pressures result in survival mechanisms within organisms?
80
Cytokinesis
Cytoplasm splits and two identical diploid cells are formed.
81
Migration enabling gene flow
Individuals can immigrate and bring their alleles with them to a new population. if the new individual breeds, their alleles are added to the gene pool. This leads to changes in allele frequency.
82
Isolation mechanisms
Ways in which groups of organisms become separated
83
Examples of isolation mechanisms
Geographical (e.g. ocean)
Behavioural (e.g. bird dance for mating)
Reproductive (e.g. seasonal breeding differences in turtle populations)
84
Genetic drift
Random changes in allele frequencies of a population gene pool over generations due to chance.
- There is usually a loss of genetic variation over generations.
- Genetic drift occurs in all populations, but its effects are strongest in small populations.
85
Why does genetic drift have a stronger effect on smaller populations
The smaller the population, the faster the fixation of alleles and the extinction of other alleles can occur.
86
Nucleic acid
Molecules that carry genetic information and are important for the growth, development, and functioning of living organisms.
87
Nucleic acid composition
They are made of nucleotides.
88
Nucleotide
A building block of nucleic acids such as DNA and RNA. Consists of a sugar molecule (deoxyribose or ribose), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, thymine, uracil). The nitrogenous base differs between nucleotides.
89
Somatic cell
Any cell in the human body that is not a reproductive cell (sperm or egg). They are diploid, meaning they have two sets of chromosomes (one from each parent).
90
What happens with homologous chromosomes during sexual reproduction?
Homologous chromosomes pair up and exchange genetic material in a process known as crossing over. This creates genetic diversity by producing new combinations of alleles.
91
Zygote
The cell that forms when an egg cell is fertilised by a sperm cell, resulting in 46 homologous chromosomes.
92
Gamete
A reproductive cell that is involved in sexual reproduction (ie. sperm or egg cells). They are haploid cells, and only contain 23 chromosomes (in humans).
93
DNA structure
Double helix structure.
Two strands joined by weak hydrogen bonds between complementary pairs of nitrogenous bases.
The two strands run in opposite directions (anti-parallel) and are twisted into a helix.
94
Direction of DNA and RNA synthesis
5' to 3'. the 5' end starts with a phosphate and the 3' end ends with a sugar.
95
Protein synthesis
Protein synthesis is a process whose end product is a protein. There are two main parts to the flow of information from gene to protein: transcription and translation.
96
Transcription
The synthesis of mRNA using the stored DNA code.
97
Translation
The synthesis of a polypeptide using the information in the mRNA.
98
Protein synthesis step 1
RNA polymerase breaks weak hydrogen bonds of one gene, separating the two DNA strands.
99
Protein synthesis step 2
Only one of the strands is copied to produce mRNA (messenger RNA)
100
Protein synthesis step 3
RNA polymerase starts attaching free floating nucleotides at a promoter-start section on the non-coding strand according to complementary base pair rules in 5’ to 3’ direction until terminator (stops DNA) section.
101
Protein synthesis step 4
The premature mRNA goes through a process known as ‘splicing’ to remove the introns as introns do not directly code for proteins. During splicing the exons are joined to create mature mRNA.
102
Alternative splicing
Some genes can be alternatively spliced, meaning exons from the same gene are joined in different combinations. This leads to different mRNA transcripts, allowing the mature mRNA molecules to produce different proteins from the same initial gene.
103
Protein synthesis Step 6
The single-stranded mRNA floats through nucleus pore and travels to ribosomes in the cytoplasm.
104
Protein synthesis step 7
Ribosomes bind to mRNA.
105
Protein synthesis step 8
A start codon indicates to the ribosome that translation should begin.
106
Protein synthesis step 9
tRNA transfers the first amino acid based on the complementary anti-codon it is carrying. Therefore, the codon determines the specific amino acid that is transferred.
107
Protein synthesis step 10
The next codon is read and the tRNA drops off the specified amino acid. This is repeated until a chain of amino acids: a polypeptide is made.
108
Protein synthesis step 11
A peptide bond is formed between amino acids.
109
Protein synthesis step 12
Polypeptide detaches and folds to become a functional protein.
110
Protein synthesis (oversimplified summary)
DNA is transcribed into mRNA. mRNA passes into the cell’s cytoplasm and binds to a ribosome. tRNA joins with an amino acid and pairs up with its complementary mRNA during translation.
111
Why are males more likely to be affected by an X-linked disorder?
The X chromosome as this is larger and contains more chromosomes than the smaller Y chromosome. This often results in more males being affected because they have only one copy of the X chromosome that carries the mutation. Females may carry the mutation, however, this may be masked by the second X chromosomes that is healthy.
112
William Paley
He believed that organisms were created to fit their environments. He came up with the watchmaker analogy: a creation implies a creator.
113
Jean-Baptiste Lamarck
Believed that traits were acquired during an organisms lifetime. Due to changes in behaviour due to changes in their environment which then changed their physical structure which then got passed on to their offspring.
114
Charles Darwin
Developed the theory of evolution: all organisms have developed from previous organisms and that all living things have a common ancestor in some initial form of primitive life
115
Alfred Russel Wallace
Also came up with the idea of natural selection. He and Darwin both came up with the theory of evolution together.
116
S phase
DNA replication. Occurs during interphase.
117
G2 phase
Growth in preparation for division. Molecules are produced. Occurs during interphase.
118
C phase
Cytokinesis.
119
G1 phase
Cell growth before DNA replication through the production of proteins and organelles.
120
Mitosis vs Meiosis
- Meiosis results in the production of four haploid cells (gametes).
- Meiosis involves two rounds of cell division
- Meiosis takes place in reproductive organs
121
Similarities in mitosis and meiosis
- Types of cell division
- Begin with the replication of DNA
- Involve separation of sister chromatids
- Essential for growth and repair
122
Prophase I
- Chromosomes condense to become visible under a microscope
- Maternal and paternal homologous chromosomes pair up, and crossing over occurs (exchange of genetic material)
- Nuclear membrane disintegrates
- Meiotic spindle forms and attaches to centromeres
- Centrosomes move to opposite poles of the cell
123
Metaphase I
- Maternal and paternal homologous chromosomes line up along the metaphase plate in the middle of the cell
- The lining up of the homologous chromosomes in metaphase I is called independent assortment because each pair is lined up on one side or the other, independent of every other pair. This results in a random assortment (random combination) of chromosomes in the four daughter cells.
- The spindle fibres are attached to centromeres
124
Anaphase I
- The spindle fibres shorten, pulling on the centromere of each chromosome
- One member of each pair of homologous chromosomes moves to each end of the cell. A random combination of maternal and paternal chromosomes are dragged to each pole.
125
Telophase I
- New nuclear membranes form and the chromosomes uncoil.
- The spindle fibres disintegrate.
126
Cytokinesis I
The cell splits into two cells. The daughter cells are considered haploid because they contain only one chromosome from each pair of homologous chromosomes. No further DNA replication occurs
127
Prophase II
- Chromatin condenses to form visible chromosomes again.
- New spindle fibres are produced
- The nuclear membrane disintegrates.
128
Metaphase II
- Individual chromosomes line up single file along the equator in random order.
- The spindle fibres attach to the sister chromatids at the centromeres.
129
Anaphase II
- The centromeres of each chromosome disconnect, allowing the sister chromatids to separate
- The spindle fibres shorten and individual sister chromatids move to opposite poles of the cell
- In animal cells, the cell membrane pinches inwards to form a cleavage, whereas in plant cells new cell wall plates form
130
Telophase II
- Chromosomes unwind, loosen and reform chromatin.
- Four new nuclear membranes form around the nuclei, one in each new daughter cell.
131
Cytokinesis II
- Separation of the cytoplasm
- The cells separate into four new non-identical, haploid daughter cells.
132
How do mutations result in the formation of different alleles?
Mutations can alter the DNA sequence of a gene, which can change the function of the protein it produces. This can lead to the formation of different alleles that may produce different phenotypes or traits
133
Extreme genetic drift
Bottleneck effect, founder effect
134
Bottleneck effect
Occurs when there is a disaster of some sort that reduces a population to a small handful, which rarely represents the actual genetic makeup of the initial population.
- this leaves smaller variation among the surviving individuals.
- every animal has equal chance of surviving
135
Founder effect
Happens when there is a dramatic decrease in genetic diversity caused by the development of small colonies of individuals, sourced from the original population, that remain isolated from other colonies.
- a few individuals who move to a new area and become isolated from a larger population might not carry all the alleles that were present in the original population.
- the new population is called the founding population
- this means that the isolated population has less genetic diversity than the original population, and deleterious recessive alleles may have a higher chance of coming together than they did in the original population.
- only a small subset of the genetic diversity of the source population is likely to be included in the new population
- the relative frequencies of these alleles may be very different from what they were in the source population.
136
Chromatin
3D network of DNA and proteins that make up eukaryotic chromosomes.
