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QCE Biology Unit 3&4 Externals > QCE Biology Unit 4 - Topic 1 - DNA > Flashcards

QCE Biology Unit 4 - Topic 1 - DNA Flashcards

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1
Q

What are the two types of nucleic acids?

A

deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)

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2
Q

What do all nucleotides have?

A

A sugar ring, a phosphate and a nitrogen base

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3
Q

What do the sugar and the phosphate combine to create in a nucleic acid?

A

the sugar creates a strong bond with the phosphate, creating a sugar-phosphate backbone

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4
Q

What does the nitrogen base do in a nucleic acid?

A

nitrogen bases help form the structure, allowing them to carry and transmit genetic information

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5
Q

RNA consists of a ______ sugar-phosphate backbone with an ________ base

A

single, unpaired
(note: unpaired here means that there’s just one strand, so no base pairs)

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6
Q

DNA consists of a _______ sugar-phosphate backbone with the base pairs bonding with the ________ _____

A

double, complementary pair

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7
Q

What are the two ends of the sugar-phosphate backbone?

A

the 3’ end (hydroxyl group exposed) and the 5’ end (phosphate exposed)

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8
Q

How can you recognise a 3’ (3 prime) end?

A

the end of the strand has the third carbon atom of the sugar molecule and free hydroxyl group (OH-) not linked to anything else

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9
Q

How can you recognise a 5’ end?

A

the end of the strand has the fifth carbon atom of the sugar molecule and a free phosphate group

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10
Q

Why are DNA strands antiparallel?

A

crucial for stability and functioning, allows for pairing with complementary bases

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11
Q

What are the four nitrogen bases in RNA?

A

adenine, guanine, cytosine, uracil

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12
Q

What are the four nitrogen bases in DNA?

A

adenine, guanine, cytosine, thymine

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13
Q

Which nitrogen bases are purines?

A

guanine and adenine

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14
Q

What are purines?

A

a double carbon-ringed nitrogen base

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15
Q

Which nitrogen bases are pyrimidines?

A

cytosine, thymine, uracil

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16
Q

What are pyrimidines?

A

only has a single carbon-ring nitrogen base

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17
Q

In DNA, the uracil is replaced with….

A

thymine

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18
Q

List the two base pairs in RNA

A

cytosine-guanine
adenine-uracil

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19
Q

List the two base pairs in DNA

A

cytosine-guanine
adenine-thymine

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20
Q

What are the base pairs (purine and pyrimidine bases) bonded by?

A

a weak hydrogen bond

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21
Q

What is the difference between the sugar used in DNA and RNA?

A

RNA uses the sugar ribose (RIBO nucleic acid) and DNA uses the sugar deoxyribose (DEOXYRIBOSE nucleic acid)

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22
Q

DNA always forms a shape known as…

A

the double helix

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23
Q

What are nucleosomes and what are they comprised of?

A

its a molecule that prevents the DNA from tangling or breaking, comprised of 8 proteins called histones

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24
Q

How do nucleosomes and DNA interact?

A

The DNA wraps around the nucleosome 1 and 3/4 times, ensuring order and structural integrity (no tangles/breaks)

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25
Q

Why are histone tails important?

A

they can be chemically modified, which means that epigenetic factors (lifestyle, stress, diet) influences how DNA behaves. as histones control how tightly the DNA is wound, it can influence how freely DNA is copied.

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26
Q

What is a gene?

A

segment of DNA that codes for a protein (which gives a trait)

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27
Q

What is a chromosome?

A

a long continuous thread of DNA that consists of numerous genes

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28
Q

no gene is the same because the ____ of the ____ are different.

A

order, bases

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29
Q

What are the two main types of chromosomes?

A

prokaryotic and eukaryotic chromosomes

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30
Q

How many chromosomes do humans have?

A

46 chromosomes in 23 pairs

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31
Q

What are the characteristics of prokaryotic chromosomes? (you should list 4 things in total)

A

no nucleus, have a single chromosome floating freely about the cell, DNA is circular and not bound to histone proteins

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32
Q

Which organelles have DNA similar to prokaryotic DNA?

A

mitochondria and chloroplasts

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33
Q

Where are the eukaryotic chromosomes found?

A

Within the nucleus of the cell

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34
Q

Eukaryotic chromosomes come in pairs, passed on to offspring via…

A

sexual reproduction

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35
Q

What are the four main steps of DNA replication? (acronym for you: SPBET 💫)

A
  1. Separation of DNA strands
  2. Primer binding
  3. Elongation
  4. Termination
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36
Q

What does DNA helicase do in DNA replication?

A

breaks the hydrogen bonds between the nitrogen bases so DNA ‘unzips’

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37
Q

What does DNA polymerase do in DNA replication?

A

Joins individual nucleotides to make complementary strands and proofreads the sequence of bases and corrects errors

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38
Q

Why is the direction of the DNA important in regards to DNA polymerase?

A

DNA direction is important because DNA polymerase can only add nucleotides from the 5’ to 3’ direction

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39
Q

What is semiconservative replication?

A

DNA replication where each replicated DNA contains one strand of the original and one newly synthesised strand

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40
Q

What is a replication bubble?

A

A locally denatured segment of DNA where replication originates

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41
Q

What is the separation step of DNA replication?

A

separating the two DNA strands of the parental molecule by DNA helicase attaching at points of origin, attaching and unwinding the DNA

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42
Q

What is the primer binding step of DNA replication?

A

RNA primase (primer) binds to the 3’ end of the leading strand, signifying the starting point of replication

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43
Q

What is the elongation step of DNA replication?

A

The leading strands starts by DNA polymerase binding to the site of the primer and beginning adding complementary nucleotides.

The lagging strand begins replication by binding with multiple primers. DNA polymerase adds pieces of DNA (Okazaki fragments) to the strand between the primers. Once the OF’s cover the whole lagging strand, RNA primers are removed and replaced with DNA ligase (basically a glue lol)

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44
Q

What are Okazaki fragments?

A

Short lengths of single-stranded DNA made on the lagging strand, and the replication is discontinuous as the newly created fragments are disjointed.

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45
Q

What is the termination step of DNA replication?

A

Occurs when the replication fork is stopped/blocked. A termination sequence is a nucleic acid sequence that marks the end of the replication site. Result is 2 identical DNA strands, joined at the centromere. This produces the X shaped chromosome with 2 chromatids.

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46
Q

What are homologous chromosomes?

A

pairs of matching chromosomes that carry the same genes

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47
Q

What are diploid cells?

A

presence of two complete sets of chromosomes (homologous) in an organism’s cells, with each parent contributing a chromosome to each pair.

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48
Q

What are haploid cells?

A

cells with a single set of chromosomes (egg and sperm cells)

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49
Q

What does n stand for in diploid (2n) and haploid (n) cells?

A

n stands for the number of chromosomes, diploid have 2 sets, haploid have one set

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50
Q

What are the six steps of mitosis?

A

interphase, prophase, metaphase, anaphase, telophase, cytokinesis

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51
Q

What is mitosis?

A

Cell division that generates new cells for growth and repair. The division of one cell into two genetically identical daughter cells with the same amount of chromosomes

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52
Q

What is interphase (mitosis)?

A

Time when the cell growing and “living” – when it is not actively dividing, about 90% of the cell’s life

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53
Q

Following DNA replication, there is twice the amount of ___ but the number of ___________ remain the same.

A

DNA, chromosomes

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54
Q

Chromosomes can be ______ or ________

A

single, bivalent (two chromatids)

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55
Q

What happens during prophase (mitosis)?

A
  1. DNA threads condense to form condensed, thick chromosomes containing two chromatids
  2. protein threads create a spindle that spans the length of the cell (the spindles are called poles), the middle region is the equator
  3. the nuclear membrane breaks down
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56
Q

What happens in metaphase (mitosis)?

A

Chromosomes line up in the middle of the cell and attach the centromere to a spindle fibre

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57
Q

What happens in anaphase (mitosis)?

A

Chromatids separate and begin to move to opposite ends of the cell

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58
Q

What happens in telophase (mitosis)?

A
  1. chromosomes congregate tightly at each pole
  2. the spindle breaks down,
  3. new nucleus formed
  4. chromosomes uncoil to revert to chromatin threads
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59
Q

What is chromatin?

A

DNA molecules that are tightly coiled around proteins call histones (uncoiled DNA)

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60
Q

What happens during cytokinesis (mitosis)?

A

Cytoplasm divides and results in 2 identical daughter cells.

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61
Q

What is meiosis?

A

a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.

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62
Q

Meiosis goes from _______ ____ to _______ ____

A

diploid cells, haploid cells

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63
Q

What are the two stages of meiosis?

A

Meiosis I (separation of bivalent chromosomes into separate cells) and Meiosis II (separation of the sister chromatids at the centromere)

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64
Q

What is crossing over?

A

the random exchange of alleles between homologous chromosomes, resulting in a mixture of parental characteristics in offspring. happens when the chromatids become entwined and genetic information is exchanged. this mixture is called RECOMBINATION, increasing variation

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65
Q

What are alleles?

A

alternative version of a gene

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66
Q

What happens in Prophase I (meiosis)? (there are 4 steps)

A
  1. starts with a diploid cell with two uncoiled, spread-out sets of DNA (one from each parent).
  2. after replication, it condenses into 4 chromosomes. then, synapsis happens. synapsis is when a chromosome pairs up and binds with its homologous chromosome, forming a tetrad.
  3. then, crossing over happens.
  4. the nucleus disappears, the centrioles move to opposite ends of the cell, and spindle fibres fan out.
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67
Q

What happens in Metaphase I (meiosis)?

A

the homologous chromosomes line up in the equator and attach to spindle fibres

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68
Q

What happens during Anaphase I (meiosis)?

A

spindles pull homologous chromosomes apart (2 on each side), but still x shaped because sister chromatids remain joined at the centromeres

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69
Q

What happens during Telophase I (meiosis)?

A

the spindle fibres disappear, nuclear membrane reforms, cytokinesis occurs

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70
Q

What happens in Prophase II (meiosis)?

A

(note: now there are two haploid cells, each with one set of chromosomes, no DNA replication happens)
the nuclear membrane disappears and spindles fan out from the centrioles.

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71
Q

What happens in Metaphase II (meiosis)?

A

Chromosomes line up in the middle of the cell and attach to spindle fibres from both poles

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72
Q

What happens in Anaphase II (meiosis)?

A

The sister chromatids are pulled apart (one half of an X to each side of the two cells) by spindle fibres and move to opposite sides of the cell. they are now not sister chromatids, but chromosomes.

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73
Q

What happens in Telophase II

A

the spindles disappear, nuclear membrane reforms, and cytokinesis occurs in BOTH cells (which means there are now 4 genetically different haploid cells)

74
Q

What is a karyotype? How many pairs are autosomes (non-sex cells)? How many pairs are sex chromosomes (X or Y)?

A

A karyotype is a pictorial display of the total complement of a species’ chromosomes. 22 pairs are autosomal and the last is a sex chromosome, which determines the sex of an individual

75
Q

What is spermatogenesis?

A

the process of haploid sperm cell production in males

76
Q

Meiosis in human males produces _____ _____ and occurs within the ______ in the ____________ _______

A

sperm cells, testes, seminiferous tubules

77
Q

A diploid cell that undergoes meiosis to produce sperm in males is called a…

A

spermatogonium

78
Q

Spermatogenesis begins when spermatogonia undergo _______ division into diploid cells called spermatocytes.

A

mitotic

79
Q

The diploid spermatocytes then undergo _______ division resulting in four haploid _________ cells.

A

meiotic, spermatid

80
Q

What are the cells that nourish the spermatid during their maturation into sperm(atozoa) called?

A

Sertoli cells

81
Q

what is oogenesis?

A

Process by which ova are produced by the female.

82
Q

the diploid cells that undergo meiosis to produce ova in females are called _______

A

oogonia

83
Q

oogenesis begins when _________ undergo _______ ________ into diploid cells called ________ _______

A

oogonia, mitotic division, primary oocytes

84
Q

primary oocytes are made _______ _____, while secondary oocytes are made _____ _______

A

before birth, after puberty

85
Q

the diploid primary oocytes undergo _______ _______ in ______ _ producing a haploid ___________ ________ and _______ _____

A

meiotic division, Meiosis 1, secondary oocyte, polar body

86
Q

What are polar bodies?

A

cells produced during meiotic division in females that don’t develop into gametes (little cytoplasm is given to cell, therefore they are small)

87
Q

the secondary oocyte progresses through ___________ __ to produce an _____

A

meiosis II, ovum

88
Q

What are proteins responsible for in DNA?

A

making proteins, creating a physical/chemical characteristic of an organism

89
Q

What is gene linkage?

A

the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction

90
Q

How many alleles can an individual carry?

A

two, (one for each homologous chromosome)

91
Q

What are homozygous genes?

A

Two of the same allele (for example, TT or tt)

92
Q

What are heterozygous genes?

A

a dominant allele paired with a recessive allele (Tt)

93
Q

What is a dominant allele?

A

an allele that is fully expressed (dominant in a heterozygous pairing)

94
Q

What is a recessive allele?

A

An allele that is masked when a dominant allele is present - two copies of the same allele needed for a trait to be exhibited in a homozygous condition

95
Q

What does ‘genotype’ mean?

A

Genotype is the genetic makeup of an organism, and represents alleles as a letter/group of letters

96
Q

What is a phenotype?

A

physical characteristics of an organism (the way a gene is expressed, determined by types of alleles and environmental conditions)

97
Q

In this gene for freckles: Ff, which one is dominant and which is recessive?

A

F is dominant (capital letter)
f is recessive (lowercase letter)
the person carrying this gene has freckles

98
Q

give an example of a homozygous dominant and a homozygous recessive genotype.

A

HD: FF
HR: ff

99
Q

What is the law of segregation?

A

during the production of gametes, the two copies of each hereditary factor segregate so that offspring acquire one factor from each parent

100
Q

What is the law of independent assortment?

A

genes are inherited independently of one another.
for example, the genetic factors that control hair colour and sex are physically separate.
because these are physically separate, they segregate independently during gamete production.

101
Q

When ONLY does the law of independent assortment apply?

A

when genes are found on different chromosomes and there is no swapping of information between homologous chromosomes

102
Q

What does the random nature of fertilisation mean for the genotype of the offspring?

A

the random nature of it means that there are many possible genotypes of offspring from both sets of parents

103
Q

external exam sample question time
**

How does independent assortment contribute to genetic variation in gametes?

A

maternal and paternal chromosomes do not separate together, instead, each haploid gamete cell will contain a mixture of chromosomes from each parent, providing new genetic combinations

104
Q

**
What does ‘gene expression’ refer to?

A

the process of producing a functional protein from a gene (transcription and translation)

105
Q

**
What is a genome of an organism?

A

The entire genetic material of an organism (including all of the chromosomes and the mitochondria).

106
Q

**
Nucleic acid molecules contain genes for the production of proteins. The code is contained in a nucleotide triplet referred to as a _____

A

codon

107
Q

**
What do codons do?

A

codons correspond to an amino acid (molecular building blocks of proteins) or to instructions to stop/start translation.

108
Q

**
some sections of DNA between genes do not code for amino acids or instructions, and therefore are not used to construct proteins. these sections are _________ ___

A

noncoding DNA

109
Q

**
What is the purpose of DNA?

A

to allow ribosomes to express a functional protein

110
Q

**
Protein synthesis has 2 main processes: _____________ and ___________

A

transcription, translation

111
Q

**
What does transcription produce?

A

single-stranded mRNA from the DNA helix

112
Q

**
what is mRNA?

A

messenger RNA that carries the DNA message from the nucleus to the ribosomes

113
Q

**
What are the three main processes of transcription?

A

initiation, elongation and termination

114
Q

**
Where does transcription take place?

A

in the nucleus of eukaryotic cells

115
Q

**
What is the initiation step of transcription?

A

RNA polymerase, assisted by proteins called transcription factors, unzips the DNA by breaking the weak hydrogen bonds between the nitrogen bases.

This exposes them, allowing them to bind with free-floating nucleotides during elongation.

116
Q

**
What is the elongation step of transcription?

A

across a transcription bubble (12-14 base pairs), RNA polymerase produces an mRNA strand.

the DNA is a template, while RNA polymerase adds corresponding nucleotides.

new nucleotides are added to the 3’ (3 prime) end of the mRNA strand (synthesis occurs in 5’ - 3’ direction)

117
Q

**
When mRNA synthesis occurs, what base pairings occur?

A

adenine - uracil
cytosine - guanine

118
Q

**
What is the termination step of transcription?

A

a stop codon signals the RNA polymerase to cease transcription and terminate the mRNA molecule

119
Q

**
What is the process of translation?

A

Ribosomes in the soma of a eukaryotic cell build a polypeptide chain from amino acids by translating mRNA codons

120
Q

**
What is the initiation step of translation?

A

a ribosomal subunit attaches and moves along an mRNA strand in the 5’ to 3’ direction until it recognises a start codon (AUG). a free-floating tRNA molecule (transfer DNA) with the anti-codon UAC carrying methionine attaches to the mRNA start codon. the ribosome can now begin translating the mRNA into a polypeptide

121
Q

**
What is the elongation step of translation?

A

as the ribosome passes along the mRNA strand, it reads and matches the codons with a corresponding anti-codon of nearby tRNA molecules. as each anticodon binds, it releases its amino acid, joining the growing polypeptide chain through a condensation polymerisation reaction.

122
Q

**
What is a condensation polymerisation reaction?

A

the reaction between two amino acids joining them by a peptide link while releasing a water molecule

123
Q

**
What is the termination step of translation?

A

elongation continues until a stop codon is reached, and then the polypeptide chain is released, then it moves to the endoplasmic reticulum or golgi apparatus

124
Q

**
DNA creates ____ creates _______

A

RNA, proteins

125
Q

genes have coding regions, called _____ and non-coding regions, called _______

A

exons, introns

126
Q

What are exons and introns?

A

exons are sequences of coding DNA that are transcribed into mRNA and then translated into proteins.

introns are sequences of non-coding DNA and have a variety of functions. spliced out of mRNA prior to translation

127
Q

what is non-coding DNA made up of? what do these do?

A

non-coding DNA is made up of long sequences of repetitive code, as well as centromeres and telomeres.

  • the sequences are used to make functional RNA (like ribosomal RNA and transfer RNA)
  • centromeres hold sister chromatids together and spindle fibres attach to them
  • telomeres are the ‘end caps’ on each chromosome. they help protect the coding regions and prolong chromosome life
128
Q

What does ‘epigenome’ mean?

A

range of chemical compounds that alter genetic functions while leaving the genetic sequence unaltered

129
Q

gene regulation (genes turned on/off) occurs at three different times during protein synthesis, one other non-cellular factor and one outside protein synthesis but still inside the cell. list them and their effects

A
  1. pre-transcription
    - regulatory genes produce transcription factors in RNA form/proteins that can block gene expression/change rate of expression
  2. post-transcription
    - non-coding DNA can prevent mRNA from remaining intact long enough to be translated by blocking post-transcriptional processes/movement through the nuclear membrane
  3. during translation
    - insufficient production of proteins and amino acids slows down translation, leading to mRNA degradation before polypeptide production.
130
Q

transcription factors determine…

A

when and where genes are expressed

131
Q

What do Hox genes do?

A

HOX genes give orders to developing embryos to activate genes. regulate spatial expression of structures along the head to tail axis, determining where the head, spine, tail, legs, etc go

132
Q

what is hereditary?

A

Passing of traits from parents to offspring

either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents.

133
Q

what is a Nucelosome?

A

a structural unit of a eukaryotic chromosome, consisting of a length of DNA coiled around a core of histones.

134
Q

what is a Chromosome?

A

a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.

135
Q

what is Helicase?

A

An enzyme that untwists the double helix of DNA at the replication forks.

  • An enzyme that breaks down the hydrogen bonds holding two DNA strands together.
136
Q

What is the purpose of the Replication fork?

A

The area where the replication of DNA takes place.

Y-shaped region on a replicating DNA molecule where new strands are growing.

137
Q

What is Topoisomerase?

A

Enzyme that functions in DNA replication, helping to relieve strain in the double helix ahead of the replication fork.

138
Q

what is the purpose of Single stranded binding protein (SSB protein)?

A
  • stabilizes single-stranded DNA prior to replication by binding to it, thus preventing the DNA from pairing with complementary sequences
139
Q

what are Epigenetic factors?

A

environmental influences that change the expression of genetic material

  • inheritable and acquired gene regulation patterns that alter gene function (phenotype) without changing gene structure (genotype)
140
Q

What is the purpose of DNA polymerase?

A

Enzyme involved in DNA replication that joins individual nucleotides to produce a DNA molecule

141
Q

What is the purpose of DNA ligase?

A

In DNA replication, ligase’s job is to join together fragments of newly synthesized DNA to form a seamless strand.

142
Q

Where is DNA located in prokaryotes and eukaryotes?

A

Prokaryotes - single, circular chromosomes existing in cytoplasm

Eukaryotes - nucleus (around histone proteins that form chromosomes) and mitochondria and chloroplasts (single, circular chromosome)

143
Q

What does exonuclease do?

A

Cuts out RNA primers and DNA that needs fixing

144
Q

Why do cells undergo DNA replication?

A

Cells carry out DNA replication to prepare for cell division - each new cell will require its own DNA.

145
Q

DNA replication is described as semi conservative because…

A

The new DNA Is composed of one strand from the original parent DNA and one strand that is newly synthesised

146
Q

What are the 7 stages in DNA replication?

A

HINT: Priming, building and extending, proofreading, gluing, stabilising, unzipping, replacing

ANSWER:
1. Unzipping (helicase unzips)

  1. Stabilising (topoisomerase relaxes super coiled structure)
  2. Priming (primase attaches RNA primers to DNA< providing a starting point)
  3. Building and extending (DNA polymerase builds new DNA strand. Only builds in the 5’ to 3’ direction. Leading and lagging strand)
  4. Replacing (exonuclease removes primers)
  5. Gluing (ligase glues)
  6. Proofreading (another DNA polymerase scans for errors)
147
Q

What is the purpose of meiosis?

A

Produces sex cells (gametes). They have half the number of chromosomes (haploid number).

148
Q

What are the phases of meiosis?

A

Interphase
Meiosis I
Meiosis II

149
Q

What are the stages of each meiotic division?

A

“PMAT”

Prophase - centriole pairs (centrosomes) moves to opposite poles, and chromosomes condense and become visible.
M1 ONLY: Crossing over occurs between homologous chromosomes

Metaphase - the spindle has formed completely.
M1 ONLY: homologous pairs of chromosomes line up in the middle of the cell
M2 ONLY: Chromosomes line up in the middle of the cell

Anaphase - spindle fibres begin to contract
M1 ONLY: homologous chromosomes get separated as they are pulled by their centromeres to poles
M2 ONLY: Sister chromatids get separated as they are (same ^)

Telophase - nuclear envelopes start to reform around the groups of chromosomes, start to condense back into chromatin

Cytokinesis: they split into two cells
M2 only: cells are now in interphase

150
Q

What is a gene expression?

A

The conversion of DNA into a protein product

151
Q

What is a Locus?

A

A fixed position on a chromosome that is occupied by a given gene or one of its alleles

152
Q

What do genes/DNA code for?

A

Genes code for proteins. That is, a specific gene codes for a specific type of protein DNA -> RNA -> protein

153
Q

Are introns or exons spliced out?

A

Introns are cut out

154
Q

What are the differences between RNA and DNA?

A

RNA is singles trand, sugar is ribose and has uracil instead of thymine

155
Q

What are the 3 kinds of RNA and differences between them?

A

mRNA - messanger, transcribes DNA code
rRNA - ribosomal RNA, primary component of the ribosome
tRNA - transfer RNA, carries an amino acid to proper position during translation

156
Q

What is a ribosome?

A

Made of ribosomal RNA (rRNA) in the form of a large subunit and small subunit. Holds the mRNA transcript and the tRNA molecule in place during the process of translation so that amino acids can be joined into a polypeptide

157
Q

What is a codon?

A

A 3-base word on mRNA that codes for one amino acid

158
Q

What is a tRNA molecule?

A

Carries an amino acid and 3 bases called the anti codon that base pair with an mRNA codon

159
Q

What are the three special sites on ribosomes?

A

A site: tRNA carrying amino pairs with mRNA codon
P site: growing polypeptide is held in place
E site: tRNA exits (w/o amino acid)

160
Q

What is a SRY gene?

A

The Y chromosome has genes that set the organism on the path of developing into a male. SRY gene encodes for proteins that act as transcription factors that bind to DNA and cause the activation of numerous genes.

SRY protein is a regulatory protein that primarily launches the genetic program for testes development. This is essential as the testes then produce hormones that steer the embryo towards differentiation of male features (mainly reproductive structures)

161
Q

What are the three causes of mutations?

A

DNA replication errors
Cell division errors (non-disjunction)
Damage by mutagens

162
Q

When can DNA replication errors occur?

A

When a base undergoes a chemical change that turns it into another base. E.g., A to C. Bases can also be added or deleted from a DNA sequence during DNA replication

163
Q

What is a point mutation (type of DNA replication error)?

A

Occurs when there is an error in a single nucleotide
Point mutations are caused by substitution, where one nucleotide is replaced by another
Only affects the codon for a single amino acid

164
Q

What is a frameshift mutation (type of DNA replication error)?

A

One that dislocates the translational reading frame; codons are read in different groups that they should be. Caused by insertion or deletion of nucleotides in a DNA sequence

165
Q

What is cell division errors (non-disjunction)?

A

The failure of two chromosomes to separate during gamete formation, resulting in gametes with either a missing chromosome (monosomy) or an extra one (trisomy)

166
Q

What is damage by mutagens

A

Mutagens are substances that cause irreversible and heritable changes (mutations) in DNA
Can be classified as chemical or physical

167
Q

Give an example of a chemical mutagen

A

Nitric acid, mustard gas and agent orange

168
Q

Give an example of a physical mutagen

A

Ionising radiation, UV and X-Rays. Can cause double-stranded breaks in chromosomes, resulting in large sections of the chromosome being rearranged

169
Q

What is a genotype?

A

The combination of alleles that an organism has

170
Q

What is a phenotype?

A

The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment

171
Q

What is a trait?

A

A particular physical feature or characteristic of an organism

172
Q

What is a dominant trait?

A

A trait that is expressed (appears) in a heterozygous individual. Expressed as a capital letter (T)

173
Q

What is a recessive trait?

A

A trait that is hidden or masked in a heterozygous individual. Expressed as a lower case letter (t)

174
Q

What does autosomal mean?

A

A chromosome that is not a sex chromosome. People normally have 22 pairs of autosomes (44 autosomes) in each cell, together with 2 sex chromosomes, X and Y in male and X and X in female

175
Q

What is autosomal dominant?

A

A pattern of inheritance in which an affected individual has one copy of a mutant gene and one normal copy on a pair of autosomal chromosomes and the mutant gene is expressed

176
Q

What is autosomal recessive?

A

A pattern of inheritance in which an affected individual must have two copies of a mutant gene for it to be expressed

177
Q

What are multiple alleles

A

Three or more alternative forms of a gene that can occupy the same locus. However, only two of the alleles can be present in a single organism

178
Q

What is incomplete dominance?

A

A intermediate inheritance allele for a specific trait is not completely expressed over its paired allele. This results in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles.

179
Q

What is gene therapy?

A

The insertion of genes into an individual’s cells and tissues to treat a disease and hereditary diseases in which a defective mutant allele is replaced with a functional allele

180
Q

What process does gene therapy use? What is it and how does it work?

A

DNA cloning - process of making multiple, identical copies of a particular piece of DNA

  1. Cutting and isolating DNA (target DNA sequence and the plasmid are cut with the same restriction enzyme to give them complementary sticky ends)
  2. Inserting the selected DNA fragment into a plasmid vector (the DNA sequence and plasmid vector are mixed together)
  3. Joining of DNA and plasmid (ligase joins the DNA fragment and plasmid together, forming recombinant DNA)
  4. Amplifying the recombinant DNA by transformation (recombinant plasmids are added to a bacterial culture where they are taken up into the cells of some of the bacteria by a process called transformation. When the bacteria replicate so does the plasmid, creating multiple copies of the desired gene)
181
Q

What is biotechnology? Give an example

A

The use of biology to solve problems and make useful products. It is a technology based on biology that harnesses cellular and biomolecular processes to develop technologies and products that help improve our lives and the health of our planet.
E.g., gene therapy

182
Q

When an organism has a large gene pool, it means…

A

it has many different alleles for its genes

QCE Biology Unit 3&4 Externals (2 decks)

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