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Biology F215 > Cellular Control, Inheritance, Variation and Evolution > Flashcards

Cellular Control, Inheritance, Variation and Evolution Flashcards

0
Q

What is a polypeptide?

A

A polymer consisting of a chain of amino acid residues joined by peptide bonds

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1
Q

What is a gene?

A

A length of DNA that codes for one (or more) polypeptides

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2
Q

What is a genome?

A

The genome of an organism is the entire DNA sequence of that organism. The human genome consists of about 3 billion nucleotide base pairs

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3
Q

What is a protein?

A

A large polypeptide - usually 100 or more amino acids. Some proteins consist of one polypeptide, and some of more than one

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4
Q

How many genes are there in the human genome?

A

About 25000

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5
Q

What is a locus?

A

The specific position on the chromosome occupied by a particular gene

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6
Q

What is the structure of DNA?

A

A double helix formed from two polynucleotide strands, made up of lots of nucleotides joined together in a long chain

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7
Q

What is the structure of a nucleotide?

A

Each nucleotide is made from a phosphate group, a pentose (5 carbon) sugar and a nitrogenous base. The sugar in DNA is a deoxyribose sugar, and each nucleotide has the same sugar and phosphate, but there are 4 possible bases.

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8
Q

What are the four possible DNA bases?

A

Adenine, thymine, cytosine and guanine

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9
Q

Where do nucleotides in a polynucleotide strand join together?

A

Between the phosphate group of one nucleotide and the sugar of another, creating a sugar-phosphate backbone

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10
Q

How do two DNA polynucleotide strands join together?

A

By hydrogen bonds between the bases

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11
Q

What are the complimentary base pairs?

A

Adenine with thymine

Guanine with cytosine

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12
Q

How many hydrogen bonds form between C and G?

A

3

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13
Q

How many hydrogen bonds form between A and T?

A

2

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14
Q

What type of bases are adenine and guanine?

A

Purines

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15
Q

What type of bases are cytosine and thymine?

A

Pyrimidines

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16
Q

How many bases code for each amino acid?

A

Three

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17
Q

What can triplets of base pairs code for?

A

Different amino acids, although some triplets code for the same amino acid, or to stop or start a protein (these triplets are found at the beginning and end of every gene

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18
Q

Where are DNA molecules found?

A

In the nucleus of the cell

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19
Q

Why can DNA not travel to the ribosomes for protein synthesis?

A

Because it is too large to move out of the nucleus

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20
Q

What is RNA?

A

A single polynucleotide strand containing the sugar ribose instead of deoxyribose and uracil instead of thymine as a base

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21
Q

What is transcription?

A

When a section of DNA is copied into RNA

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22
Q

What is translation?

A

When RNA leaves the nucleus and joins with a ribosome in the cytoplasm, where it can be used to synthesise a protein

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23
Q

What are the two types of RNA?

A 
Messenger RNA (mRNA)
Transfer RNA (tRNA)
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24
Q

What is the structure of mRNA?

A

A single polypeptide strand made in the nucleus during transcription

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25
Q

What is the function of mRNA?

A

It carries the genetic code from the DNA in the nucleus to the cytoplasm, where it’s used to make a protein during translation

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26
Q

What is a group of three adjacent base pairs called?

A

A codon

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27
Q

What is the structure of tRNA?

A

A single polynucleotide strand folded into a clover shape. Hydrogen bonds between specific base pairs hold the molecule in this shape. Every tRNA molecule has a specific sequence of three base pairs at one end called an anticodon, as well as an amino acid binding site at the other end

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28
Q

What is the function of tRNA?

A

It is found in the cytoplasm where it is involved in translation. It carries the amino acids that are used to make proteins

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29
Q

What happens during the process of transcription?

A
  • RNA polymerase attached to the DNA
  • complimentary mRNA is formed
  • RNA polymerase moves down the DNA strand
  • mRNA leaves the nucleus
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30
Q

What is RNA polymerase and what does it do?

A

It is an enzyme which attaches to the DNA double helix at the beginning of a gene and causes the hydrogen bonds between the polynucleotide strands to break, separating the strands and causing the DNA molecule to uncoil. One of the strands is then used as a template to make an mRNA copy

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31
Q

How is mRNA formed?

A

RNA polymerase lines up free RNA nucleotides along the template strand of DNA. Complementary base pairing means that the mRNA strand ends up being a complimentary copy of the DNA. Once the complimentary RNA nucleotides are lined up, they are joined together to form an mRNA molecule

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32
Q

What happens to the DNA strands after the mRNA strand has been formed?

A

The hydrogen bonds between the two strands reform and they coil back into a double helix

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33
Q

When does RNA polymerase stop making mRNA?

A

When it reaches a particular sequence of DNA called a stop codon, it stops making mRNA and detaches from the DNA.

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34
Q

What happens to the strand of mRNA when it has finished being copied from the DNA?

A

It moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, ready for translation to take place

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35
Q

Where does translation take place?

A

At the ribosomes in the cytoplasm

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36
Q

What happens during translation?

A

Amino acids are joined together by a ribosome to make a polypeptide chain, following the sequence of codons carried by the mRNA.

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37
Q

How does translation work?

A

The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to the ribosome. A tRNA molecule with an anticodon complimentary to the first codon on the mRNA attaches itself to the mRNA by complimentary base pairing. A second tRNA molecule attaches to the second codon in the same way.
The first tRNA molecule then moves away, leaving it’s amino acid attached to the second tRNA’s amino acid by a peptide bond
This process continues until a stop codon is reached, and the polypeptide moves away from the ribosome

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38
Q

Why is the sequence of amino acids in a protein crucial?

A

It forms the primary structure of a protein, which determines the tertiary structure - how the protein folds up into its 3D shape and the bonds that hold it in that shape. The tertiary structure is what allows a protein to function, e.g. the active site of an enzyme is a specific shape to fit with a substrate

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39
Q

How is protein synthesis different in prokaryotes?

A

The DNA is not inside a nucleus, so translation begins as soon as some mRNA has been made

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40
Q

How is protein synthesis controlled?

A

At the genetic level by starting or stopping transcription of genes. Not all genes are transcribed in all cells all the time. Genes that aren’t being transcribed are said to be switched off, while those being transcribed are switched on

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41
Q

What is an operon?

A

A section of DNA that contains structural genes, control elements and sometimes a regulatory gene. Operons are often found in prokaryotes, and they are involved in genetic control of protein synthesis

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42
Q

What do the structural genes in an operon code for?

A

Useful proteins, such as enzymes. All of the structural genes in an operon are transcribed together

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43
Q

What do the control elements in an operon consist of?

A

A promoter: this is a DNA sequence, located before the structural genes, which RNA polymerase binds to
An operator: a DNA sequence next to the structural genes that can switch them on and off

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44
Q

What does the regulator gene do?

A

The regulator gene codes for a transcription factor. The regulator gene is not part of the operon, and could be some distance away from it

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45
Q

What is a transcription factor?

A

A protein that binds to DNA and switches genes on or off by starting or stopping transcription. Factors that start transcription are called activators, and factors which stop it are called repressors

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46
Q

How do the quantities of certain molecules in an environment or cell affect the synthesis of certain proteins?

A

The shape of a transcription factor determines whether it can bind to DNA or not, and this shape can be altered by the binding of certain molecules, such as hormones and sugars, to the transcription factor. Therefore, the amount of these molecules present will affect the binding of the transcription factor, and therefore control whether or not certain proteins are synthesised

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47
Q

What is an example of an operon?

A

The lac operon, which responds to the presence or absence of lactose in its surroundings

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48
Q

What do E.Coli use to respire?

A

Glucose, but they can use lactose if glucose is unavailable, once the genes needed to respire lactose are switched on

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49
Q

How does the lac operon work when lactose is not present?

A

The regulator gene is expressed and the repressor protein synthesised. The repressor binds to the operator site and stops RNA polymerase from attaching to the promotor region, so transcription of the enzymes needed to respire lactose is blocked

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50
Q

How does the lac operon work when lactose is present?

A

The repressor protein that binds to the operator site and blocks transcription has a second active site, which allows it to bind to lactose. When this happens, the protein changes shape and can no longer bind to the operator site, allowing transcription to occur.

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51
Q

What are the enzymes used in the metabolism of lactose in E.coli?

A

Beta-galactosidase is used to catalyse the hydrolysis of lactose to glucose and galactose
Lactose permease transports lactose into the cell

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52
Q

How is protein activation controlled?

A

Some molecules that control protein activation work by binding to cell membranes and triggering production of cyclic AMP inside the cell. cAMP then activates proteins inside the cell by altering their 3D structure

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53
Q

What is a body plan?

A

The structure of an organism

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54
Q

What type of genes code for the proteins that control body plan?

A

Homeotic genes

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55
Q

Similar homeotic genes are found in…

A

Animals, plants and fungi, meaning that body plan is controlled in a similar way in flies, mice, humans, etc

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56
Q

How do homeotic genes control development?

A

They have regions called homeobox sequences that code for a part of the protein called the homeodomain. The homeodomain binds to a specific site on DNA, allowing the protein to work as a transcription factor. The proteins bind to DNA at the start of development genes, activating or repressing transcription and so altering the production of proteins involved on the development of the body plan

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57
Q

What is the process of programmed c death called?

A

Apoptosis

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58
Q

What are the steps involved in apoptosis?

A
  • enzymes are released from lysosomes inside the cell. The enzymes break down cell components, eg proteins, DNA
  • the cell shrinks and begins to fragment
  • phagocytes engulf and digest the cell fragments
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59
Q

How is apoptosis involved in the development of body plans?

A

Mitosis and differentiation create the bulk of body parts and then apoptosis refines the parts by removing unwanted structures, e.g, connecting tissue between fingers

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60
Q

How is apoptosis coded for in DNA?

A

All cells contain genes that code for proteins that promote or inhibit apoptosis. During development, the genes controlling apoptosis are switched on and off in appropriate cells, so that some die and the correct body plan develops

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61
Q

What is a mutation?

A

Any change to the base sequence of DNA

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62
Q

What are the types of mutations that can occur?

A

Substitution - one base is swapped for another
Deletion - one or more bases are removed
Insertion - one or more bases are added
Duplication - one or more bases are repeated
Inversion - a sequence of bases is reversed

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63
Q

What effect can a mutation have on a protein?

A

The order of DNA bases in a gene determines the order of amino acids in a protein. If a mutation occurs in the gene, the primary structure of the protein could be altered, which may change the final 3D shape of the protein, causing it to not work correctly

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64
Q

What is a frameshift mutation?

A

When an insertion or deletion changes the way the rest of the base sequence is read, as the number of bases present has changed and all of the base triplets that follow will be shifted. Depending on how far along the sequence the mutation occurs, frame shift mutations can have huge effects on the protein

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65
Q

Why might a mutation not affect an organism?

A
  • the mutation may change a base in a triplet, but the new triplet still codes for the same amino acid
  • the mutation may code for a chemically similar amino acid to the original, so it functions the same
  • the mutated triplet may code for an amino acid unrelated to the protein’s function
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66
Q

Are mutations that alter a protein’s function always harmful to the organism?

A

No, they may have a beneficial effect, in which case they will increase the organism’s chance of survival and be passed on by natural selection, or they could affect the protein’s function but not in a harmful or beneficial way to the organism

67
Q

What is an example of a mutation with a harmful effect on an organism?

A

Cystic fibrosis can be caused by a deletion of 3 bases in the gene coding for a particular protein, causing it to fold incorrectly. This results in excess mucus production, affecting the lungs of sufferers.

68
Q

What is meiosis?

A

A type of cell division that happens in the reproductive organs to produce gametes. Cells that divide by meiosis are diploid to start with, but the cells produced are haploid - the chromosome number halves. Cells formed by meiosis are all genetically different because each new cell ends up withs different combination of chromosomes

69
Q

What is interphase?

A

The stage before meiosis, the cell’s DNA unravels and replicates so there are two copies of each chromosome in each cell

70
Q

What do the chromosomes look like at the start of meiosis?

A

They are made of two strands joined in the middle by a centromere. The separate strands are identical copies called chromatids. Two strands on the same chromosome are called sister chromatids

71
Q

What is a centromere?

A

The join between the two chromatids in a double stranded chromosome

72
Q

What happens during prophase I?

A

The chromosomes condense, getting shorter and fatter.
Homologous chromosomes pair up, and crossing over occurs.
Centrioles start moving to opposite ends of the cell
A spindle forms

73
Q

What happens during metaphase I?

A

The homologous pairs line up across the centre of the cell and attach to the spindle fibres by their centromeres. Bivalents are arranged randomly, with each member of a homologous pair facing opposite poles

74
Q

What happens during anaphase I?

A

The spindles contract, pulling the homologous pairs to opposite ends of the cell. The centromeres do not divide. Chiasmata separate and crossed over lengths of chromatid remain with their new chromosome

75
Q

What is crossing over?

A

During prophase I, homologous chromosomes come together and pair up. Non sister chromatids wrap around each other and attach at points called chiasmata. The sections of the chromatids after the chiasmata are switched between the homologous pair

76
Q

What is a chiasma?

A

The point at which non sister chromatids attach during the process of crossing over

77
Q

What is a homologous pair?

A

Two copies of the same chromosome containing the same genes, but different alleles. In a homologous pair, one chromosome is maternal and one is paternal.

78
Q

What is a bivalent?

A

Another word for a homologous pair

79
Q

What happens during telophase I?

A

A nuclear envelope forms around each group of chromosomes and the cytoplasm divides so there are now two haploid daughter cells.
In most plant cells telophase I does not happen

80
Q

What happens in prophase II?

A

The nucleolus disappears, chromosomes condense, spindles form, the nuclear envelope breaks down

81
Q

What happens during metaphase II?

A

The chromosomes arrange themselves at the equator of the spindle, and are attached to the spindle fibres at the centromeres. The chromatids of each chromosome are randomly arranged.

82
Q

What happens during anaphase II?

A

The centromeres divide and the chromatids are pulled to opposite poles by the spindle fibres

83
Q

What happens during telophase II?

A

Nuclear envelopes reform around the haploid daughter nuclei. there are now four haploid cells.

84
Q

What order do the stages of meiosis take place in?

A 
Prophase I 
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II
85
Q

What are the three ways in which meiosis created genetic variation?

A

Crossing over of chromatids
Independent assortment of chromosomes (meiosis I)
Independent assortment of chromatids (meiosis II)

86
Q

How does the crossing over of chromatids ensure genetic variation?

A

Alleles are shuffled between homologous pairs, meaning that there are new combinations of alleles

87
Q

How does the reassortment of chromosomes in meiosis I ensure genetic variation?

A

The maternal and paternal chromosomes are randomly distributed on the spindle equator in metaphase I, meaning that the daughter nuclei have a random combination of maternal and paternal chromosomes

88
Q

How does the reassortment of chromatids in meiosis II ensure genetic variation?

A

The reassortment of chromatids is the result of the random distribution on the spindle equator, of the sister chromatids, at metaphase II. Because of crossing over, sister chromatids are no longer identical, so each new cell ends up with a different combination of alleles

89
Q

What is monohybrid inheritance?

A

The inheritance of a single characteristic (gene) controlled by different alleles

90
Q

What do monohybrid crosses show?

A

The likelihood of alleles being inherited by the offspring of particular parents

91
Q

What is a phenotypic ratio?

A

The ratio of different phenotypes in the offspring. Genetic diagrams allow you to predict the phenotypic ratios in f1 and f2 offspring

92
Q

What would the phenotypic ratio be in a monohybrid cross with two heterozygous parents?

A

A 3:1 ratio of dominant:recessive characteristics

93
Q

For what reason would the expected phenotypic ratio of a monohybrid cross not be achieved?

A

epistasis

94
Q

What is linkage?

A

When alleles are on the same chromosome, so are inherited together

95
Q

What is a Punnett square?

A

A way of showing a genetic diagram to work out the phenotypic ratio of two parents’ offspring

96
Q

What are codominant alleles?

A

When both alleles are expressed in the phenotype and neither one is recessive

97
Q

What is an example in humans of codominance?

A

The allele for sickle cell anaemia, a genetic disorder caused by a mutation in the haemoglobin gene. It causes red blood cells to be sickle shaped. People who are homozygous for normal haemoglobin don’t have the disease. People who are homozygous for sickle haemoglobin have sickle cell anaemia, and all their blood cells are sickle shaped. People who are heterozygous have sickle cell trait, meaning they have some normal and some sickle haemoglobin. The two alleles are codominant because they’re both expressed in the phenotype

98
Q

Why are some characteristics linked to sex?

A

The alleles that code for them are located on a sex chromosome. The Y chromosome is smaller than the X chromosome, and carries fewer genes, so most genes on sex chromosomes are only carried on the X chromosome. As males only have one X chromosome they only have one allele, meaning even if that allele is recessive it will be expressed. Therefore males are more likely than females to show recessive phenotypes for sex-linked genes

99
Q

What are examples of sex-linked genetic disorders?

A

Colour blindness and haemophilia

100
Q

What is dihybrid inheritance?

A

The inheritance of two characteristics which are controlled by different genes. Each of the two genes will have different alleles

101
Q

What do dihybrid crosses show?

A

The likelihood of offspring inheriting certain combinations of the two characteristics from particular parents

102
Q

What is epistasis?

A

The interaction of different gene loci so that one gene locus masks or suppresses the expression of another gene locus

103
Q

What are the two ways in which the genes involved in epistasis may work to control the expression of one phenotypic characteristic?

A

They may work against each other (antagonistically) resulting in masking
They may work together in a complimentary fashion

104
Q

How might epistasis work antagonistically?

A

The homozygous presence of a recessive allele may prevent the expression of another allele at a second locus. The alleles at the first locus are epistatic to the alleles at the second locus, which are described as hypostatic

105
Q

What effect does epistasis have on phenotypic variation?

A

It reduces it

106
Q

What is the expected phenotypic ratio of the offspring of double heterozygous parents from recessive epistasis?

A

9:3:4

107
Q

What is the expected phenotypic ratio of the offspring of double heterozygous parents from dominant epistasis?

A

12:3:1 or 13:3

108
Q

What is the expected phenotypic ratio of two heterozygous parents from epistasis in a complimentary fashion?

A

9:7

109
Q

What is the expected phenotypic ratio of two heterozygous parents from a typical dihybrid cross?

A

9:3:3:1

110
Q

What is recessive epistasis?

A

Recessive epistasis is when the epistatic allele is recessive, meaning that two copies of it will block the expression of the other gene.

111
Q

What is dominant epistasis?

A

Dominant epistasis is when a dominant allele at the epistatic gene locus masks the expression of the alleles at the hypostatic gene locus

112
Q

How might epistasis work in a complimentary fashion?

A

If the homozygous recessive condition at either locus masks the expression of the dominant allele at the other locus, meaning that double heterozygous individuals will have a phenotype not expressed by any other genotype combinations

113
Q

What is the chi squared test?

A

A statistical test that is used to see if the results of an experiment support a theory, by using the theory to predict a result and then carrying out the experiment to find an actual result

114
Q

What is the null hypothesis?

A

The hypothesis made when doing the chi squared test that there will be no significant difference between the expected and observed results. The null hypothesis is made to see if the results of an experiment support the theory of what should happen.

115
Q

What is the purpose of the chi squared value?

A

The chi squared value shows the statistical difference between the observed and expected results, so that you can work out if the difference is significant enough to mean that your theory is wrong

116
Q

What does it mean if the null hypothesis is rejected?

A

If the null hypothesis is rejected this means that the difference between observed and expected results is significant, so the theory that the expected results are based on is wrong

117
Q

How do you tell if the value of chi squared for an experiment means that you should reject or accept the null hypothesis?

A

By comparing it to the critical value

118
Q

What is the critical value?

A

The value of chi squared that corresponds to a 5% probability of the difference between observed and expected results being due to chance

119
Q

If the value of chi squared is smaller than the critical value this means…

A

…that the null hypothesis can be accepted, and that the difference between the expected and observed values is due to chance only, and is not significant.

120
Q

If the value of chi squared is greater than the critical value…

A

…the null hypothesis must be rejected, as the difference between the expected and observed values is too large to be just down to chance, and is significant.

121
Q

How do you work out how many degrees of freedom an experiment has?

A

Minus one from the number of classes in the experiment, the number of classes being the number of categories the independent variable has

122
Q

What is variation?

A

The differences that exist between individuals

123
Q

What is intraspecific variation?

A

Variation that occurs within a species

124
Q

What is interspecific variation?

A

Variation that occurs between different species

125
Q

What is continuous variation?

A

When individuals in a population vary within a range - there are no distinct categories

126
Q

What is discontinuous variation?

A

When there are two or more distinct categories, with no intermediates and individuals falling clearly into one

127
Q

What is the genetic basis of continuous variation?

A
  • traits exhibiting continuous variation are controlled by two or more genes
  • each gene provides an additional component to the phenotype
  • different alleles at each gene locus have a small effect on the phenotype
  • a large number of different genes may have a combined effect on the phenotype - the characteristic is polygenic
128
Q

What does it mean if a characteristic is polygenic?

A

It is controlled by a large number of genes called polygenes, which are unlinked and on different chromosomes. The polygenes have a combined effect on the phenotype

129
Q

What is the genetic basis for discontinuous variation?

A
  • Often only one gene involved
  • if more than one gene is involved, these genes interact in an epistatic way
  • different alleles at a single gene locus have large effects on the phenotype
  • different gene loci have quite different effects on the phenotype
  • examples of discontinuous variation include codominance, dominance and recessive patterns of inheritance
130
Q

What is a monogenic characteristic?

A

A characteristic controlled by only one gene

131
Q

In which type of variation (continuous or discontinuous) do different alleles at a single gene locus have a large effect on the phenotype?

A

Discontinuous

132
Q

What are the two causes of phenotypic variation?

A

The genotype and the environment

133
Q

How does the environment affect an organisms phenotype?

A

Limiting factors in the environment such as lack of nutrients, water, light, education etc can stop organisms from reaching the genetic potential determined by their genotype. Other characteristics are caused by the environment too: accent, pierced ears

134
Q

Which type of variation (continuous or discontinuous) is more likely to be influenced by both genotype and environment?

A

Continuous

135
Q

What does gene pool mean?

A

The complete range of alleles present in a population

136
Q

What does allele frequency mean?

A

How often an allele occurs in a population. This is usually given as a percentage of the total population or as a decimal

137
Q

How does evolution by natural selection take place?

A

There is intraspecific variation between organisms in a population which have different alleles due to mutations.
Selection pressures create a struggle for survival.
Due to variation, some organisms are better adapted to the selection pressures than others.
These are more likely to survive, reproduce and pass on the beneficial allele than organisms with other alleles.
A greater proportion of the next generation inherit the beneficial allele.
The allele frequency increases from generation to generation

138
Q

What type of selection occurs in a stable environment?

A

Stabilising selection

139
Q

What is stabilising selection?

A

When the environment isn’t changing much, individuals with alleles for characteristics towards the middle of the range are more likely to survive & reproduce. Stabilising selection reduces the range of possible phenotypes

140
Q

What is directional selection?

A

When there’s a change in the environment, individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce

141
Q

What type of selection occurs in a changing environment?

A

Directional selection

142
Q

What process other that natural selection can cause evolution?

A

Genetic drift

143
Q

What is genetic drift?

A

The passing on of alleles dictated by chance rather than by suitability to the environment. If an allele is repeatedly passed onto offspring by chance, it will become more common in the population over time

144
Q

How does population size relate to genetic drift?

A

The smaller the population the greater the affect that genetic drift can have, as chance has a greater influence, whereas in larger populations any chance factors tend to even out across the whole population.

145
Q

What is a genetic bottleneck?

A

An event that causes a big reduction in the size of a population, e.g. When a large population suddenly becomes smaller due to a natural disaster. Evolution by genetic drift has a greater effect if there’s a genetic bottleneck

146
Q

What is the Hardy-Weinberg principle?

A

A mathematic model which predicts that the frequencies of alleles in a population won’t change from one generation to the next. This is only true under certain conditions.

147
Q

What conditions need to be fulfilled for the Hardy-Weinberg principle to be true?

A
  • The population must be very large
  • mating within the population must be random
  • there must not be a selective advantage for any genotype
  • there must not be any mutation, migration or genetic drift
148
Q

What can the Hardy-Weinberg principle be used for?

A

It is used for the Hardy-Weinberg equations, one of which works out allele frequencies and the other works out frequency of genotypes

149
Q

What is the Hardy-Weinberg equation for allele frequency?

A

P+Q=1 where P=frequency of dominant allele and Q=frequency of recessive allele

150
Q

What is the Hardy-Weinberg equation for genotype frequency?

A

P^2+2PQ+Q^2=1
Where P^2=frequency of homozygous dominant genotype
2PQ=frequency of heterozygous genotype
Q^2=frequency of homozygous recessive genotype

151
Q

What is artificial selection?

A

When humans select individuals in a population to breed together to get desirable traits

152
Q

How has artificial selection been used to produce the modern dairy cow?

A

Farmers select a female with a high milk yield and a male whose mother had a high milk yield and breed the two together.
They select the offspring with the highest milk yield and breed these together
This is continued over several generations, increasing milk yield each time.

153
Q

What characteristics do farmers select for in dairy cows?

A
  • high milk yield
  • high milk quality
  • a long lactation period (cow produces milk for longer)
  • large udders (easy milking)
  • resistance to diseases
  • calm temperament
154
Q

How have modern techniques made artificial selection easier than it was hundreds of years ago?

A

Artificial insemination and IVF give farmers more control over which animals reproduce, whilst cloning allows farmers to produce genetically identical copies of their best animals, so they can be certain of the offspring’s characteristics

155
Q

How has artificial selection been used to produce bread wheat?

A

Farmers breed wheat plants with high yields together
The offspring with the highest yields are again bred together
Over several generations a plant with a very high wheat yield is produced

156
Q

What are the characteristics artificially selected for in bread wheat?

A
  • High wheat yield
  • high tolerance to the cold
  • short stalks (can hold weight of wheat ears better)
  • uniform stalk height (to make harvesting easier)
157
Q

How does reproductive isolation occur?

A

Because changes in the alleles and phenotypes of the two populations prevent them from successfully breeding together

158
Q

What changes can lead to reproductive isolation?

A
  • seasonal changes - individuals from the same population develop different flowering or mating seasons, or become sexually active at different times of the year
  • mechanical changes - changes in genitalia prevent successful mating
  • behavioural changes - a group of individuals develop courtship rituals that aren’t attractive to the main population
159
Q

What is the biological species concept?

A

A species is a group of similar organisms that can reproduce to give fertile offspring

160
Q

What are the limitations of the biological species concept?

A

You can’t always tell if different organisms could reproduce to give fertile offspring because they could be extinct, reproduce asexually (such as bacteria), there could be practical and ethical issues involved such as geography, and no one has or would ever try mating humans and chimpanzees. This means it can be difficult to determine what species am organism is, or if it is a new, distinct species.

161
Q

What concept do scientists sometimes use in place of the biological species concept?

A

The phylogenetic species concept

162
Q

What is phylogenetics?

A

The study of the evolutionary history of groups of organisms. All organisms have evolved from common ancestors, and the more closely related two species are, the more recent their last common ancestor will be. This tells us what is related to what and how closely related they are

163
Q

What is the phylogenetic species concept?

A

The use of phylogenetics to determine which species am organism belongs to, or if it’s a new species - if it is closely related to members of another species then it is probably the same species, but if it is quite different to any known species then it’s probably new.

164
Q

What is a limitation of the phylogenetic species concept?

A

There is no cut off to say how different two organisms have to be to be different species

Biology F215 (4 decks)

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