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biology_3_genetics_20150520080604 Flashcards

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1
Q

What is a genome?

A

Genome is the whole of the genetic information of an organism.

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2
Q

What is a gene?

A

Gene is a heritable factor that controls a specific characteristic.

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3
Q

What is an allele?

A

An allele is one of a number of different version of a gene

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4
Q

What is the Human Genome Project?

A

The HGP is an international research effort to sequence , map and understand all the genes of members of species, homeosapiens. 18 different countries were involved. It began in 1990 and finished in 2003

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5
Q

What importance does the Human Genome Project have? Why do we need the sequencing of the complete human genome?

A

By being able to read nature’s complete genetic blueprint of a human being:- to learn about the causes of genetic diseases and thus find cures and treatments.- to discover more about how different people are related to each other and to other species /evolutionary relationships - to understand more about the aging process

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6
Q

What is gene mutation?

A

Gene mutation is natural process that causes changes in the DNA sequence caused by a mutagen. The change in DNA sequence causes a change in mRNA, and amino acid sequence and thus produce new alleles.

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7
Q

What is mutagen?

A

Mutagen is a physical or chemical factor that causes a change in DNA base sequence.

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8
Q

What are the consequences of mutations?

A

There negative effects of mutations such as cancer. Positive effects of mutation are the creation of new alleles for adaption. Sometimes there are no consequences at all as the it codes for the same amino acid.

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9
Q

What is a consequence of a base substitution mutation?

A

Base substitution mutation is a change of a single base in a sequence of DNA. Example: Sickle Cell Anemia Base substitution mutation: - the sequence of nucleotide bases in DNA codes for the sequence of amino acids in proteins- DNA is transcribed into mRNA, which is translated into amino acids of protein- normal (ß chain) hemoglobin gene / DNA produces - normal (ß chain) hemoglobin protein / amino acidssubstitution= the replacement of one (or more) nucleotide base with another- caused by a copying mistake during DNA replicationas a result of a mutagen / X-rays / chemical / UV radiation / other mutagen- mutation in normal (ß chain) hemoglobin gene alters the sequence of nucleotide bases- normal nucleotide sequence = CTC altered to CACresulting in altered mRNA (GAG to GUG) during transcription- resulting in altered sequence of amino acids in (ß chain) hemoglobin protein (glutamic acid to valine) during translation- causing red blood cells to change shape / sickle under low oxygen conditions- causing sickle cells anemia when two copies of the mutated gene are inherited- producing a sickle cell carrier when one copy of the mutated gene is inherited- sickle cells anemia reduces oxygen flow to organs, leading to their deterioration

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10
Q

Compare eukaryotic and prokaryotic chromosomes

A

Prokaryotes have one chromosome consisting of a circular DNA molecule. Eukaryotes have chromosomes that have linear DNA molecules.Prokaryotic DNA is naked. Eukaryotic DNA molecules are wrapped around histone proteins. The circular prokaryotic chromosome contains all genes.. Eukaryotes have different chromosomes with different genes.Prokaryotes sometimes have plasmids. Eukaryotes do not.

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11
Q

What are homologous chromosomes?

A

Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles.

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12
Q

What are diploid nuclei?

A

A diploid nucleus contain two copies of each homologous chromosome/ have pairs of homologous chromosome/ two chromosomes of each type. number of chromosomes = 2N

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13
Q

What are haploid nuclei?

A

A haploid nuclei has one chromosome of each homologous chromosome. number of chromosomes = N

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14
Q

What was used to establish the length of DNA molecules?

A

Due to developments in scientific research, improvements were made in their techniques that included using autoradiography to establish the length of DNA molecules in chromosomes as they discovered specific substances located in cells/tissues.

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15
Q

What does the number of chromosomes indicate?

A

Number of chromosomes is a characteristic feature of members of a species.

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16
Q

How are genders determined on a karyogram?

A

Gender is determined by sex chromosomes.

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17
Q

What are autosomal chromosomes?

A

Autosomal chromosomes are chromosomes that determine the sex. (1st to 22nd Pair)

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18
Q

What can we deduce on a karyogram of an unborn baby?

A

We can identify the gender.We can identify chromosomal abnormalities in health.

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19
Q

What is a karyogram?

A

Karyograms show the chromosomes of an organism in homologous pairs of decreasing length

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20
Q

How can you diagnose Down syndrome and what its syndromes?

A

If there are three copies of chromosome 21 instead of two, the individual as down syndrome. Some of the component features of the syndrome are hearing loss, heart and vision disorder. Mental and growth retardation are also very common.

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21
Q

Outline Cairns technique for measuring the length of DNA molecules.

A
  • radioactively labelled chromosomes of the DNA by growing them in a medium containing thymidine- Using an enzyme cell walls were digested so that cells could release their DNA- a thin film of photographic emulsion was applied to the membrane so that when DNA decayed, it reacted with the film - Dark grains are seen where DNA decayed which indicates the position.
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22
Q

What are Pan troglodytes?

A

Chimpanzees

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23
Q

What are Canis familiaris

A

Dogs

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24
Q

What are the methods to collect cells from embryo for karyotyping?

A

Amniocentesis and chorionic villus sampling are two methods to collect the amniotic fluid.

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25
Q

What is Meiosis?

A

Meiosis is one of the two ways in which the nucleus of a eukaryotic cell can divide. (The other is Mitosis)

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26
Q

Why use Meiosis and not Mitosis?

A

Meiosis allows the halving of chromosome numbers that allow sexual life cycle with fusion of gametes. This allows genetic variation.

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27
Q

When does Meiosis occur?

A

Meiosis can happen at any stage during sexual life cycle, but in animals it happens during the process of creating the gametes. Body cells are diploid.

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28
Q

List all stages of Meisosis

A
  1. Interphase2. Prophase I3. Metaphase I4. Anaphase I5. Telophase I/Cytokinesis6. Prophase II7. Metaphase II8. Anaphase II9. Telophase II
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29
Q

What happens before Meiosis?

A

During the last stage of interface, DNA is replicated.

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30
Q

What happens during Prophase I (Meiosis)?

A
  1. Nuclear membrane breaks down2. Homologous chromosomes pair up to form bivalents/tetrads.3. Homologous chromosomes are held together by points called chiasma4. Homologous chromosomes undergo a process called synapsis whereby sections of DNA are exchanged between homologous chromosomes.5. Crossing over of genetic material between non-sister chromatids can occur at these points, resulting in new gene combinations (recombination)
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31
Q

What happens during Metaphase I?

A
  1. Centrioles form on either side of the cell2. Microtubulos grow and attach themselves to the centromeres of homologous tetrads3. Homologous tetrads line up along the equator
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32
Q

What happens during Anaphase I?

A
  1. Homologous chromosomes split apart and move to opposite poles
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33
Q

What happens during Telophase I?

A
  1. Nuclear membrane reforms 2. Centrioles and microtubules break down 3. Cell splits into two haploid daughter cells as cytokinesis occurs.
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34
Q

What happens during Prophase II?

A
  1. Nuclear membrane breaks down
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35
Q

What happens during Metaphase II?

A
  1. Chromosomes line up along the equator of the cell 2. Spindle fibres reform and reconnect to the chromosomes
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36
Q

What happens during Anaphase II?

A
  1. Spindle fibers shorten and pull sister chromatids apart as they move to opposite poles.
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37
Q

What happens during Telophase II?

A
  1. The cell splits in two as cytokinesis happens concurrently.
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38
Q

What is the result of Meiosis?

A

Because sister chromatids may no longer be genetically identical as a result of potential recombination, the process of meiosis results in the formation of four genetically distinct haploid daughter cells.

39
Q

Outline the process of crossing over.

A

Crossing over involves the exchange of segments of DNA between homologous chromosomes.During synapsis in prophase I, homologous chromosomes pair up to form bivalents/tetrads. Portions of non-sister chromatids overlap. The positions in which they are attached are called chiasma.The chromatids break at chiasmata, reattach to new sister chromatids in a system of reciprocal exchange. The new combinations are known as recombinants.

40
Q

How does meiosis produce genetic variation?

A
  1. Random orientation of bivalents/Independent Assortment: Bivalents line up along the equator in metaphase I. This means that chromosomes assort independently into two daughter cells during anaphase I. Chromosomes align along the equator independently during metaphase II. This means that chromatids assort independently into daughter cells during anaphase II2. Chiasma formation:During Prophase I, genetic exchange occurs between homologous chromosome during synapsis. This creates chromosomes with new combinations of alleles. 3. Offspring of sexual reproduction have two parents (Fusion of gametes)
41
Q

What are the genetic basis for Down’s syndrome to occur?

A

Non-disjunction can cause Down syndrome.The failure of the chromosomes to separate may either occur via:
* Failure of homologues to separate during Anaphase I (resulting in four affected daughter cells)
* Failure of sister chromatids to separate during Anaphase II (resulting in two affected daughter cells)
Thus, both of the chromosomes move to one pole while none to the other.This results the gametes, sperms or eggs, to have incorrect number of chromosomes.Down syndrome (trisomy 21) is an example. The person would have three homologous chromosomes #21.

42
Q

Explain how meiosis results in an effectively infinite genetic variety in gametes

A

independent assortment: - variety produced by recombination of maternal and paternal chromosomes- for each pair of homologous chromosomes, maternal and paternal chromosomes assort to daughter cells randomly- possible arrangements of chromosomes in haploid daughter cells = (2)nth, where n = number of homologous pairscrossing over: - variety produced by recombination within individual chromosomes- during synapsis, prophase I, homologous chromosomes pair forming bivalents- portions of non-sister chromatids overlap, break at chiasmata, reattach to new chromatid in a system of reciprocal exchange- new combinations known as recombinants

43
Q

What is a phenotype?

A

Phenotype is an observable trait or characteristic.

44
Q

What is a genotype?

A

Genotype is an organism’s genetic make up

45
Q

What is an allele?

A

An allele is a version of a gene.

46
Q

What is a dominant allele?

A

An allele which determines the phenotype of a heterozygote.

47
Q

What is a recessive allele?

A

An allele which can only influence the phenotype of a homozygote.

48
Q

What is the locus?

A

A position in a chromosome.

49
Q

What is homozygous?

A

An organism is homozygous when it has two identical alleles of the same gene.

50
Q

What is heterozygous?

A

An organism is heterozygous when it has two different alleles of the same gene.

51
Q

When a test cross is performed what happens?

A

Testing a suspected heterozygote by crossing it with a known homozygous recessive.

52
Q

What is a monohybrid cross?

A

A monohybrid cross determines the allele combinations of offspring for one particular gene only (HL students may refer to topic 10.2 for dihybrid crosses)

53
Q

A parent organism of unknown genotype is mated in a test cross. Half of the offspring have the same phenotype as the parent. What can be concluded from this result?

A

The parent of unknown genotype is heterozygous.

54
Q

The gene for brown hair is B and the gene for blond hair is ba) Write down the genotype of a woman who is heterozygous for brown hair.b) Write down the genotype of a man who has blond hair.c) Work out the possible offspring of these two people.

A

a) Bbb) bbc) 50% Brown hair & 50% blond hair

55
Q

What is the use of test cross?

A

A genetic cross is a means of determining the genetic characteristics of potential offspring based on the genetic characteristics of the prospective parents.By test crossing we can determine the parent’s unknown genotype.

56
Q

What is codominance?

A

Codominance means that two different alleles both affect the phenotype of a heterozygote.

57
Q

How many alleles can a gene have?

A

A gene can have multiple alleles that means more than 2 versions of the same gene.

58
Q

What is an example of codominance and multiple alleles?

A

ABO blood groups have codominant alleles as well as more than 2 alleles for the same gene. (Recessive allele is i which does not produce glycoprotein. Phenotype = Blood group O)

59
Q

What is sex linkage?

A

Sex linkage occurs when a gene is located on one the sex chromosomes (chromosome #23)

60
Q

What are examples of sex linkage?

A

Red Green Color Blindness & Hemophilia are both examples of X-linked recessive conditionsThe gene loci for these conditions are found on the non-homologous region of the X chromosome (they are not present of the Y chromosome)As males only have one allele for this gene they cannot be a carrier for the condition This means they have a higher frequency of being recessive and expressing the traitMales will always inherit an X-linked recessive condition from their motherFemales will only inherit an X-linked recessive condition if they receive a recessive allele from both parents

61
Q

Can males be both homozygous and heterozygous with respect to sex-linked genes?

A

No. As human females have two X chromosomes (and therefore two alleles for any given X-linked gene), they can be either homozygous or heterozygousMales only have one X chromosome (and therefore only one allele) and are hemizygous

62
Q

Explain that female carriers are heterozygous for X-linked recessive alleles

A

An individual with a recessive allele for a disease condition that is masked by a normal dominant allele is said to be a carrierCarriers are heterozygous and can potentially pass the trait on to the next generation, but do not suffer from the defective condition themselvesFemales can be carriers for X-linked recessive conditions because they have two X chromosomes - males (XY) cannot be carriersBecause a male only inherits an X chromosome from his mother, his chances of inheriting the disease condition from a carrier mother is greater

63
Q

What is the cause of most genetic diseases?

A

Many genetic diseases in humans are caused due the recessive allele of autosomal genes, although some genetic diseases are due to dominant or codominant alleles.

64
Q

What is cystic fibrosis?

A

• Autosomal disease • Recessive• C = healthy/ c = cystic fibrosis• Suffers produce a thick mucus in their lungs which gives them trouble breathing• No cure, no effective treatment.

65
Q

What is Huntington’s disease?

A
  • Autosomal Dominant
  • H = Huntington’s disease h = healthy
  • patients incur damage to nerve tissues, mental decline aged 30+
66
Q

Explain why large sample sizes are necessary in genetics investigations

A

• Large sample sizes increases reliability of the data• Large sample sizes reduce the impact of random effects/ small sample sizes increases the impact of random effects

67
Q

What is mutagen?

A

Mutagens a physical or chemical factor that causes DNA mutations • Physical (UV rays, gamma radiation, X-rays) • Chemical (polonium, radium, dioxins, carbon monoxide, uranium)

68
Q

What are the consequences of radiation after a nuclear bomb?

A

• Higher rate of cancer among survivors • Blood disorders (e.g. Leukemia)• Down syndrome • Soil contamination

69
Q

What is a dihybrid cross?

A

A dihybrid cross determines the allele combinations of offspring for two particular genes that are unlinked (not on the same chromosome)To work out gamete combinations remember FOIL:• First (AaBb = AB)• Outside (AaBb = Ab)• Inside (AaBb = aB)• Last (AaBb = ab)

70
Q

Assuming that the flowers’ dominant alleles are phenotypes for tall and purple. If there are two heterozygous tall purple flowers crossed, what is the probability of getting offspring with the same phenotype?

A

9/16

71
Q

What is used to determine whether the difference between an observed and expected frequency distribution is statistically significant?

A

Chi squared/ X2Degrees of freedom are determined by the number of types of offsprings, minus one.

72
Q

Explain how crossing over between non-sister chromatids of a homologous pair in prophase I can result in the exchange of alleles

A
  • crossing over/chiasmata formed during prophase I of meiosis;
  • pairing of homologous chromosomes/synapsis; chromatids break (at same point); (do not accept chromatids overlap)
  • non-sister chromatids join up/swap/exchange alleles/parts;
  • X-shaped structure formed / chiasmata are X-shaped structures;
  • chiasma formed at position where crossing over occurred;
  • chiasmata become visible when homologous chromosomes unpair;
  • chiasma holds homologous chromosomes together (until anaphase
73
Q

Draw a diagram of chiasma formed by crossing over

A

Recombinants formed by crossing over

74
Q

Explain the relationship between Mendel’s Law of Independent Assortment and Meiosis

A

Meiosis divides the chromosomes into groups of four. Each allele for one trait has a 50% chance of being passed on. But the two alleles combined make four different options, which makes the chances for these being passed on 25%.

75
Q

State Mendel’s Law of Independent Assortment

A

The alleles of two genes pass into gametes without influencing each other.

76
Q

What is an autosomal linkage group?

A

When two genes are located on the same autosomal chromosome

77
Q

What is polygenic inheritance?

A

When many genes control the same phenotype (or characteristics). A good example is skin colour.

78
Q

What do phenotypes of polygenetic characteristic tend to show?

A

The phenotypes of polygenic characteristics tend to show continuous variation

79
Q

Explain an example of a cross between two linked genes.

A

Unlinked genes assort independently in a dihybrid cross between heterozygotes, producing a 9:3:3:1 phenotypic ratio Linked genes, without crossing over, do not follow the expected 9:3:3:1 phenotypic ratio for a dihybrid cross between heterozygotes
* Instead the result will follow the 3:1 phenotypic ratio of a monohybrid cross, as the two linked genes are inherited together
* This means that all the offspring will produce parental phenotypes
Linked genes with crossing over produce recombinant phenotypes in numbers that reflect the distance between the linked genes
* distant genes will cross over more frequently, producing a higher percentage of recombinants
* genes that are close together will cross over less frequently, producing a lower percentage of recombinants
A test cross involving two linked genes, A and C: AaCc x aacc
* 80% of offspring are parental, either AaCc or aacc
* 20% of offspring are recombinant, Aacc or aaCc
* thus, the two genes are linked and are 20 cM apart on the same chromosome

80
Q

Outline the process of polymerase chain reaction (PCR)?

A
  1. DNA is collected and heated to a very high temperature to break the hydrogen bonds between the double stranded DNA. 2. When the mixture is then slightly cooled, DNA primers are inserted using DNA complementary base pairing rules that form hydrogen bonds.3. When the mixture heats up again, Taq polymerase i added to create a new complementary strand of DNA using free DNA nucleotides and the base pairing rules4. This process repeats several dozen times so that millions of copies are produced
81
Q

What is the process of PCR (artificial DNA replication) called?

A

Amplification

82
Q

During PCR, are small or larger amounts of DNA used?

A

Only minute/very small amount of DNA is needed to amplify.

83
Q

What is used to separate proteins or fragments of DNA?

A

Gel electrophoresis is used to separate proteins or fragments of DNA according to size.

84
Q

What is used for DNA profiling?

A

Amplification/PCR, restriction enzymes to cut the DNA, gel electrophoresis to separate the DNA fragments.

85
Q

How does gel electrophoresis separate proteins or DNA fragments?

A

When DNA is in fragments, they can be placed into the gel.An electric field is applied which makes the molecules move to their opposite charge. The smallest fragments travel furthest towards positive charge. UV probe is used to make them visible.

86
Q

What are the uses for DNA profiling?

A

Solving crimes, Identifying paternity & analyzing evolutionary relationships.

87
Q

What is GMO?

A

Genetically modified organisms where gene transfer between specifies has been carried out.

88
Q

What is an example of a technique used for gene transfer to bacteria?

A

Production of Human InsulinStep 1: Bacteria has plasmids that contain a small ring of naked DNA that can be copied and shared with other bacteria in order to share useful genesStep 2: Restriction enzymes are used to cut the plasmid DNA. Step 3: The gene for human insulin is inserted into the Plasmid. The sticky ends of the gene and the plasmid have to be complementary. DNA ligase sticks them together. The plasmid has now a recombinant DNA.Step 4: The plasmid is inserted back into the bacteria where it acts as a vector. Step 5: Under a suitable environment, the bacteria will quickly reproduce and be able to synthesize protein for human insulin due to the recombinant DNA.

89
Q

Outline 2 examples of current uses of GMOs

A

Golden Rice: Was enriched with Vitamin A which helps improve the health of poor rural communities whose diet is dependent on rice but lack Vitamin A levels. However, may go against religious, cultural heritage and beliefs because the food is no longer pure. Poor communities may become dependent on the golden rice and not focus on a general improvement in their diet. Bt corn: Bt corn has increased resistance to attack from insects, farmers need to use less insecticide. This reduces the cost of farming as well as environmental contaminationBt corn plants have been genetically engineered to produce a toxic chemical that kills insects. This chemical is also present in the harvested crop. This may pose a threat to human health

90
Q

Discuss potential benefits and possible harmful effects of genetic modification

A

MUST have examples:Benefits:• benefits include more specific (less random) breeding than with traditional methods• faster than traditional methods•some characteristics from other species are unlikely in the gene pool / selective breeding cannot produce desired phenotype•increased productivity of food production / less land required for production• less use of chemical (e.g. pesticides in Bt Corn)• food production possible in extreme conditions (Amflora - GM potatoes are cold/drought resistant)• less expensive drug preparation e.g. pharmaceuticals in milk• human insulin engineered so no allergic reactions• may cure genetic diseasesRisks:• Could have currently unknown harmful effects (e.g. toxin may cause allergic reactions in a percentage of the population)• Accidental release of transgenic organism into the environment may result in competition with native plant species• Possibility of cross pollination (if gene crosses the species barrier and is introduced to weeds, may have a hard time controlling weed growth)• Reduces genetic variation / biodiversity (corn borer may play a crucial role in local ecosystem)

91
Q

What are clones?

A

Clones are a group of genetically identical organisms or a group of cells derived from a single parent cell

92
Q

Does cloning only occur artificially?

A

No. Cloning can occur naturally for some animal species and many plants such as potatoes, garlic, onions and wild strawberries.

93
Q

Outline 2 techniques for cloning

A

Cloning at embryo stage:Animals can be cloned at the embryo stage by breaking up the embryo into more than one group of cellsCloning at adult stage:using somatic-cell which are differentiated cell transfer

94
Q

Outline the technique to clone adult animals

A
  1. Remove a somatic cell (usually a skin cell) from the mouse that you want to clone.Obtain an egg cell from another organism2. Remove the nucleus from the egg cell using a harp pipette. The egg now contains no DNA which makes it enucleated 3. Remove the nucleus from the somatic cell using a sharp pipette4. The nucleus from the somatic cell is injected into the enucleated egg cell5. The cloned cell is treated with chemicals in order to stimulate it to begin cell division which makes a cloned embryo6. Implant the cloned embryo into the uterus of a surrogate organism. Once pregnancy is completed, the surrogate will give birth to the cloned organism ​

Biology 3. Genetics (1 decks)

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