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Genetics Flashcards

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1
Q

What is a haploid?

What is a diploid?

A

Haploid: 1 set of chromosomes
Diploid: 2 sets of chromosomes

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2
Q

What is a gene?

A

A unit of heredity, located on a specific part off a chromosome, comprised of DNA sequence that codes for a protein.

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3
Q

What is an allele?

A

A different version of a gene

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4
Q

What is phenotype and genotype?

A

Phenotype: Observable properties of an organism, defined by the genotype
Genotype: The genes of an organism

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5
Q

What is ‘wild type’?

A

The genotype that that is most commonly found in nature.

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6
Q

What is a ‘disruptive mutant’?

A

An allele that blocks the activity of the wild type gene. An allele of a protein that is dominant can be blocked by a disruptive mutant allele.

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7
Q

What doe meiosis and mitosis achieve?

A

Mitosis: produces 2 diploid cells from 1 diploid cell
Meiosis: produces 4 haploid cells from 1 diploid cell

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8
Q

Chi-squared test and all……

A

STATS SHIT

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9
Q

Pedigree analysis example

A

https://cdn.britannica.com/73/72173-004-87D1E1BB/hemophilia-pedigree-chart-inheritance-trait-generations-gene.jpg

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10
Q

What is monoecious?

A

Both male and female reproductive structures in the same organism (hermaphrodites)

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11
Q

What is dioecious?

A

Individuals possessing only male or female reproductive structures

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12
Q

What is intersex?

A

Reserved for individuals of an intermediate sexual condition

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13
Q

How are the gametes of a monoecious organism formed?

A

Maize
Production of male gametes: diploid microspore goes through meiosis so 4 haploid microspores. Each haploid microspore undergoes one round of mitosis to give one pollen grain with two haploid nuclei.

Production of female gametes: diploid megaspore goes through meiosis so 4 haploid nuclei are made. 3 out of 4 haploid nuclei degenerate so one haploid nucleus is left.
There are 3 rounds of mitosis to form 8 haploid nuclei, where 3 aggregate to form antipodal nuclei, 2 aggregate to endosperm nuclei, 2 aggregate to form synergids and 1 is the oocyte nucleus.

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14
Q

How does pollination and maturation of plants occur?

A

Pollen transfer from stamen to stigma.
Pollen tube grows towards embryo sac.
Two sperm nuclei enter embryo sac.

One sperm nucleus untie with the two endosperm nuclei to fomr a triploid endosperm nucleus
One sperm nucleus unites with haploid oocyte nucleus to form a diploid zygote nucleus

Endosperm provides nutrition to the embryo
Diploid zygote nucleus forms the embryo

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15
Q

What are homogametic and hetrogametic?

A

Homogametic, only produce one type of gamete (human females)

Heterogametic, carry two types of gametes (human males)

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16
Q

What is trisomy?

A

Three instances of a chromosome.

This potentially includes three sex chromosomes

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17
Q

What is monosomy?

A

One instance of a chromosome. This potentially includes one sex chromosome.

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18
Q

What is aneuploidy?

A

Non-disjunction of chromosomes. This is the failure of homologous chromosomes to separate properly during meiosis. There is aneuploidy when chromosomes are more or less than normal.

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19
Q

How much of the Y chromosome confers maleness?

A

The tip of the Y chromosome defines maleness. The SRY region of the Y chromosome is the sex-determining region because is encodes for the testis determining region (TDF).
https://steemitimages.com/DQmXEAtmQJmFsjuL8H7QTGJMPTweyjh13Zb1v6CSDmn6dVq/SRY%20gene.png

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20
Q

What is the PAR region?

A

Pseudoautosomal region. This is the region at the tip of both the X and the Y chromosome. This is what allows the X and Y chromosome to group up when split in meiosis.

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21
Q

What happens if SRY is absentt?

A

At the 6th week of development of the embryo, if SRY is not present, the ‘default pathway’ will occur.

  • gonadal structures develop into ovaries
  • Wolffian duct degenerates
  • Mullerian duct gives rise to oviduct, uterus and upper portion of vagina
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22
Q

What happens if SRY is present?

A

At the 6th week of development of the embryo, if SRY is present, genes are activated in the gonad that lead to development of the testes.

  • anti-Mullerian hormone will lead to Mullerian duct degeneration
  • testosterone
  • Wolffian duct develops into epididymis, vas deferens and seminal vesicles
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23
Q

What is hemigametic?

A

Organism only possesses one sex chromosome.

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24
Q

What are symptoms of the XXY chromosome?

A

This disease is known as Klinefelter Syndrome. Genitals are male, but testes are small and infertile. There is limited development of secondary sexual characteristics.

Patients are MALE

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25
Q

What are symptoms of patients with one single X chromosome, and no other sex chromosomes?

A

This diseases is known as Turner Syndrome.

Patients are FEMALE

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26
Q

What evidence is there that the Y chromosome determines ‘maleness’?

A

In patients with aneuploidy of the sex chromosomes, patients containing XXY chromosomes are still male, and patients with X only chromosomes are female.

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27
Q

What is primary and secondary sexual differentiation?

A

Primary: Expression of SRY leads to development of testes, lack of SRY lead to ovaries

Secondary: All sexual development controlled by hormones after gonads have developed

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28
Q

What is significant in bird sex determination?

A

Female is heterogametic sex and male is homogametic. ZZ is male and ZW is female

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29
Q

What is sex determination by ratio of X chromosomes?

A

The ratio of X chromosomes to the number of haploid sets of autosomes determines sex.
This occurs in Drosophila. Ratio of above 0.5 leads to females and 0.5 or below leads to males.

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30
Q

What is the haplodiploid system?

A

Males are produced from unfertilized haploid eggs, whereas female are produces from fertilized eggs.
Only females are produced by sexual reproduction.
This occurs in bees

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31
Q

What is dosage compensation?

A

The Xic region of the X chromosome contains the Xist gene. When transcribed,the Xist gene produces a 25kb non-coding RNA which leads to heterochromatin (condensed) formation which spreads to the inactivation center.

Basically condensed DNA cannot be transcribed.

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32
Q

Why does dosage compensation occur?

A

Females have twice as many X genes in comparison to male, but twice the amount of transcription is not observed. This suggest that twice the transcription would be lethal.

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33
Q

What are Barr bodies?

A

Where dosage compensation has occurred.

The number of Barr bodies is always one less than the number of X chromosomes.

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34
Q

What are bilateral gynadromorphs?

A

One side of the organism is male and the other is female.

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35
Q

What is temperature sensitive sex determination?

A

Temperature determines sex.

This is an environmental factor

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36
Q

What are social factors in clownfish that determine sex?

A

There is one large female, medium sized reproductive males and small nonreproductive juveniles.
When female dies, reproductive males changes sex to become female and the juveniles mature into reproductive males.

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37
Q

What is amorphic?

A

Loss of functions of a gene.

No protein is produces, or protein produces has completely no function.

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38
Q

What is cystic fibrosis and what causes it?

A

CFTRΔ508 allele. (cystic fibrosis transmembrane conductance regulator)
This allele is recessive, so only appears in homozygous recessive individuals.

Cystic fibrosis is the loss of this transmembrane protein, which causes a loss in Cl- gradient of cells (affecting lung epithelial cells, as well as gastrointestinal tract, endocrine system and reproductive systems). In lungs, this causes mucus to become thicker, leading to lung infections.

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39
Q

What is hypomorphic?

A

Protein function is reduced, due to less protein being made, or protein having less activity.

40
Q

What is hypermorphic?

A

Either more protein is made, or the protein has greater function, leading to an increase in activity.

41
Q

What is antimorphic?

A

Disturbance in function that interferes with protein encoded by a normal allele.

42
Q

What is lethal alleles?

A

Alleles that causes death to organisms.
This is only present in the gene-pool if the cause of death is accumulation of the mutant product, as opposed to immediate death/non-viability.
An example are Manx cats

43
Q

What is neomorphic?

A

Protein function is altered entirely.

44
Q

What is incomplete domiance?

A

Basically, a blend of characteristics.
Homozygous dominant and heterozygous are different from each other (In comparison to Mendelian ratios where hetero- and homo-dom produce the same phenotype)

45
Q

What is codominance?

A

Presence of both alleles is detected equally.

Example is blood groups.

46
Q

What are dominant lethal alleles?

A

Alleles that when present in homozygous or heterozygous organisms, will cause death.
This is only present in the gene-pool if the cause of death is accumulation of the mutant product, as opposed to immediate death/non-viability.
An example is Huntington’s Disease.

47
Q

What is maternal inheritance?

A

In the embryo, the mitochondria/chloroplast of the male gamete are excluded whilst the mitochondria/chloroplast are included, unequivocally.
This means if the mother of an offspring has a defect in the mitochondria/chloroplast, the offspring always have the defect.
(this means its non-mendelian)

48
Q

What is penetrance?

A

‘The probability that the phenotype matched the genotype’
Full penetrance: 100% chance phenotype and genotype match
Incomplete penetrance: <100% chance phenotype and genotype match

49
Q

What is variable expressivity?

A

When phenotype varies in the degree of magnitude.

50
Q

What is epistasis?

A

Phenotype being affected by various genes interacting with each other.
Rarely are there cases where a single gene solely affects the phenotype.

51
Q

What does a 9:7 Mendelian ratio indicate?

A

The genotype that displays this characteristic are AaBb. (Produced from AAbb and aaBB parents)

9:7 ratio suggests ‘complementary gene action relationship between two genes’. This means that both genes must be homozygous dominant for phenotype to occur, and if one of either gene isnt homo- dom-, the wild-type phenotype will not be present.

Mendelian ratio
A-/B- = 9
A-/bb + aa/B- + aa/bb = 3 + 3 + 1 (7)

52
Q

What does 9:3:4 Mendelian ratio indicate?

A

The genotype that displays this characteristic are AaBb. (Produced from AAbb and aaBB parents)

9:3:4 ratio suggests ‘recessive epistasis relationship between two genes’. One of the two genes when homozygous recessive, masks the effects of the other gene. For the sake of the argument, B gene is the gene that masks the effects.

Mendelian ratio
A-/B- = 9
aa/B- = 3
A-/bb + aa/bb = 3 + 1 (4)

In bb organisms, phenotype is always the same, meaning regardless of AA, Aa or aa, bb masks the effects of gene A.

53
Q

What does 12:3:1 Mendelian ratio indicate?

A

The genotype that displays this characteristic are AaBb. (Produced from AAbb and aaBB parents)

12:3:1 ratio suggests ‘dominant epistasis relationship between two genes’. One of the genes when dominant homozygous, produces the same phenotype, regardless of the other gene. For the sake of the argument, B gene is the gene that masks the effects.

Mendelian ratio
A-/B- + aa/ B- = 9 + 3 (12)
A-/bb = 3
aa/bb = 1

In B- organisms, phenotype is always the same, meaning regardless of AA, Aa or aa, B- masks the effects of gene A.

54
Q

What does 15:1 Mendelian ratio indicate?

A

The genotype that displays this characteristic are AaBb. (Produced from AAbb and aaBB parents)

15:1 suggests ‘duplicate dominant gene action relationship between the two genes’.
Basically, the two genes produce the same effect, so if either are heterozygous, or homo- dom-, the same phenotype.

Mendelian ratio
A-/B- + aa/ B- + A-/bb = 9 + 3 +3 (15)
aa/bb = 1

55
Q

What are chiasma?

What are chiasmata?

A

Region where non-sister chromatids cross over.

Chiasmata is the plural of chiasma

56
Q

What is homologous recombination?

A

Nucleotide sequences are exchanged between two very or identical similar molecules of DNA.
Occurs at meiosis for crossing over, but is also part of a mechanism that repairs double strand DNA breaks.

57
Q

What is heterologous recombination?

A

Genetic recombination in which nucleotide sequences are exchanged between two similar molecules of DNA.
In eukaryotes most commonly part of a mechanism that repairs of double strand DNA breaks.

58
Q

How does homologous recombination at meiosis for eukaryotes occur?

A

1) Spo11 creates a double-strand break in one DNA duplex
2) Enzymatic digestion 5’-3’ by Mrx creates single stranded segments
3) Dmc1 and Rad51 assemble strand-exchange nucleoprotein filaments
4) The strand exchanges filaments promote strand invasion
5) Strand invasion creates one D loop and the first heteroduplex region
6) Strand extension by DNA polymerase displaces D loop DNA, which pairs with complementary single-stranded DNA to form the second heteroduplex region
7) Strand extension and ligation fills the single-stranded gap in the stands paired with D loop DNA
8) Double Holliday junctions form after the nick is sealed; chromatids contain offset heteroduplexes

59
Q

What is recombinant frequency and what information does it allow us to obtain?

A

Its a measure of genetic linkage. The closer the genes are together on the chromosome, the fewer crossover events will happen at meiosis.
It allows use to map the distance between genes.

Equation: RF = (number of recombinants)/(total number of progeny) x 100

60
Q

How is recombinant frequency mapping in gamete most easily performed?

A

LC

61
Q

Maths of recombination

A

LC

62
Q

What is a centimorgan?

A

1 map unit of the chromosome. (1%)

63
Q

Chromosome mapping using recombination…..

A

LC

64
Q

What is a germ-line mutation?

A

A mutation that occurs in the gametes. Theses mutations are inherited by offspring.

65
Q

What is mutation frequency?

A

The number of mutational

events in a given gene over a defined period of time.

66
Q

What are the types of base pair mutations?

A

Silent- base change does not affect resultant AA
Missense- base change affects the resultant AA
Nonsense- base change codes for a stop codon

67
Q

What are the types of frameshift mutation?

A

Insertion of a single base pair

Deletion of a single base pair

68
Q

What are effects of promoter mutation?

A

Mutations of the promoter region can cause reduced transcription, no transcription whatsoever or even enhanced transcription.

69
Q

What are intron splicing mutations?

A

These are mutations that cause the exon-intron splice sites to either not splice the mRNA properly or not at all

70
Q

What are cryptic splice sites?

A

When mutations cause new splice sites for mNRA processing.

71
Q

What are reverse mutations?

What are types of reverse mutations?

A

When mutations to mutant alleles cause wild-type/ near wild type alleles

True reversion is when the DNA sequence is restored by a second mutation within the same codon

Second site reversion is when two mutations occur of different genes to restore the organism to wild-type

72
Q

What cause trinucleotide repeat disorders?

A

When DNA polymerase slips during DNA replication and increases the number of trinucleotide repeats within a gene to result in longer stretched of the same amino acid within a protein

73
Q

How do tautomers cause mutations?

A

adenine and cytosine can spontaneously change their amino groups to imino groups
Thymine and guanine can spontaneously change their keto groups to enol groups
Both of these spontaneous changes occur randomly and rarely.

These tautomeric shifts lad to base-pair mismatches and incorporation of incorrect bases during replication

74
Q

What are transposable elements?

A

They are sections of nucleotide strands that can modify genome and have the ability to cause mutations on insertion into genes.

75
Q

What are the 7 types of induced mutations?

A 
Nucleotide base analogs
Deaminating agents 
Alkylating agents
Hydroxylating agents
Oxidative agents 
Intercalating agents
Radiation induced DNA damage
76
Q

What are base analogs?

A

Bases with similar compositions to nitrogenous bases of DNA, but have altered pairing properties

77
Q

What are intercalating agents?

A

Flat, planar molecules which intercalate between base pairs, distorting the DNA helix which disrupts DNA replications and causes addition or deletion of nucleotides

78
Q

What is photoreactivation repair?

A

DNA damage repaired by photoreactivation enzyme (PRE) which cleaves the thymine dimer bond.

79
Q

What is base excision repair?

A

Specific DNA glycosylase recognises and excises incorrect base
AP endonuclease recognises lesion and nicks DNA strand
DNA polymerase and DNA ligase fill gap

80
Q

What is nucleotide excision repair?

A

DNA is damaged in one way or another
Nuclease excises lesion
GAP is filled by DNA polymerase and gap is sealed by DNA ligase

81
Q

What is TBP?

A

TATA binding protein.
Its a transcription factor that binds to the DNA, allowing RNA polymerase (and potentially other proteins) to recognize and bind promoter.

82
Q

What is a nucleosome?

A

The basic subunit of chromatin.
2 histone molecules with 146 bp of DNA wrapped around them form the nucleosome. There is linker DNA at each side which equates to 200 bp of DNA in total

83
Q

What are scaffolds purpose in DNA?

A

Once the DNA has been wrapped around the histones, it goes through further folding by ‘chromosome scaffolds’. This condenses the DNA further.

84
Q

What happens when histones are deacetylated?

A

Wikipedia

85
Q

What happens when histones are acetylated?

A

WIkipedia

86
Q

Which enzymes deacetylate histones?

A

HAT: Histone acetyl transferase
HDAC: Histone deacetylase

87
Q

How can frequency of alleles within a population be altered?

A

Natural selection for a particular environmental situation
Mutation of a gene
Migration of individuals between populations
Genetic drift

88
Q

What is the Hardy-Weinberg Equation?

A

p + q = 1

p^2 + 2pq + q^2 = 1

89
Q

What is the purpose of the Hardy-Weinberg relationship?

A

Its a model to calculate the frequencies of alleles and genotype ina population

90
Q

What are the assumptions of the Hardy-Weinberg Equilibrium?

There are 6

A

1) Population size is infinite
2) Random mating occurs
3) No natural selection
4) No migration
5) No mutation
6) No genetic drift

91
Q

What are the Wallace-Darwin concepts of natural selection?

A

1) Individuals of a species exhibit variations in phenotype
2) Variations are heritable
3) More offspring are produced than can survive. There is struggle for survival
4) Some phenotypes are more successful at survival and reproduce at higher rates

92
Q

What is genetic drift?

A

When the gene pool changes by chance alone, and not due to natural selection.

93
Q

What is the founder effect?

A

.

94
Q

What are genetic bottlenecks?

A

When a population is significantly reduced in size, usually due to natural disasters.

95
Q

What are the consequences to inbreeding?

A

There is a higher chance that the frequency of homozygous genotypes, which allows for higher frequency of particular inherited genetic disorders.

96
Q

What are phylogenetic trees?

A

Them tree diagrams that show the relatedness of various species

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