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Genetics, Heredity and DNA Flashcards

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1
Q

Give a brief overview of the history of Genetics from 1860’s to 2018

A

1860s- Mendel published his research on inheritance of unit factors. Cytologists describe chromosomes & their behaviour during mitosis & meiosis.
1900s- Rediscovery of Mendel’s work. Chromosomes behave like unit factors. The term “Gene” proposed to replace unit factors. Genetics becomes a discipline in itself.
1905- William Bateson first uses the term ‘genetics’ to describe the study of inheritance
1940s- Confirmation that the genetic material is DNA not protein.
1950s- Watson and Crick describe double-helical structure of DNA - Molecular Biology Era Begins
1960s- Cracking the triplet ‘code’ and defining the pathway of information flow: ‘DNA makes RNA makes protein’
1970s- Discovery of restriction enzymes: Recombinant DNA technology becomes possible. Expression of human growth hormone gene in E. coli; Discovery of split genes in eukaryotes - introns & exons; methods for sequencing DNA.
1980s- Commercialization of Recombinant DNA technology. Methods for making transgenic plants & animals.
1990s- Genome sequencing: Human, plant, drosophila, nematode, microbial genomes & many other genomes sequenced.
2000s- First complete human genome sequence 2003. Cost approx. $3 billion!
2000s- Technology for expression profiling of the entire gene complement in a genome.
2000s - RNA interference; genome editing; induced pluripotent stem (iPS) cells & many others
2018- Whole human genome sequence (WGS) costs less than $1,000!

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2
Q

What did Mendel discover in the 1860’s

A

1860s- Mendel published his research on inheritance of unit factors. Mendel studied “trait inheritance”, patterns in the way traits are handed down from parents to offspring. He observed that organisms (pea plants) inherit traits by way of discrete “units of inheritance”. Cytologists describe chromosomes & their behaviour during mitosis & meiosis.

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3
Q

When was it confirmed that the genetic material is DNA not protein.

A

1940s

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4
Q

What did Watson and Crick discover and in what year?

A

1950s- described double-helical structure of DNA - Chargaff’s realization that A = T and C = G, combined with some crucially important X-ray crystallography work by English researchers Rosalind Franklin and Maurice Wilkins, contributed to Watson and Crick’s derivation of the three-dimensional, double-helical model for the structure of DNA. Watson and Crick’s discovery was also made possible by recent advances in model building, or the assembly of possible three-dimensional structures based upon known molecular distances and bond angles, a technique advanced by American biochemist Linus Pauling. Molecular Biology Era Begins

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5
Q

Within cells, what are the structures which contain genetic material?

A

Within cells, structures called chromosomes contain genetic material in the form of DNA (deoxyribonucleic acid)

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6
Q

What does each chromosome consist of?

A

Each chromosome contains one long DNA molecule with hundreds or thousands of genes around proteins called histones that support its structure.

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7
Q

What are genes?

A

Genes are the units of inheritance - they encode information for building the molecules synthesized within the cell

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8
Q

What does the genetic information encoded by DNA do?

A

The genetic information encoded by DNA directs the development of an organism and the maintenance of cells in the organism

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9
Q

What is the central dogma?

A

describes the two-step process, transcription and translation, by which the information in genes flows into proteins DNA → RNA → protein

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10
Q

Describe the structure of each DNA molecule

A

Each DNA molecule is made up of two long chains arranged in a double helix
Each chain is made up of four kinds of chemical building blocks called nucleotides and abbreviated A, G, C, and T

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11
Q

How does DNA structure relate to its function?

A

DNA coils up into a double helix so that it’s more compact, so lots of information is stored in a small place.
The sequence of bases allows it to carry coded information for making proteins.
It is very long so it stores lots of information. Complementary base pairing allows the molecule to replicate itself accurately

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12
Q

What are mendelian diseases and how many are there approx

A

There are over 3,000 genetic diseases in humans which are termed ‘mendelian’ – due to a mutation in a single gene eg, Cystic fibrosis

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13
Q 
How much of 
-chromosomes
- DNA
- DNA subunit bases (nucleotides)
-genes
does each cell have?
A
  • 46
  • 2 meters of DNA
  • 3 billion DNA subunits (A,T,C,G)
  • 30,000 genes code for proteins that perform most life functions
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14
Q

What is a karyotype?

A

A karyotype is the number and appearance of chromosomes in the nucleus of an eukaryotic cell

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15
Q

What does the normal human karyotype contain?

A

The normal human karyotypes contain 22 pairs of autosomal chromosomes and one pair of sex chromosomes (allosomes).

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16
Q

How does each cell function so differently if you have the same 3 billion base pairs of DNA, same 20,00 genes present in every cell of your body?

A

Not all genes are active in all cell types.
Genes make RNA which is translated into proteins, the building blocks required for each cell to function. Different cell types need different proteins to function.

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17
Q

Mutations in the DNA sequence can result in what?

A

No protein or incorrect proteins being formed giving rise to genetic disorders.

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18
Q

What percentage of our genome codes for protein?

A

It turns out that only about 1.5% of our genome codes for proteins.
Much of our genome makes RNA but does not code for protein – termed non-coding RNAs..

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19
Q

What is gene expression?

A

The process of converting information from gene to cellular product.

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20
Q

How do protein-encoding genes control protein production?

A

indirectly, DNA is transcribed into RNA, which is then translated into a protein.

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21
Q

What is a genome?

A

The genetic material of an organism and it includes both the genes and the noncoding DNA, as well as mitochondrial DNA and chloroplast DNA.

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22
Q

What is genomics?

A

The study of sets of genes in one or more species

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23
Q

What is proteomics?

A

The study of whole sets of proteins and their properties

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24
Q

What is a proteome?

A

The entire set of proteins expressed by a given cell, tissue, or organ

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25
Q

What was the human genome sequencing project??

A

The Genome Project was an international scientific research project with the goal of determining the sequence of nucleotide base pairs that make up human DNA, and of identifying and mapping all of the genes of the human genome from both a physical and a functional standpoint. (1990 – 2003) (estimated cost $2-3 billion (2003) )

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26
Q

If the mendelian disorder is autosomal dominant, with an affected parent and a non affected, what percentage of the children have the disease?

A

On average 50% of children are affected with the disease and 50% are unaffected
Dn + nn
Dn, nn, Dn, nn

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27
Q

If the mendelian disorder is autosomal recessive, with two parents who are carries, what percentage of the children will have the disease?

A

On average 25% of children are normal, 50% are
carriers and 25% are affected with the disease
Nd + Nd
NN, Nd, Nd, dd

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28
Q

Why are RNA messengers important?

A

Important for the expression of genes of each cell type

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29
Q

What is x- linked inheritance?

A

LOOOK AT LC FLASHCARDS

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30
Q

How can dominant diseases be dealt with to (intervene)?

A

Dominant diseases: The strategy may require suppression of expression of the mutant gene (& thereby the mutant protein)

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31
Q

How can recessive diseases be dealt with (intervene) ?

A

Recessive diseases: The strategy involves supply of the wild type / normal copy of the gene to supply the wild type protein Gene Replacement - see video LCA (vision loss - RPE65 gene)

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32
Q

How does knowledge of the underlying genetic basis of a condition enables the development of designer therapies?

A

Because they are targeted towards the cause of the disease, as opposed to the somewhat random approach (serendipity) at times used to develop drugs in the past. Knowledge of the cause of a genetic disease together with a method to get the normal gene into the target cell type represents a powerful therapeutic approach for many genetic disorders.

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33
Q

What is Leber Congenital Amaurosis (LCA), what causes it and how was it treated?

A

It is an autosomal recessive eye disorder. The RPE65 gene is one of the causes of LCA which encodes an important enzyme involved in regenerating light sensitive molecules in the retina. the patient is injected in one eye with a virus (AAV) that carries the normal gene (RPE65 gene).

34
Q

What applications does genetics have relating to human health?

A
  1. Production of safer vaccines: recombinant single subunit vaccines e.g. hepatitis B vaccine
  2. Production of recombinant human “therapeutic” proteins e.g. insulin, growth hormone, clot dissolving proteins
  3. Inherited disorders can be diagnosed prenatally
  4. Prenatal genotyping – in vitro fertilisation & pre implantation diagnosis
  5. Pharmacogenomics: using genomics to genotype populations & individuals for alleles that determine responsiveness to drug therapies
35
Q

Research is on-going into understanding differences in drug response that exist between patients, what is this known as?

A

Pharmacogenomics.

36
Q

What genes influence drug response?

A

In liver & intestine a large number of genes are expressed into drug metabolising enzymes (DMEs). Allelic variants of the genes encoding DMEs exist in human populations resulting in heritable differences in DMEs between people. These genetic variants are in part responsible for the differences between people in response to drugs including chemotherapeutics, immuno-suppressants, anti-depressants, pain killers etc.

37
Q

Give an example of a DME

A

TPMT is a DME that is involved in the metabolism of chemotherapeutic drugs. Homozygotes can experience extreme toxicity to chemotherapeutic drugs which can at times be fatal.

38
Q

What is a DME?

A

They are drug metabolising enzymes

39
Q

What is the purpose of pharmcogenomics?

A

Pharmcogenomics should enable the identification of such people who may die prior to adminstering a drug thereby prevention such adverse events.

40
Q

What enzyme metabolises codeine and what is it influenced by?

A

The prodrug codeine is metabolised to the active drug morphine by an enzyme termed CYP2D6 (involving O-demethylation of codeine into morphine). Plasma morphine concentrations in patients after codeine administration is influenced by genotype at CYP2D6 (with almost no morphine present in some poor metabolisers).

41
Q

What happens if CYP2D6 are poor metabolisers?

A

CYP2D6 poor metabolisers encode either dysfunctional or partially inactive CYP2D6 enzyme due to variants in the CYP2D6 gene - approximately 10% of Caucasians. In such individuals codeine may be an ineffective analgesic as the active drug is not formed or is formed at low levels. For patients reporting lack of pain relief from analgesics based on codeine, in many cases it may be that CYP2D6 genotype is responsible.

42
Q

Where can you find Codeine?

A

Codeine is an active ingredient in a lot of non-prescription analgesic medications, e.g. Solpadeine etc

43
Q

What is genetics?

A

The study of inheritance

44
Q

What is inheritance?

A

The flow of biological information from one generation to the next

45
Q

The biological information which flows from one generation to the next consists of what?

A

info on :
How to construct a living organism
How the organism’s physical characteristics are determined

46
Q

Mendel studied 7 traits, what were they?

A 
Flower color
Flower position
Seed color
Seed texture
Pod texture
Pod color
Plant height
47
Q

Why was Mendel’s experiment strategy successful?

A
  1. Chose an organism that is known to “breed true” i.e. when crossed with itself it gives only offspring that are the same as itself
  2. Choice of experimental organism: pea (Pisum sativum) Why?
    a. Many physically distinct varieties available
    b. Varieties with alternative forms of a given trait
  3. He investigated the inheritance of only one or two traits at a time
  4. He kept accurate quantitative data about:
    (a) how many different types of offspring were obtained from a cross
    (b) the frequency of occurrence of the various types
48
Q

What is a monohybrid cross?

A

Inheritance of a single trait

49
Q

In mendels first experiment, he crossed a purple flower with a white flower and what did he notice?

A

Parental generation P1 P2
purple X white

F1 offspring generation all purple
Let F1 plants self-fertilize = F1 X F1
F2 offspring generation purple: 705
white: 224
Ratio: purple : white = 3 : 1
F1 offspring show one parent’s phenotype only said to be the DOMINANT phenotype
F2 reappearance of the second phenotype called the RECESSIVE phenotype
Ratio of DOMINANT : RECESSIVE = 3 : 1

50
Q

What was Mendel’s explanation for his first experiment?

A
  1. Each trait is determined by a pair of unit factors which we now call genes. Why a pair? Because each parent supplies one
  2. There are two alternative forms = alleles of each gene that determines a given trait: a dominant allele a recessive allele
  3. The two alleles segregate randomly during gamete formation i.e. the male and female gametes each contain one allele. This is known as Mendel’s “law of segregation”
  4. During fertilization, when an egg cell fuses with a sperm cell, the resulting zygote contains one allele from each parent
  5. Since there are two alleles of each gene, there are three ways in which pairs of allele can be combined e.g. Flower colour: Dominant P allele + Recessive p allele
51
Q

What are alleles and what do they do??

A

Alternative versions of a gene are termed alleles.

They account for variations in inherited characters.

52
Q

What is a homozygote?

A

An organism with two identical alleles for a character is called a homozygote. It is said to be homozygous for the gene controlling that character.

53
Q

What is a heterozygote?

A

An organism with two different alleles for a gene is a heterozygote and is said to be heterozygous for the gene controlling that character. Unlike homozygotes, heterozygotes are not true-breeding.

54
Q

Why do we distinguish between an organisms genotype and phenotype?

A

An organism’s traits do not always reveal its genetic composition. Therefore, we distinguish between an organism’s phenotype, or physical appearance, and its genotype, or genetic makeup.
In the example of flower color in pea plants, PP and Pp plants have the same phenotype (purple) but different genotypes

55
Q

What is Mendel’s model?

A
  • Alternative versions of genes account for variation in inherited characteristics
  • For each character, an organism inherits two copies (two alleles) of a gene, one from each parent
  • If the two alleles at a locus (gene) differ then:
    a. the dominant allele determines the organism’s appearance
    b. the recessive allele has no noticeable effect on the organism’s appearance
  • The Law of Segregation: the two alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes
56
Q

If the two alleles at a locus (gene) differ then, what happens?

A

a. the dominant allele determines the organism’s appearance

b. the recessive allele has no noticeable effect on the organism’s appearance

57
Q

What is Mendel’s law of Segregation?

A

The two alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes

58
Q

How do we determine the genotype?

A

We can carry out a testcross: breeding the mystery individual with a homozygous recessive individual (because we will know its genoype, pp)
If any offspring display the recessive phenotype, the mystery parent must be heterozygous.

59
Q

What is a di-hybrid cross?

A

the study of the inheritance of two traits

60
Q

Will the inheritance of one influence the inheritance of the other? i.e. dependent or independent inheritance: which?

A

Independent inheritance

61
Q

What is the Law of Independent Assortment?

A
  • Mendel identified his second law of inheritance by following two characters at the same time
  • Crossing two true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters
  • A dihybrid cross, a cross between F1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independently
62
Q

Inheritance patterns can be more complex than predicted by simple Mendelian genetics, how?

A
  • The relationship between genotype and phenotype at times is not as simple as in the pea plant characters Mendel studied.
  • Many heritable characters are not determined by only one gene with two alleles
  • However, the basic principles of segregation and independent assortment apply even to more complex patterns of inheritance
  • Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations:
    When alleles are not completely dominant or recessive
    When a gene has more than two alleles
    When a gene produces multiple phenotypes
63
Q

How does inheritance of characters by a single gene deviate from simple Mendelian patterns?

A
  • When alleles are not completely dominant or recessive
  • When a gene has more than two alleles
  • When a gene produces multiple phenotypes
64
Q

What are the three degrees of dominance?

A

1) Complete Dominance
2) Incomplete Dominance
3) Co-dominance

65
Q

What is complete dominance?

A

Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical

66
Q

What is incomplete dominance?

A

In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

67
Q

What is co-dominance?

A

In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways

68
Q

Most genes exist in populations in more than two allelic forms, give an example

A

The Collective Set of Alleles in a Population Is Its Gene Pool.
Example : The four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme that attaches A or B carbohydrates to red blood cells: IA, IB, and I
The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither

69
Q

What is pleiotropy and give an example?

A

Most genes have multiple phenotype effects, a property termed pleiotropy
This feature particularly obvious for syndromic diseases where a mutation in one gene can cause defects in multiple tissues. For example, Usher syndrome (hearing and vision loss), Bardet Biedl syndrome (mental retardation, vision loss and polydactyly & others.

70
Q

What is cell division involving somatic cells?

A

Mitosis

71
Q

What is cell division involving gametes (egg & sperm cells)?

A

Meiosis

72
Q

How is crossing over during the Meiosis (during gamete formation) central to genetics?

A

It is central to the concepts of linkage and recombination. Recombination/crossing over is one of the key concepts in genome mapping including mapping human disease genes.
Crossing over in essence results in some random shuffling of genetic material during the process of gamete formation.

73
Q

Describe crossing over in meiosis

A

A process in genetics by which the two chromosomes of a homologous pair exchange equal segments with each other. During prophase I, homologous chromosomes pair up with each other. This pairing involves the synaptonemal complex (a protein scaffold)
that joins the homologous chromosomes along their lengths. Cohesin crosslinking occurs between the homologous chromosomes & helps them resist being pulled apart until anaphase.

74
Q

What is chiasma?

A

a point at which paired chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands.

75
Q

Give an example of how crossing over in meiosis lead to localising a gene?

A 
Retinitis Pigmentosa (RP) – dominantly inherited eye disease
Cause: Rhodopsin gene on chromosome 3q
etc..
76
Q

How was it first established that genes are located on Chromosomes?

A
  • Cytologists worked out the process of mitosis in 1875 & meiosis in the 1890s using improved techniques of microscopy.
  • In the early 20th century, biologists realised that chromosomes behaved just like the hypothetical “unit factors” proposed by Mendel to explain inheritance.
  • Around 1902, Sutton and Boveri and others independently noted these parallels and began to develop the chromosome theory of inheritance
  • they occur in pairs in diploid cells
  • their number is halved during gamete formation
  • fertilisation restores the diploid number
    They eventually proved that genetic information (genes) is located on the chromosomes
77
Q

When Mendel Studied the 7 traits, what did the observe with the ratios?

A

He observed the following ratios in the offspring
1. Monohybrid cross (inheritance of a single trait)
3 : 1 (dominant : recessive)
2. Dihybrid cross (inheritance of two traits)
9 : 3 : 3 : 1

78
Q

Is “independent assortment” always the case?

A

No, it depends on whether the genes are linked or not

(a) Genes located on different chromosomes are NOT linked. This allows independent assortment -in a di-hybrid cross the traits show the classic 9:3:3:1 inheritance pattern
(b) Genes that are located very close together on the same chromosome may show complete linkage. They may be so close to each other that they cannot be separated by recombination (crossing-over) during meiosis
(c) Genes located far apart on the same chromosome typically show incomplete (partial) linkage because they are easily separated by recombination (crossing-over)

79
Q

What is linkage?

A

Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. All of the genes on a given chromosome are said to be linked or to belong to the same linkage group

80
Q

if 2 genes are located on the same chromosome, how will they be inherited?

A

They will tend to be inherited together whereas genes located on different chromosomes will show independent inheritance.

81
Q

What makes fruit flies a convenient organism for genetic studies?

A

They produce many offspring
A generation can be bred every two weeks
They have only four pairs of chromosomes

82
Q

How did morgan show that chromosomes are the location of Mendel’s heritable factors?

A
  • Morgan chose to study Drosophila melanogaster, a common species of fruit fly.
  • Thomas Hunt Morgan noted that wild type, or normal, phenotypes that were common in the fly populations
    Traits alternative to the wild type are called mutant phenotype. The first mutant Morgan discovered was a fly with white eyes instead of the wild-type red eyes
  • Aroused by curiosity, he bred the fly with normal (red-eyed) females. All of the offspring (F1) were red-eyed. Brother–sister matings among the F1 generation produced a second generation (F2) with some white-eyed flies, all of which were males. To explain this curious phenomenon, Morgan developed the hypothesis of sex-limited—today called sex-linked—characters, which he postulated were part of the X-chromosome of females.
    Because all the sex-linked characters were usually inherited together, Morgan became convinced that the X-chromosome carried a number of discrete hereditary units, or factors.

Genetics (1 decks)

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