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Classic genetics Flashcards

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1
Q

What is our genetic information stored in?

A

the chromosomes, which are composed of DNA

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2
Q

What does DNA have?

A

Exists as 2 complimentary chains of nucleotides- exist in nucelus in form of a double helix

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3
Q

What does a nucleotide contain?

A

Pentose sugar
phosphate
base- C,G,A,T

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4
Q

How are the chains joined together?

A

adjacent bases joined by hydrogen bonds.
Pentose and phosphate make up of backbone of DNA
2 chains of DNA are mirror images

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5
Q

What is in Human DNA?

A

DNA split into 46 chromosomes occuring as 23 homologous pairs

  • each chromosome are a chain of genes
  • There are 22pairs of autosomes and one pair of sex chromosomes
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6
Q

What is a gene?

A

series of nucleotides (piece of DNA) which codes for production of a particular/specific protein

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7
Q

How do bases code for amino acids?

A

coded for by a triplet codon consisting of 3 adjacent nucleotides.

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8
Q

What happens in protein synthesis?

A

Transcription- transfer the triplet codons (copied) on DNA to mRNA
mRNA - leaves nucleus
mRNA binds to ribosomes and combines with complimentary tRNA molecules (translation)/
The amino acids on adjacent tRNA molecules join to form a protein- with peptide bonds.

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9
Q

Where is DNA?

A

DNA lies within the nucleus and is closely associated with histone proteins

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10
Q

What are the non-coding DNA?

A

Introns
They do not code for our proteins
97% of our DNA

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11
Q

What are the coding DNA?

A

Exons (3% codes proteins)

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12
Q

How many genes do we have in total?

A

30,000

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13
Q

What are 2 copies of the same gene?

A

homozygous alleles

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14
Q

What are 2 copies of different genes?

A

Heterozygous alleles

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15
Q

What are the 2 genes?

A

alleles

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16
Q

What are our full genes?

A

genotype

phenotype- physical aspects expressed i.e hair colour

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17
Q

How many genes do we have for most traits?

A

2

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18
Q

Where are the genes for traits located?

A

At the same locus on homologous chromosomes

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19
Q

What do most cells have?

A

a limited life span for e.g. red blood cells = 120 days hence need to be replaced

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20
Q

Wha are the cell types which do not get replaced?

A

CNS neurons
cardiac muscle
corneal endothelial cells

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21
Q

How do most cells replicate?

A

by division

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22
Q

What happens when a parent cell divides?

A

it must pass on all its DNA to the 2 daughter cells

This is achieved by the process of MITOSIS

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23
Q

What is mitosis?

A

cell division- division of a nucleus

which makes sure each cell gets DNA

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24
Q

How can the life of most cells be expressed?

A

cell cycle

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25
Q

What are the 2 phases in the cell cycle?

A

Interphase

M-phase - cell divison (mitosis) and cytokinesis

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26
Q

What is interphase?

A 
Split into 4 phases
-G0
-G1
- S phase
G2
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27
Q

What is in G0?

A

Normal cell metabolism ocurs- duration variable

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28
Q

What is G1?

A

organelles are duplicated

  • prepares cell for replication by the multiplication of organelles
  • Cell growth and protein synthesis
    e. g centrioles replicate
  • cell gets ready to divide
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29
Q

What is the S phase?

A

DNA replicates
-DNA polymerase binds onto DNA and unzips it into 2 complementary chains
-DNA polymerase moves along the exposed chains adding complimentary nucleotides from a pool within the nuceloplasm.
Forms 2 identical strands of DNA (4 strands)

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30
Q

What is the G2 ?

A

Proteins needed for cell division are synthesised.
The cell is now ready for division.
Replication of the cytoplasm
Division of the nucleus= MITOSIS

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31
Q

What is the M phase?

A

division of nucleus

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32
Q

What is prophase?

A 
DNA condenses to chromosomes
each chromosome have 2 copies of DNA
Each copy of DNA is known as a chromatid
They are joined by a centrosome
-nuclear membrane disintegrate
-nucleolus breaks down
-2 centrioles move to opposite ends of cells
-Secrete microtubules- mitotic spindle
- Chromosome attach to mitotic spindle
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33
Q

How are chromatids joined?

A

by a centrosome

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34
Q

What happens in metaphase?

A
  • Spindle fibres form

- chromosomes arrange themselves along the equator of the cell

35
Q

what happens in anaphase?

A
  • the 2 chromatids of each chromosome split apart
  • centrosome divides
  • Spindle fibre shorten
  • mitotic spindle contracts and pulls each chromatid to opposite ends of the cell.
  • Ends of cell receives identical DNA
36
Q

what is telophase?

A

-The nuclear membrane reforms
-Chromsome elongate as chromatid uncoils
-DNA is loose
-Nucleolus forms
-Cell division occurs
opposite sides of cell start to grow together and bud off via cytokinesis forming
2 IDENTICAL DAUGHTER CELLS

37
Q

What do all cells have ?

A

contain the full genotype

cells differ as only a few genes are turned on in each cell

38
Q

In meiosis , What are most of our cells?

A

diploid- as they contain 2 copies of each chromosome

39
Q

What are gametes/sex cells?

A

haploid- contain one copy of each chromosome

40
Q

What do the 2 gametes produce?

A

a diploid- -zygote

41
Q

How is male gametes form?

A

by spermatogenesis

42
Q

How is female gametes formed?

A

eggs formed by oogenesis

43
Q

What do meiosis produce?

A

4 daughter cells

44
Q

What is the process of meiosis?

A

Goes through

  • Interphase
  • Meiosis 1- first cell division
  • Meiosis 2
45
Q

What happens in meiosis 1- prophase 1?

A 
chromosome condense
Spindle forms
Centrioles go to opposite poles of cell
Mitotic spindle secreted
Difference to mitosis- Homologous pair of chromosomes seek each other out- Synapsis
They form Tetrads
Tetrads perform crossing over
46
Q

What happens in metaphase 1?

A

homologous pair of chromosomes (Tetrad) line up in middle of cell as pair ( they are a pair and not single like in mitosis)
-maternal or paternal chromosomes arranged randomly

47
Q

What happens in anaphase 1?

A

Homologous chromsome pair (Tetrads) divide

  • Mitotic spindle contract and break down
  • Pulling 2 members of homologous chromosome to opposite poles of cell
48
Q

What happens in telophase 1?

A 
Nucelar membrane reforms
Cytokinesis occurs
Cell division occurs
Due to homologous pairs- 2 daughter cells formed have different DNA- haploid- have only 1 copy of each chromosome
- 2 ends of cell recieve different DNA
49
Q

What is interkinesis?

A

Meiosis 1 and 2 are separated by this which no DNA replication occurs.

50
Q

What is Meiosis 2?

A

Same as mitosis- exactly same.

produces 2 more daughter cells- haploid- carry half of genetic info

51
Q

What is crossing over?

A

trade genes/ bits of DNA

52
Q

What happens overall in meiosis?

A

come together to form a diploid zygote

53
Q

How does meiosis introduces a lot of genetic variability?

A

Independent assortment during metaphase 1

  • Genetic recombination during prophase 1- trade bits of DNA
  • Random fertilisation
54
Q

what is the main difference between meiosis and mitosis ?

A

. mitosis - chromosome line up singly in metaphase

. meiosis - chromosome line up in pairs so when pairs split apart two ends of cell receive different DNA.

55
Q

How can non-disjunction occur?

A

During Meiosis 1 resulting in one daughter cell having an extra chromosome (and other one less)- due to a tetrad not splitting apart.
- At the end of Meiosis 2 , some daughter cells will not contain a particular chromosome while others will have an extra copy.

56
Q

What is non-disjunction in gametes?

A

If this occurs in an egg and is fertilised by a haploid sperm, the resulting diploid zygote will have one extra copy of a chromosome.
-Fertilisation using a gamete with an extra chromosome will result in a zygote with 3 copies of that chromosome

57
Q

What is a zygote with 3 copies of that chromosome called?

A

Trisomy

58
Q

What is the most common trisomy?

A

Chromosome 21 - has 3 chromosomes (trisomy) which results in Down syndrome

59
Q

What are other trisomys?

A 
Trisomy 18 (chromosome 18)- Edwards disease
Trisomy 13- pataus disease
60
Q

What are the trisomys of the sex chromosomes?

A

also subject to non-disjunction.

  • Females may have 1 X chromsome- suffer from Turners syndrome
  • 3 X chromosomes- metafemale syndrome
  • XXY chromosome- males- Kleinfelters syndrome
61
Q

Who is the father of genetics?

A 
Gregor mendel (1822- 1884)
Austrian monk
62
Q

What are the simple assumptions?

A
  • A trait is determined by a single gene
  • A chromosomes are paired, each gene is present as 2 alleles
  • Alleles can either be dominant (D) or recessive (d)
  • When both alleles are the same (DD or dd)- the individual is homozygous for that trait
  • When the 2 alleles are different (Dd) the individual is heterozygous.
63
Q

How are diseases and normal traits be inherited?

A

by a simple dominant manner

64
Q

What is an example of a disease that is inherited?

A

Huntingtons disease- degeneration of ganglia in brain - fatal

  • Code for by dominant gene
  • Develop around 40s
65
Q

What is an example to explain the Hunington disease?

A

Punett square

  • Male is heterozygous- Hh (half dominant gene for the disease and recessive gene not for the disease)
  • Female is homozygous recessive (hh)

1/2 of offspring will inherit the disease

66
Q

How does that gene cause disease?

A

The gene undergoes a mutation then will have that negative consequence- causing the disease.

67
Q

How can genes which can cause disease be beneficial?

A

A gene that causes sickle cell anaemia also protects against malaria

68
Q

What are most diseases?

A

Recessive and hence are only expressed in the homozygous condition. (e.g hh)

69
Q

What are example for the diseases which are recessive?

A

Albinism
Cystic fibrosis

E.g if you assume that both parents are heterozygous for albinism. - they do not express the disease however are carriers.
1/4 of offspiring will be albinos (hh) (aa)
1/2 will be carriers (Aa, aA)
1/4 will not even be carriers (AA)

70
Q

Not all traits are?

A

simple dominant or recessive.

-Many show intermediate inheritance.

71
Q

What is intermediate inheritance?

What is an example of a disease inherited this way?

A

When both alleles are expressed

Sickle cell anaemia

72
Q

How is Sickle cell anaemia intermediate inheritance?

note: all autosomal inheritance

A

A single aa in one of the haemoglobin chains is abnormal.- Makes it much less effective in carrying oxygen
SS- Homozygous dominant are completely normal
ss- Homozygous recessive have severe respiratory problems as none of their haemoglobin can carry enough oxygen
Ss- heterozygous individuals produce both normal and sickled haemoglobin. They are normally symptomless, but in times of increased respiratory demand they have problems.- If excess demand- have respiratory problems- inherited in intermediate ways as both alleles are expressed.

73
Q

What are the 2 inheritances?

A

Autosomal inheritance

Sex-linked inheritance.

74
Q

What is sex-linked inheritance?

A

Females are XX
Males are XY - something on Y chromosome therefore makes them male
-The sex of the child is determined by the father
-Theoretically 50% of all children should be male

75
Q

What is the male female ratio?

A 
106 :100
by age of 18: 100:100
by age of 50 85:100
by age of 85: 50:100
100 years: 20:100
76
Q

What are the basics of the sex-linked inheritance?

A

Y chromosome is smaller than X. There is a region on the X chromosome where there is the X-linked trait (allele) whereby there is no corresponding allele on Y chromosome.
Any trait which is coded for in the X chromosome for which there is no corresponding part on the Y chromosome- It is SEX-LINKED

77
Q

What is a trait that is inherited via sex-linked inheritance?

A
  • Possession of a green sensitive visual pigment.
  • If the allele on the X chromosome is dominant (G) we have the pigment- Colour vision is normal
  • If it is a recessive (g) we do not and are red/green colour blind (deuteranopia)
78
Q

How are females and men express the genes for colour vision?

A

Female has - is heterozygous Gg- will be a carrier for denteranopia however will have normal colour vision as she has one copy of the dominant gene- ensuring she has the green pigment
Male- however he will express the trait even if he has only one copy of the recessive allele as he has no corresponding allele on the shorter Y chromosome.- Thus is more common in men - deuteranopia.

79
Q

How is a female colour blind?

A

If both her alleles are recessive- Which is rare.

80
Q

What do many traits depend on?

A

Polygenic inheritance

81
Q

What determines pheotype?

A

some genes are only expressed in environmental conditions such as (e,g the genes for freckles expressed more in sunlight).
Thus both nature (genotype) and nurture ( environment) determine phenotype.

Just having a gene doesn’t mean it will be expressed, that depends on environmental factors aswell.

82
Q

Why do some genes not have a similar function?

A

because some are controlling genes which turn other genes on and off.

83
Q

What is the point mutations?

A

An original codon (the gene)- 01C ARE ALL BAD FAT COW

Point mutation- during DNA replication, a wrong nucleotide is pulled in- now the gene is changed - one a.a is wrong- O1C ARE ALL BAD RAT COW
by a simple mistake during DNA replication in meiosis

This mutation does not have much of an effect/severe consequences

84
Q

What is the frameshift mutations?

A

More serious mutation causing severe consequenes.
-A simple insertion of one nucleotide would change our odon of 01C ARE ALL BAD FAT COW
into
A1X ARE BAL LBA DFA TCO W
-A single deletion would have the same effect
Sometimes larger pieces of DNA are involve din deletion, insertion and even inversion

Such frameshift mutations are much more serious

Biology (30 decks)

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