Classic genetics Flashcards
1
Q
What is our genetic information stored in?
A
the chromosomes, which are composed of DNA
2
Q
What does DNA have?
A
Exists as 2 complimentary chains of nucleotides- exist in nucelus in form of a double helix
3
Q
What does a nucleotide contain?
A
Pentose sugar
phosphate
base- C,G,A,T
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
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
6
Q
What is a gene?
A
series of nucleotides (piece of DNA) which codes for production of a particular/specific protein
7
Q
How do bases code for amino acids?
A
coded for by a triplet codon consisting of 3 adjacent nucleotides.
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.
9
Q
Where is DNA?
A
DNA lies within the nucleus and is closely associated with histone proteins
10
Q
What are the non-coding DNA?
A
Introns
They do not code for our proteins
97% of our DNA
11
Q
What are the coding DNA?
A
Exons (3% codes proteins)
12
Q
How many genes do we have in total?
A
30,000
13
Q
What are 2 copies of the same gene?
A
homozygous alleles
14
Q
What are 2 copies of different genes?
A
Heterozygous alleles
15
Q
What are the 2 genes?
A
alleles
16
Q
What are our full genes?
A
genotype
phenotype- physical aspects expressed i.e hair colour
17
Q
How many genes do we have for most traits?
A
2
18
Q
Where are the genes for traits located?
A
At the same locus on homologous chromosomes
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
20
Q
Wha are the cell types which do not get replaced?
A
CNS neurons
cardiac muscle
corneal endothelial cells
21
Q
How do most cells replicate?
A
by division
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
23
Q
What is mitosis?
A
cell division- division of a nucleus
which makes sure each cell gets DNA
24
Q
How can the life of most cells be expressed?
A
cell cycle
25
What are the 2 phases in the cell cycle?
Interphase
| M-phase - cell divison (mitosis) and cytokinesis
26
What is interphase?
```
Split into 4 phases
-G0
-G1
- S phase
G2
```
27
What is in G0?
Normal cell metabolism ocurs- duration variable
28
What is G1?
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
29
What is the S phase?
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)
30
What is the G2 ?
Proteins needed for cell division are synthesised.
The cell is now ready for division.
Replication of the cytoplasm
Division of the nucleus= MITOSIS
31
What is the M phase?
division of nucleus
32
What is prophase?
```
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
```
33
How are chromatids joined?
by a centrosome
34
What happens in metaphase?
- Spindle fibres form
| - chromosomes arrange themselves along the equator of the cell
35
what happens in anaphase?
- 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
what is telophase?
-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
What do all cells have ?
contain the full genotype
| cells differ as only a few genes are turned on in each cell
38
In meiosis , What are most of our cells?
diploid- as they contain 2 copies of each chromosome
39
What are gametes/sex cells?
haploid- contain one copy of each chromosome
40
What do the 2 gametes produce?
a diploid- -zygote
41
How is male gametes form?
by spermatogenesis
42
How is female gametes formed?
eggs formed by oogenesis
43
What do meiosis produce?
4 daughter cells
44
What is the process of meiosis?
Goes through
- Interphase
- Meiosis 1- first cell division
- Meiosis 2
45
What happens in meiosis 1- prophase 1?
```
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
What happens in metaphase 1?
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
What happens in anaphase 1?
Homologous chromsome pair (Tetrads) divide
- Mitotic spindle contract and break down
- Pulling 2 members of homologous chromosome to opposite poles of cell
48
What happens in telophase 1?
```
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
What is interkinesis?
Meiosis 1 and 2 are separated by this which no DNA replication occurs.
50
What is Meiosis 2?
Same as mitosis- exactly same.
| produces 2 more daughter cells- haploid- carry half of genetic info
51
What is crossing over?
trade genes/ bits of DNA
52
What happens overall in meiosis?
come together to form a diploid zygote
53
How does meiosis introduces a lot of genetic variability?
Independent assortment during metaphase 1
- Genetic recombination during prophase 1- trade bits of DNA
- Random fertilisation
54
what is the main difference between meiosis and mitosis ?
. 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
How can non-disjunction occur?
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
What is non-disjunction in gametes?
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
What is a zygote with 3 copies of that chromosome called?
Trisomy
58
What is the most common trisomy?
Chromosome 21 - has 3 chromosomes (trisomy) which results in Down syndrome
59
What are other trisomys?
```
Trisomy 18 (chromosome 18)- Edwards disease
Trisomy 13- pataus disease
```
60
What are the trisomys of the sex chromosomes?
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
Who is the father of genetics?
```
Gregor mendel (1822- 1884)
Austrian monk
```
62
What are the simple assumptions?
- 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
How are diseases and normal traits be inherited?
by a simple dominant manner
64
What is an example of a disease that is inherited?
Huntingtons disease- degeneration of ganglia in brain - fatal
- Code for by dominant gene
- Develop around 40s
65
What is an example to explain the Hunington disease?
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
How does that gene cause disease?
The gene undergoes a mutation then will have that negative consequence- causing the disease.
67
How can genes which can cause disease be beneficial?
A gene that causes sickle cell anaemia also protects against malaria
68
What are most diseases?
Recessive and hence are only expressed in the homozygous condition. (e.g hh)
69
What are example for the diseases which are recessive?
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
Not all traits are?
simple dominant or recessive.
| -Many show intermediate inheritance.
71
What is intermediate inheritance?
| What is an example of a disease inherited this way?
When both alleles are expressed
| Sickle cell anaemia
72
How is Sickle cell anaemia intermediate inheritance?
note: all autosomal inheritance
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
What are the 2 inheritances?
Autosomal inheritance
| Sex-linked inheritance.
74
What is sex-linked inheritance?
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
What is the male female ratio?
```
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
What are the basics of the sex-linked inheritance?
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
What is a trait that is inherited via sex-linked inheritance?
- 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
How are females and men express the genes for colour vision?
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
How is a female colour blind?
If both her alleles are recessive- Which is rare.
80
What do many traits depend on?
Polygenic inheritance
81
What determines pheotype?
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
Why do some genes not have a similar function?
because some are controlling genes which turn other genes on and off.
83
What is the point mutations?
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
What is the frameshift mutations?
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
