Genetics 1.6, 3.3, 3.4, 10.1, 10.2 Flashcards
(50 cards)
1
Q
When does mitosis occur?
A
- tissue repair
- growth
- embryonic development
- asexual reproduction
2
Q
How is the cell cycle divided?
A
Interphase: G1, S, G2, *G0
Division: mitosis and meiosis
3
Q
What happens in S phase?
A
- DNA replication
- indicator for division
- 2n + c —> 2n + 2c
- chromatin = relaxed chromosome
4
Q
What happens in growth phases?
A
- G1: organelles are duplicating
- G2: cell growth + preparation for mitosis
5
Q
How do chromosomes condense?
A
- condensation needed to pack DNA
- DNA coils to make chromosomes shorter = supercooling
- around histones
6
Q
What happens at the end of G2?
A
- centrosomes (perpendicular centrioles) duplicate
7
Q
What happens in the prophase?
A
- centrosomes move to opposite sides of the cell
- mitotic spindle starts to form
- nucleus disappears
- nuclear membrane breaks down
- DNA coils (very tightly) and separates into individual chromosomes (= metaphase chromosomes)
8
Q
What happens in metaphase?
A
- microtubules attach to centromeres
- kinetochore — protein connected to microtubules (in centromere)
- sends signals when cell is ready to split
- microtubules are put under tension to test attachment
- shortening attachment
- chromosomes line at metaphase pate (cell equator)
9
Q
What happens in anaphase?
A
- centromeres divide
- microtubules shorten
- chromatids are separated and pulled to the opposite sides of the cell
10
Q
What happens in telophase?
A
- separated chromatids form a new nucleus
- nucleolus and nuclear envelope reappears
- chromosomes uncoil
Cytokinesis — cytoplasm divides
11
Q
What is mitotic index?
A
- ratio between cells undergoing mitosis and whole population
- too high indicates cancerogenesis
12
Q
What is the difference between plant and animal cell cytokinesis?
A
- cytokinesis occurs when there are 2 nuclei (telophase)
In animals - plasma membrane pulled inwards - cleavage furrow - accomplished by ring of contractile protein inside plasma membrane - pinches apart
In plants - vesicles move to the equator - fuse and form tubular structures - 2 layers of membrane formed - by exocytosis cells receives pectins
13
Q
What are cyclins?
A
- proteins that control cell cycle
- activating cyclin dependent kinase enzymes (CDK)
- different types of cyclins activating different CDKs
- right concentration of cyclins reached → cell to the next stage
- decreases cancer risk
14
Q
What are CDKs?
A
- enzymes activating proteins into the new stage of cell cycle
- phosphorylation
15
Q
How is cycle regulated?
A
- growth hormones, proteins stimulating quicker division
- checkpoints
- G1: nutrients, growth factor and DNA damage
- G2: cell size
16
Q
What are carcinogens?
A
- chemicals and agents that cause cancer
17
Q
What is a tumour?
A
- abnormal group of cells developing at any stage of life
18
Q
What are mutagens?
A
- set of genes that causes cancer → mutagens
- radiation (UV, X-ray)
- ionising nucleotides in DNA → switch into different nucleotide
- chemicals
- cigarettes ingredients (nitrosamines), metals (As, Ni)
- alcohol increases cell division
- destroys cells which have to recover = higher possibility of mutation
- viruses (HPV, HepC virus)
19
Q
What are protooncogenes and oncogenes?
A
- mutated gene may become oncogene (cancerous gene)
- stimulates cell division and inhibit cell differentiation
- oncogene = protooncogene gains potential to cause cancerogenesis
20
Q
What are different types of tumours?
A
- primary — place in which it occurred first (organs, tissue)
- metastasis = movement of cells from primary tumour to set up secondary
- metastatic tumour — moves onto different tissues (affects multiple organs)
- increased risk of mutation = cancer change
- secondary — place in which cancer develops after moving
21
Q
What is the difference between mitosis and meiosis?
A
- mitosis creates two diploid cells
- meiosis creates four haploid cells
22
Q
What is sexual and asexual reproduction?
A
- sexual = differences between offsprings and parents chromosomes
- asexual = the same chromosomes in parents and children
23
Q
What is fertilisation?
A
- union of sex cells (gametes) from 2 different parents
24
Q
What happens in prophase I?
A
- homologous chromosomes form pairs = bivalents
- before condensation
- process called synapsis
- protein structure - synaptonemal complex connects chromosomes
- crossing over
- 2 new chromosomes (mix of parent chromosomes) → genetic variety
- microtubules attach to different chromosomes (instead of chromatids)
- disjunction = separation of bivalent chromosomes
25
How do chromosomes cross over?
- in non sister chromatids junction is created
- chromatid breaks and rejoins with the non sister
- connection points called chiasmata
- later slides down the bivalent to separate chromosomes
- random, at least 1
- new allele combination are produced
- recombination
26
How are chromosomes orientated before meiosis?
- randomly
- spindle microtubules attach to each centromere
- a whole chromosome is pulled to one pole
- orientation = the way the pair of chromosomes is facing
- orientation of 1 bivalent, doesn’t affect the others
27
What are methods used to obtain cells for karyotype analysis?
- amniocentesis = passing needle through abdomen wall of a woman
- using ultrasound
- amniotic fluid taken (has fetal cells)
- chorionic villus sampling = obtaining cells through chorion (membrane from which placenta develops)
- risks of miscarriage
- 2% chorionic villus
- 1% amniocentesis
28
What creates genetic diversity?
- random orientation
- 2^23
- crossing over
- increases number of allele combinations
29
Why is fusion important?
- new life
- alleles from different individuals into one new individual
- fusion of gametes = genetic variation of species
- genetic variation essential for evolution
30
What is the law of segregation?
- one allele to every gamete (equal chances)
31
What is the law of independent assortment?
- pairs of alleles are sorted out independently
- orientation of chromosomes is random and independent
- determines which allele will move where
32
What is the principle of dominance?
There are dominant and recessive alleles
33
What is a non-disjunction?
- disjunction — the act of being disjoined or disjoining
- when non-disjunction occurs, the homologous pairs are not split
- unequal number of chromosomes
- diseases connected:
- Trisomy (3 chromosomes) 21 → Down’s syndrome
- Trisomy 18 → Edward’s syndrome
- XXY → Klinefertel’s syndrome
- X → Turner’s syndrome
- the older the parents are, the more likely is a disjunction happening
34
What was the procedure in Mendel’s experiment?
```
- reproducing plants with the same phenotype (self-pollination)
- crossing different plants
- transferring male pollen to female
- P x P —> F1
- reproducing offsprings
- F1 x F1 = F2
- observing characteristics
```
35
What are gametes and zygotes?
- fuse together to create zygote
- male gametes < female gametes
- equal contribution of mother and father
36
What are co-dominant alleles?
- both alleles have affect on phenotype
- example: M. jalapa
- red and white flower = pink
37
How are blood types distinguished?
- blood groups = co-dominance
- antigens present on red blood cells
- A = antibodies B
- alleles A and B are dominant ABO recessive
- production of glycoprotein
- A adds acetylgalactosamine
- red blood cells have antigen A
- in AB group neither antibodies are produced
- group O produces basic glycoprotein
38
Which alleles cause genetic diseases?
- mostly recessive
- one can be carrier but not ill
- some can be caused by dominant or co-dominant or sex-linked
39
What is cystic fibrosis?
- recessive genetic disease
- allele of CFTR gene
- gene product are chloride channels
- sweat, mucus
- mutation = too much NaCl in sweat and too little in mucus and digestive juices
- osmosis is not proper → viscous
- sticky mucus in lungs
40
What is Huntington’s disease?
- dominant allele disease
- mutation of HTT gene
- gene produces huntingtin
- degenerative changes in brain
- thinking, emotions problems
41
How are diseases inherited on sex-linked genes?
- Morgan in D. melanogaster (fruit fly)
- some male had white eyes (w)
- female only red-eyed (w+)
- sex-linkage because the allele is on chromosome X
42
What are examples of sex-linked diseases?
```
Red-green colour-blindness
- recessive allele of gene for a photoreceptor proteins on X chromosome
- detect wavelengths of light
- male with recessive gene → affected
- female could be a carrier
```
```
Haemophilia
- X chromosome
- inability to make Factor VIII
- proteins needed to clot blood
- life expectancy = 10 yo (if untreated)
```
43
Why are genetic diseases rare?
There’s a small likelihood that both parents will have the recessive gene and that the child will receive both e alleles.
44
What are the consequences of radiation after nuclear bombing?
- cancer
- mutations causing stillbirths, malformation and death
- stigmatisation
```
Chernobyl
- death of nature around
- thyroid gland collects iodine
- radioactive iodine causes cancer
```
45
What is gene linkage?
- genes on the same chromosome
- more likely to occur together (than if they were unlinked)
- disproves Mendelian theory
46
On what does crossing over depend?
- the closer to each other on the chromosome the 2 genes are (2 different traits), the less likely the chiasmata formed between them
- random places
- the smaller the distance the lower chance
47
What are types of genetic variations?
- discrete
- blood type
- no in between types
- discontinuous
48
What is continuous variation?
- a lot of genes affect the same trait
- number of genes increases
- distribution comes close to normal distribution
- height, intelligence
- polygenic inheritance
49
How can polygenic inheritance be influenced by environment?
- skin colour
- sunlight stimulates production of pigment melanin
- nutrition received
- in cats: temperature (colour of fur)
50
What is chi square?
- statistical test
- compares observed to expected values
