1- Cells and Contents Flashcards
What is the definition of the Karyotype?
Number and appearance of chromosomes in a cell. Arranged in size order, largest is pair 1 with the smallest pair 22.
What is the purpose of mitosis
Replace dead cells, growth and to produce two genetically identical daughter cells.
Repair
What stage of the cell cycle are cells that are not diving found in?
G0 phase
What occurs in the G1 growth phase of the cell cycle?
Rapid growth
Organelle production
Protein synthesis: including spindle formation
Normal metabolic function
What occurs in the synthesis stage of the cell cycle?
DNA replication
Centromere replication
Histone proteins double- 2x DNA at the end of the S phase.
What occurs during the G2 growth phase of the cell cycle?
Chromosomes condense (coil up and become visible). Energy stores accumulate Mitochondria and centrioles double
Checks for mutations that are a risk in S phase
What are the stages of mitosis ?
Interphase Prophase Prometaphase Metaphase Anaphase Telophase
What occurs during interphase?
DNA and centrosome replication occurs, producing identical sister chromatids.
Lasts between 16 and 24 hrs
What occurs during prophase?
Chromatin condenses into chromosomes and mitosis spindle is formed.
Centrioles (centrioles) move to opposite poles of the nucleus.
Nuclear membrane begins to break down
What occurs during premetaphase
Nuclear membrane completely breaks down, releasing chromosomes into the cytoplasm (no nucleus present).
What occurs during metaphase?
Chromosomes line up along the equatorial plate (metaphase plate) of the cell.
Spindles attach to centromeres
What occurs during anaphase?
Centromerers split separating sister chromatids- they are pulled to opposite poles of the cell as the spindle fibres contract towards nuclear poles.
What occurs during telophase?
Cytokinesis
Chromosomes unfold into chromatin
Nuclear membrane forms
Organelles become evenly distributed around each nucleus
Cell divides producing two genetically identical daughter cells (2N)
46 chromosomes in each.
How would a nucleus appear on a histological slide if the cell was undergoing mitosis?
Dark- the chromatids have condensed into chromosomes
Nuclei would not be the same size
What is an indication that a tumour is malignant and not benign?
Increase in the number of mitotic divisions
Number of mitotic figures is used to determine severity of the cancer: more there is, the worse is it.
What are the key differences between mitosis and meiosis?
Only occurs in gametes
Two divisions
Produces 4 haploid daughter cells
Recombination of genetic material produces diversity
Produces 4 genetically different daughter cells
It is NOT cycle process: there is a start and finish
What are the stages of meiosis?
Meiosis 1
Meiosis II
Each can be seen to have a prophase, metaphase, anaphase and telophase
What occurs during meiosis I?
Prophase 1- crossing over occurs
Metaphase 1- random assortment occurs as chromosomes align at the equatorial plate
After this initial meiosis I division two daughter cells are produced with 2N number of chromosomes
What occurs during meiosis II?
Cells divide again producing 4 haploid daughter cells
What is gametogenesis?
Process in which preecursor cells undergo divisions and differentiate to form haploid gametes
In oogenesis when do oogonia enter prophase of meiosis I?
Eggs begin as premordia cells before undergoing 20-30 mitotic divisions too form oogonia
Following the formation of oogonia they enter prophase of meiosis I by the 8th month of intrauterine life
The meiosis process is then suspended
In oogenesis when is meiosis I completed and when does meiosis II commence?
Meiosis I is completed at ovulation forming a secondary oocyte (this receives most of the cytoplasm making it a big cell)
The other small cell is termed a polar body
Meiosis II is completed at fertilisation: this forms 3 polar bodies and one egg
During spermatogenesis when do meiotic divisions commence?
Primordial cells undergo around 30 mitotic divisions forming spermatogonia
Meiotic divisions do not commence until puberty
What are the stages of spermatogenesis?
Primary spermatocytes enter meiosis 1 emerging as haploid secondary spermatocytes
These undergo second meiotic divisions to form spermatids which develop into mature spermatozoa
Definition of non disjunction
Failure of chromosome pairs to separate in meiosis I or sister chromatids to separate in meiosis II
What is gonadal mosaicism? I
When precursor germ line cells to ova or spermatozoa are a mixture of two or more genetically different cell lines (one is mutated the other is not)- certain sperm cells will be mutated
Individual is not affected as mutation not in somatic cells- however all gametes from mutated germ line is affected.
When does risk of gonadal mosaicism increase?
With increasing paternal age- more time for mutations
What does mitosis produce
2 diploid daughter cells that are genetically identical to parent cell.
What phases of the cell cycle make up interphase?
G1, S and G2
What is meiosis used for?
Production of gametes
What does meiosis produce?
4 haploid daughter cells genetically different to the parent cell
How is genetic diversity produced in meiosis I?
Prophase I- crossing over
Metaphase I- random assortment
What is a multifactorial disease?
Disease due to genetic and environmental factors (e.g schizophrenia and diabetes).
An individual may have a genetic predisposition but am adverse environmental trigger is required for onset.
Definition of genotype
Genetic constitution of an individual
Definition of phenotype
Appearance of an individual (physical, biochemical and physiological) which results from interaction of genotype with the environment.
Definition of allele
One of several alternative forms of a gene at a specific loci.
What is the longest phase of the cell cycle?
Interphase
What is the most common inheritance pattern for gonadal mosaicism?
X-linked or autosomal dominant
It’s more common in males
What conditions is gonadal mosaicism observed in?
Osteogenesis imperfecta and duchenne muscular dystrophy
Definition of locus
Position of gene/ DNA on the genetic map
What is a wild type allele?
Non mutagenic alleles are termed wild types whilst pathogenic mutations / variants are carried on disease alleles
What is consanguinity ?
Reproductive union between 2 relatives: descended from the same ancestor.
Definitions of homozygous, heterozygous and hemizygous.
Homozygous: both alleles of a gene at a particular loci are the same.
Heterozygous: both alleles of the same gene at a particular loci are different
Hemizygous: only one allele of a gene is present at a particular locus.
What are polymorphisms?
Frequent hereditary variations at a particular locus- they do not cause problems, the mutations do.
They can make you more / less efficient or more / less susceptible to a disease.
Define autozygosity
Homozygous by descent
Inheritance of the same mutant allele through two branches of the same family
Define penetrance
Proportion of people with a particular gene / genotype that show the expected phenotype.
Difference between complete and incomplete
Complete: gene / genes for a trait are expressed in all the population.
Incomplete: genetic trait is only expressed in parts of the population.
Definition of variable expression
Variation in clinical features (type and severity) between individuals with the same gene alteration.
Define sex limitation
Expression of a particular characteristic is limited to one of the sexes.
Term for a condition that manifested at birth
Congenital
What is KNudson’s two hot hypothesis?
Gene mutations can be inherited OR acquired during a person’s life
- sporadic cancers: 2 acquired mutations
- hereditary cancers: 1 inherited and 1 acquired mutation
4 examples of genetically inherited diseases
Down’s syndrome- non dysfunction chromosome 21
Cystic fibrosis
Huntington disease
Haemophilia
Individually rare but cumulatively enough to have genetic services
4 examples of multifactorial diseases
Spina bifida
Cleft lip
Diabetes
Schizophrenia
Main cause of disease in developed countries
4 environmental causes of disease?
Poor diet
Infection
Drugs
Accidents
Main cause of disease in third world countries and A&E
What are the two Mendelian forms of inheritance?
Autosomal vs sex linked
Dominant vs recessive
Give the typical features of autosomal recessive inheritance
- Occurs in homozygous state (two copies of recessive allele must be present)
- Affects males and females equally
- If two parents are carries = 25% chance offspring will have disease and 50% chance they will be carriers.
- Calculations at conception: healthy siblings have 2/3 chance of being carriers
- Affected individuals in a single generation
- Parents can be related e.g consanguineous (recessive conditions most common in these types of families.
When calculating risk probabilities of offspring, the affected child in disregarded.
Give an example of an autosomal recessive condition
Cystic fibrosis:
- most common autosomal recessive condition affecting white males in the UK
- incidence of 1 in 25,000
- Population carrier frequency is 1 in 25
Definition of expressivity
Range of phenotypes expressed by a specific genotype
Definition of anticipation
Where a genetic disorder affects successive generations earlier or more severely.
Give the key features of autosomal dominant inheritance
- Disease that manifests in heterozygous state
- Affects males and females in equal proportions
- Affected individuals in multiple generations
- ONLY WAY TO PASS DISEASE FROM MALE TO MALE
- 50% chance of offspring having the condition
- Can appears to skip a generation but this is due to penetrance and variable expression
- Example: Huntington’s disease
Give the key features of X-linked inheritance
- Caused by a mutation on the X chromosome
- Usually affects females more than males
- Affected males cannot pass mutation to son, all daughters of affected males are carries.
- Males cannot be carriers
- Usually inherited from unaffected mothers
- X-linked dominant condition: Alports syndrome
- X-linked recessive condition: Duchenne muscular dystrophy
Define lyonisation
Process of X chromosome Inactivation
One of the 2 X chromosomes in randomly inactivated in early embryonic development
The X chromosome is inactivated to prevent women having twice as many gene products from the X chromosome as males
Only functional copy of the X chromosome
What is an ideogram
A diagrammatic form of chromosome bands
The bands are numbered according to their distance from the centromere
What is Mendel’s second law?
- Law of independent assortment
- Alleles of one gene sort into gametes independently of alleles of another gene.
Would an X-linked dominant condition be more common in males or females?
They occur twice as frequently in females as they do males.
Is an x-linked recessive condition more common in males or females?
Males
Define sex limitation
Both sexes have a particular gene but it’s expression is limited to only one of the sexes
Which parent is all our mitochondrial DNA inherited?
Mother
Stages in the production of a thin cell microscope slide
- Tissue fixed in formalin
- Samples embedded in paraffin
- Fine slices mounted on microscope slide
What does H&E stain
Haematoxyoin- stains nuclie and other acidic substances blue
Eosin- stains cytoplasm and extra cellular fibres pink
Used of periodic acid schiff
Stains sugars magenta !
Use of van giesan stain?
Stains elastic tissue brown !
Use of trichrome stain?
To stain 3 different types of cell 3 different colours all within the same section
Most common = Masson’s trichrome
Use of Alcian blue stain?
Stains mucins blue
