IMMS Flashcards
Where is DNA found?
Nucleus and Mitochondria
What is the structure of DNA?
Double helix
Complementary base pairs of A- -T and C- - -G
Could around to form nucleosomes and then again to form supercoils and then again to form chromosomes
How many chromosomes in human genome?
46 chromosomes (22 pairs of autosomes that are non sex determining and one pair of sex chromosomes -XY=male and XX=female)
What is a Karyotype?
Number and appearance of chromosomes in a cell in a chart layout. Arranged in size order from biggest to smallest with the sex pair at the end
How many base pairs and genes in a chromosome? How many genes in a human?
Each chromosome contains a continuous DNA duplex of roughly 10^7 base pairs and several hundred genes.
Humans have around 22,000 genes
What does a chromosome look like?
Has a long arm (q) and short arm (p- for petite) separated by a centromere
What is mitosis for?
Producing 2 daughter cells that are genetically identical to the parent cell. And for growth and to replace dead cells
Note: cell not in replication=chromatin, during=chromosomes and after=chromatids
What is chromatin?
Nuclear DNA and proteins
For mitosis to occur cells must be in the cell cycle from interphase. What happens at interphase and what comes after?
Interphase- longest phase
G1- rapid growth, new organelles produced and proteins synthesised for spindle formation (no visible activity)
S- DNA replication and centrosome replication
G2- chromosomes condense, coil up and become visible, energy stores accumulate and mitochondria and centrioles double
Next steps- Prophase, Prometaphase, metaphase, anaphase, telophase, cytokinesis
What happens in prophase?
Chromatin condensed into chromosomes
Centrosomes nucleate microfibres and move to opposite poles of nucleus
What happens in prometaphase?
Nuclear membrane breaks down
Microtubules invade nuclear space
Chromatids attach to microtubules
What happens in metaphase?
Chromosomes line up along the equator (metaphase plate)
What happens in anaphase?
Sister chromatids separate and are pushed to opposite poles of cell
What happens in telophase?
Nuclear membranes reform
Chromosomes unfold into chromatin
Cytokinesis begins
What is Down syndrome?
Where there is 1 extra chromosome at 21 (trisomy 21)
How can you tell a cell is undergoing mitosis in histology?
If the nucleus is dark (chromatin has condenses to form chromosomes) and nuclei are not the same size
How can you tell if cells are malignant (cancerous)?
Too many cells undergoing mitosis eg lots of dark nuclei of different sizes. The more of this is, the worse the cancer
Drugs can help stop mitosis when it is cancerous? What are these drugs and what do they do?
Stops formation of mitotic spindle: taxol and vinca alkaloids
Stops formation of spindle poles: ispinesib
Stops anaphase: colchicine-like drugs
What is meiosis?
Similar to mitosis but Only in gametes Recombination of genetic material results in genetic diversity Two cell divisions 4haploid daughter cells
Meiosis is NOT a cycle
What happens in meiosis 1?
Chromosome number halved
Prophase 1-crossing over occurs between non sister chromatids which results in genetic diversity
Metaphase 1- random assortment occurs on the metaphase plate also resulting in genetic diversity
What happens in meiosis 2?
Sister chromatids seperate and haploid cells produced
Describe what mitosis and meiosis is like in sperm production
Primordial germ cells undergo lots of mitosis to form spermatogonia
Then meiosis starts at puberty
The cytoplasm divided evenly and four equal gametes produced after meiosis 2
Millions of mature sperm continuously produced
Process takes 60-65 days
100-200 million sperm per ejaculate
Describe what happens in egg production during mitosis and meiosis
Primordial germ cell undergoes 30 mitoses to form oogonia
Oogonia enter prophase of meiosis 1 by 8 month of life
Then the process stops
Cells enter ovulation 10-50 years later
Cytoplasm divides unequally-1 egg and 3 polar bodies that apoptose
Meiosis 1 completed at ovulation
Meiosis 2 only completed if fertilisation occurs
A problem with meiosis that can occur is non-disjunction. What is it?
Failure of chromosome pairs to seperate at meiosis 1 or sister chromatids at meiosis 2
Can result in Down syndrome if non disjunction occurs at chromosome 21 resulting in trisomy 21
Likelihood of this happen increases with age of both men and women
A problem that can occur with mitosis is gonadal mosaicism. What is it?
Occurs when precursor germline cells to ova or spermatozoa are a mixture of 2 or more genetically diff cell lines due to mitosis errors
One cell line is normal and the other mutated
More likely the older the father
Parent is healthy but fetus May have genetic disease
Who is gonadal mosaicism more common for and what inheritance pattern does is most commonly happen in? What conditions can it cause?
More common in males
Can happen in any inheritance pattern but more common on autosomal dominant and x-linked
Conditions include osteogenesis imperfect and duchenne muscular dystrophy
How does meiosis allow for genetic diversity?
Crossing over in prophase 1, Independant assortment in metaphase 1 and 2
Give 4 examples of genetic diseases
Down syndrome
Cystic fibrosis
Huntington’s disease
Haemophelia
Give 4 examples of multifactorial diseases
Spina bifida, cleft lip/palate, diabetes, schizophrenia
Give 4 examples of environmental diseases
Poor diet, infection, drugs, accidents
Define genotype
Genetic constitution of an individual
Define phenotype
Appearance of an individual l physical, biochemical, physiological) which results from the interaction of the environment and the genotype
Define allele
One of several forms of a gene at a specific locus. Also known as normal alleles or wild type. Disease allele carrying a pathogenic variant.
Define polymorphism
Frequent hereditary variations at a Locus
Define homozygous
Both alleles the same at a locus
Define heterozygous
Alleles at a locus are different
Define hemizygous
Only one allies refers to a locus on an X chromosome in a male
Define autosomal dominance
Diseases which manifests in the heterozygous state. 50% of offspring have disease.
Define autosomal recessive
Disease which manifests in the homozygous state. 25% have disease and 50% are carriers
Define x linked recessive inheritance
Causes by pathogenic variants in genes on the X chromosome
