Genetics, Cogenital Anomalies And Prematurity Flashcards
Chromosomes
Chromosomes contain deoxyribonucleic acid or DNA which holds the genetic information in chromosomes
Every somatic cell in the body contains 23 pairs of chromosomes = diploid cells
Hamsters contain 23 single chromosomes = haploid cells
22 pairs of chromosomes are autosomes (1 to 22) and 1 pairs are the sex chromosomes (XY or XX)
Karyotype
Is a test that identifies the size, standing and number of chromosomes in the body cells
X and Y chromosome means it’s a boy
Chromosome
Gene locus
P arm ( short arm )
Centromere
Homozygous gene pair
Heterozygous gene pair
Q arm ( long arm )
Deoxyribonucleic acid (DNA)
Chromosomes have a folded double helix structure and are located in the nucleus
The double helix holds a linear sequence of information in the form of base pairs
Bases on one strand compliment the bases on the other DNA strand
- adenine : thymine (A-T, T-A)
- cytosine : guanine (C-G, G-C)
Together our chromosomes contain 3 billion DNA bases
Mitochondria contains a small amount of DNA
DNA deoxyribonucleic acid
Alternating pentode sugar phosphate groups
Base pairs (A-G)
Cell
Nucleus
Supercooled DNA
Histones
Chromosomes are only visible when the cells are preparing to divide
What is a gene
A gene is a region of DNA that holds information that codes for a protein
DNA is a linear sequence of bases and a protein is a linear sequence-of amino acid
The correspondence between 3 base pairs and on amino acid is what is called the genetic code
From gene to protein
DNA is transcribed into RNA
RNA exits the nucleus
At a ribosome in the cytoplasm the DNA is translated into a protein
I.e DNA makes RNA and RNA makes protein
If there is a maturation in the DNA, the protein is either not made or the protein is abnormal - this is the basis of genetic diseases
Transcription of RNA from DNA
S
Proteins are folded linear molecules
Proteins are made up of one or more polypeptide molecules
Polypeptides are chains of amino acids
Functional proteins eg enzymes, hormones, haemoglobin
Structural proteins eg collagen, cytoskeleton
The human genome
Sequences in total in 2002
20000 protein coding genes per somatic cell
99.9% DNA bases identical in humans
Protein producing genes which account for about 1.5% of the genome
The rest of the DNA is associated with a number of functions but much is its functions is yet to be determined
Genetic terminology
Genotype : the genetic make up of a person
Phenotype : the physical characteristics, as determined by the genotype, eg blue eyes, dark hair, features that present as in a genetic disease
Pedigree: family tree detailing ages, sexes and disease history; aids prediction of how current or future individuals may be affected
Genetic terminology
Signal gene or monogenean can disorders
- autosomal dominant
- autosomal recessive
- x linked recessive
- Y linked
- mitochondrial
Polygenic disorders
Multifactorial disorders
Genetic terminology
Heterozygous: a genotype with 2 different forms of a gene for example one normal one mutated
Homozygous a genotype with 2 identical forms of the gene for example both normal or both mutated
Penetrant was is a term used to describe the percentage chance of someone with the mutation actually developing the disease for example familial breast cancer due to mutations in the BRCA1 gene, females with a mutation in this gene have an 80% lifetime risk of developing breast cancer
Genetic terminology
Aneuplody is where there are an abnormal number of chromosomes, examples of these are
Monosomy is where there is one chromosome instead of two for example turners syndrome
Trisomy is where there are three chromosomes instead of two for example trisomy 21 Down’s syndrome
Genetic terminology
Single gene disease one mutated gene is the cause of disease Ed sickle cell diseases CF
Polygenic disease Several mutated genes are the cause of the disease for example diabetes
Multifactorial disease environmental influences for example hypertension
Genetic syndrome variety of common signs and symptoms leading to the disease phenotype for example Down syndrome
Genetic terminology
Mutations : permanent changes to the genetic information in an indivisible that usually means that the protein coded for is affected
Insertion - insertion of one or more base pairs
Deletion - deletion of one or more base pairs
Substitution - the same number of base pairs, but there is a critical change in the amino acid coded for
Patterns of inheritance
Dominant conditions : one of the two genes is mutated leading to disease for example Huntingdonshire disease
Recessive conditions both genes need to be mutated for the disease to occur; if only one is mutated, the individual is called a carrier for example CF or sickle cell anaemia
Sex linked disorders: arise due to mutated genes on the sex chromosomes for example haemophilia affects males, females and usually carriers
Autosomal dominant
Require only one carrier parent of the dominant gene for child to acquire the disease
Eg
Achondroplasia
Osteogenesis imperfecta
Huntington’s disease
NB some case are new mutations
Father Hh (has one gene for Huntington’s) Mother hh (normal genes)
Hh Hh Hh hh
Autosomal recessive
Father As (carrier) Mother As (carrier)
AA As sA ss
Require two carrier parents for the child to acquire the disease
CF
Sickle cell disorders
Thalassaemia
Sex linked inheritance for example haemophilia
Father XY (unaffected) Mother XXh (carrier)
XX girl
XXh girl
XY boy
YXh boy
X linked disorders
Mutation occurs on the X chromosomes
Females are mainly carriers
Males inherit the disease
Eg duchenne muscular dystrophy, haemophilia
Gene therapy
Much promise, but limited delivery to date
Challenge is getting a gene or genes into cells and the genome of the affected individual
More potential when treating an early stage embryo
Ethical and legal issues to be considered the idea of designer babies is regularly seen in the press
Summary
Genetics is icreasiningly recon gnoses as the cause of or is contributory to illness
The function of DNA and the genome continues to be research- the holy grail is a cure for genetic diseases
It is important to have a working knowledge of genetic terminology and patterns of inheritance for clinical work
Embryonic development and congenital anomalies
Terminology
Haploid cells - containing 23 signal chromosomes (sperm and ovum)
Diploid cell - cells contains 23 pairs of chromosomes
Zygote - the diploid cell produces at conception before further cell division
Embryo - the baby during the first 2 months
Foetus- after the first 2 months and when the individual organs are identifiable
