Genetics And Genetics In Practise Flashcards
1- describe the structure of DNA
Deoxyribose (sugar)
Nucleic (nucleotides)
Acid (phosphate)
Nucleotides ate made up of 4 nitrogenous bases (A-T, C-G)
Nucleotides are joined together by sugar phosphate backbone
There are two strands of DNA held together by weak hydrogen bonds
-A and T are bonded by two hydrogen bonds
-C and G are bonded using three hydrogen bonds
1- describe the function of DNA
To store all of the genetic information that an organism needs to develop
Sequences convert to messages, messages produce proteins, proteins are complex molecules that carry out most of the work in our bodies
1- describe the structure of RNA
Ribo (sugar)
Nucleic (nucleotide)
Acid (phosphate)
Single stranded (unlike DNA which is double)
Shorter chain of nucleotides (unlike DNA which is longer)
Nucleic base pairs are different, RNA contains URACIL which pairs with Adenine- RNA hasn’t got any thymine!
1- describe the function of RNA
Involved in regulating gene expression
So the DNA contains the genetic material, which is then used to make the RNA and allow it to work with proteins carry out functions in the human body
1- describe the structure of genes
Genes are groupings of DNA
Genetic code is based on 3 base groupings called CODONS
E.g. ATT, GGC, GTA
Each codon codes for a PROTEIN
1- describe the function of genes
Each codon within a gene codes for a specific protein
This is done through a process of transcription (decoding)
Once decided they go through transcription (become a protein)
Proteins carry out jobs within the body
Full set of codons = the genetic code/genome/25,000 genes
Genes construct characteristics in humans
1- describe the structure of chromosomes
Tightly coiled strand of DNA around a histone
Cells in the body contain 46 chromosomes (23 pairs)- DIPLOID cells
Sex cells only contain 1 copy of each chromosome, they aren’t paired- HAPLOID cells
1- describe the function of chromosomes
To carry DNA
Transfer genetic information from parents to their offspring
Allow the DNA to be accurately copied
Stop the DNA from getting tangled
2- what is an allele?
A variant form of a gene
One of two versions of DNA at one genomic location
An offspring inherits two alleles, one from each parent for each genomic location
Identical alleles= homozygous
Different alleles= heterozygous
2- what is a locus?
The physical location of a specific gene or chromosome
“Humans are diploid organisms because they have two alleles at each genetic locus”
2- what is genotype?
The genetic makeup of an organism
Determines/contributes to phenotype
Represented in symbols, e.g. BB, Bb, bb
2- what is phenotype?
The observable characteristics of an individual, result from expression of genes
E.g. blue eyes, brown hair, Huntington’s disease
2- what is homozygous?
When two alleles are the same
E.g. BB, bb
2- what is heterozygous?
When two alleles are different
E.g. Bb
2- what is dominance?
When one allele of a gene, on one copy of chromosomes, overrides the impact of the other allele
2- what is co-dominance?
A type of inheritance where two versions of an allele of the same gene are fully expressed in the phenotype
E.g. flower alleles for colour gene are Rr, the flowers phenotype will be red and white!
2- what is recessive?
A trait only expressed when a genotype is homozygous, it is always masked by a dominant gene
E.g. bb
2- what are homologous chromosomes?
Pairs of matching chromosomes in an organism, where one comes from each parent
Same gene sequence, loci and length
E.g. the sex chromosomes XX are homologous (XY are not)
2- what is a mutation?
An alteration of bases in the genetic pair
The outcome is that the proteins transcribed are malformed
2- what are autosomes?
Any chromosome that is not a sex chromosome
The gene in question is located on one of the numbered, non sex chromosomes
2- what are sex chromosomes?
One pair (of the 23 pairs) of chromosomes that determine the biological sex of an individual
XX= female
XY= male
2- what is karyotype?
The whole collection of an individuals chromosomes (the whole 46 pairs)
It is used as a lab technique, we can screen an individuals karyotype and look for abnormal numbers or structure of chromosomes to diagnose genetic diseases
3- draw a punnet square to indicate the genotypic and phenotypic traits to demonstrate the inheritance of autosomal dominant traits in HUNTINGTONS
E.g. mother- Hh, father- hh
3- draw a punnet square to indicate the genotypic and phenotypic traits to demonstrate the inheritance of autosomal recessive traits in PKU
E.g. mother- Pp, father- Pp
3- draw a punnet square to indicate the genotypic and phenotypic traits to demonstrate the inheritance of sex-linked traits in HAEMOPHILIA A
E.g. mother- XhXH, father- XHY
3- what is meant by autosomal dominant (single gene) diseases? Give some examples
The more dominant gene is the abnormal gene
E.g. Huntington’s disease (HH or Hh), achondroplasia (AA or Aa)
3- what is meant by autosomal recessive (single gene) diseases? Give some examples
The abnormal gene requires two copies to cause the disorder, as it is the recessive allele that carries it
E.g. cystic fibrosis (cc), sickle cell anaemia (ss)
3- what is meant by sex-linked diseases? Give some examples of ‘X linked recessive’, X linked dominant’ and ‘Y linked’
Diseases passed down through families via one of the sex chromosomes, either X or Y chromosome
X linked recessive: haemophilia, colour blindness
X linked dominant: Fragile X syndrome
Y linked: male infertility
3- what is meant by ‘co-dominance’ inheritance? (An example of complex inheritance)
Some genes don’t show complete dominance, instead they share the phenotype between two alleles
E.g. Flower- Rr, it will be red and white in phenotype because both alleles are ad dominant as each other
3- what is meant by ‘multiple allele’ inheritance? (An example of complex inheritance)
Some genes have more than two alternate forms
E.g. ABO blood groups
3- what is meant by ‘polygenic’ inheritance? (An example of complex inheritance)
Several genes responsible for one trait
E.g. eye colour, hair colour
Diseases like cancers and heart disease are an example of this
3- what is meant by ‘multifactoral’ inheritance? An example of complex inheritance
A complex interaction of genes with the environment causes some diseases
E.g. skin cancer- sunlight and genes
4- discuss co-dominance in relation to the ABO blood group
ABO blood groups are an example of multiple allele (more than two alternate forms) and co-dominance inheritance (phenotype is shared between the alleles)
There are 4 blood types (phenotypes)
They result from 6 possible combinations (IAIA, IAi, IBIB, IBi, IAIB, ii)
Of 3 different alleles (IA, IB, i)
Of a single gene (I)
4- for the genotype IAIA or IAi, what would the phenotype be?
Blood type A
4- for the genotype IBIB or IBi, what would the phenotype be?
Blood type B
4- for the genotype IAIB, what would the phenotype be?
Blood type AB
4- for the genotype ii, what would the phenotype be?
Blood type O
4- could a mother of blood group A and a father of blood group B have a child with blood group O?
Yes, if they were both heterozygous
4- draw a punnet square to demonstrate the potential phenotype inheritance of offspring from a mother with blood group A heterozygous (IAi) and father of blood group B heterozygous (IBi)
5- briefly differentiate between chromosome, single gene, polygenic and multifactoral disorders
Chromosomal disorder-
Result from changes in the number or structure of the chromosomes
Single gene disorder-
Caused by mutations in the DNA sequence of one specific gene
Polygenic disorder-
Disorders that arise from the mutations on more than one gene
Multifactorial disorder-
Associated with the effects of multiple genes interacting with the environment
6- what is the difference between mitosis and meiosis?
MITOSIS
Occurs in all organisms (except viruses)
Creates all body cells
Involves four cell divisions
Produces two diploid daughter cells (2n)
Daughter cells are genetically identical
Creates a human cell with 46 chromosomes
MEIOSIS
Occurs only in plants, animals and fungi
Creates only sex cells
Involves two successive cell divisions
Produces four haploid daughter cells (n)
Daughter cells are genetically different
Creates a human cell with 23 chromosomes
7- what are the symbols called in a family tree? Try and draw/remember as many as you can
Pedigree symbols
8- name some antenatal screening tests used to identify genetic conditions
The NHS offers screening tests to all pregnant women in order to detect any of the five most common chromosomal disorders
This is done through a blood test where they will find three copies of a chromosome instead of two
If abnormalities are found in this test, mothers will be offered:
‘CVS’ or ‘amino’ tests which will give a definitive answer
CVS= chorionic villus sampling. Takes a sample of placental tissue to test
Amino= removing and testing a small sample of cells from amniotic fluid
Ultrasound scans are also offered at 12 and 20 weeks gestation
They show images of a baby’s body inside and out. It can’t detect genetic abnormalities but may show physical abnormalities that can indicate towards a genetic abnormality.
Unexpected findings will lead to more invasive investigations like CVS or amino screening
9- name some multifactoral genetic disorders and briefly describe them
Type 2 diabetes- Genes, low exercise, poor diet
Heart disease- Genes, smoking, fatty diet, low exercise levels, undernourishment
Depression- Genes, lack of sunlight, bereavement, unemployment, undernourishment
Multiple sclerosis- Genes, smoking, lack of sunlight, poor diet
10- what is the role of a genetic counsellor and specialist service?
Genetic counsellors work with patients in order to offer genomic information and support. This allows the patient to make better health decisions
Jobs:
Ordering and recommending genetic tests
Clarify health risks
Support and empower
Work with scientists to diagnose, manage and predict conditions
Helping patients to interpret test results
Work as an MDT (midwives, cancer teams, neurology, ophthalmology etc)
