Genetics Flashcards
Alleles are
Homozygous
Heterozygous
2 genes at the same locus of homologous chromosomes
If identical
If different
Genotype
Genetic make-up of Alan organism
Phenotype
Observable characteristics of an organism - can go down to a biochem level
Karyotypes
Method of studying chromosomes - make a chromosomal squash, photograph print and pair them
Can spot extra ones such as downs - trisomy 21
Can see sex chromosomes
Sex linked inheritance
Inheritance of genes located on the x or Y chromosomes - as x is bigger most sex linked diseases are x linked e.g. Heamophilia
Autosomal inheritance
Genes located on any of the other 22 chromosomes
Mandels law of segregation
During gamete formation each member of an allelic pair segregates from the other member to form the genetic constitution of the gamete
Mandela law of independent assortment
Separate genes for separate traits are passed independently of one another from parents to offspring
Punnet squares
Diagram
Dihybrid cross
Diagram
Gene expression
DNA > (transcription}> mRNA > (translation}> proteins
Gene > control region and coding region
rRNA - ribosomal RNA
tRNA - transfer RNA carries aas in ribosomes to make proteins
Incomplete dominance
One allele for a trait not completely dominant over the other
Results in a combined phenotype e.g. Sickle cell trait (vs sickle cell anaemia)
Codominance
Both alleles independently express
E.g. ABO blood typing
I - recessive, Ia and Ib which are Codominance so proteins a and b are expressed
If antigen A is expressed so is anti-b antibodies and vice versa. If both antigens then no antibodies, if no antigens both antibodies
Polyallelic series
Only 2 alleles can be present at 1 locus of a homologous pair of chromosomes but a series of alleles may be present in a population - gene pool
Polymorphism
Various forms of an allele - formed by mutations to the genes - most favourable selected for ( Darwin)
Lethal genes
Death of organism carrying it
Usually recessive and expressed only in homozygotes
E.g. Chlorophyll production in plants
Epistasis
Recessive
Dominant
Effect of a gene is masked by one or more other genes located at different loci (vs dominance which is the interaction of genes at the SAME loci)
Recessive allele of one gene masks the effects of either allele of the second gene
Dominant allele of one gene masks the effects of either allele of the second gene
Pleiotropy
Single gene influences multiple phenotypic traits
Therefore mutation will have an effect in some/all traits simultaneously
Variable expressivity
Variability of the manifestation of a characteristic
Reduced Penetrance
Proportion of people with a particular gene mutation who exhibit signs and symptoms of a genetic disorder
If some people with the mutation do not develop features of the disorder = reduced/incomplete Penetrance
Polygenic inheritance
More than one gene controls one character
