chapter 2 Flashcards
difference in DNA and RNA
DNA - each nucleotide contains a deoxyribose sugar, a phosphate group and either cytosine, guanine, adenine or thymine. forms a double helix, each strand has a 3’ end and 5’ end
A-T
C-G
RNA- each nucleotide has a ribose sugar, phosphate group and either cytosine, guanine, adenine or uracil. one strand
A-U
C-G
mRNA and codons
mRNA get genetic information from DNA and bring it to ribosomes which translate mRNA into proteins ( composed of amino acids )
a set of 3 pairs is called a codon and will translate a specific amino acid or a stop codon
human diploid cells
contains 46 chromosomes ( 22 pairs of autosomes & a pair of sex chromosomes )
they undergo mitosis and produce two identical daughter cells
except sex cells ( parent diploid cell) undergo meiosis creating 4 unique haploid daughter cells
- this is how we get genetic variation
haploid cells have 23 chromosomes total
phenotype vs genotype
observable expression is phenotype
genetic makeup is genotype; may be inferred by phenotype
cross over
can occur during meiosis
homologous chromosomes can become intertwined, and exchange genetic material; new genetic material is call recombination
this has the potential to create new phenotypes
which can be fatal or beneficial
most common blood group antigens result from a single nucleotide substitution = single- nucleotide polymorphism (SNP)
Locus & Allele
locus is the site of a gene on the chromosome
allele is one of two or more different forms of gene at specific locus on a chromosome
Antithetical
antigens that represent different forms of a gene product from the same locus are called antithetical
antithetical alleles are represented by nomenclature to indicate that.
ex. Kidd blood group has Jka & Jkb alleles which are responsible for expressing their individual antigens
dominant gene ( such as huntington’s )
anyone who inherits one copy will be impacted by it
recessive gene ( such as cystic fibrosis )
doesn’t express itself in the presence of a dominant allele; only if it is homozygous recessive will it show
can be an unaffected carrier
co-dominant
gene expresses trait regardless of which allele is at the locus
ex. Jka & Jkb will both show Jk antigens and will phenotype at JK (a+b+)
homozygous vs heterozygous expression
homozygous = same allele heterozygous = nonidentical alleles
dosage effect, controls and screening cells
some antigen systems have dosage meaning depending if it is heterozygous or homozygous it will either cause a weaker or stronger reaction
ABO doesn’t have dosage
when testing other antigen systems:
- positive controls for antisera should be heterozygous ( weaker reaction) to ensure even the weakest of expressions will be picked up by our positive control antisera
- screening cells should be homozygous ( stronger reaction) so they will pick up events smallest amounts of antibodies in someone plasma
propositus
the person whose phenotype of genotype on a pedigree chart that prompted the family study (identified by an arrow)
consanguineous mating
root cause for inheritance of very rare genes
protein vs carbohydrates antigens
DNA can directly code for a protein but not a carbohydrate
DNA will make a protein ( enzyme) that will catalyze the addition of a carbohydrate antigen to cell surface
