chapter 5 - beyond mendel's laws Flashcards
3 general phenomena that seem to be exceptions to mendel’s laws but actually are not
gene expression, mitochondrial inheritance, and linkage
lethal alleles
causes death before the individual can reproduce
multiple alleles
individual carries 2 alleles for each autosomal gene
different allele combinations can produce ____ in the phenotype
variations
what is a compound heterozygote
individual with 2 different mutant recessive alleles for the same gene
what is a common example of a compound heterozygote?
cystic fibrosis, there are more than 1700 variants known in the CTFR gene with various symptoms
incomplete dominance
there is a heterozygous phenotype that is an intermediate of 2 homozygous phenotypes
codominance
a heterozygous phenotype results from the expression of both alleles
epistasis
phenomenon where one gene affects the expression of a second gene, also called modifier genes
bombay phenotype
individual was discovered with blood type that reacted to other blood types not seen before. contained antibodies that reacted with all red blood cells from normal ABO phenotypes, but the individual’s red blood cells lacked all the ABO group antigens
without ______, the A or B antigens cannot be attached to the surface of the red blood cell
H protein
penetrance
all or none expression of a single gene
expressivity
severity or extent of a phenotype
huntington dz
nearly complete penetrance, almost all who inherit the dominant mutant allele will develop HD
genotype is _______ _______ if some individuals do not express the phenotype
incompletely penetrant
pleiotropy
phenomenon where 1 gene controls several functions or has more than 1 effect
why can pleiotropy be difficult to trace through families?
people with different subsets of symptoms may seem to have different diseases
genetic heterogeneity
different genes can produce identical phenotypes
how does genetic heterogeneity come about
genes may encode enzymes that catalyze the same biochemical pathway, or different proteins that are part of the pathway
examples of genetic heterogeneity
osteogenesis imperfecta, retinal dystrophies
what are retinal dystrophies
mutations in more than 270 genes whose protein products cause blindness. it disrupts the functioning of the rods in the retina and the retinal pigment epithelium that cleans up debris
phenocopy
trait that appears inherited but is actually caused by the environment
examples of phenocopy include
exposure to teratogens - thalidomide causes limb defects similar to inherited phocomelia and infection - AIDS can be passed from mother to child, looking like it’s inherited
example of lethal allele
achondroplasia
example of multiple alleles
cystic fibrosis
example of incomplete dominance
familial hypercholersterolemia
example of codominance
ABO blood types
example of pleiotropy
marfan syndrome
what is marfan syndrom
a defect in elastic connective tissue - fibrillin. symptoms include lens dislocation, long limbs, spindly fingers, caved in chest, weakening in aorta
what is a mitochondrion
an organelle that provides cellular energy
what DNA does the mitochondrion contain?
mtDNA
how many genes does mtDNA contain?
37 genes
mitochondrial genes are _____ inherited
maternally
mtDNA does not ____
cross over
mtDNA mutates _____ than DNA in the nucleus. why?
faster; there are less DNA repair radicals produced in the energy rxns
mitochondrial genes are not interrupted by DNA sequences that do not encode _____
protein
mitochondria with different ____ for the same gene can reside in the same cell
alleles
what proteins do mitochondrial genes encode?
those involved in protein synthesis and energy production
examples of diseases due to mutations in mtDNA
mitochondrial myopathies, leber optical atrophy
what is mitochondrial myopathies
weak and flaccid muscles
what is eber optical atrophy
impaired vision
how can a woman with a mitochondrial disease avoid transmitting it to her children?
if her mitochondria can be replaced with a healthy mitochondria from a donor
genes that are close to the same chromosome are _____
linked
linked genes do not _____ _________ in meiosis
assort independently
how are linked genes inherited?
inherited together when the chromosome is packaged into a gamete
linked genes do not produce typical _______ ____
mendelian ratios
what is recombination
when chromosomes recombine during crossing over in prophase 1 of meiosis
what does recombination create
new combinations of alleles
what is the difference between parental chromosomes and recombinant chromosomes?
parental have the original configuration, recombinant have the new combinations of alleles
cis
two dominant or two recessive alleles are on each chromosomes
trans
one dominant and one recessive allele are on each chromosome
correlation between cross over frequency and gene distance is used to construct ______ ____
linkage maps
frequency of a crossover between any 2 linked genes is inferred from _______________________
the proportion of offspring from a cross that are recombinant
what is frequency of recombination based on?
the percentage of meiotic divisions that break the linkage between 2 parental alleles
frequency of recombination is proportional to the _____ of the 2 genes recombining
distance
the probability that genes on opposite ends of a chromosome cross over is about
50%
linkage map
a diagram indicating the relative distance between genes
1% recombination = 1 map unit =
1 centimorgan
what is linkage disequilibrium
nonrandom association between DNA sequences. they are inherited more often than would be predicted from their frequency
human genome consists of many LD blocks where alleles ____ together
stick
halpotypes
LD blocks
what are haplotypes used to track?
genes in populations
nail-patella syndrome
rare autosomal dominant disease that cause underdeveloped nails and painful arthritis in knee and elbow joints
genetic marker
dna sequences that serve as landmarks near genes of interest, do not need to encode proteins that cause a phenotype. the sequence also alters where a dna cutting enzyme cuts; can be differing numbers of short repeated sequences of DNA with no obvious function. single sites where the base varies among individuals
LOD score
logarithm of the odds; indicates tightness of linkage between a genetic marker and a gene of interest
what score of LOD signifies linkage
3 or higher
what does the LOD score provide?
likelihood that particular cross over frequency data suggests linkage rather than inheritance by chance
observed data are _____ times more likely to be due to a linkage than chance
1000
haplotype
groups of linked genes that are always inherited together and not separated by crossing over. disruptions of a marker sequence indicate cross over sites
