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IB 141 human genetics > chapter 5 - beyond mendel's laws > Flashcards

chapter 5 - beyond mendel's laws Flashcards

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1
Q

3 general phenomena that seem to be exceptions to mendel’s laws but actually are not

A

gene expression, mitochondrial inheritance, and linkage

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2
Q

lethal alleles

A

causes death before the individual can reproduce

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3
Q

multiple alleles

A

individual carries 2 alleles for each autosomal gene

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4
Q

different allele combinations can produce ____ in the phenotype

A

variations

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5
Q

what is a compound heterozygote

A

individual with 2 different mutant recessive alleles for the same gene

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6
Q

what is a common example of a compound heterozygote?

A

cystic fibrosis, there are more than 1700 variants known in the CTFR gene with various symptoms

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7
Q

incomplete dominance

A

there is a heterozygous phenotype that is an intermediate of 2 homozygous phenotypes

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8
Q

codominance

A

a heterozygous phenotype results from the expression of both alleles

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9
Q

epistasis

A

phenomenon where one gene affects the expression of a second gene, also called modifier genes

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10
Q

bombay phenotype

A

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

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11
Q

without ______, the A or B antigens cannot be attached to the surface of the red blood cell

A

H protein

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12
Q

penetrance

A

all or none expression of a single gene

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13
Q

expressivity

A

severity or extent of a phenotype

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14
Q

huntington dz

A

nearly complete penetrance, almost all who inherit the dominant mutant allele will develop HD

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15
Q

genotype is _______ _______ if some individuals do not express the phenotype

A

incompletely penetrant

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16
Q

pleiotropy

A

phenomenon where 1 gene controls several functions or has more than 1 effect

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17
Q

why can pleiotropy be difficult to trace through families?

A

people with different subsets of symptoms may seem to have different diseases

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18
Q

genetic heterogeneity

A

different genes can produce identical phenotypes

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19
Q

how does genetic heterogeneity come about

A

genes may encode enzymes that catalyze the same biochemical pathway, or different proteins that are part of the pathway

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20
Q

examples of genetic heterogeneity

A

osteogenesis imperfecta, retinal dystrophies

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21
Q

what are retinal dystrophies

A

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

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22
Q

phenocopy

A

trait that appears inherited but is actually caused by the environment

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23
Q

examples of phenocopy include

A

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

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24
Q

example of lethal allele

A

achondroplasia

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25
example of multiple alleles
cystic fibrosis
26
example of incomplete dominance
familial hypercholersterolemia
27
example of codominance
ABO blood types
28
example of pleiotropy
marfan syndrome
29
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
30
what is a mitochondrion
an organelle that provides cellular energy
31
what DNA does the mitochondrion contain?
mtDNA
32
how many genes does mtDNA contain?
37 genes
33
mitochondrial genes are _____ inherited
maternally
34
mtDNA does not ____
cross over
35
mtDNA mutates _____ than DNA in the nucleus. why?
faster; there are less DNA repair radicals produced in the energy rxns
36
mitochondrial genes are not interrupted by DNA sequences that do not encode _____
protein
37
mitochondria with different ____ for the same gene can reside in the same cell
alleles
38
what proteins do mitochondrial genes encode?
those involved in protein synthesis and energy production
39
examples of diseases due to mutations in mtDNA
mitochondrial myopathies, leber optical atrophy
40
what is mitochondrial myopathies
weak and flaccid muscles
41
what is eber optical atrophy
impaired vision
42
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
43
genes that are close to the same chromosome are _____
linked
44
linked genes do not _____ _________ in meiosis
assort independently
45
how are linked genes inherited?
inherited together when the chromosome is packaged into a gamete
46
linked genes do not produce typical _______ ____
mendelian ratios
47
what is recombination
when chromosomes recombine during crossing over in prophase 1 of meiosis
48
what does recombination create
new combinations of alleles
49
what is the difference between parental chromosomes and recombinant chromosomes?
parental have the original configuration, recombinant have the new combinations of alleles
50
cis
two dominant or two recessive alleles are on each chromosomes
51
trans
one dominant and one recessive allele are on each chromosome
52
correlation between cross over frequency and gene distance is used to construct ______ ____
linkage maps
53
frequency of a crossover between any 2 linked genes is inferred from _______________________
the proportion of offspring from a cross that are recombinant
54
what is frequency of recombination based on?
the percentage of meiotic divisions that break the linkage between 2 parental alleles
55
frequency of recombination is proportional to the _____ of the 2 genes recombining
distance
56
the probability that genes on opposite ends of a chromosome cross over is about
50%
57
linkage map
a diagram indicating the relative distance between genes
58
1% recombination = 1 map unit =
1 centimorgan
59
what is linkage disequilibrium
nonrandom association between DNA sequences. they are inherited more often than would be predicted from their frequency
60
human genome consists of many LD blocks where alleles ____ together
stick
61
halpotypes
LD blocks
62
what are haplotypes used to track?
genes in populations
63
nail-patella syndrome
rare autosomal dominant disease that cause underdeveloped nails and painful arthritis in knee and elbow joints
64
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
65
LOD score
logarithm of the odds; indicates tightness of linkage between a genetic marker and a gene of interest
66
what score of LOD signifies linkage
3 or higher
67
what does the LOD score provide?
likelihood that particular cross over frequency data suggests linkage rather than inheritance by chance
68
observed data are _____ times more likely to be due to a linkage than chance
1000
69
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

IB 141 human genetics (6 decks)

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