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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
Q

example of multiple alleles

A

cystic fibrosis

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26
Q

example of incomplete dominance

A

familial hypercholersterolemia

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27
Q

example of codominance

A

ABO blood types

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28
Q

example of pleiotropy

A

marfan syndrome

29
Q

what is marfan syndrom

A

a defect in elastic connective tissue - fibrillin. symptoms include lens dislocation, long limbs, spindly fingers, caved in chest, weakening in aorta

30
Q

what is a mitochondrion

A

an organelle that provides cellular energy

31
Q

what DNA does the mitochondrion contain?

A

mtDNA

32
Q

how many genes does mtDNA contain?

A

37 genes

33
Q

mitochondrial genes are _____ inherited

A

maternally

34
Q

mtDNA does not ____

A

cross over

35
Q

mtDNA mutates _____ than DNA in the nucleus. why?

A

faster; there are less DNA repair radicals produced in the energy rxns

36
Q

mitochondrial genes are not interrupted by DNA sequences that do not encode _____

A

protein

37
Q

mitochondria with different ____ for the same gene can reside in the same cell

A

alleles

38
Q

what proteins do mitochondrial genes encode?

A

those involved in protein synthesis and energy production

39
Q

examples of diseases due to mutations in mtDNA

A

mitochondrial myopathies, leber optical atrophy

40
Q

what is mitochondrial myopathies

A

weak and flaccid muscles

41
Q

what is eber optical atrophy

A

impaired vision

42
Q

how can a woman with a mitochondrial disease avoid transmitting it to her children?

A

if her mitochondria can be replaced with a healthy mitochondria from a donor

43
Q

genes that are close to the same chromosome are _____

A

linked

44
Q

linked genes do not _____ _________ in meiosis

A

assort independently

45
Q

how are linked genes inherited?

A

inherited together when the chromosome is packaged into a gamete

46
Q

linked genes do not produce typical _______ ____

A

mendelian ratios

47
Q

what is recombination

A

when chromosomes recombine during crossing over in prophase 1 of meiosis

48
Q

what does recombination create

A

new combinations of alleles

49
Q

what is the difference between parental chromosomes and recombinant chromosomes?

A

parental have the original configuration, recombinant have the new combinations of alleles

50
Q

cis

A

two dominant or two recessive alleles are on each chromosomes

51
Q

trans

A

one dominant and one recessive allele are on each chromosome

52
Q

correlation between cross over frequency and gene distance is used to construct ______ ____

A

linkage maps

53
Q

frequency of a crossover between any 2 linked genes is inferred from _______________________

A

the proportion of offspring from a cross that are recombinant

54
Q

what is frequency of recombination based on?

A

the percentage of meiotic divisions that break the linkage between 2 parental alleles

55
Q

frequency of recombination is proportional to the _____ of the 2 genes recombining

A

distance

56
Q

the probability that genes on opposite ends of a chromosome cross over is about

A

50%

57
Q

linkage map

A

a diagram indicating the relative distance between genes

58
Q

1% recombination = 1 map unit =

A

1 centimorgan

59
Q

what is linkage disequilibrium

A

nonrandom association between DNA sequences. they are inherited more often than would be predicted from their frequency

60
Q

human genome consists of many LD blocks where alleles ____ together

A

stick

61
Q

halpotypes

A

LD blocks

62
Q

what are haplotypes used to track?

A

genes in populations

63
Q

nail-patella syndrome

A

rare autosomal dominant disease that cause underdeveloped nails and painful arthritis in knee and elbow joints

64
Q

genetic marker

A

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
Q

LOD score

A

logarithm of the odds; indicates tightness of linkage between a genetic marker and a gene of interest

66
Q

what score of LOD signifies linkage

A

3 or higher

67
Q

what does the LOD score provide?

A

likelihood that particular cross over frequency data suggests linkage rather than inheritance by chance

68
Q

observed data are _____ times more likely to be due to a linkage than chance

A

1000

69
Q

haplotype

A

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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