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BIOL2500 > Unit 03/04: Mendelian Genetics and Sex Linked Inheritance > Flashcards

Unit 03/04: Mendelian Genetics and Sex Linked Inheritance Flashcards

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1
Q

what aims to determine the genes responsible for any given trait?

A

gene discovery

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2
Q

what is the wildtype?

A

the most common form of the trait (all the rest are mutants)

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3
Q

what are the general steps to analyze a trait?

A
  1. gather mutants
  2. mate mutants and wild type to see if their offspring show typical inheritance ratios
  3. deduce the functions of genes at a molecular level
  4. deduce how gene interactions contribute to the trait
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4
Q

what is genetic dissection?

A

when mutants are crossed with wild type and then the offspring are observed to see if they follow typical inheritance ratios

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5
Q

what is forward genetics?

A

when we find phenotypic mutants and then look at their DNA to determine what the DNA mutation is

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6
Q

what is reverse genetics?

A

when we start by looking at DNA for candidate genes and then introducing changes to see what the effect is on the phenotype.

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7
Q

who showed that inheritance is particulate?

A

mendel

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8
Q

what was mendels ratio of yellow to green peas in the F2 generation?

A

3:1

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9
Q

what is mendels first law? what does it mean? when does it occur.

A

law of segregation. states that each gamete only has “one member of the gene pair” aka only one version of the allele.

anaphase 1.

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10
Q

describe meiosis involving haploid yeast

A

2 haploid cells of opposite mating types fuse tgt to form a diploid meiocyte.

meiocyte undergoes meiosis to produce sexual ascopores

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11
Q

what are dihybrid individuals?

A

individuals that are heterozygous for both traits

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12
Q

what is the observed phenotypic ratio of the F2 generation in dihybrid crosses?

A

9:3:3:1

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13
Q

what is the formula to determine number of phenotypes given a certain number of traits (n)

A

2^n

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14
Q

what is the formula to determine the number of genotypes given a number of traits (n)

A

3^n

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15
Q

what is mendel’s second law? what does it mean? when does it occur?

A

the law of independent assortment. means that unlinked gene pairs assort independently of eachother during meiosis.

occurs during metaphase 1.

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16
Q

what 2 things are evidence of independent assortment?

A

gamete ratio

phenotype ratio

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17
Q

when should the produce rule be used?

A

when looking for probability that 2 independent events will both occur

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18
Q

when should the sum rule be used?

A

when looking for probability that either one or the other of 2 independent outcomes will occur

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19
Q

what are conditional probabilities? give an example.

A

a probability prediction that is dependent on another event haven taken place.

ex. “what is the probability that F2 yellow seeded plants are heterozygous like their parents?” we know that 3/4 in F2 will be yellow and of those, 2 will be heterozygous, therefore 2/3 chance

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20
Q

when do we fail to reject H0?

A

when the p-value > alpha value and the chi-square value < critical value

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21
Q

how do we get our expected values for each trait?

A

multiply the total number of individuals observed, and multiply by expected phenotypic ratio for each trait.

ex. in a dihybrid to find expected number of individuals with both dominant traits we will multiply total number observed by 9/16

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22
Q

how many unique chromosomes does a human male have?

A

24 (22 autosomes, 1 X, 1 Y)

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23
Q

how many unique chromosomes does a human female have?

A

23 (22 autosomes, X)

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24
Q

which region on X and Y chromosomes are homologous?

A

pseudoautosomal

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25
which region on X and Y chromosomes are not homologous?
differential
26
who discovered sex linked genes via experiments with fruit flies?
thomas hunt morgan
27
what are some indications of sex linked inheritance?
- males and females have diff phenotypic ratios in F1 and F2 - reciprocal crosses give different results in ratios - "criss cross inheritance". ex. recessive trait goes from affected dad -> carrier daughter -> affected grandson
28
what is the cause of the white eyed gene in flies being x-linked recessive?
non-disjunction
29
what are some examples of human X-linked recessive genes?
colourblindness, hemophilia A, muscular dystrophy
30
what are some examples of human X-linked dominant genes?
rett syndrome, amelogenesis imperfecta.
31
what is an example of a y-linked trait?
hairy ears
32
what does mitochondrial DNA code for?
cellular respiration tasks (ATP synthases, proton pumps)
33
what is complete penetrance?
when a genotype always produces the same phenotype
34
what are sex-limited traits? give an example.
autosomal traits that has alleles carried in both sexes, but the phenotype only ever shows up in one sex. ex. milk production
35
what are sex-influenced traits? give an example.
autosomal traits that have varied inheritance patterns even if genotypes are the same. ex. heterozygous for pattern baldness in females causes recessive phenotype of hairy while in males heterozygous gives dominant baldness
36
what is chromosomal sex?
the presence of sex chromosomes associated with males and females in a species.
37
what is phenotypic sex?
internal and external morphology found in each sex.
38
what determines sex in drosophila ?
X chromosome to Autosome ratio
39
what sex is a fruit fly when its X:A ratio is <.5
male
40
what sex is a fruit fly when its X:A ratio is >1
female
41
what sex is a fruit fly when its X:A ratio is between .5 and 1
intersex
42
what determines sex in mammals?
presence of Y chromosome
43
the expression of the SRY gene causes Wolffian ducts to form into which reproductive structures?
male
44
the lack of expression of the SRY gene causes Mullerian ducts to form into which reproductive structures?
female
45
which animals use the Z/W system?
birds, some reptiles and fish, moths and butterflies
46
what genotype is female in the ZW system?
ZW
47
what genotype is male in the ZW system?
ZZ
48
z-linked genes are analogous to what genes in mammals?
X linked
49
which genotype is hermaphroditic in nematodes?
XX (higher X:A ratio)
50
which genotype is supermale in nematodes?
X0 (lower X:A ratio)
51
when a supermale mates with a hermaphroditic nematode, what is the ratio of sexes?
1:1
52
how many pairs of sex chromosomes do monotremes have?
5!
53
which temperatures determine what sex in sea turtles?
<28C = males >32C = female 28-32C = both
54
which fish can change sex due to changes in sex pop. density?
clown fish!
55
what percent of plants are hermaphroditic?
90%
56
why is dosage compensation needed?
bc females have double the X chromosomes, therefore would have double the X-linked expression than males.
57
dosage compensation mechanisms balance the expression of ________ genes
X/Z linked genes
58
describe dosage compensation in fruit flies
X-linked expression in males is doubled
59
describe dosage compensation in roundworms
x-linked expression in hermaphrodite is halved compared to supermale
60
describe dosage compensation in marsupials
paternally derived X-chromosome inactivated in female somatic cells
61
describe dosage compensation in placental mammals
one random X-chromosome (maternal or paternal) is inactivated in each female somatic cell
62
describe the lyon hypothesis.
1/2 of the somatic cells in females have an inactivated paternal X chromosome and the other 1/2 of the somatic cells have an inactivated maternal chromosome
63
an inactivated X chromosome becomes a _____
barr body, localized to the nuclear envelope
64
x inactivation is a form of _____
epigenetic regulation
65
which molecules perform the X-chromosome silencing?
Xist and Tsix
66
in early female embryo development, is Xist or Tsix expressed?
both X chromosome are active in early development, with Tsix being expressed.
67
how is Tsix repressed in early chromosome development? what does it cause?
by the pairing of the x chromosomes, causing Tsix to be repressed in one. the one in which Tsix is repressd is the one to be inactivated.
68
in which X chromosome does Xist activate? what does it do? how is it blocked in the other?
- the chromosome in which Tsix is active blocks the activation of Xist on that chromosome - YY1 facilitates the Xist IncRNA spreading along the inactivated X, silencing it by Xist binding to both the DNA and then IncRNA
69
what establishes and maintain heterochromatin in the barr body?
IncRNAs and other structural changes in the chromatin
70
on the Xa chromosome _____ is active while _____ is repressed
Tsix active, Xist repressed
71
on the Xi chromosome _____ is active while _____ is repressed
Xist active, Tsix repressed
72
describe how female cats can have a calico/tortoise shell fur colour pattern
have a dominant black allele and a recessive orange allele where one X chromosome is inactivated, resulting in the mosaic
73
describe how male cats can have a calico/tortoise shell fur colour pattern
only if they are klinefelter males (XXY)
74
what is the name of the person to come to a geneticist with the problem in a pedigree?
propositus
75
how can you identify the mode of inheritance as autosomal recessive in a pedigree?
- most individuals have a normal phenotype - trait often skips generations and is commonly seen among siblings - males and females affected similarly - mating of close relatives is more likely to result in affected individuals
76
how can you identify the mode of inheritance as autosomal dominant in a pedigree?
- males and females equally effected - an affected person has at least 1 parent with the trait - parents of either sex transmit trait to offspring - if one parent has the trait and the other does not, 50% of children will have the trait
77
how can you identify the mode of inheritance as x-linked recessive in a pedigree?
- more males affected than females - appears to skip generations - affected female passes on trait to all sons - carrier female passes allele onto 1/2 her sons and 1/2 her daughters - affected male passes on his allele to all his daughters but none of his sons
78
how can you identify the mode of inheritance as x-linked dominant in a pedigree?
- more females affected than males - an affected female is usually heterozygous, passing on the trait to half her offspring - does not skip generations - affected male with normal female passes on allele/trait to all daughter but no sons

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