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genetics > sex determination & gene interaction (I,II) > Flashcards

sex determination & gene interaction (I,II) Flashcards

1
Q

what is a monoecious organism

A

male and female reproductive structures in same organism

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2
Q

what is a dioecious organism

A

either male or female reproductive structures - US

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3
Q

what is an intersex organism

A

individuals with intermediate sexual condition (sterile)

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4
Q

monoecious plant - stamen is the male/female reproductive structure
-stigma+pistil is the male/female reproductive structure

A

stamen - male
stigma + pistil - female

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5
Q

production of pollen (male gametes) in stamen

A

-diploid microspore to 4 haploid microspores by meiosis
-haploid microspore to pollen grain by mitosis
-pollen grain has 2 haploid nuclei

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6
Q

production of female gametes in pistil

A

-diploid megaspore to megaspore (4 haploid nuclei) by meiosis
- megametophyte (1 haploid nucleus) undergoes 3 rounds of mitosis to form embryo sac with 8 haploid nuclei
–>endosperm nuclei provides growth for new seed to germinate
–>oocyte nucleus contributes DNA to next generation of plants

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7
Q

females XX - how are they homogametic

A

produce 1 type of gamete carrying a single X chromosome

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8
Q

males XY - how are they heterogametic

A

produce 2 types of gamete carrying X or Y chromosome

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9
Q

in mammals - sex determination determined by … chromosome - absence of this means you’re a female

A

Y

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10
Q

how does aneuploidy 47 XXY show that Y chromosome determines maleness

A

extra sex chromosome
2 X but still male because of Y

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11
Q

how does aneuploidy 45 X show that Y chromosome determines maleness

A

missing sex chromosome
1 X but female because of no Y

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12
Q

how does aneuploidy 47 XYY show that Y chromosome determines maleness

A

extra sex chromosome
aneuploidies caused by non-disjunction - non-disjunction - irregular segregation of homologous chromosomes during meiosis

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13
Q

what is non-disjunction

A

homologous chromosomes fail to separate properly during meiosis
-homologous chromosomes travel to same pole instead of segregating to opposite poles

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14
Q

what region on Y chromosome is needed for male development and what does it code for

A

SRY gene codes for TDF - testis determining factor

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15
Q

how can SRY gene be present on X chromosome if there’s no Y chromosome
-so XX but a male

A

abnormal non-homologous recombination event

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16
Q

how SRY leads to development of a male

A

SRY - means TDF protein is coded for
-anti-mullerian hormone means female duct (mullerian duct) is degraded by apoptosis
-development of testes
-testosterone hormone

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17
Q

how absence of SRY leads to development of a female

A

gonads become ovaries
-male duct (wolffian duct) degenerates
-female duct (mullerian duct) becomes oviduct - connecting ovaries to uterus, and upper portion of vagina

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18
Q

in birds, female is homogametic/heterogametic

A

heterogametic
ZW
NO SRY GENE

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19
Q

in fruit flies, X or Y determines sex determination?

A

ratio of X chromosomes : no. of autosome haploid set
> 0.5 = development of females
- Y has no role in sex determination - NO SRY GENE

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20
Q

in bees - haplodiploid system

A
  • no. of haploid sets present
  • sex chromosomes are irrelevant
    male produced from unfertilised haploid eggs
    female produced from fertilised diploid eggs - only females produced by sexual reproduction
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21
Q

what is dosage compensation

A

females have 1 switched off X gene (random)

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22
Q

inactivated condensed X chromosome is called

A

Barr body

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23
Q

inactivated X chromosome (Barr body) is visible by …

A

light microscopy of interphase cells

24
Q

number of Barr bodies is always -

A

1 less than the number of X chromosomes
X = 3
Barr body = 2

25
Q

X inactivation is random so all females are

A

mosaics for all X-linked alleles

26
Q

loss of function mutation (amorphic) produces no protein/protein - lacks function, is dominant/recessive?

A

recessive - mutant if both copies carry mutation

27
Q

mutant CFTR is recessive or dominant

A

recessive - 2 copies of mutant allele
-misfolded protein degrades so vesicles don’t have CFTR
-no Cl- gradient, no water exiting
-thick mucus

28
Q

loss of function mutation (hypomorphic) reduces protein function, is dominant/recessive

A

recessive

29
Q

gain of function mutation (hypermorphic) - produces more protein, protein has greater activity, is dominant/recessive

A

dominant

30
Q

gain of function mutation (antimorphic) - dominant or recessive

A

dominant - mutant copy affects normal copy

31
Q

gain of function mutation (dominant lethal) - dominant or recessive

A

dominant - mutant product accumulates over time so see symptoms later on in life

32
Q

gain of function mutation (neomorphic) -

A

new form of protein - changed protein function
-dominant

33
Q

mendel - all traits have clear dominant/recessive effects but departure from mendelian ratios:
INCOMPLETE DOMINANCE ratio

A

blend of characteristics
1:2:1 not 3:1

34
Q

mendel - all traits have clear dominant/recessive effects but departure from mendelian ratios:
CO-DOMINANCE

A

both alleles detected equally
codominance = blood type IA IB - blood type AB - as much A antigen as B antigen on RBC
makes no A or B antibodies
blood type ii - blood type O - no A or B antigen

35
Q

how do lethal alleles distort Mendelian segregation ratios

A

expect 3:1 mutant : wild type Mendelian ratio
but get 2:1 mutant : wild type - homozygous dominant impossible to obtain (recessive lethal)

36
Q

haemophilia - …linked recessive disease

A

X linked recessive trait
-half the sons of a carrier are affected
-half the daughters of a carrier are carriers

37
Q

mitochondria and chloroplasts have their own genome - maternal or paternal inheritance

A

maternal inheritance

38
Q

mutations in mtDNA - mitochondrial cytopathy =

A

can only be passed on by the mother
-affected mother passes on to all offspring so affects both sexes

39
Q

how are mutations in mtDNA matrilineal

A

doesn’t follow autosomal or sex-linked inheritance patterns

40
Q

departure from mendelian ratios - what is incomplete penetrance

A

when the phenotype associated with a genotype fails to appear in some cases

41
Q

departure from mendelian ratios - what is variable expressivity

A

when phenotype varies
eg. wardenburg syndrome can have any 4 symptoms
-allele is pleiotropic - affects more than 1 trait

42
Q

departure from mendelian ratios - incomplete penetrance and expressivity are controlled by (2)

A
  1. genotype at other loci
  2. environmental factors
43
Q

mendelian ratio is

A

9:3:3:1

44
Q

epistasis =

A

gene interaction, operates in the same pathway contributing to the same phenotype

45
Q

example of epistasis - complementary gene action - ratio:

A

9:7 ratio
2 independent dominant alleles interact

46
Q

example of epistasis - recessive epistasis

A

9:3:4 ratio
recessive homozygous masks the expression of dominant

47
Q

example of epistasis - dominant epistasis

A

dominant allele of 1 gene masks the genotype at another locus
12:3:1 ratio

48
Q

example of epistasis - duplicate gene action

A

both genes perform the same function
-redundancy eg. both enzymes are redundant can live without 1 of them, but they both make same enzyme so duplicate each other
15:1 ratio

49
Q

to identify genes that control a trait - (2)

A

model organisms and the complementation test

50
Q

to identify gene determinants

A

introduce mutations in the model organism - leads to no. of organisms mutant for the trait

51
Q

complementation analysis - to work out how many genes have mutated

A
  1. make mutants
  2. isolate mutants - make sure these are homozygous and pure breeding
  3. cross mutant with wild type
  4. CROSS MUTANTS WITH EACH OTHER
  5. SEE IF WILD TYPE IS RECOVERED FROM THE PROGENY
52
Q

mendel - all traits have clear dominant/recessive effects but departure from mendelian ratios:
INCOMPLETE DOMINANCE ratio

A

1:2:1 not 3:1
blend of characteristics

53
Q

complementation analysis:
-if wild type is not recovered from progeny - all progeny are mutant - lack of complementation:

A

loss of function of the same gene
MUTATION IS IN THE SAME GENE

54
Q

complementation analysis:
-if wild type is recovered from progeny - complementation:

A

each parent provides what the other one lacks
MUTATIONS ARE IN DIFF GENES

55
Q

no. of complementation groups =

A

no. of genes that have been mutated

56
Q

during production of female gametes in the pistil of plants, how many haploid nuclei do megaspores contain

A

4

57
Q

what is epistasis

A

when a phenotype is controlled by various genes interacting with each other

genetics (10 decks)

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