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Genetics > Week 3 > Flashcards

Week 3 Flashcards

1
Q

Non-Disjunction

A

Anomalous chromosome numbers caused by improper segregation (aneuploidy)

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2
Q

Types of non-disjunction

A
  • Non-disjunction is meiosis I: each gamete has 2 Xs or none
  • Non-disjunction is meiosis II: Each gamete has 2, 1, or no Xs
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3
Q

Non-disjunction example in flies

A

ORIGINAL FINDING
- Started with white eyed female and red eyed male
- Produced all daughters with red eyes and all sons with white eyes
CYTOLOGICAL STUDIES RESULTS
- The unusual males with red eyes had one X chromosome from father and no Y (male in flies but female in humans)
- The unusual females had two X chromosomes from their mother and a Y from the father (Female in flies but male in humans)

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4
Q

Non-disjunction of autosomes: trisomy 21

A

Down Syndrome
- At least 0.3% of newborns and 25% of spontaneous abortions
- Most common form of mental retardation
- Least several viable autosomal trisomy

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5
Q

Non-disjunction of autosomes: Trisomy 18

A

Edwards syndrome X
- Severe intellectual disability, decreased muscle tone, low-set ears, internal organ defects

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6
Q

Non-disjunction of autosomes: Trisomy 13

A

Patau Syndrome
- Severe intellectual disability and other problems
- 90% die in first year of life

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7
Q

Chiasmata and Nondisjunction

A
  • The rate of recombination may differ between males and females (in females more recombination in the center, in males more recombination on the tips_
  • Nondisjunction is sometimes associated with chromosomes that did not recombine, which suggests that recombination may be important for proper chromosomal segregation
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8
Q

What are suggested mechanism for non- disjunction?

A
  • lack of recombination
  • Checkpoint failure
  • age-related degradation of the cohension complex
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9
Q

Cohension Complex

A

Inhibits microtubule attachment during cell division

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10
Q

What 2 factors can influence sex determination?

A

Environmental and Genetic

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11
Q

Def: Genetic Sex

A

Based on what chromosomes an individual has; multiple types

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12
Q

Def: Phenotypic Sex

A

Based on external appearance - many species have two sexes, some have one, some have more than two

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13
Q

Def: Gender identity

A

Based on how someone feels or identifies

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14
Q

Sex determination in Drosophila

A

The X/A ratio determines gender
- Females X/A ratio of 1.0
- Males X/A ratio of 0.5

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15
Q

Sex determination in placental and marsupial mammals

A

Determined by the presence or absence of the Y-linked gen SRY
- Sexual differentiation results in a continuum of phenotypes that includes intermediates
- Genetic sex doesn’t always match the typical phenotypic sex

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16
Q

Development of genitals based on presence or absence of SRY gene

A
  • Start with undifferentiated gonad, wolffian duct and Mullerian duct
    SRY PRESENT
  • wolffian duct becomes vas deferens and gonads becomes testis
    SRY ABSENT
  • Mullerian duct becomes fallopian tubes and gonads becomes ovaries
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17
Q

Congenital Adrenal hyperplasia (CAH)

A
  • Mutations in the CYP21 gene prevent degradation of testosterone and derivatives
  • In boys it results in very early pubescence
  • In girls it results in an enlarged clitoris and masculinized body hair
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18
Q

5’-Alpha Reductase Deficiency

A
  • Decrease in DHT production
  • Leads to lack of external genitalia development until puberty
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19
Q

Androgen Insensitivity syndrome

A

Genetically male individuals have a defective androgen receptor: external appearance is female, but gonads are undifferentiated (Individuals are sterile)

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20
Q

ZW sex determineation

A

In birds, butterflies, moths, some reptiles and amphibians there is female heterogamy, meaning they are determining sex of offspring

21
Q

Congenital Hypertrichosis

A

Excessive body hair affecting both males and females
- All carriers of the mutant allele also express the trait

22
Q

Y-linked inheritance

A
  • Exclusively male to male transmission
  • Mammals have about 80 genes on the Y chromosome
  • Genes on the human Y chromosome do not have homolog on the X chromosome
23
Q

Dosage compensation of X-linked Genes

A
  • In placental mammals, one X in females is silenced (X inactivation) - not 100% and different in each cell
  • In fruit flies, the X in the males is upregulated (Hypertranscription)
  • In nematodes, both X-linked alleles in females have lower expression (Hypotranscription)
24
Q

How does X inactivation happen in placental mammals?

A
  • Random X inactivation
  • One chromosomes is coded by RNA to be transcriptionally inert forming inactive Barr body
  • Descendant cells have same activation
25
Q

Coat Color in cats as an application for X inactivation

A
  • Heterozygous individuals will have one allele producing black and another producing orange
  • Inactivation leads to pattern of orange and black cats
26
Q

Mechanism of X inactivation in placental mammals

A
  • Requires expression of an X-lined gene called XIST (X-inactivation-specific-transcript)
  • XIST encodes a long RNA molecule that covers the chromosome to be inactivated
  • XIST transcript acts in cis, meaning it only affects the chromosome from which it is transcribed
27
Q

Wildtype Allele

A
  • The most common allele
  • Can be dominant or recessive
28
Q

Functional effects of Mutations

A

WILD TYPE
- if genotype is homozygous wildtype, both alleles produce some amount of protein
NULL ALLELE
- Produces no protein
LOSS OF FUNCTION ALLELE (hypomorphic)
- produces less protein than the wildtype (diminished function compared to the wildtype)
GAIN OF MUTATIONS (hypermorphic)
- produce excess protein
NOVEL FUNCTION (Neomorphic)
- produce different protein

29
Q

Dominant negative mutations

A
  • Type of loss of function mutation
  • type of mutant phenotype is often due to impaired interactions with other proteins
  • interfere with the function of a wildtype allele at the same locus`
30
Q

Complete Penetrance

A

If a genotype always produces the same phenotype

31
Q

Possible causes for one genotype having multiple phenotypes

A
  • Sex-limited traits
  • Sex-influenced traits
  • Incomplete penetrance
  • Variable expressivity
32
Q

Incomplete/partial dominance

A

Heterozygous individuals have a phenotype that is intermediate to each homozygous phenotype

33
Q

Allelic Series

A

Hierarchical dominance relationships among several alleles at a locus

34
Q

Co-dominance

A
  • Heterozygous phenotype is different from either homozygous phenotype
  • Not necessarily intermediate, but instead different from either homozygous phenotype
35
Q

Lethal Alleles

A
  • Inviable when homozygous
  • Alters the phenotypic ratio of crosses
36
Q

How do lethal alleles persist in populations?

A
  • The onset of symptoms is during or after reproduction, passing the allele on to the next generation
  • Disease causing mutation are frequently introduced into populations by de novo mutations
37
Q

Mutation-selection equilibrium

A
  • There is a balance between removal by natural selection and introduction by new mutation
38
Q

Sex-limited traits

A

Both sexes carry genes but only one sex expresses the phenotype
- E.g. Mammalian lactation is a female-specific phenotype, horn development is males-specific in some sheep, cows and other hoofed animals

39
Q

Sex-Influenced traits

A

Both sexes carry a gene, but the phenotype varies between the sexes

40
Q

Incomplete penetrance

A

Traits that are nonpenetrant in some individuals but penetrant in other individuals

41
Q

Variable expressivity

A

One genotype has multiple phenotypes that are variable
- variation is caused by interactions with other genes that may differ among individuals and/or environmental effects

42
Q

Phenylketonuria

A
  • Human disease characterized by an inability to metabolize the amino acid phenylalanine
  • Over time, build up of phenylalanine causes serious problems
  • Requires environmental manipulation of restricting diet
43
Q

Pleiotropy

A

When one gene affects many phenotypes

44
Q

Epistasis

A

The phenomenon where the effects of one gene is dependent on the alleles of one or more modifier genes

45
Q

Complementary epistatic interaction

A

Both alleles are required for expression
- offspring phenotype proportion of 9:7

46
Q

Dominant suppression epistatic interaction

A

The dominant expression of one allele suppresses the expression of another
- 13:3

47
Q

Syntenic Genes

A

Genes on the same chromosome

48
Q

Linked genes

A

Syntenic genes that are so close together that their alleles cannot be sorted independently

49
Q

Purpose of genetic linkage mapping

A

Plots the positions of genes and their relative distances from each other on chromosomes

Genetics (18 decks)

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