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BIOSCI 2223: Genetics > Test 2 > Flashcards

Test 2 Flashcards

1
Q

Describe sex determination in yeast

A

SINGLE GENE LOCUS called MAT on chromosome 3 is either alpha or a, which determines the mating type, each type can only fuse with opposite

can also switch mating type, as each has all the other genes for each mating type, only the MAT is different

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2
Q

Describe sex determination in Hymenoptera (bees, wasps, ants)

A

diploid eggs are female (unless homozygous at all sex genes), haploid eggs are male (will always be homozygous)

half of the eggs are unfertilized (males) and half are fertilized (females)

HAPLODIPLOIDY

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3
Q

Describe sex determination in the genus Ophryotrocha (marine annelid)

A

the young produce sperm and the adults produce eggs

DEVELOPMENTAL SWITCH

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4
Q

Describe sex determination in the genus Bonellia (marine animal)

A

free-swimming sexless larvae settle to the bottom and develop into one sex or the other -> female if land on substrate, male if land on female

males live as parasites in females

ENVIRONMENTAL SWITCH

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5
Q

Describe sex determination in mammals

A

males have XY, females have XX

determined by maleness gene “SRY” on differential (non-pseudoautosomal) region of Y chromosome

when present, produces TDF which switches off Od and produces males

when absent, Od produces females

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6
Q

Describe sex determination in dipterans (flies, mosquitos, gnats, midges, no-see-ums)

A

ratio of X chromosomes to autosomal sets (less than or equal to .5 is male, greater than or equal to 1 is female, between is intersex)

normal diploid XX is female (2/2)
normal diploid XY is male (1/2)

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7
Q

How do mammals deal with dosage effects with the X chromosome?

A

one copy of X chromosome is inactivated “Barr” body

became clinical test for female (normally 1=female and 0=male, but XXY=1=male and XXX=2=female)

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8
Q

How do dipterans deal with dosage effects with the X chromosome?

A

male copy is hyperactivated

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9
Q 
Gender of special sexes in dipterans:
XX haploid
X haploid
XX triploid
X triploid
XXY diploid
X diploid
XXX diploid
A 
2/1=female
1/1=female
2/3=intersex
1/3=male
2/2=female
1/2=male
3/2=female
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10
Q

Define sex-limited traits

A

Traits that are expressed in only one sex or the other, causing sexual dimorphism and secondary sexual characteristics

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11
Q

Define sex-influenced traits

A

The expression of the gene/allele is influenced but not limited to the sex it is

Ex: Baldness gene is dominant in males and recessive in females

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12
Q

Define sex-linked traits

A

Gene is on the X or Y chromosome, produces a different pattern of inheritance

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13
Q

Describe the inheritance of traits on the y chromosome

A

Males will have it, females will not, no carriers

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14
Q

Describe the inheritance of traits on the x chromosome

A

Heterogametic sex can express a recessive trait with only one copy
May produce a criss-cross inheritance

Ex: WhiteEye female by WildType Male produces WhiteEye males and RedEye females

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15
Q

Describe incomplete dominance

A

One allele contributes to the phenotype while the other allele does not
The phenotypic ratio is the same as the genotypic ratio because all genotypes produce different phenotypes
“Dose makes a difference”

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16
Q

Describe complete dominance

A

Dose does not make a difference

Nonfunctional mutants

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17
Q

Describe codominance

A

Each of the two different alleles contributes equally to the phenotype
It’s not that one is working while the other is not working, both are working in different ways
Phenotype depends on what you are measuring (may be more than codominance)

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18
Q

Describe the inheritance pattern of a recessive lethal

A

Produces a 2:1 phenotype
Two copies are required for lethality
*Dominant lethal traits do not exist

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19
Q

Define pleiotrophic

A

Alleles that control more than one aspect of the phenotype

Ex: Taillessness gene is dominant for tail vs no tail, but recessive for viability

20
Q

What is the basic definition of gene interaction?

A

Two or more genes interact to control the same aspect of the phenotype

21
Q

When does a 9/3/3/1 phenotypic ratio occur?

A

A 9:3:3:1 ratio of phenotypes occurs when there are two genes that interact to produce a trait and can produce four phenotypes with a dihybrid

22
Q

What is masking or epistasis?

A

When one gene locus masks or modifies the phenotype of a second gene locus

23
Q

Give some modified 9/3/3/1 ratios

A

9:7, 15:1, 9:3:4, 12:3:1, 9:6:1, 13:3, 10:3:3, or 10:6

24
Q

What are the two types of hypothesis in chi squares?

A

The null hypothesis is that the data represents an x:y:z raio
The alternative hypothesis is that the data does not represent an x:y:z ratio

25
Q

What is the equation for the chi square?

A

X2=Σ of (O-E)2/E
O is observed and E is expected
The expected will be the same from experiment to experiment, while the observed with change
For each phenotype, take the number you got minus the number you would expect if your ratio was correct, square it, and divide by the number you would expect
Sum the X2 for each phenotype

26
Q

What is df?

A

Df = degrees of freedom, which is equal to n-1 (n=# of phenotypic classes)

27
Q

How do you determine if you should accept or reject the hypothesis using a chi square?

A

Compare the X2 of the experiment with the X2 values for the degree of freedom and the p value (usually .05)
If our X2 value is less than or equal to the critical value, we can accept the null hypothesis

28
Q

Describe Sex Determination in Lepidoptera (moths, butterflies)

A

ZW system of sex chromosomes. ZZ is male

29
Q

What are recombinant gametes? What are recombinant progeny?

A

Recombinant gametes are those that do not match either of their parental/grandparent gamete allele combinations (ex: parent AaBb came from AB and ab, but donated Ab)

Recombinant progeny are those that came from at least 1 recombinant gamete

30
Q

What ratio of recombinant to parental (non-recombinant) progeny is expected for unlinked genes?

A

Genes on separate chromosomes will exhibit a 1:1 ratio, genes more than 50 map units apart on the same chromosome will show something higher than 1:1

31
Q

What ratio of recombinant to parental (non-recombinant) progeny is expected for linked genes?

A

Recombinant progeny will be fewer than parental progeny

32
Q

What is a map unit?

A

one map unit (mu) is the distance between genes that results in 1% of the offspring being recombinant

this can be used to determine the distance between genes

33
Q

How do you identify the classes (parental, recombinant, double recombinant) of progeny in a three-point cross?

A

Parentals result from no crossovers, so the most numerous two classes are parental in respect to all genes

Double recombinants have two crossovers, so they will be the most rare two classes

The other four classes will be single recombinants

34
Q

What is meant by the allele configurations of cis and trans?

A

Cis: recessive alleles from different genes are on the same chromatid

Trans: recessive alleles from different genes are on different chromatids

35
Q

How do you determine gene order in a three-point cross?

A

The double recombinants will have the opposite configuration than the parentals for two out of the three gene pairs (a-b, b-c), but will have the same configuration for one out of the three gene pairs (a-c)

The gene pair with the same configuration in both the parentals and double recombinants is the outside pair (a–b–c)

36
Q

How do you determine the distance between an outer gene and an inner gene in a three-point cross?

A

Add up the amount of progeny that are recombinant for that gene pair (opposite configuration)

Will be the double recombinants and two other classes

Take the number of recombinants over total progeny ->
Percentage is map units

37
Q

How do you determine the distance between the two outer genes in a three-point cross?

A

Add up the amount of progeny that are recombinant for that gene pair, plus twice the number of double recombinants -> Double recombinants will appear to be in the same configuration as the parentals for the outer gene pair (see gene order above) and each represents two crossover events

Take the number of recombinants (2*DR and the four single recombinant classes) over total progeny

Percentage is map units

38
Q

What is meant by interference?

A

Does a crossover event in the interval between the first and second genes interfere with a crossover event in the interval between the second and the third genes?

39
Q

How do you determine the coefficient of coincidence? (the percentage of expected recombinants present)

A

Observed number of double recombinants over expected number of double recombinants (if no interference) is the coefficient of coincidence

Expected number comes from (% recombinants A-B) * (% recombinants B-C) = expected % of double recombinants

remember that % recombinants is map units

40
Q

How do you determine interference?

A

1 - coefficient of coincidence

41
Q

In the progeny from a haploid organism, how do you determine if a crossover occurred in an ordered tetrad? (FDS/SDS)

A

A four by four phenotypic arrangement is FDS

Any other phenotypic arrangement is SDS

42
Q

How do you determine the distance from a gene to its centromere in ordered tetrads of haploid progeny?

A

(½ SDS)/total * 100

43
Q

How do you determine the classes used to calculate the distance between two genes in an ordered or unordered tetrad of haploid progeny?

A

Parental Ditype (PD) - two parental genotypes

Nonparental Ditype (NPD) - only recombinants

Tetratype (TT) - all four genotypes

Will have 2 PD, 3 TT, and 1 NPD

44
Q

How do you determine the distance between two genes with a haploid tetrad?

A

(½ TT + 3 NPD)/total * 100 = distance in mu

45
Q

How do you determine if genes are linked by looking at progeny from a haploid tetrad?

A

If NPD «< PD → linked

If NPD ~ PD → unlinked

BIOSCI 2223: Genetics (4 decks)

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