Lecture 19

Question 1

3 grape colours and the difference in pigment gene expression

Answer 1

purple = WT
green = LOF
red = partially-functional allele

Question 2

what causes the differences in pigment gene expressioni?

Answer 2

insertion of transposable element

Question 3

what causes the LOF allele for green colour?

Answer 3

insertion of Gret1 retrotransposon with flanking repeats upstream of gene –> exons intact but can’t be expressed so LOF

Question 4

what causes the partially-functional allele for red colour?

Answer 4

Gret1 cut out but repeats remain

Question 5

biology of maize

Answer 5

ENDOSPERM
- haploid sperm cell combines with diploid central cell in ovary to form triploid endosperm

EMBRYO
- haploid sperm cell combines with haploid egg cell in ovary to form diploid embryo

Question 6

genotype of endosperm is the same as _____

Answer 6

genotype of endosperm is the same as the next generation bc has chromosomes from male and female

Question 7

which maize cells have the same sets of chromosomes?

Answer 7

egg cell and central cell have the same sets of chromosomes

both sperm cells have the same sets of chromosomes

Question 8

3 alleles involved in maize pigment

Answer 8

C = dominant, purple
c = recessive, no pigment
C1 = dominant negative, no pigment

Question 9

phenotype ratio of F2 with C/C x c/c parental cross

Answer 9

3:1

Question 10

what is the prediction if you cross C/C ovule with C1/C1 pollen? what actually happens

Answer 10

make C1/C

PREDICTION: predict fully colourless bc C1 dominant neg

ACTUAL: spotted kernel, therefore something allowing pigment to be made

Question 11

since there was a spotted kernel, what is the hypothesis?

what is the experiment?

what is the result?

what is the conclusion?

Answer 11

hypothesis: C1 allele is lost in some cells of the developing endosperm

experiment: look for breakage in Chr of pollen parent

result: high rate of breakage

therefore: loss of C1 allele due to chromosome breakage

Question 12

kernel phenotype without Ac

Answer 12

Ds is stable –> no cleavage –> yellow kernel

Question 13

kernel phenotype with Ac

Answer 13

Ac allows Ds to cleave C1 off the chromosome –> yellow kernel with purple spots

loss of C1 means C function is no longer blocked to allow purple

Question 14

kernel phenotype with recessive alleles and Ac

Answer 14

Ac allows Ds to cleave, allowing the recessive alleles to be uncovered and give the bronze phenotype

therefore, the break always occurs at the same place –> not random breakage

Question 15

do the breaks occur in the same location in all strains? how do they know?

Answer 15

breaks occur in diff location in related strains, can see by which phenotypes are uncovered

Question 16

kernel phenotype with recessive allele and Ac when Ds JUMPS to diff place

Answer 16

yellow kernel –> just jumps so it maintains WT alleles and recessive alleles not recovered bc C1 maintained

Question 17

kernel phenotype with recessive allele and Ac when Ds cleaves after jumping

Answer 17

yellow kernel with purple spots, complementation is maintained by C1 is cleaved

Question 18

what is the progeny when homozygous c is crossed with homozygous C (where one of the chromosomes has Ac)?

Answer 18

50% are fully purple (C/c)
50% are purple with yellow spots
*some rare ones are yellow with purple spots

Question 19

why are 50% of progeny fully purple?

Answer 19

inherited chromosome without Ac –> no Ac = Ds is stable = maintain C = all cells C/c

Question 20

why are 50% of progeny purple with yellow spots?

Answer 20

inherited chromosome with Ac –> Ac allows Ds to cleave C = some cells are c/c = some spots yellow

Question 21

why is there a rare type of progeny where kernels are yellow with purple spots?

Answer 21

inherited chromosome with Ac –> Ds jumps INTO C, creating new c-m1 allele to make yellow

purple parts = Ds jumps out of c-m1 and restores ability of C to make pigment

Question 22

Ds vs Ac

Answer 22

Ds = non-autonomous
Ac = autonomous

Question 23

non-autonomous transposable element

Answer 23

does not make its own transposition machinery, relies on another transposable element

Question 24

autonomous transposable element

Answer 24

encodes its own transposition machinery

Question 25

what determines spot size?

Answer 25

depends on when Ds jumps out to make C gene become active during endosperm development

Question 26

what happens if Ds jumps out EARLY in endosperm development?

Answer 26

large spot

Question 27

what happens if Ds jumps out LATE in endosperm development?

Answer 27

small spot

Question 28

which organisms have transposable elements?

Answer 28

all organisms

Question 29

2 classes of transposable elements

Answer 29

1. retrotransposons
2. DNA transposons

Question 30

what type of organisms have retrotransposons?

Answer 30

eukaryotes

Question 31

what are retrotransposons similar to?

Answer 31

retrotransposons

Question 32

describe movement of retrotransposons (6 steps)

Answer 32

1. in DNA, flanked by LTR
2. transcribed into transposon genome by cell machinery
3. exported
4. translated
5. RT makes ds transposon genome
6. goes back to nucleus to insert into DNA at terminal repeats

Question 33

evolution of retrotransposons

Answer 33

retroviruses got into cell, integrated into genome but lost env gene so gets trapped in cell

Question 34

what organisms are DNA transposons in?

Answer 34

prokaryotes and eukaryotes

Question 35

describe movement of DNA transposons

Answer 35

1. Ac encodes transposon
2. transposon cleaves Ac/Ds
3. transposon + Ac/Ds integrate into target DNA in new location

Question 36

what is the P element in drosophila?

Answer 36

encodes 1 protein (transposase) which is flanked by 31 bp inverted repeats in DNA