Lecture 16

Question 1

if a cell is 4n, what does the 4 mean and what does the n mean?

Answer 1

4 = the number of sets of a chromosome (ex. 4 red chromosomes)

n = the number of chromosomes in a set (ex. if n = 1, there is only one type of chromosome, which is red. if n = 2, there are red and blue chromosomes)

Question 2

what causes triploidy that originates from defective meiosis?

Answer 2

failure in segregation

Question 3

how does defective meiosis lead to triploidy?

Answer 3

diploid parent 1: defective meiosis making diploid gamete

diploid parent 2: normal meiosis so gametes are haploid

parents fertilize and create triploid gamete

Question 4

what is the most common cause of human triploidy?

Answer 4

dispermy

Question 5

what is produced when radish and cabbage are crossed? what type of ploidy?

Answer 5

creates a sterile F1 hybrid –> allopolyploid

Question 6

why is the F1 from a radish and cabbage sterile?

Answer 6

both radish and cabbage plants are 2n and the gametes are n, with n = 9

when crossed, the F1 is n + n, which is the same as the parents

but it is sterile because the chromosomes are from different species so cannot pair properly and therefore cannot segregate properly during meiosis

Question 7

what can the sterile F1 hybrid of radish and cabbage become? how?

Answer 7

becomes a fertile amphidiploid via spontaneous doubling

Question 8

why does spontaneous doubling create a fertile cell?

Answer 8

now the cells are 2n + 2n so they can pair properly and segregate properly in meiosis

Question 9

what are the F1 and F2 produced if fertile amphidiploid is crossed with parent cabbage

Answer 9

amphidiploid gametes are 2n (1 from cabbage and 1 from radish)

F1: viable but sterile bc chromosomes cannot pair properly

F2: no F2

Question 10

difference btwn triploid and trisomy

Answer 10

triploid: 3 of each type chromosome

trisomy: 2 of each chromosome but one has an extra

Question 11

4 examples of viable trisomy

Answer 11

1. XXX - normal
2. XYY - normal
3. XXY - Klinefelter syndrome
4. trisomy 21 - down syndrome

Question 12

1 example of viable monosomy

Answer 12

1. X_ - turner syndrome

Question 13

how does aneuploidy affect genes?

Answer 13

affects gene dosage

Question 14

ratio of genes in euploids

Answer 14

1:1 always!

Question 15

ratio of genes in aneuploids and the consequence

Answer 15

incorrect ratio –> genes cannot do processes properly

Question 16

describe trisomy in plants vs animals

Answer 16

plants are more tolerant to trisomy

Question 17

describe the different trisomies of Jimsonweed

Answer 17

all are 2n + 1, but depending on which chromosome is extra, there is a diff phenotype

Question 18

describe the meiosis outcomes in this situation

Answer 18

Question 19

what is non-disjunction?

Answer 19

failure of chromosomes to properly segregate in anaphase

Question 20

when can non-disjunction occur?

Answer 20

in mitosis, meiosis I, meiosis II

Question 21

describe what happens in non-disjunction in meiosis I

Answer 21

Question 22

describe what happens in non-disjunction in meiosis II

Answer 22