Meiosis

Question 1

Meiosis I

Answer 1

• “reductive division” (diploid -> haploid)

* separates homologous chromosomes

Question 2

crossover/recombination

Answer 2

mixing of genes between homologous chromosomes during meiosis

Question 3

meiosis II

Answer 3

chromatids separate -> 4 daughter cells (haploid)

Question 4

spermatogenesis

Answer 4

• begins at puberty
• spermatogonium (2n) -> mitosis -> 1° spermatocyte (2n) -> meiosis I -> 2° spermatocyte (1n) -> meiosis II -> spermatid (1n) -> spermiogenesis -> spermatozoa

Question 5

oogenesis

Answer 5

• 1° oocytes formed in utero -> arrested in prophase I
• at puberty 1° oocytes begin completing meiosis I each cycle -> 2° oocytes (1n) and polar bodies
• 2° oocytes arrested in metaphase II until fertilization

Question 6

aneuploidy

Answer 6

• abnormal chromosome number (not multiple of 23), ie monosomy and trisomy
• disomy=normal

Question 7

meiotic nondisjunction (NDJ)

Answer 7

• failure of chromosome pairs to separate

* most common mechanism of aneuploidy

Question 8

Meiosis I NDJ

Answer 8

• homologous chromosomes fail to separate

* gametes have chromosomes from both parents

Question 9

meiosis II NDJ

Answer 9

• sister chromatids fail to separate

* Ex: XYY males

Question 10

crossover/recombination in occurances of NDJ

Answer 10

RARE

Question 11

monosomy occurs with

Answer 11

• fertilization of 1n and 0n gametes
• usually not viable
• turner syndrome (45,X) is an example of a viable monosomy

Question 12

trisomy occurs with

Answer 12

•fertilization of 1n and 2n gametes
•not viable with most chromosomes
•exceptions: 
trisomy 21 = down syndrome (95% due to NDJ)
trisomy 18 = edward syndrome
trisomy 13 = patau syndrome

Question 13

maternal meiosis I NDJ

Answer 13

•common cause of trisomy

*higher risk because meiosis I is so drawn out in females

Question 14

robertsonian translocation

Answer 14

• fusion of long arms of 2 acrocentric chromosomes; the short arms are lost
• no important consequence for individual with the translocation, but likely to have many offspring with chromosomal anomalies and many spontaneous abortions

Question 15

acrocentric chromosome

Answer 15

chromosomes with centromeres near the end (13, 14, 21, 22)

Question 16

most common robertsonian translocations

Answer 16

• 13-14

* 14-21

Question 17

what test may be done in cases of infertility that could indicate a robertsonian translocation

Answer 17

karyotyping