16.3- meiosis- forming gametes

Question 1

in humans gametes are ____ cells

Answer 1

haploid cells (n=23)

Question 2

what is meiosis

Answer 2

process of producing haploid gametes from diploid cells (1 2n cell (46 chromosomes), two 1n cells (23 chromosomes, 46 chromatids) - four 1n cells (gametes)

Question 3

2 key outcomes of meiosis

Answer 3

1) reduction division
2) recomnination

Question 4

what is reduction division

Answer 4

produces daughter cells with fewer chromosomes than parent cells

Question 5

what is recombination

Answer 5

produces daughter cells with different combinations of genes then parents (independent assortment and crossing over)

Question 6

what 2 things are involved in recombination

Answer 6

independent assortment and crossing over

Question 7

what’s independent assortment

Answer 7

homologous chromosomes pair up a long the equator with some maternal and some paternal on each side therefore daughter cells may contain some chromosomes from each parent

Question 8

what is crossing over and when does it occur

Answer 8

occurs at the synapsis stage of prophase
when non sister chromatids ‘cross over’ and exchange pieces of chromosomes (some genes are traded)

Question 9

what is nondisjunction and when does it occur

Answer 9

errors during separation of chromatids resulting in gametes with too few or too many chromosomes

occurs in anaphase 1 or 2

Question 10

describe nondisjunction in anaphase 1

Answer 10

homologous pairs do not separate (both go to same pole)

Question 11

describe nondisjunction in anaphase 2

Answer 11

sister chromatids do no separate (both go to the same pole)

Question 12

monosomy= ____ and an example of it

Answer 12

missing one chromosome of a homologous pair
eg- turner syndrome (X0)

Question 13

trisomy= ___ and an example

Answer 13

three copies of a chromosome/one gamete had both chromosomes of a homologous pair
eg- down syndrome

Question 14

describe the 5 steps of spermatogenisis

Answer 14

• 2n cell called spermatogonium divides by mitosis to produce 2 daughter cells
• one cell replaces OG and the other becomes a primary 2n spermatocyte
• primary spermatocyte performs meiosis 1 - 2 secondary spermatocytes (n)
• 2 secondary spermatocytes result in 4 spermatids (N)
• spermatids result in sperm

Question 15

3 characteristics of fraternal twins

Answer 15

1) 2 secondary oocytes fertilized in ovulation
2) each has its own chorion, amnion and placenta
3) non identical

Question 16

3 chracteristics of identical twins

Answer 16

1) developed from one zygote that splits
2) have separate amnions but share one chorion and placenta
3) identical

Question 17

spermatogonium- ___ __-______-___ ___-____

Answer 17

primary spermatocyte, secondary spermatocytes, spermatids