L4 - sex determination

Question 1

define monoecious

Answer 1

both male and female reproductive structures in same organism
(most plants)

Question 2

define dioecious

Answer 2

individual possesses only M OR F reproductive structures

Question 3

define intersex

Answer 3

intermediate sexual condition eg sterile

Question 4

what is the name of the male reproductive structure in plants

Answer 4

stamen

produces pollen

Question 5

what is the name of the female reproductive structure in plants

Answer 5

stigma & pistil

Question 6

what part of the plant produces pollen

Answer 6

stamen

Question 7

describe process of gamete production in stamen

Answer 7

1. diploid microspore mother cell (2n) undergoes meiosis forming 4 haploid microspores
2. a microspore undergoes mitosis forming a pollen grain which contains 2 haploid nuclei (macrogametophyte)

Question 8

what is a microgametophyte

Answer 8

pollen grain produced by stamen containing 2 haploid nuclei

Question 9

describe process of female gamete production in plant

Answer 9

1. diploid megaspore mother cell undergoes meiosis forming 4 haploid microspores
2. 3 of the 4 degenerate leaving 1 haploid nucleus (megagametophyte)
3. cell undergoes 3 rounds of mitosis forming embryo sac containing 8 haploid nuclei

Question 10

define megagametophyte

Answer 10

haploid nucleus formed by pistil

Question 11

where are female plant gametes produced?

Answer 11

in pistil

Question 12

what is found in the embryo sac

Answer 12

8 haploid nuclei 
3x antipodal nuclei 
2x endosperm nuclei 
2x synergids 
1x oocyte

Question 13

describe process of pollination in plants

Answer 13

1. pollen tube grows towards embryo sac
2. two sperm nuclei enter embryo sac
3. • one sperm nuclei + 2 endosperm nuclei form triploid endosperm nucleus
   • one sperm nuclei + oocyte form diploid zygote
4. matures and form seed - endosperm provides nutrients

Question 14

role of endosperm

Answer 14

provides nutrients

Question 15

what are the sex chromosomes in birds and which sex do they belong to

Answer 15

ZW - females

ZZ - males

Question 16

how is the sex of drosophila and nematode worms determined

Answer 16

by the ratio of X chromosomes to autosome sets

Question 17

define homogametic

define heterogametic

Answer 17

only produce one type of gamete (X - females)

can produce two types of gamete (X/Y - males)

Question 18

define heteromorphic chromosomes

Answer 18

X and Y are different structures

X contains more genes

Question 19

what evidence is there that the Y chrom determines maleness in mammals

Answer 19

1. Klinefelter syndrome (XXY and male) shows that 2 X’s don’t determine female
2. turner syndrome (X and female) shows that 2 X’s aren’t needed to be female and suggests female structures develop by default

Question 20

what causes aneuploidy’s?

Answer 20

failure of separation of homologous chromosomes during meiosis (non disjunction)

Question 21

what evidence is there that only a small region of the Y chromosome confers maleness?

Answer 21

1. some males found to be XX but have short region of Y attached to X
2. some females found to be XY but small region of Y missing

Question 22

define acrocentric

Answer 22

centromere pushed towards one end of chrom giving short and long arm

Question 23

what are PAR regions and where are they located

Answer 23

pseudo autosomal regions
either end of the Y chrom
sequences similar to the X chromosome

Question 24

where can crossing over of X and Y chromosomes occur

Answer 24

PAR regions only

Question 25

how does SRY result in development of males

Answer 25

1. embryos identical up to 6 weeks
2. at 6 weeks, if SRY present genes are activated that lead to testes development
3. testes produce anti - Mullerian hormone which degenerates Mullerian duct (no ovaries)
4. testes produce testosterone

Question 26

what is primary sexual differentiation

Answer 26

controlled by presence of SRY

formation of testes / ovaries

Question 27

what is secondary sexual differentiation

Answer 27

refers to all sex development controlled by hormones

eg external genetailia

Question 28

how is sex determined in drosophila (describe process)

Answer 28

ratio of no. of X : no. of autosome sets
usually 2 autosome sets

so XX is 2:2 which is female
XY is 1:2 which is male
X is 1:2 which is male

if ratio of X:autosome sets is >0.5 then female

Question 29

what is dosage compensation

Answer 29

in females one of the X’s is transcriptionally silent

Question 30

explain process of dosage compensation

Answer 30

1. Xic (inactivation centre) causes condensation of one of the X chromosomes to heterochromatin which is too condensed for genes to be accessed for transcription

Question 31

what is barr body

Answer 31

condensed X chromosome

Question 32

how is X inactivation inherited?

Answer 32

somatically
all descendants of initial X inactivated chromosome will have the same inactivated X (could be maternal or paternal - random)

Question 33

what are bilateral gynandromorphs

Answer 33

male on one side female on other

Question 34

how can bilateral gynandromorphs of drosophila develop?

Answer 34

X chromosome is lost in first mitotic division
one cell is XX one is X
XX and subsequent cells will develop female
X and subsequent cells will develop male

Question 35

examples of non genetic sex determination

Answer 35

1. environmental

2. social factors

Question 36

how can environment determine sex?

give example

Answer 36

temperature sensitive determination
reptiles such as crocodiles / lizards sex is determined by the temp their eggs are incubated at

the temp that can result in M&F is narrow

Question 37

how can social factors determine sex

give example

Answer 37

clownfish
live in groups of 1 F , 1 reproductive M , and many non reproductive juveniles
if F dies they all ‘move up one’

the female is aggressive which suppresses areas in others brains responsible for female hormones