Sex linkage and determination

Question 1

monoecious

Answer 1

individual has both male and female reproductive structures (hermaphrodite)

Question 2

dioecious

Answer 2

individual has either male or female reproductive structures

Question 3

3 models for sexual phenotypes

Answer 3

strict binary
bimodal (two peaks of a single trait with continuous variation)
multivariate (collection of traits that contribute to overall sex phenotype, each trait has its own distribution)

Question 4

heterogametic sex

Answer 4

produces gametes with different types of sex chromosome

Question 5

homogametic sex

Answer 5

produces gametes that all contain the same type of sex chromosome

Question 6

ZW system

Answer 6

ZZ male homogametic
ZW female heterogametic

Question 7

XX-XO system

Answer 7

XX female
XO male where O means no chromosome

Question 8

X1X2-X1X2O system

Answer 8

X1X2X1X2 female
X1X2O male where O means no chromosome

Question 9

haplo-diploidy in wasps

Answer 9

females develop from fertilised eggs
males develop from unfertilised eggs so males have one set on chromosomes (haploids) so pass on the same chromosomes to daughters-identical
sisters 75% related

Question 10

genic sex determination

Answer 10

no sex chromosomes; only sex determining genes that exist on regular chromosomes (autosome)
no difference in chromosome size or recombination patterns between sexes

Question 11

genic sex determination in yeast

Answer 11

mating types are determined by two alleles, a and alpha, at a single locus where cell types of a can only mate with cell types of alpha

Question 12

genic vs chromosome sex determination (humans)

Answer 12

Sry gene on Y chromosome determines male
does not recombine with X chromosome in meiosis leading to Y chromosome becoming highly specialised and degenerative over time

Question 13

environmental sex determination

Answer 13

eg temperature dependent sex determination (turtles burying eggs)

Question 14

sequential hermaphrodite

Answer 14

organism that can change sex at some point in its life cycle

Question 15

limpets and environmental sex determination

Answer 15

1. larva settles on unoccupied substrate and develops into a female. produces chemicals to attract more larvae
2. larvae settle on top of her and develop into males that mate with original female
3. males switch to female
4. attract more larvae to develop into males

Question 16

true or false: variation exists within species in sex determination mechanisms

Answer 16

true
sex determination mechanisms evolve rapidly

Question 17

variable XY mechanisms

Answer 17

humans: simply XX or XY
flies: the ratio of X to autosomes is the determinant
1:1 female
0.5:1 male
XO are sterile males

Question 18

drosphilia, non disjunction and proving sex determination/linked traits

Answer 18

normal: XX female red eyes
XY male white eyes
due to non disjunction in meiosis:
XXY female white eyes
XO male red eyes (sterile)

Question 19

turner syndrome as a sex chromosome aneuploidy

Answer 19

XO

Question 20

klinefelter syndrome

Answer 20

XXY
XXXY
XXXXY
XXYY

Question 21

poly-X females

Answer 21

female with more than 2 X chromosomes

Question 22

jacobs syndrome

Answer 22

XYY males

Question 23

if extra X chromosomes are inactivated, why don’t multi X individuals show a normal phenotype?

Answer 23

extra dose of the genes escaping X inactivation

Question 24

which has more effects: extra or missing sex chromosomes or autosomes

Answer 24

autosomes

Question 25

androgen-insensitivity syndrome

Answer 25

XY females that make Sry and testosterone
testosterone acts through the androgen receptor-mutations lead to this

Question 26

parthogenesis

Answer 26

asexual reproduction
no fertilisation
produces haploids
can produce diploids through replication of mothers genome

Question 27

sex limited

Answer 27

genes present in both sexes but expressed only in one

Question 28

sex biased

Answer 28

genes present in both but expressed more in one sex than the other

Question 29

sex linked

Answer 29

genes on sex chromosomes

Question 30

findings of X linked genes in drosphilia

Answer 30

Morgan found a mutant male fruit fly with white eyes.
He crossed this mutant male with a red-eyed female, the wild type, or the most common phenotype in a population.
The F1 generation produced all red-eyed offspring, which was expected of a recessive mutation.
When the F1 generation was crossed, Morgan found that the white-eyed flies returned to the population, which was expected.
An unexpected finding was that the white-eyed offspring were male and that, of the males in the F2 generation, half had red eyes and the other half had white eyes.
The ratio was 1:1 among the males.
No females with white eyes were observed; all the females had red eyes.

Question 31

criss cross inheritance

Answer 31

gene on X chromosome passed from a parent of one sex to an offspring of opposite sex
An X chromosome present in a male in one generation must be transmitted to a female in the next generation, and in the generation after that can be transmitted back to a male.
An X chromosome can “crisscross,” or alternate, between the sexes in successive generations.

Question 32

examples of x linked disorder in humans

Answer 32

red green colour blindness
haemophilia

Question 33

features of x linked inheritance

Answer 33

almost always males (no counterpart on Y)
affected males have unaffected sons as males pass affected X to daughters
A female whose father is affected can have affected sons because such a female must be a heterozygous carrier of the recessive mutant allele

Question 34

genes on Y chromosome

Answer 34

78 (vs 800), although X and Y in mammmals evolved from an autosome, Y has lost many genes
keeps genes necessary for male functioning such as spermatogenesis or body colouration

Question 35

Y linked genes

Answer 35

all embryos initially develop immature internal sexual structures of both sexes
SRY gene triggers male development
Y linked genes in region of Y where cannot cross over with X
transmitted to sons over generations

Question 36

X inactivation

Answer 36

In every cell one of two X chromosomes in inactivated.
Which is inactivated is chosen at random.
ensures dosage compensation

Question 37

X mosaicism

Answer 37

Some genes escape X-inactivation.
Once the choice of which chromosome to inactivate is made it is irreversible.
Females are thus patchy mosaics for heterozygous X-linked genes.
(some cells express one allele, others express the other)

Question 38

barr body

Answer 38

inactivated structure of an X chromosome

Question 39

example for X mosaicism (cats)

Answer 39

calico cats
One X codes for orange, one for black.
Random X inactivation leads to patches of orange and patches of black
always female as requires 2 X
(calicocats rexpress an additional genetic condition known aspiebalding. A piebald animal has patches of white (i.e., unpigmented) skin/fur. This is controlled by a different locus (S) than the black/orange fur colors.)

Question 40

human example for X mosaicism

Answer 40

Anhidrotic ectodermal dysplasia
Heterozygous females - patches lacking sweat glands

Question 41

Y chromosome lineages

Answer 41

ancestry can be traced
mutations create new Y chromosome haplotypes
neighbouring populations tend to have more closely related Y haplotypes than distant
paternity testing

Question 42

haplotype

Answer 42

group of alleles inherited together on the same chromosome from a single parent
linked