Module 4 Part 1

Question 1

define sexual dimorphism

Answer 1

morphological differences between the sexes

Question 2

how to know sex while looking at karyotype

Answer 2

check the 23rd chromosome

Question 3

What are Pseudo-Autosomal Regions (PAR) 1 and 2

Answer 3

short, autosomal like homologous regions
- around 30 genes
- one XY or both XX regions pair and cross over during meiosis

Question 4

what are differential regions

Answer 4

regions of x and y chromosomes which contain genes that are unique to these chromosomes
- sex linked genes and show sex linked patterns

Question 5

describe y linked patterns of inheritance

Answer 5

the trait is seen only in males
- all male descendants of an affected man will exhibit trait

Question 6

can females inherit y linked patterns

Answer 6

no, and cannot pass it on either

Question 7

describe x dosage compensation

Answer 7

one x chromosome is randomly selected for epigenetic silencing
- NO transition from the silenced X chromosome

Question 8

what does the silenced chromosome form

Answer 8

a condensed, transcriptionally inactive mass in nucleus of female somatic cells
- BARR BODY

Question 9

exaplain x inactivation on the tortoiiseshell cat

Answer 9

Gene responsible for the fur colour on X chromosome
X^B= orange
X^b= black

male cats= no x inactivation- either orange or black

female cats= one chromosome inactivated
homo= either black or orange
hetero= MOSAIC fur coat

Question 10

describe normal x-inactivation

Answer 10

• healthy cells have two unaffected/normal copies of the x chromosome, which may carry homo or hetero alleles
  -each cell has one x chromosome that is epigenetically silenced
• silenced x is chosen randomly

Question 11

describe disease causing mutation in x-linked gene

Answer 11

• in biologically female
• mutation is heterozygous
  x linked recessive= the presence of normal/healthy X in non-silenced cells is sufficient for normal tissue function

x linked dominant= the presence of the normal/healthy X in non-silenced cells is insufficient for normal tissue function

Question 12

what happens in biological males for x linked diseases

Answer 12

all cells will be affected since only one copy of x chromosomes (more severely affected)

Question 13

describe hemophilia

Answer 13

blood clotting disorder- recessive x linked

Question 14

describe red-greem colour blindness

Answer 14

between 7-10% of men and 0.5-1% of women affected- recessive x linked

Question 15

describe becker’s muscular dystrophy

Answer 15

a milder form of DMD, causing slowly progressive muscle weakness of the legs and pelvis- recessive x linked

Question 16

describe hypophosphataemia

Answer 16

aka vitamin d resistant rickets- dominant x linked

Question 17

describe rhett syndrome

Answer 17

a brain disorder that occurs almost exclusively in girls- recessive x linked
lethal in men

Question 18

what is hemophilia a

Answer 18

deficiency in clotting factor VIII
- 1/5000 births

Question 19

describe haemophilia b

Answer 19

deficiency in clotting factor IX
- 1/20 000 births

Question 20

describe x linked dominance in males vs females

Answer 20

more females than males will express the phenotype, but will have milder clinical course than males with the mutation

Question 21

define gender

Answer 21

describes the characteristics of women and men that are SOCIALLY CONSTRUCTED

Question 22

what is sex

Answer 22

refers to what is biologically determined

Question 23

is sry male or female

Answer 23

male

Question 24

describe sex reversed xx males

Answer 24

often have part of y including the sry gene one on of their x chromosomes

Question 25

describe sex reversed xy females

Answer 25

lack sry on their y chromosome either bc it has been replaced by part of the x chromosome or because it is inactived by mutation

Question 26

describe intersex

Answer 26

umbrella term used to describe person born without the reproductive or sexual anatomy which do not fit into typical definitions of biological sex binary- male or female

Question 27

possible causes of intersex

Answer 27

• sex chromosome mutations: loss of androgen sensitivity due to x linked recessive mutation of androgen receptor
• sex chromosome aneuploidy
  = xxy klinefelters
  = xyy jacobs syndrome
  = xo turners syndrome