Unit 5 - Sex Linkage and Pedagrees

Question 1

Autosomal Inheritance

Answer 1

Refers to the transmission of genes carried on autosomes, the 22 non-sex chromosomes

Question 2

Autosomal dominant inheritance (4)

Answer 2

1. males and females have approx the same frequency of trait
2. Each individual with trait must also have one parent with the trait
3. If neither parent has the trait, none of their children will have it
4. if the trait is rare, (15% ish) then those with the trait are likely heterozygous

Question 3

Autosomal Recessive inheritance (4)

Answer 3

1. males and females have approx the same frequency of trait
2. Those with trait are often born from those without it (heterozygotes)
3. If both parents have trait, then all children will have it
4. If only one parent has the trait, a child can only have it if the other parent is heterozygous

Question 4

Pedegrees

Answer 4

Square = male
circle = female
black = has trait
white = no trait
line through = dead

Question 5

Wild type

Answer 5

the phenotype most common in the population

Question 6

Sex-linked inheritance

Answer 6

transmission of genes on sex chromosomes. X and Y

Question 7

Sex determination

Answer 7

the genetic and biological processes that produce the male and female characteristics of a species

Question 8

Sex determination in drosophila (Fruit flies) (4)

Answer 8

*Females have two X chromosomes and males have one X chromosomes
*So males have XY (normal), XYY or XO
*Females are XX(Normal), or XXY
*XXX flies are very rare and YO flies dont exist

Question 9

X/A ratio (2)

Answer 9

*The X / Autosome ratio determines gender for some species based on the number of X chromosomes to sets of autosomes
*Males typically have a 0.5 ratio and females have a 1.0. So in fruit flies, the female has 2 X’s and 2 sets of autosomes so 2/2 is 1. In males they have one X and 2 sets of autosomes so 1/2 =0.5

Question 10

Mammalian Sex determination (3)

Answer 10

*Depends on the presence or albescence of a single gene (SRY) found on the Y chromosome which produces a transcription factor needed for male-specific gene expression
* In mammals, females can be XX (Normal), XO or XXX.
*Males can be XY (Normal), XXY or XY

Question 11

SRY (3)

Answer 11

*all mammal embryos have clusters of tissue called undifferentiated gonads, which develop into ovaries or testes
*Expression of SRY initiates testicular development of the undifferentiated gonads
*The absence of SRY expression allows the default state, female, to develop.

Question 12

Z/W system (2)

Answer 12

*used by many birds, reptiles, fish, butterflies and moths
*Females have two different sex chromosomes (ZW) and males have two of the same (ZZ)

Question 13

Hemizygous

Answer 13

refers to only having one copy of a gene rather than the normal two. For example in male mammals, they have one copy of X and one copy of Y, so they are hemizygous for those genes.

Question 14

X-Linked recessive inheritance (3)

Answer 14

*Females are homozygous for the recessive allele
*Males are hemizygous for it and display the recessive phenotype as there is no second X to mask the trait
*Expression of trait is much more common in males than in females

Question 15

X-linked dominant Inheritance (3)

Answer 15

*Females are heterozygous or homozygous dominant (assume hetero)
*males are hemizygous for the dominant allele
*both express the dominant phenotype

Question 16

Y-linked inheritance

Answer 16

exclusively patrilineal (passed from father to son)

Question 17

X-linked recessive pattern (5)

Answer 17

*skips generations when male -> female -> male as the 2nd X for females masks the recessive allele
*Much more frequent in men than women
*A male with the trait mating with a homozygous dominant female will produce all offspring with the dominant phenotype, where all female offspring are carriers
*Mating with recessive male and carrier females will produce about half dominant and half recessive offspring
*mating of dominant male with recessive female results in all carrier female offspring and all recessive male offspring

Question 18

X-linked dominant pattern (2)

Answer 18

*Heterozygous females mated to recessive males transmit the dominant allele to half their offspring regardless of sex
*Dominant males mated to recessive females pass the dominant trait to all daughters and none of their sons

Question 19

Y-linked pattern

Answer 19

*exclusively male-to-male as genes on the Y chromosome do not have a copy on the X chromosome to mask them

Question 20

Dosage compensation (2)

Answer 20

*In any organism with sex chromosomes, there is an imbalance with the number of genes on the sex chromosomes (X is bigger and has more than Y)

*Any mechanism that compensates for this is called dosage compensation

Question 21

4 Types of Dosage compensation

Answer 21

1. In fruit flies, expression of X-linked genes in males is doubles compared to females
2. In roundworms, expression of X-linked genes is halved in females compared to males
3. in marsupial mammals, the paternal X chromosome in females in inactivated
4. In placental mammals, one random X chromosome in females is inactivated

Question 22

Random X-inactivation hypothesis (4)

Answer 22

• as a form of dosage compensation, one random X chromosome is inactivated
  *once this occurs it is locked in for all decedents of said cell
  *Female mammals are mosaics of two populations of cells; one expressing the maternal X and the other expressing the paternal X
  *expression for maternal and paternal X chromosomes is approx equal

Question 23

Homogametic

Answer 23

produce two copies of a sex chromosome (XX or ZZ)

Question 24

Heterogametic

Answer 24

produce two different sex chromosomes (XY or ZW)