Download Chapter 4 - Angelfire

Benjamin A. Pierce
GENETICS
A Conceptual Approach
FOURTH EDITION
CHAPTER 4
Sex Determination and Sex-Linked
Characteristics
© 2012 W. H. Freeman and Company
Chapter 4 Outline
• 4.1 Sex Is Determined by a Number of Different
Mechanisms, 74
• 4.2 Sex-Linked Characteristics Are Determined by
Genes on the Sex Chromosomes, 81
Sex Determination Mechanisms
• Hermaphroditism: both sexes in the same
organism
• Monoecious: both male and female
reproductive structures in the same organism
• Dioecious: either male or female
reproductive structures in one organism
Chromosomal Sex-Determination Systems:
Sex chromosomes and non-sex chromosomes
(autosomes)
• XX-XO system:
• XX – female
• XO – male
• grasshoppers
• XX-XY system:
• XX – female
• XY – male
• mammals
Concept Check 1
How does the heterogametic sex differ from the
homogametic sex?
a. The heterogametic sex is male; the homogametic
sex is female.
b. Gametes of the heterogametic sex have different
sex chromosomes; gametes of homogametic sex
have the same sex chromosome.
c. Gametes of the heterogametic sex all contain a Y
chromosome.
d. Gametes of the homogametic sex all contain an X
chromosome.
Concept Check 1
How does the heterogametic sex differ from the
homogametic sex?
a. The heterogametic sex is male; the homogametic
sex is female.
b. Gametes of the heterogametic sex have different
sex chromosomes; gametes of homogametic sex
have the same sex chromosome.
c. Gametes of the heterogametic sex all contain a Y
chromosome.
d. Gametes of the homogametic sex all contain an X
chromosome.
Chromosomal Sex-Determination
Systems
• ZZ-ZW system:
• ZZ – male
• ZW – female
• Birds, snakes, butterflies, some amphibians,
and fishes
• Haplodiploidy system:
• Haploid set – male
• Diploid set – female
• Bees, wasps, and ants
Genic Sex-Determining System
• No sex chromosomes, only the sex-determining
genes
Environmental Sex Determination
• Environmental factors
• Limpet’s position in the stack
• Temperature in turtles
Sex Determination in Drosophila
melanogaster
• genic balance system
• X : A ratio (X, number of X chromosomes;
A, number of haploid sets of autosomes)
Concept Check 2
What is the sexual phenotype of a fruit fly that
has XXYYY sex chromosomes and two sets of
autosomes?
a.
b.
c.
d.
Male
Female
Intersex
Metamale
Concept Check 2
What is the sexual phenotype of a fruit fly that
has XXYYY sex chromosomes and two sets of
autosomes?
a.
b.
c.
d.
Male
Female
Intersex
Metamale
Sex Determination in Humans XX-XY
• SRY gene on the Y chromosome determines
maleness
• Turner syndrome: XO; 1/3000 female births
• Klinefelter syndrome: XXY, or XXXY, or
XXXXY, or XXYY; 1/1000 male births
• Poly-X females: 1/1000 female births
The Role of Sex Chromosomes
• The X chromosome contains genetic information
essential for both sexes; at least one copy of an
X is required.
• The male-determining gene is located on the Y
chromosome. A single Y, even in the presence of
several X, still produces a male phenotype.
• The absence of Y results in a female phenotype.
The male-determining gene in humans
• Sex-determining region Y (SRY) gene
• Androgen-insensitivity syndrome
• Caused by the defective androgen receptor
4.2 Sex-Linked Characteristics Are Determined
by Genes on the Sex Chromosomes
• X –Linked characteristics
– X-linked white eye in Drosophila
• Fig. 4.12
– X-linked color blindness in humans
• Fig. 4.14
Concept Check 3
What was the genotype of the few live F1
red-eyed males obtained by Bridges
when+ he crossed a white-eyed female
a. X
with aw red-eyed
male?
+
b. X X Y
c. X+Y
d. X+X+Y
Concept Check 3
What was the genotype of the few live F1
red-eyed males obtained by Bridges
when+ he crossed a white-eyed female
a. X
with aw red-eyed
male?
+
b. X X Y
c. X+Y
d. X+X+Y
Concept Check 4
Hemophilia (reduced blood clotting) is an X-linked
recessive disease in humans. A woman with
hemophilia mates with a man who exhibits normal
blood clotting. What is the probability that their
child will have hemophilia?
Concept Check 4
Hemophilia (reduced blood clotting) is an X-linked
recessive disease in humans. A woman with
hemophilia mates with a man who exhibits normal
blood clotting. What is the probability that their
child will have hemophilia?
1/2
X-Linked Characteristics
• Dosage compensation: the amount of protein
produced by X-linked genes and randomly
inactivated in two sexes
• Fig. 4.17
4.2 Sex-Linked Characteristics Are Determined
by Genes on the Sex Chromosomes
• Z-linked characteristics
• Y-linked characteristics
• Characteristics of the Y and Y-linked genetic
markers