Sex Linked Traits
Objectives:
After completing this section, you should:
1. Define autosomal, x-linked, y-linked and sex linked
2. Contrast the inheritance of traits controlled by X-linked or Y-linked genes
compared with autosomal traits.
3. Contrast sex-influenced, sex-limited and sex linked traits
Some key terms:
Autosomal traits
X-linked
Y-linked
Sex-limited
Sex-influenced
Criss cross inheritance
Reciprocal cross
Homogametic
Heterogametic
On line lessons: None
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Sex Linkage in Drosophila
Morgan (1909), inheritance of eye color red (+) and white (w)
Cross 1
Red female x white male
Cross 2
White female x red male
All red
Female
Male
red
white
Same “crisscross” inheritance. One important difference. In moths and
chickens this was observed when males carried the recessive gene. In
drosophila it was observed when females carried the recessive gene.
What is going on in these studies?
Uniting Evidence from Cytology and Genetics
Meiosis: Cytological Observations
Autosomes. Always pair with a chromosome of like morphology.
Sex Chromosomes. Sometimes pair with a chromosome of like
morphology, sometimes with a chromosome of different morphology and
sometimes they are not paired. The cytology is correlated with the sex of
the individuals.
Heterogametic: Different sex chromosomes or a single unpaired sex
chromosome. (XY or XO)
Sex determination: Varies with each species;
Moths and chickens--
Females:
Males:
Homogametic (XX)
Heterogametic (XY)
Morgan’s Reciprocal Cross
cross 1
Xw
X+
X+
cross 2
X+
Y
X+Xw
X+Y
X+Xw
X+Y
Xw
Xw
Y
XwX+
XwY
XwX+
XwY
Y
Z
XB
Y
Xb
XBXb
XbY
Xb
XBXb
XbY
Xb
Y
XB
XBXb
XBY
XB
XBXb
XBY
The Punnet Square that best describes the results
of Bateson’s cross #2 is.
A. Y
B. Z
C. neither are good descriptions
Question #2:
Bateson was interested in the inheritance of the Barred trait in
chickens. He made the reciprocal to cross #1 (p. 56) And got the
following result:
female
All
Female
offspring
X
male
All
Male
offspring
Sex-Related Inheritance:
1) Sex linked traits:
2) Sex-influenced traits:
3) Sex-limited traits: