Inheritance of Sex
and Sex-Linked or
Influenced Traits
Sex Determination

Sex chromosomes
determined at fertilization



_____ = female
_____= male
Sperm determines sex


Females only make ___
eggs
Males make ________
sperm
Can We Influence the Sex?

Historical Views
 Thought
__________ determined the sex
 Thought the __________________
determined the sex

Some Current Theories
 Chemical
environment of female reproductive
tract
 Timing of sex around _______________
Comparing the Chromosomes

X chromosome
 ____________

genes
Y chromosome
 ___________
genes
 Sex-determining region of the Y
(_______ gene)- gene that
codes for maleness
Looking Closer at the Y


Very small
Tips are called pseudoautosomal regions
 Genes
similar to genes on X
 Can recombine with X

Middle section called male-specific region (MSY)
 Genes
essential to fertility including SRY
 Genes nearly identical to X
 Amplicons- regions of palindromes
Sex Development

During fifth week of development
 Unspecified
gonads form
 Two duct systems form
Mullerian ducts- will develop into ________
structures
 Wolffian ducts- will develop into ________
structures

 During
sixth week
In males- SRY gene is activated
 In females- no SRY gene, other genes control
development

What does SRY do?


Codes for a __________________that activates
other genes controlling male development
Indifferent gonads develop into testes
 Secrete
anti-Mullerian hormones which causes these
ducts to degenerate
 Secrete testosterone to stimulate some internal male
structures to develop
 Some testosterone is converted to
dihydrotestosterone (DHT) which cause external and
some internal male structures to develop
When Things Go Wrong

Androgen insensitivity




XY chromosomes
Testosterone is produced but receptors are absent or faulty
Phenotypic, but infertile, she
Male pseudohermaphroditism




XY chromosome
Block in testosterone production
Phenotypic she at birth
At puberty, other sources of testosterone are produced and male
characteristics start to develop
Severe Combined Immune
Deficiency Syndrome
Sex-Linked Traits

Y-linked Traits
 Rare
because so few genes
 None currently well understood besides
infertility
 Trait would be passed from ______________

X-linked Traits
 Can
be recessive or dominant
Recessive X-Linked Traits

Expression



Females______________________
Males- only need one copy
(_____________)
Inheritance


Fathers pass mutated
allele to all ___________
Mothers pass mutated
allele to _______________
Dominant X-Linked Trait



Both females and
males only need one
copy
Females are usually
less severely affected
because one X is still
ok
Some disorders are
_________ in males
Sex-Linked Punnett Squares
Same as other
Punnett squares
 Mom on one side,
Dad on other
 Need to write it like
this: ___________
 Y does not have a
letter

Calico Cats
X Inactivation




Occurs during early
embryonic development
Each cell inactivated
about ______ of one of
the X chromosomes
Which X is chosen at
random
All cells in that lineage
will have the same
inactivation
Barr Bodies



X chromosome is
inactivated by attaching
__________(epigenetics)
Inactive X chromosomes
absorb more stain
creating a Barr body in
the cell
Males do not have a Barr
body
Consequences of Inactivation

In _____________ disorders
 Females
can have patches of tissue that express
mutant allele
 Most of the time enough parts are normal to not have
the effects of the disorder
 Manifesting heterozygote- female who expresses mild
form of disorder because of inactivation

In _____________ disorders
 Females
have normal and abnormal tissues
throughout body
Sex-Limited Traits
Traits can be inherited on autosomal or
sex chromosome
 Trait only affects __________________

 For
example
Beard growth
 Pregnancy- Preeclampsia
 Milk production

Sex-Influenced Trait
May be inherited on autosomal or sex
chromosome
 Sex of individual __________________

 May
be dominant in one and recessive in the
other
Genomic Imprinting




Another form of epigenetics
Gene from specific parent is
silenced in each generation
using attached methyl groups
Methyl group are removed
during meiosis and replaced
once new embryo forms
Most seem to control early
embryonic development