The document discusses sex-influenced traits, which are traits controlled by alleles on autosomal chromosomes, with their expression influenced by hormones like testosterone. An example is pattern baldness, more common in males due to the dominant nature of the baldness allele in the presence of high testosterone levels. It also details genetic terms such as heterozygous and homozygous, explaining how different genotypes can result in varying phenotypic expressions based on sex.

1. Sex-Influenced Traits
By : Faizan Ilyas

2. Sex-Influenced Traits

3. Basic Terminologies
Alleles : An allele or allel, is one of a
number of alternative forms of the same
gene.
Autosomal chromosomes : The
autosomal chromosomes do not
determine the sex of offspring. Rather,
they contain many genes that code for
the production of thousands of
proteins.

4. Sex chromosomes : The sex
chromosomes determine the sex of
offspring. Sex chromosomes determine
whether the offspring are male or
female.
Lipoma : A lipoma is a benign tumor of
fat cells that can cause rubbery tumors
of varying size beneath the skin.
A benign tumor is a mass of cells that
lacks the ability to invade neighboring
tissue .

5. Heterozygous : The genetics term
heterozygous refers to a pair of genes
where one is dominant and one is
recessive.

6. Homozygous : The genetics term
homozygous refers to a pair of genes
where both genes are dominant or both
are recessive.

7. Testosterone : It is a steroid
hormone which is found in mammals,
reptiles, birds and other vertebrates. In
mammals, testosterone is secreted
primarily in the testicles of males and
the ovaries of females. It promotes
secondary sexual characteristics such
as increased muscle, bone mass, and
the growth of body hair.

8. Where we are heading….
Sex-linked traits are controlled by
alleles found on the sex-chromosomes.
Sex-influenced traits are controlled by
alleles on autosomal chromosomes.

9. What is a sex-influenced trait?
A sex-influenced trait is a trait controlled by a pair
of alleles found on the autosomal chromosomes
(pairs 1 through 22) but it’s phenotypic
expression is influenced by the presence of
certain hormones.
Sex-influenced traits can be seen in BOTH
sexes, but will vary in frequency between the
sexes, or in the degree of the phenotypic
expression.
Estrogen, Progesterone, Testosterone, etc.

10. Example of Sex-Influenced
Traits
Pattern Baldness
– Pattern Baldness can occur in both males
and females, however it is much more
common in males.
– Why is this?
Because the pattern baldness trait is
influenced by the hormone testosterone.

11. Pattern baldness in humans
(sometimes called “male pattern
baldness,” though the condition isn’t
restricted to males). This gene has two
alleles, “bald” and “non-bald.” The
behaviors of the products of these
genes are highly influenced by the
hormones in the individual, particularly
by the hormone testosterone.

12. . In the presence of high levels of
testosterone, the baldness allele has a
very powerful influence. In the presence
of low levels of testosterone, this allele
is quite ineffectual. All humans have
testosterone, but males have much
higher levels of this hormone than
females do. The result is that in males,
the baldness allele behaves like a
dominant allele, while in females it
behaves like a recessive allele.

13. Sex-Influenced Traits
Male and Female Pattern Baldness

14. Basic Symbols

15. Sex-Influenced Trait
Assume that the trait is
dominant in males but
recessive in females.
Assume all outsiders are
homozygotes.
Thus:
– DD is always affected
– dd is always normal
– Dd is affected in males, but
normal in females

16. Pattern Baldness
The combination of alleles for pattern
baldness will lead to different phenotypic
expressions depending on the sex of the
individual.
For example: Let B represent the non-bald allele
- BB genotype: non-bald in both sexes
- bb genotype: bald in both sexes
- Bb genotype: bald in men; non-bald in females

17. Pattern Baldness
The “B” allele acts as a dominant allele
in the heterozygous genotype in
females, but acts as a recessive allele
in the heterozygous genotype of the
male.

18. Pattern Baldness
What would this bald guy’s genotype
be?
Bb or bb
What about his balding mother?
bb

19. Try this out!
What is the probability that YOU will be
bald if your father is homozygous and
balding, and your mother is
homozygous and not balding?
Father’s genotype: bb X Mother’s genotype: BB
All offspring are Bb
If you are a male, you will be bald! If you are a
female, you will not demonstrate pattern baldness.

20. You can solve using Monohybrid
crosses
Complete the simple cross and then express
the phenotype based on whether we are
talking about males or females.
Ex. A heterozygous balding male reproduces
with a heterozygous normal female.
Do the cross and determine the phenotypic
rations for males and females

21. Let’s try a few problems involving
sex influenced traits…
A male homozygous for clubfoot reproduces
with a normal homozygous female. What are
the genotypes and phenotypes of their
children if testosterone alters the phenotypic
expression of the trait in the heterozygous
expression?
Let F represent normal feet
Let f represent clubfoot.

22. Let’s try a few problems…
Two heterozygous individuals get married
and have lots of children. The father suffers
with a painful condition called gout. What are
the parent’s genotypes? What are the
genotypes and phenotypes of the children?
Let G represent no gout, and g represent
gout.

23. How about this one:
Rheumatoid arthritis occurs more
often in females than males due to
the presence of estrogen. A
heterozygous woman marries a
heterozygous male. RR would cause
the condition in both sexes. A
homozygous recessive, rr, genotype
would prevent the disorder in both
sexes