Transcript Sex-linked Traits

Human Genetics
Linkage & Gene Maps
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Some traits almost always appear together (red
hair & freckles)
Each chromosome is a group of linked genes.
The chromosomes sort independently, not the
individual genes
Two genes found on the same chromosome are
not linked forever due to crossing-over. (Genetic
diversity!)
The farther apart the genes, the more likely they
are to be separated during crossing-over
Gene map: relative location of each known
gene on one chromosome
Human Genetics
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Karyotype: Set of
photographs of
chromosomes
grouped in order in
pairs
Sex Chromosomesfemales have two X
chromosomes, males
have one X & one Y
Autosome: the
remaining 44
chromosomes (non
sex chromosomes)
Male vs. Female
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Males and females
are born in an almost
50:50 ratio. This is
because all egg cells
carry a single X
chromosome and half
of all sperm carry an
X chromosome and
half carry a Y
chromosome
Human Chromosomes
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Human chromosomes
contain both DNA and
protein. Each
chromosome contains
a single, doublestranded DNA
molecule. Human
genes are coded
directly in the
sequences of
nucleotides in DNA
Sex-Linked Traits
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Sex-linked Traits: Traits that are
controlled by a gene on a sex
chromosome.
Ex. – Eye color in fruit flies
R – Red
r - White
Sex-Linked Traits in Humans
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Several “defective” alleles are sex-linked. Few
females suffer from sex-linked traits, they are
most often the carriers rather than affected by
the disorder.
Ex – Colorblindness, hemophilia, muscular
dystrophy, night blindness.
Since the father can contribute only a Y, the
mother determines if the son will have the
defective alleles.
Multiple Gene Inheritance
(Polygenic Inheritance)
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Many traits (in both plant and animals) do
not appear in two contrasting forms.
Ex: Height, skin color
Traits that vary between 2 extremes, are
controlled by alleles of a single gene, but
by alleles of two or more genes.
Misconceptions
A widespread misconception is that traits due to
dominant alleles are the most common in the
population. While this is sometimes true, it is not
always the case. For example, the allele for
Huntington’s Disease is dominant, while the
allele for not developing this disorder is
recessive. At most, only 1 in 20,000 people will
get Huntington’s; most people have two
recessive, normal alleles.
Inherited Traits
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Tongue Rolling
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Dimples
Inherited Traits
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Detached/Attached
Earlobes
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Freckles
Inherited Traits
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Cleft Chin
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Hairline
Other Inherited Traits
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Taste PTC paper
Right handed
Curly hair
Allergies