Transcript sex chromosome

Heredity
Chapter 14
Linked Genes
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Genes may occur in patterns if two loci are on
the same chromosome
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During crossing over, these loci are so close
they typically will remain together
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Ex: blonde hair, blue eyes
Chromosome Mapping
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The farther apart a gene is on a
chromosome, the more likely they
will cross over
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Mapping a chromosome is a diagram
of the loci the chromosome codes for
Karyotype
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A picture of chromosomes arranged in size
order
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Used to determine the sex of an individual and
to see if there are any chromosomal disorders
Karyotype
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Trisomy karyotype
Karyotype
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Monosomy karyotype
http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html
http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping2.html
Sex Chromosomes/Autosomes
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Sex chromosomes
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Contain genes that determine the sex of an
individual (X & Y chromosomes)
Autosomes
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Remaining chromosomes that do not
determine sex of an individual
(chromosomes 1-22)
Sex Determination
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In mammals, egg cells only contain an X
chromosome and sperm can either have an X or
Y chromosome
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If the new baby cell has XX  girl
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If the new baby cell has XY  boy
https://www.youtube.com/watch?v=kMWxuF9YW38
Gene Location
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Sex-Linked genes
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Characteristics that typically only show up in
a certain sex of the organism
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Ex: color blindness in males
Traits that are on one sex chromosome and
not the other
https://www.youtube.com/watch?v=8Aaivktz8G0
CB Glasses: https://www.youtube.com/watch?v=ea_xOqNvntA
https://www.youtube.com/watch?v=-Iz8xZD9LcI
Sex Linked Genes
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Colorblindness
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Full color vision is dominant over colorblindness
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X = color vision, XC = colorblindness
Colorblind male, color vision female
(homozygous)
Color vision male, color vision female
(heterozygous)
Sex Linked Genes
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Eye Color in Drosophila
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Red eyes are dominant over white
XR = red eyes , Xr = white eyes
Red eyed male, white eyed female
White eyed male, red eyed female
(heterozygous)
X-linked Traits
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X-Linked traits are usually recessive
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Males inherit X from mom which holds
a huge amount of base pairs
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If there is no other X to mask the trait,
then the individual shows the X-linked
trait
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Individuals that have one copy of a
recessive trait are known as carriers
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Carriers do not express trait, but can
pass to offspring
Sex-Influenced Traits
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Males and females can
show different phenotypes
even if genotype is the same
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Ex: pattern baldness
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% higher in men due to
higher levels of
testosterone
Pedigrees
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Diagram that shows how a trait is inherited
over generations
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Male = 
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Female = 
Pedigrees
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Horizontal line between a male and female
means they are married or have offspring
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Vertical line between a male and female
indicates offspring

https://www.youtube.com/watch?v=Wuk0W10EveU
Pedigree
http://www.ualberta.ca/~pletendr/tm-modules/genetics/70gen-hemophil.html
Single-Allele Traits
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Some traits are controlled by just one single
dominant allele
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Ex: Huntington's disease
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If individual has one allele for this disease,
they have it
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There are no carriers
Mutations
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Change in a sequence of a gene
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Germ-cell mutation (gamete/sex cell)
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Change in the individual’s gametes
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May be passed onto offspring
Somatic-cell mutation
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Change in the individual’s body cells and can affect
the person
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Ex: skin cancer
Chromosomal Mutation
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Nondisjunction
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When a chromosome fails to split during
meiosis (anaphase) and sex cell
chromosomes are uneven in number
Karyotype
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Nondisjunction mutations in autosomes
Karyotype
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Nondisjunction mutations in sex chromosomes
Kleinfelter’s syndrome