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