Human
Genetics
A Pedigree of a Recessive Human Trait
Note that the trait can appear in offspring of parents without the trait.
Heterozygotes who do not show the trait are termed carriers.
A Pedigree of a Dominant Human Trait
Note that the trait appears in every generation and ½ the offspring
of an affected heterozygote are expected to show the trait.
X-linked Inheritance – When Men and Woman Play by Different Rules
Behind the 8-ball? Colorblindness is an X-linked recessive trait.
X-linked Inheritance
There are many X-linked recessive traits.
Pedigree Analysis is a Key Tool in Human Genetics
Analyzing a pedigree is like puzzle-building – you try things (assigning
potential genotypes) until the pieces fit (you’re as certain as you can be about
genotypes and modes of transmission (autosomal vs. X-linked; dominant vs.
recessive).
Lab Karyotyping
http://www.ncbi.nlm.nih.gov/books/
bv.fcgi?rid=gnd
http://www.biology.arizona.edu/hum
an_bio/activities/karyotyping/kary
otyping.html
http://explorelearning.com
Searching for Chromosomal Defects - Amniocentesis and Chorionic
Villus Sampling
Many new
techniques for
learning about
individual genes
rather than whole
chromosomes are
available or under
development.
Searching for Chromosome and Gene Defects – Pre-Implantation
Genetic Diagnosis (PGD)
Removing a cell for
diagnosis from a human
embryo.
The diagnosis: trisomy
21 (Down syndrome).
Chromosomes and Inheritance
Since genes are carried
on chromosomes,
knowledge of
chromosome number
and structure has farreaching implications
for basic genetics,
human health, and
evolution.
A normal human male
karyotype.
Chromosome Non-Disjunction in Meiosis Causes Aneuploidy
Changes in Chromosome Number and Structure
Changes in chromosome number and structure are important for health and
evolution.
Down syndrome is caused by a change in chromosome number.
Aneuploidy
Aneuploidy occurs when one of the chromosomes is present in an
abnormal number of copies.
Trisomy and monosomy are two forms of aneuploidy.
Down Syndrome is Caused by
Trisomy for Chromosome 21
Aneuploidy is remarkably common, causing
termination of at least 25% of human
conceptions.
Aneuploidy is also a driving force in cancer
progression (virtually all cancer cells are
aneuploid).
The Frequency of Chromosome Non-Disjunction And Down
Syndrome Rises Sharply with Maternal Age
The phenomenon is clear – the explanation isn’t.
Patau
Syndrome
Edwards
Syndrome
Sex Chromosome Aneuploid Conditions are Common
Turner
Syndrome
Klinefelter syndrome
Klinefelter
syndrome
Jacob
Syndrome
Triple X
Syndrome
Turner
Syndrome Xo
Chromosome Structural Changes
There are 4 types of
chromosome structural change
– all of them associated with
human disorders
A Boy with Cri-du-Chat Syndrome – a Debilitating Disorder
Caused by Chromosome Deletion
Cri-du-Chat is Caused by the Loss of the Short Arm of One Copy
of Chromosome 5
Translocations Lead to a Number of Human Cancers
In Burkitt’s lymphoma, a chromosome translocation
causes a cell cycle-promoting gene to always be
active.
Polyploidy
Polyploidy occurs when all the chromosomes are present in three
or more copies.
Polyploidy is common in plants and rare in animals.
Polyploids Are Created When Chromosome Number Doubles
A common way for this to occur is for the mitotic spindle to fail,
leaving all chromosomes in one cell.
Polyploidy is a Major Force in Plant Evolution
Roughly 35% of flowering plants (the most familiar plant
species) arose through polyploidization.
Most Crop Species are Polyploid
Polyploids, like the one on the left, are larger than their diploid
progenitors (strawberry on right).