Transcript Slide 1

Biology
Human Genetics
Info within the Nucleus
 Genome: complete set of genetic info in an organism (or
group of organisms).
 DNA wraps around proteins called histones; this allows
the coiling (or condensing) of DNA within the nucleus.
 Humans have 46 chromosomes in every cell (except
RBCs & gametes).
 Human genome contains ~3 billion bases.
http://www.google.com/imgres
The Human Genome Project:
 This is the sequencing of all of the DNA of
humans (as well as other organisms)
 This begun in 1988 and ended in 2000.
 They originally thought there were 90,000 genes
but there are only about 25,000-30,000 genes.
 The goal was to sequence all genes for both
normal and abnormal functions (normal and
diseased genes).
Project’s Goal:
 To use this information for in the fields of genetic
engineering (the use of biotechnology, using
biochemical techniques to identify, study and modify
genes).
 (The hope is to gain understanding in) genetic therapy
(medical treatments that attempt to change a
genome with the use of genetic engineering).
 Other organisms’ genomes have also been sequenced:
mice, cats, dogs, fruit fly (Drosophila), yeast,
Escherichia coli (bacteria), Helicobacter pylori (ulcer
causing bacteria), and some viruses (not living).
The Human Gene Map
 A karyotype is a chart of chromosomes that scientists use
to study the differences in chromosome shape, structure &
size.
 In humans, doctors use karyotypes to determine the baby’s
genetic sex & to see if there is an abnormal chromosomal #
or chromosomal abnormalities.
http://www.miscarriage.com.au/images/pages/karyotype_normal.jpg
http://www.slh.wisc.edu/outreach/images/genetics/karyotype.gif
Chromosomal Abnormalities:
 Chromosomal Abnormalities show on karyotypes.

They can be too many or too few chromosomes.
 This is the result of chromosome pairs not separating in meiosis:
during anaphase I in meiosis I or during anaphase II in meiosis II.
 This is called nondisjunction, meaning not separating.
http://embryology.med.unsw.edu.au/Defect/images/trisomy21female.jpg
Nondisjunction:
 1 daughter cell receives an extra copy of a
chromosome while another daughter cell does
not receive a copy of the chromosome

Result = gametes have an abnormal amount of
chromosomes (or genetic material).
 If this gamete joins with another, the resulting
offspring will be abnormal if it survives.
 A monosomy is when a zygote has 1
less chromosome (2n-1, or 45
chromosomes).
 A trisomy is when a zygote has 1
extra chromosome (2n + 1, or 47
chromosomes)
Very few monosomies or trisomies in
humans survive. Some that survive are:
 Down Syndrome is trisomy 21 (3
chromosome #21).
 The sex chromosomes tolerate far
more manipulations.

Trisomy X (XXX) or XXY survives as well
as monosomy X (Xo) survives.
http://www.nacdbookstore.com/images/downsyndrome.jpg
 A polyploidy is the result of a complete set
of chromosomes not separating.
 In animals, the organism generally does
not survive but in plants, a hardy plant is
produced.

In general, the best characteristics of both parents
are taken and the plants are healthier and
stronger.
 25-50% of ALL plants are polyploids.
 This includes wheat used to make bread,
potatoes, oats, bananas, peanuts, barley,
plums, apples, sugar-cane, coffee, &
cotton.
Gene Mutations:
These may involve single
nucleotides or small sections of
DNA.
These include Frameshift
mutations, Point mutations, and
Jumping genes
1. Frameshift Mutations:
 The addition or
deletion of
nucleotides that alters
the sequence of
bases (or reading
frame).
http://www.google.com/imgres
2. Point Mutations:
 Result in substitution of only 1 nucleotide that only affects 1
codon.
may
affect affect 1 a.a.
About
30% of point mutations produce no changes in
proteins. These are called silent mutations.
http://www.google.com/imgres
3. Jumping Genes:
 Insertions of
larges stretches of
DNA into the gene.
Barbara
McClintock
(1947), an American
geneticist studying
corn, discovered
these.
Jumping
genes are
called transposons
http://www.google.com/imgres
Damaged Chromosomes:
 Deletions: when
pieces of
chromosomes
are removed
http://images1.clinicaltools.com/images/gene/5
_deletion_large.jpg
Damaged Chromosomes:
 Duplications: when
fragment of the
deleted
chromosome
attaches to the
homologous
chromosome,
resulting in extra
copies of genes
http://images2.wikia.nocookie.net/psychology/ima
ges/thumb/1/1d/Chromosome_duplication.jpg/220
px-Chromosome_duplication.jpg
Damaged Chromosomes:
 Inversion: when fragment of deleted
chromosome attaches to original
chromosome but upside down
http://www.web-books.com/MoBio/Free/images/Ch8E2.gif
Damaged Chromosomes:
 Translocation: when fragment of deleted
chromosome attaches to nonhomologous
chromosome.
http://members.cox.net/amgough/mutation_chromosome_translocation.gif
Predictions & People:
Pedigree Studies:
 Human studies are not as easy to study like pea plants.
WHY?

Generations are slow, humans reproduce too slowly, humans
have few offspring and genetic studies on humans can be
unethical.
 A pedigree is a chart that shows how a trait and the
gene that controls it are inherited within a family.
Key:
 A circle =female; a square = male
 Shaded =has the trait; ½ shaded =carrier of the trait;
horizontal line between male & female =marriage line;
Roman numerals =indicate generations; Arabic numerals
=individuals within generations
Pedigree Key:
http://dbs.umt.edu/courses/biol101S04/labs/Wyrick_s04/14
_human_pedigree_analysis_files/image002.gif
http://www.uic.edu/classes/bms/bms655/gfx/pedigree1.gif
Genetic Counseling:
 A genetic counselor is a person who provides
information about probabilities of offspring and
genetic disorders.
 They use pedigrees, Punnett squares & genetic
tests.
 They explain probabilities and possibilities.
 If the people they are counseling are pregnant,
they also give options and possibly more tests
that may determine, for example, if the child has
Down Syndrome (an extra chromosome).
 PKU, or phenylketonuria, is a genetic disease
that is tested for on newborn babies in the US.

A person with this disease lacks the enzyme to
break down phenylalanine (an amino acid found
in many food products, like milk and gum).

If a person eats this, phenylalanine builds up &
causes developmental disabilities and
eventually death.

The treatment is to avoid phenylalanine.
Diseases:
It takes 2 recessive alleles to
reveal a recessive disease
or trait (otherwise the trait or
disease will “hide” behind the
dominant allele and the person
is a carrier).
1. Tay-Sachs Disease is a
disease in which a person
cannot break down lipids.


They accumulate in the brain
and this results in blindness &
brain damage.
Eventually, death occurs.
http://www.google.com/imgres
2. Cystic Fibrosis
(found on
chromosome #7) is a
disease that results
in excessive
secretions of
mucus which
accumulates in the
digestive tract &
lungs.
http://www.google.com/imgres
3. Albinism has
various forms that
is the result of
lack of pigment.
A true albino lacks
skin pigment.
 Other forms have
pale skin and whiteblond hair.
 Albinism affects all
races and animals.

http://www.google.com/imgres
Dominant Traits:
 Some dominant traits are:

freckles, widow’s peak, farsightedness, and
polydactylly (extra fingers &
toes).
http://www.google.com/imgres
http://oneparticularwave.files.wo
rdpress.com/2006/04/517pxPolydactyly_01_Rhand_AP.jpg
http://www.google.com/imgres
Dominant Diseases:
 Achondroplasia
(dwarfism)

Individuals are
heterozygous
(homozygous =
fatal)
http://www.google.com/imgres
Dominant Diseases:
 Huntington disease.
(results in the
deterioration of the
nervous system which
develops in the late 30’s
or early 40’s)

There is a genetic test
that can be performed
to determine if one will
develop this disease.

Found on
chromosome #4
http://www.google.com/imgres
Genetic Cancers
 Growth factors: proteins that initiate cell division
 Tumor-suppressor genes: make proteins that stop cell division
(prevent cancer)
 When mutations accumulate to genes that regulate control of the cell
cycle, tumors (possibly cancer) may develop.
 Oncogenes: cancer-causing genes
http://www.google.com/imgres
 Technically, cancer is
“genetic” b/c it results
from a mutation in the
DNA.
 However, The REALITY
is: inherited mutations
that cause cancer
(inherited cancer
genes) ONLY result in
a higher risk of cancer.
If inherited it does not
mean the person WILL
get cancer.

Ex: BRCA1 (mutated
tumor-suppressor gene
for breast cancer)
http://www.google.com/imgres