The document discusses the human genome and genetic disorders. It defines what a genome is and describes human chromosomes. It explains different types of genetic disorders including recessive, dominant, sex-linked, and chromosomal disorders. As examples, it discusses disorders like phenylketonuria (PKU), cystic fibrosis, sickle cell anemia, color blindness, and Down syndrome. It also describes chromosomal abnormalities that can occur like trisomies and monosomies.

1. The Human Genome
From Peas and fruit flies to humans…

3. What is a genome???
• All the genetic information (genes) that make
up an organism

4. What makes us human?
• Analyze human chromosome…
• Karotype
– Picture of all the chromosomes
in an organism
– Autosomes
• CHROMOSOMES 1-44 (pairs 1-22)
• Autosomal chromsomes
– Sex chromosomes
• Determine a person’s sex (male XY
or female XX)
• Chromosome 45 and 46 (set 23)

6. Pedigree Charts
• Shows relationships within a family
• Genetic counselors use these to infer the
genotypes of family members
• Look at each generation different symbols
used

8. Disorders can be recessive or
dominant

10. Recessive disorders
• Disorder phenylketonuria (PKU)
• Caused by an autosomal recessive allele on
chromosome 12
• People with this disorder lack the enzyme to
break down phenylalanine (amino acid found in
milk and many other foods)
– In newborns, this causes a build up of phenylalanine
in tissues during the first few years of life and lead to
mental retardation
– Newborns are commonly tested for PKU and then put
on a low phenylalanine diet if they have the disorder

11. Autosomal Recessive Allele
• Tay-Sachs Disease
– Recessive allele in Jewish families of central and eastern
Europe ancestry
– Lack the enzyme to break down lipids in neural cells
• Lipid accumulation in brain cells
– Leads to nervous system break-down and death in the
first few years of life

12. Autosomal Recessive
Disorders
• Cystic Fibrosis
– Do not have the gene that
regulates mucus production
– Excess mucus in lungs, digestive
tract, and liver
– Increased susceptibility to
disorders
– Lung transplants usually
needed after childhood

13. Autosomal Dominant Disorders
• You will express disorder if
you are homozygous or
heterozygous dominant for
that trait
– You also have higher chances
of passing onto your children
• Dwarfism (achondroplasia)
• Huntington’s Disease
– Nervous system disorder

14. Co-Dominant Alleles Disorders
• Sickle cell anemia
• 1/500 African Americans have the
disorder
• Co-dominant allele
• Causes blockages in blood vessels,
preventing oxygen from getting to
other cells and tissues
• Beneficial in central and east Africa
because it helped destroy malaria
– If you had SCA, your body would
destroy the sickle cells to protect itself
and in the process, destroy the
malaria parasite as well

16. Sex-Linked Disorders
• Many sex-linked genes are
found on x-chromosome
• Many genetic disorders are
sex-linked
• Males have just ONE x
chromosome, so whatever
the X chromosome is
carrying (dominant or
recessive) will be expressed
• Fathers can pass it to their
daughters and the disorder
can show up in the
daughters sons

17. Sex-linked Disorders
• Red-green Color-blindness
– 1/10 men
– 1/100 women
• Hemophilia
– Two important genes on x-chr control
blood clotting
– Person with disorder can die from minor
cuts
– Recessive allele in either gene can cause it
• Duchenne Muscular Dystrophy
– Caused by defective version of a gene for a
muscle protein
– Progressive weakening and loss of skeletal
muscle1/3000 males

18. X-chromosome Inactivation
• Females have XX and males have XY…is
the second X chr in females needed??
• British Geneticist Mary Lyon
• In female cells, one x-chromosome is
randomly shut off…this “shut off”
chromosome is called a Barr Body
• Different X-chrm are switched off in
different cells
• Generally not found in males b/c X-chrm
needs to be ACTIVE
• Occurs in other mammals as well

19. • Barr bodies in cats
• Gene that controls color of coat spots is located
on the X-chrm
– In a female, one X-chrm may have the allele for
orange spots and the other X-chrm may have the
allele for black spots
– Different cells in different parts of the cat’s body are
switched off= different colored spots on different
parts of the cat…mix or orange and black spots
– Males only have ONE active X-chrm…therefore, will
they have different colored spots?
• No…only psots of ONE color (b/c on ONE active X)
• This is one way to determine the sex of a cat…cat
with black AND orange spots is almost always
certainly female

21. Chromosomal Disorders
• Mechanics of meiosis (where we separate
chromosomes) is usually pretty good
• But nobody’s perfect…mistakes happen….
• Most common problem…
– Nondisjunction: when homologous chromosomes fail
to separate properly
– Literally means “not coming apart”
– If this occurs, ABNORMAL #s of chromosomes may
find their way into gametes and a disorder of
chromosome number may result

22. Nondisjunction
• If one of the gametes with an ABNORMAL #
ends up getting fertilized, MAJOR problems!!!
– Trisomy: “three bodies”
• Occurs when an autosomal chromosome fails to
separate during meiosis
– When do chrm separate?
» Anaphase I and Anaphase 2
• One gamete ends up with an extra copy of a
chromosome and then the fertilized zygote ends up
with 3 copies of a chrm instead of 2
• Example: Downs Syndrome

25. Down Syndrome
• Extra copy of chromosome 21
– 1/800 baby’s are born with this
disorder
• Produces mild to severe retardation
• Increased susceptibility to diseases,
slower development, and higher
frequency of birth defects
• How can one little extra copy cause
so many problems?
– Scientists are still trying to figure that
out…now that they have used gene
mapping and identified all the genes
on chromosome 21, they can begin
experimenting on this problem

26. Sex Chromosome Disorders
• What happens if nondisjunction happens to the sex
chromosomes???
• We know we need at least one X chromosome….
– No embryos have been found with just a Y chromosome so we now X
chrm contains vital genes!
• Turners Syndrome
– Females receive only one X chromosome
– Karotype 45, X
– Unable to reproduce, sex organs do not develop at puberty
• Klinefelters Syndrome
– Males receive an extra X chromosome
– Karotype 47, XXY
– Prevents individuals from reproducing
– Cases of individuals with XXXY and XXXXY
– Y chromosome contains “sex determining region” SDR, which gives
male characteristics and development
– If region is absent, embryo develops into female

27. Turner’s Syndrome

29. • What about an extra Y?
• Males with 47, XYY produce
more male hormones and
express a more expressive
behavior
– More testosterone=more
aggressive behavior
• Higher number of men in prison
for violent crimes have XYY
however there is a large
population of men with XYY
that do not exhibit (or at least
act upon) this aggression
– Cannot use this as an excuse for
aggressive behavior or else
criminals would be pleading an
extra Y instead of insanity :-o