1. Human Genetics
Chapter 14

2. Quick Chromosome Review
What are chromosomes made of?
DNA & PROTEINS
When are chromosomes visible?
CELL DIVISION
What does it mean to be diploid?
Have two sets of chromosomes
One from mom & one from dad!
Which cells are not diploid? Why?
Gametes: haploid sperm (23) haploid egg (23)
They must combine to form a diploid
zygote (46)!

3. Sex Chromosomes Determine an individual’s gender
Two chromosomes within the genome
XX – Female
All human eggs carry an X chromosome (23, X)
X chromosome has > 1200 genes
XY – Male
About half of sperm cells carry an X, the other half carry a Y (23, X or 23, Y)
Y chromosome is much smaller and has only about 140 genes
mostly associated with male sex
determination and sperm development

4. Autosomal Chromosomes
Remaining 44 human chromosomes
Humans have 46 total chromosomes
44 autosomal chromosomes (22 pairs)
2 sex chromosomes
To correctly label a karyotype or summarize the number of chromosomes in a human cell:
46, XX (females); 46, XY (males)

5. Human Pedigrees Chart that shows relationships within a family
Shows presence or absence of a trait and how it is passed on through a family
used for any species
used to infer genotypes of family members
can determine if allele is dominant,
recessive, autosomal, or sex-linked
used to determine who in a family is
at risk for genetic conditions by
genetic researchers or counselors

6. Human Pedigree Children are placed from oldest  youngest
Key explains what trait is!

7. ff Ff Ff Steps: Identify all people who have the trait.
For the purpose of this class all traits will be given to you. In other instances, you would have to determine whether or not the trait is autosomal dominant, autosomal recessive, or sex-linked.
In this example, all those who have the trait are homozygous recessive.
Can you correctly identify all genotypes of this family?
F- Normal
f- cystic fibrosis Ff
Key: affected male affected female
unaffected male unaffected female

8. PKU P- Unaffected p- phenylketonuria Pp Pp Pp pp PP or Pp pp pp Pp Pp
Key: affected male affected female
unaffected male unaffected female

9. H-huntington’s disease h-Unaffected
Key: affected male affected female
unaffected male unaffected female

10. Sex-Linked Inheritance
Colorblindness
XCY
XcXc
XcY
XCXc
XcY
XCXc
XcY
Key: affected male affected female
unaffected male unaffected female

11. Karyotypes
To look at the human genome, biologists photograph human chromosomes during mitosis (usually metaphase)
Cut them out and arrange them into a picture called a karyotype
Shows the complete diploid set of chromosomes grouped together
in pairs
Arranged in order of decreasing
size

12. Normal Human Male (46, XY)

13. Normal Human Female (46, XX)

14. X Chromosome Inactivation
Females have an extra X chromosome
Most of genes in one of X chromosomes turned off
Forms dense region in nucleus called a Barr body
Same process in other mammals
i.e. calico cats

15. Human Genetic Disorders
Review: what is a mutation?
Change in DNA sequence
Changes proteins by altering amino acid sequence!
Can directly affect the phenotype expressed!
Many genetic disorders are caused
by changes in an individual gene!

16. Sickle Cell Disease
Caused by a defective allele for a protein in hemoglobin
Causes hemoglobin molecules to stick together and form sickle shape
More rigid and get stuck in capillaries
Results in loss of blood flow and damage to cells, tissues, and organs

17. Cystic Fibrosis Known as CF
Results from deletion of just three bases in gene for a protein called CFTR
Protein is destroyed and doesn’t work as a transport protein, so proper ions aren’t transported across cell membrane
Recessive trait – need two copies of defective allele for CF
Serious digestive problems and
thick, heavy mucus clogs lungs and
breathing passageways

18. Huntington’s Disease
Caused by dominant allele for a protein found in brain cells
Mental deterioration, uncontrollable movements, appears in middle age
Dominant, Autosomal

19. Genetic Advantages How do fatal alleles remain in the gene pool?
Heterozygous individuals often show genetic advantages in certain situations
Those heterozygous for sickle-cell are highly resistant to malaria
Those heterozygous for CF had an advantage in medieval times and
were resistant to Typhoid Fever

20. Chromosomal Disorders
Errors can occur in meiosis
Homologous chromosomes can fail to separate during Anaphase I
Nondisjunction
Results in gametes with an abnormal number of chromosomes
Trisomy = 3 copies of a chromosome
Down syndrome = Trisomy 21
Mild to severe mental retardation
High frequency of birth defects

21. Male: 47, XY, +21 Female: 47, XX, +21
Trisomy 21

22. Sex Chromosome Disorders
Klinefelter’s Syndrome, 47 XXY
Turner’s Syndrome
Nondisjunction of X chromosome
Female inherits only one X chromosome
Results in sterility and reproductive organs do not develop properly
Klinefelter’s syndrome
Males inherit extra X chromosome
Interferes with meiosis and
usually causes sterility
No cases of babies born without X!
Necessary for survival of embryo
XXY

23. Human Genome Project Launched in 1990
Main goal: sequence 3 billion base pairs of human DNA and identify all human genes
Completed in 2003
Completed genomes of many other organisms while working through human genome
40% of our proteins have strong similarity to proteins in many of those organisms (fruit fly, worms, yeast)

24. Human Genome Project
Only about 2% of genome encodes instructions for synthesis of proteins
Large areas of chromosomes with very few genes
Pinpointed genes and associated particular sequences in those genes with diseases and disorders
Identified about three million locations where single-base DNA differences occur in humans
Help us find sequences associated with diabetes, cancer, and other health problems

25. HGP: What now? Ethical, legal, social issues
Who owns and controls genetic information?
How does genetic privacy relate to medical privacy?
May 2008: Genetic Information Nondiscrimination Act
Prohibits US insurance companies and employers from discriminating on basis of information derived from genetic tests
Still don’t understand as many as 50% of the human genes thus far discovered