1. Chapter 14: The Human Genome
14-1: Human Heredity
14-2: Human Chromosomes
14-3: Human Molecular Genetics

2. 14-1: Human Heredity Objective: How is sex determined?
How do small changes in DNA cause genetic disorders?

3. Human Chromosomes Cell biologists Photograph cells in mitosis
Chromosomes are fully condensed
Easy to see
Cut out the chromosomes from the photographs
Group them in pairs
karyotype: set of photographs of chromosomes grouped in order in pairs

4. Human Chromosomes Cont’d
Humans have 46 chromosomes
23 from each parent
One of the 23 chromosomes given is a sex chromosome
sex chromosome: determine an individual’s sex
Females can only give an “X” chromosome
Large chromosome
Males can give an “X” or “Y” chromosome
Ratio is 50:50
“Y” chromosomes are small
The other chromosomes are called autosomes
autosomes:chromosome that is not a sex chromosome

5. QUICK QUESTION
What is a karyotype?

6. QUICK ANSWER
A picture of chromosomes arranged in pairs

7. Human Traits
Human genes are inherited according to Mendle’s Principles
Biologists must identify an inherited trait controlled by a single gene
determine that the trait is inherited and not environmentally influenced
study how the trait is passed from one generation to the next

8. Human Traits Cont’d
Genetic counselors analyze pedigree charts to infer the genotypes of family members
pedigree: shows the relationships within a family

9. Human Traits Cont’d
Some of the most obvious human traits are almost impossible to associate with single genes
many traits are polygenic
many personal traits are determined by genes and environment
2 types
nutrition
exercise
Not inherited
Genes may be denied a proper environment in which to reach full expression

10. Group Activity
Complete the “Problem Solving” pedigree on page 343.

11. Human Genes The human genome our complete genetic information
tens of thousands of genes
specify many characteristics
Exploration of the human genome sequence of the human genome has been a major scientific undertaking
identify genes that directly control a single human trait
blood type

12. Blood Group Genes Human blood Variety of blood groups
ABO Rh
Receiving the wrong type of blood can be fatal

13. Blood Group Genes cont’d
Rh blood group
Named for the “rhesus monkey” in which this factor was found
Determined by a single gene
2 possible alleles
Positive (dominant)
Negative (recessive)

14. Blood Group Genes cont’d
ABO blood group
3 alleles for this gene
IA (codominant)
IB (codominant)
I (recessive)

15. Blood Group Genes cont’d
Blood types
Type A
Make the A antigen
IAIA
IAi
Type B
Make the B antigen
IBIB
IBi
Type AB
Make the A and B antigens
IAIB
Type O
Make no antigens ii

16. Recessive Alleles Autosomal recessive
The presence of a normal, functioning gene is revealed only when an abnormal or nonfunctioning allele affects the phenotype

17. Recessive Alleles cont’d
PKU
Lack the enzyme that is needed to break down an amino acid found in milk and many other foods
Build up of this amino acid can cause mental retardation
Tay-Sachs disease
Found mostly in Jewish families of central and eastern European ancestry
Nervous system breakdown and death in the first few years of life

18. Dominant Alleles Autosomal dominant
A dominant allele for a genetic disorder
Example
Achondroplasia
Dwarfism
Nervous system disorder
Huntington’s disease
Progressive loss of muscle control and mental function until death

19. Codominant Alleles
Diseases and disorders caused by a codominant allele (both alleles are dominant)
Example
Sickle cell disease
1 out of 5 African Americans

20. Quick Question
What type of allele causes Huntington’s disease?

21. Quick Answer
An autosomal dominant allele

22. From Gene to Molecule
Scientists are still working to find the answer for
How DNA sequences in genes affect phenotype
The link between the DNA bases in the allele for a genetic disorder
Example
In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder

23. Cystic Fibrosis Common genetic disease
Most common among people whose ancestors came from Northern Europe
Caused by a recessive allele on chromosome 7
Deletion of 3 bases in the middle of a sequence for a protein
Cells do not transport the protein to the cell membrane
Misfolded protein is destroyed
Serious digestive problems
Produce a thick, heavy mucus that clogs their lungs and breathing passageways
Tissues throughout the body malfunction

24. Sickle Cell Disease
A common genetic disorder found in African Americans
Ancestry traced to west central Africa
Malaria is common
Heterozygous people are resistant to malaria

25. Sickle Cell Disease cont’d
Characterization
Bent and twisted shape of the red blood cells
Decrease in blood oxygen levels
Body destroys the sickled cells and malaria parasite
More rigid
Gets stuck in capillaries
Damages cells, tissues and organs
Produces physical weakness
Damage to the brain, heart, and spleen
Can be fatal

26. Dominant or Recessive?
Deciding if an allele is dominant, recessive, or codominant depends on the nature of a gene’s protein product and its role in the cell.

27. Exit Ticket Answer the following questions. Use complete sentences.
You may NOT use your book. You MAY use your notes.
This is a quiz grade.
How is sex determined?
How do small changes in DNA cause genetic disorders?