Download Chapter 14 Section 14_2 Human Genetic Disorders

5/22/15 CHAPTER 14: HUMAN HEREDITY 14.2 – Human Genetic Disorders
A. From Molecule to Phenotype
B. Chromosomal Disorders
Mr. M. Varco Saint Joseph High School From Molecule to Phenotype
•  How do small changes in DNA molecules affect human traits?
•  Example: European/African people are more likely to have wet earwax;
Asians/Native Americans more often have dry earwax
•  A simple base change from (G) to (A) causes a membrane-transport
protein to produce dry earwax instead of wet.
1 5/22/15 Gene Study Shows Blond Hair Color Is Just Skin Deep By Karen Weintraub, for NaPonal Geographic News A new study shows that many can thank a Pny genePc mutaPon – a single leVer change from an A to a G in the enPre human genome. From Molecule to Phenotype
•  Changes in a gene’s DNA sequence can change proteins by altering their
amino acid sequences, which affect one’s phenotype.
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Disorders Caused by a Single Gene
•  Sickle Cell Disease: Autosomal recessive inheritance (ss)
•  Caused by a defective allele for beta-globin, a polypeptide in normal
hemoglobin.
•  As the blood’s oxygen level decreases, the abnormal hemoglobin begins
clumping together, forcing blood cells into long fibers.
From Molecule to Phenotype
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Disorders Caused by a Single Gene
•  Cystic Fibrosis: Autosomal recessive inheritance (cc)
•  Most cases result from the deletion of just three bases in the gene coding
for the CFTR protein, removing a single amino acid from the protein.
From Molecule to Phenotype
Genetic Advantages
•  In the US, 1 in 12 people of African ancestry carry the sickle cell allele
•  Individuals descended from populations living in
west central Africa, and who carry the sickle cell
allele, are highly resistant to malaria.
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Genetic Advantages
•  In the US, 1 in 25 people of European ancestry carry the CF allele.
•  The protein produced by the CF allele helps block the entry of the
bacteria that causes typhoid fever, a disease that caused an epidemic
1,000 years ago in Europe
Chromosomal Disorders
•  What are the effects of errors in meiosis?
•  The most common error in meiosis occurs
when homologous chromosomes fail to separate
in a process known as disjunction
•  Gametes with abnormal # of chromosomes
may result, leading to a disorder
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Normal Female Normal Male Chromosomal Disorders
Example: Trisomy
•  If two copies of an autosomal chromosome fail to separate during
meiosis, an individual will be born with three copies of that chromosome.
•  An example of trisomy is Down Syndrome.
6 5/22/15 Trisomy 21 – Down Syndrome
Chromosomal Disorders
•  Nondisjunction of the X-chromosome affect males and females differently.
•  Females (X): known as Turner’s Syndrome, and results in the failure of
the sex organs to develop during puberty
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•  Males (XXY): results in Kleinfelter’s Syndrome, which usually prevents
males from reproducing.
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