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Chapter 11 Complex Inheritance and Human Heredity

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1 Chapter 11 Complex Inheritance and Human Heredity
11.1 Basic Patterns of Human Inheritance

2 Recessive Genetic Disorders
Mendel’s work went unnoticed by the scientific community for about 30 years then it was rediscovered in the early 1900s. At that time many scientists were interested in the cause of diseases and noticed that some diseases “ran in families”. Alkaptonuria was the first identified (recessive) genetic disorder. Alkaptonuria, from an enzyme deficiency, causes black acidic urine and later in life affects bones and joints.

3 Recessive Genetic Disorders
A recessive trait is expressed when the individual is homozygous recessive for the trait. Both parents would need to have at least one recessive allele. Usually the parents are heterozygous (carriers) for the disorder.


5 Cystic Fibrosis Affects the mucus-producing glands, digestive enzymes, and sweat glands Chloride ions are not absorbed into the cells of a person with cystic fibrosis but are excreted in the sweat. Without sufficient chloride ions in the cells, a thick mucus is secreted

6 Cystic Fibrosis

7 Cystic Fibrosis

8 Albinism Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes White hair. Very pale skin Pink pupils

9 Albinism

10 Tay-Sachs Disease Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration. Death by age 2

11 Dominant Genetic Disorders
99.9% of population is homozygous recessive for achondroplasia

12 Huntington’s Disease Affects the nervous system
Latent disorder affects age 30 to 50 Gradual loss of brain function (“holes” in brain) Genetic test available Result of allele mutation at tip of chromosome #4

13 Achondroplasia Most common form of dwarfism
75% of individuals born to parents of average size, result of new mutation Lethal spontaneous abortion in homozygous dominant genotype

14 Pedigree Analysis

15 Pedigree Analysis Are females Are males
Shaded in circles and squares are affected individuals Roman Numerals (I – IV) are generations Lines across represent mating Lines down represent offspring

16 Pedigree Analysis Count the number of affected males and affected females. If most males and few or no females most likely sex linked trait. Look at the affected individuals. If every individual with the trait has a parent with the trait then this trait is dominant. If non-affected parents produce an offspring with the trait then it is recessive. Determine the phenotype and genotype of every individual

17 Pedigree Analysis Affected males: 1
Affected females: 2 (not sex linked) No affected individual has parent with the trait, means recessive All affected individuals would be homozygous recessive, aa All parents of affected individuals would be heterozygous, Aa Siblings of affected individuals would be heterozygous (Aa) or homozygous dominant (AA)

18 Pedigree Analysis

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