7 1 Chromosomes and Phenotype KEY CONCEPT The

7. 1 Chromosomes and Phenotype KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

7. 1 Chromosomes and Phenotype Objectives • Explain how homologous chromosomes affect traits • Describe the inheritance of sex-linked traits • Predict traits using Punnett squares

7. 1 Chromosomes and Phenotype Two copies of each autosomal gene affect phenotype. • Mendel studied autosomal gene traits, like hair texture.

7. 1 Chromosomes and Phenotype • Mendel’s rules of inheritance apply to autosomal genetic disorders. – A heterozygote for a recessive disorder is a carrier. – Disorders caused by dominant alleles are uncommon. (dominant)

7. 1 Chromosomes and Phenotype Cystic Fibrosis • The defective CF gene contains a slight change called a mutation. There are more than 1, 700 known mutations (gene of 230 000 base pairs on chromosome 7) of the disease. • Recessive disorder • More than 30, 000 people are living with cystic fibrosis (more than 70, 000 worldwide). • Approximately 1, 000 new cases of CF are diagnosed each year. • Symptoms: – Salty tasting skin – Persistent coughing – Frequent lung infections – Wheezing, shortness of breath – Poor growth – Frequent greasy bowel movements

7. 1 Chromosomes and Phenotype Huntington's Disease • Autosomal dominant gene • Protein expressed interacts with another protein to disrupt the way cholesterol accumulates in the brain • Progressive degenerative disease that destroys nerve cells of brain • Today, there approximately 30, 000 symptomatic Americans and more than 200, 000 at-risk of inheriting the disease. • Symptoms: – Personality change – Decreased cognitive ability – Balance problems – Involuntary facial movements – Jerky spasms of muscles – Dementia – Death after 10 -30 years

7. 1 Chromosomes and Phenotype