Ch. 29 Heredity
Hoehn, Haynes, Abbott12th EditionMarieb Human Anatomy & PhysiologyISBN: 9780138242732
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Table of contents
- Ch. 1 The Human Body: An Orientation25
- Ch. 2 Chemistry Comes Alive24
- Ch. 3 Cells: The Living Units24
- Ch. 4 Tissue: The Living Fabric19
- Ch. 5 The Integumentary System12
- Ch. 6 Bones and Skeletal Tissues19
- Ch. 7 The Skeleton14
- Ch. 8 Joints7
- Ch. 9 Muscles and Muscle Tissue26
- Ch. 10 The Muscular System25
- Ch. 11 Fundamentals of the Nervous System and Nervous Tissue23
- Ch. 12 The Central Nervous System25
- Ch. 13 The Peripheral Nervous System and Reflex Activity30
- Ch. 14 The Autonomic Nervous System16
- Ch. 15 The Special Senses26
- Ch. 16 The Endocrine System26
- Ch. 17 Blood27
- Ch. 18 The Cardiovascular System: The Heart25
- Ch. 19 The Cardiovascular System: Blood Vessels27
- Ch. 20 The Lymphatic System and Lymphoid Organs and Tissues16
- Ch. 21 The Immune System: Innate and Adaptive Body Defenses27
- Ch. 22 The Respiratory System21
- Ch. 23 The Digestive System31
- Ch. 24 Nutrition, Metabolism, and Energy Balance26
- Ch. 25 The Urinary System26
- Ch. 26 Fluid, Electrolyte, and Acid-Base Balance24
- Ch. 27 The Reproductive System24
- Ch. 28 Pregnancy and Human Development25
- Ch. 29 Heredity11
Hoehn, Haynes, Abbott12th EditionMarieb Human Anatomy & PhysiologyISBN: 9780138242732Not the one you use?Change textbook
Chapter 29, Problem 5
Most children with cystic fibrosis are born to normal parents. Children with cystic fibrosis are homozygous for the recessive gene (cc). What can you conclude about the genotypes of the normal parents?
Verified step by step guidance1
Understand that cystic fibrosis is caused by a recessive allele, represented here as 'c'. A child with cystic fibrosis has the genotype 'cc', meaning they inherited one recessive allele from each parent.
Since the child is 'cc' and has cystic fibrosis, each parent must have contributed one 'c' allele. This means neither parent can be 'CC' (homozygous dominant), because then they would not have the 'c' allele to pass on.
Therefore, both parents must be carriers of the recessive allele, meaning their genotypes are heterozygous 'Cc'. They have one normal dominant allele 'C' and one recessive allele 'c'.
Parents with the genotype 'Cc' are phenotypically normal (do not have cystic fibrosis) but can pass the recessive allele to their offspring.
In summary, the normal parents are most likely both heterozygous carriers (genotype 'Cc'), which explains how their child can be homozygous recessive 'cc' and have cystic fibrosis.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Autosomal Recessive Inheritance
Cystic fibrosis is inherited in an autosomal recessive pattern, meaning a child must inherit two copies of the recessive allele (cc) to express the disease. Parents who do not show symptoms can still carry one recessive allele each, making them carriers.
Recommended video:
01:02
Autosomal Inheritance
Carrier (Heterozygous) Genotype
Carriers have one normal dominant allele (C) and one recessive allele (c), so they do not exhibit symptoms but can pass the recessive gene to offspring. If both parents are carriers (Cc), there is a 25% chance their child will inherit cystic fibrosis (cc).
Recommended video:
06:36Genotype & Phenotype
Punnett Square and Probability
A Punnett square helps predict the genotypes of offspring based on parental alleles. For two carrier parents (Cc x Cc), the possible genotypes are CC, Cc, and cc, with cc resulting in cystic fibrosis. This explains why affected children can be born to normal parents.
Recommended video:
07:23X-Linked Inheritance
Related Practice