11: Genetics 2: Inheritance Patterns and Genetic Testing

Question 1

Autosomal

Answer 1

Gene is on one of the autosomes i.e. chromosomes 1-22

Question 2

Sex-Linked

Answer 2

Gene is located on one of the sex chromosomes i.e. X or Y

Question 3

Autosomal Dominant Inheritance

Answer 3

• Can’t skip a generation
• Boys and girls affected equally
• Both homozygous and heterozygous express trait
• Many traits but few diseases show this inheritance pattern
• E.g. Huntington’s

Question 4

Autosomal Recessive Inheritance

Answer 4

• Can skip a generation
• Boys and girls affected equally
• Heterozygous are carriers with dominant phenotype
• More diseases show this inheritance pattern – because it can be hidden by the dominant allele
• E.g. CF

Question 5

ABO Blood Typing

Answer 5

• Blood type is determined by the presence/absence of antigens on red blood cell membranes
• Blood also carries antibodies against any blood type antigens not expressed
• Determines the compatibility of blood transfusions

Question 6

Incomplete Dominance

Answer 6

• Homozygous traits are still observed

- Heterozygous traits are mixed – a new form of phenotype

Question 7

Incomplete Dominance in Humans

Answer 7

• Rare in humans
• One example is the sickling gene
• Individuals who are homozygous for the diseased allele have sickle-cell anaemia
• Individuals who are heterozygous have sickle-cell trait, and make some normal and some abnormal haemoglobin

Question 8

Haemophilia

Answer 8

• Defective recessive gene for clotting factors VIII & IX
• Located on X chromosome
• Y chromosome has no equivalent gene
• Heterozygous women carriers but not haemophiliacs
• Males with defective gene are haemophiliacs

Question 9

Genotype/DNA Sequencing

Answer 9

Genotypes can give almost unlimited information:
> Complete gene sequences
> Allows determination of alleles
> Also, smaller variable regions e.g. SNPs

Question 10

Gene Sequencing

Answer 10

• Sample of DNA taken from a person
• Individual chromosomes separated
• Entire sequence of nucleotide bases on every chromosome mapped
• Compiles a full list of genes/alleles
• Recent advances in sequencing technologies offer faster and cheaper results

Question 11

Advantages of Genetic Testing

Answer 11

• Determine risk of passing genetic defects on to offspring
• Informed lifestyle choices (risk factor reduction, future planning)
• Make decisions regarding medical treatments
• Examine ‘good genomes’
• Reduced anxiety
• Curiosity

Question 12

Disadvantages of Genetic Testing

Answer 12

• Better not to know
• May affect health insurance or employment
• May produce social prejudice
• Religious beliefs
• Cost/availability

Question 13

Human Genome Project

Answer 13

• Completed* in 2003 (US $3 billion)
• Used a composite genome from 10-20 humans
• Aims: to identify all 20,000-25,000 genes in human DNA & determine the sequences of the 3 billion base pairs that make up human DNA
• Store this information in databases
• Address the ethical, legal, and social issues that may arise from the project