Topic 3.4 Modes of Inheritance

Question 1

Principles of inheritance

Answer 1

Gregor Mendel established the principles of inheritance via experiments (he crosses large number of pea plants). His findings pioneered current scientific understandings:

• Organisms have heritable factors (genes)
• Parents contribute equally to inheritance by supplying one version of the gene each (alleles)
• Gametes contain only one allele of each gene (haploid)
• Fusion of gametes results in zygotes with two alleles of each gene (diploid)

It is now known that the separation of the two alleles of each gene into separate haploid gametes occurs via. meiosis.

Question 2

Genotype

Answer 2

A genotype is the allele combinations for a specific trait

There Are three possible types of allele combinations

• Homozygous: Both alleles are the same (e.g. AA)
• Heterozygous: Alleles are different (e.g. Aa)
• Homozygous: Only one allele (e.g. X/Y genes in males)

Question 3

Phenotype

Answer 3

A phenotype is the physical expression of a specific trait

• It is determines by genotype and environmental factor

Question 4

Modes of inheritance Complete Dominance

Answer 4

Complete Dominance is when one allele is expressed over another.

• Dominant allele is expresses in heterozygote (capital letter)
• Recessive allele is masked in heterozygote (lowercase letter)

A recessive phenotype can only be expressed in homozygotes.

• Heterozygote will display the dominant phenotype

Question 5

Modes of inheritance: Codominance

Answer 5

Both alleles are equally expressed in the phenotype.

• Heterozygotes have distinct phenotype (superscript letter)
• An example of co-dominance is the ABO blood system

Question 6

Genetic Diseases

Answer 6

genetic Disease can be due to recessive, dominant or co-dominant alleles

• Recessive conditions are most common as heterozygotes are carriers.

Question 7

Genetic Disease: Autosomal Recessive

Answer 7

• Cystic fibrosis is caused by mutated CFTR gene (chromosome 7)
• Produces thick muscus that clogs airways and causes respiratory issues

Question 8

Genetic Diseases: Autosomal Dominant

Answer 8

• Huntington’s disease us causes by a mutated HTT gene (chromosome 4)
• An amplification of CAG repeats (>40) leads to neuro-degeneration.

Question 9

Genetic Diseases: Autosomal Co-dominant

Answer 9

• Sickle cell anemia is caused by mutated HBB gene (chromosome 11)
• Sickling of blood cells leads to anemia and other complications

Question 10

Radiation Exposure

Answer 10

Radiation and mutagenic chemicals increase mutation rates and can cause genetic diseases.

• most genetic diseases is humans are rare.

Question 11

Radiation Exposure examples

Answer 11

• Nuclear bombing of Hiroshima (1945)
• Accident / meltdown in Chernobyl (1986)

Question 12

Radiation exposure Long-Term consequences

Answer 12

• In increase incidence of caner
• Reduced immunity (↓ T cell count)
• Congenital abnormalities (Chernobyl only)
• A variety of organ-specific health effects (e.g. liver cirrhosis, cataract induction, etc)