Study Notes
Inheritance is the process by which genetic information is passed from parents to offspring. Gregor Mendel's experiments with pea plants established the foundational principles of inheritance, including the concepts of dominant and recessive alleles, segregation, and independent assortment.
- Gene — a unit of heredity that is transferred from a parent to offspring. Example: Determines traits like eye color.
- Allele — a variant form of a gene. Example: Alleles for flower color can be purple or white.
- Dominant Allele — an allele that expresses its phenotype even when heterozygous. Example: In pea plants, the allele for tall plants (T) is dominant over the allele for short plants (t).
- Recessive Allele — an allele that only expresses its phenotype when homozygous. Example: The allele for short plants (t) in pea plants is recessive.
- Gamete — a haploid cell that fuses with another during fertilization. Example: Sperm and egg cells.
- Zygote — a diploid cell resulting from the fusion of two haploid gametes. Example: The fertilized egg cell.
- Codominance — a situation where both alleles in a heterozygote are fully expressed. Example: Blood type AB, where both A and B alleles are expressed.
- Sex-linked Gene — a gene located on a sex chromosome. Example: The gene for red-green color blindness is located on the X chromosome.
Exam Tips
Key Definitions to Remember
- Gene: A unit of heredity.
- Allele: A variant form of a gene.
- Dominant Allele: An allele that masks the effect of a recessive allele.
- Recessive Allele: An allele that is masked by a dominant allele.
- Gamete: A haploid sex cell.
- Zygote: A diploid cell formed from the fusion of two gametes.
- Codominance: Both alleles are expressed equally.
- Sex-linked Gene: A gene located on a sex chromosome.
Common Confusions
- Dominant vs. Recessive: Dominant alleles mask recessive ones, not the other way around.
- Codominance vs. Incomplete Dominance: Codominance shows both traits, while incomplete dominance blends them.
- Sex-linked vs. Autosomal: Sex-linked genes are on sex chromosomes, autosomal genes are on non-sex chromosomes.
Typical Exam Questions
- What is the principle of dominance? Dominant alleles mask the effects of recessive alleles.
- How do alleles segregate during meiosis? Alleles segregate so each gamete receives one allele per gene.
- What is the probability of two carriers of cystic fibrosis having an affected child? 25% chance if both parents are carriers.
What Examiners Usually Test
- Understanding of Mendel's laws of inheritance.
- Ability to use Punnett squares to predict genetic outcomes.
- Knowledge of genetic disorders and their inheritance patterns.