Genetic Traits, Genes and Alleles

Genetic Traits

• Genetic traits are inherited characteristics of an organism.
• Invariant traits are the same in all individuals of a species.
  • Examples include having two eyes, two legs, and two arms.
• Variable traits differ among individuals.
  • Examples include curly hair and eye color changes.

Genes and Alleles

• A gene is the basic unit of information that affects genetic traits.
  • Genes contain the information or code for a particular genetic trait.
• Alleles are slightly different versions of a given gene.
• Genotype refers to the genetic makeup of an individual for a given trait and cannot be seen.
• Phenotype is the physical expression of a trait's genetic makeup and can be seen.

Dominant vs. Recessive Alleles

• A dominant allele prevents a second allele from affecting the phenotype when the two alleles are together.
  • If a child gets one dominant gene from either parent, they will show that trait.
• A recessive allele has no effect on the phenotype when paired with a dominant allele.
  • A child needs two copies of the recessive gene, one from each parent, to show that trait.

Homozygous vs. Heterozygous

• Homozygous refers to a genotype consisting of two copies of the same allele.
  • Homo=same.
  • Example: BB or bb
• Heterozygous individuals have two different versions of a gene, one inherited from each parent.
  • Hetero=Different.
  • Example: Bb
  • The individual will show the phenotype of the dominant allele.

X-Linked (Sex-Linked)

• The gene is found on the X chromosome.
• Males, having only one X chromosome, are more likely to show these traits, even if the gene is recessive.

Gregor Mendel's Principles of Genetics

• Law of Segregation: During gamete formation (sperm and egg cells), the two alleles for a given trait separate (segregate) so that each gamete carries only one allele for each gene.
  • The two alleles of a gene are separated during meiosis 1 and end up in different gametes.
• Law of Dominance: When two different alleles for a trait are present in an organism, the dominant allele is expressed, while the recessive allele is masked.
• Law of Independent Assortment: Genes for different traits are inherited independently of each other, provided they are located on different chromosomes or are far apart on the same chromosome.
• Chromosome Theory of Inheritance: Genes are located on chromosomes, and the inheritance of traits is determined by the movement of chromosomes during meiosis.
• Codominance: When the effects of two alleles are equally visible in the phenotype.
• Pleiotropy: When a single gene influences a number of genetic traits.
• Polytrophy:

Mendel's Genetic Crosses

• Genetic crosses were performed as controlled mating experiments to examine how a particular trait is inherited.
• P generation: Parental offspring.
• F1 Generation: First generation of offspring.
• F2 Generation: Results of crossing the F1 generation.
• Crossing the P1 generation results in the F1 generation, and crossing the F1 generation results in the F2 generation.