Genetics
= The study of heredity/how
characteristics are passed from
parents to offspring.
Gregor Mendel
• = The father of genetics.
• Mendel was a monk who crossed pea plants
with varying traits, hence discovering simple
laws of heredity.
Mendel’s Experiment:
• 1. Created pure- breeding strains of pea plants
and used these as the parental generation.
• 2. Crossed plants different in a particular trait
and found only dominant phenotype in the
resulting F1 offspring.
• 3. Allowed F1 to self-fertilize and found a 3:1
ratio of the dominant: recessive trait in the F2
generation.
Mendel’s Laws:
• Law of Segregation = During meiosis, homologous pairs
of chromosomes segregate from each other and end
up in different gametes.
• Gametes are haploid reproductive cells such as the
sperm and egg in humans.
• Law of Independent Assortment = Alleles for different
traits are distributed to gametes independent of one
another.
• ie. Inheritance of a gene for one trait does NOT affect
the inheritance of the gene for a different trait.
• Exception to this law are sex-linked traits.
Important terms:
• Heredity = Biological inheritance/transmission
of characteristics from parents to offspring.
• Traits = Characteristics.
• Genes = Structures/segments on
chromosomes that control traits.
Alleles = Different forms of a gene.
Ex. Blue vs. brown eye color.
• Dominant = Allele that prevents the
expression of a recessive allele.
• Represent using a capital letter. Ex. B
• Recessive = Allele that is hidden by a
dominant allele.
• Represent using a lower case letter. Ex. b
• Genotype = The genetic makeup of an
organism.
• Phenotype = The physical appearance of a
trait.
• Phenotype is a result of the genotype.
• Homozygous = Having two of the same alleles
for a single trait.
• Also known as purebred. Ex. BB or bb
• Heterozygous = Having two different alleles for
the same trait.
• Also known as hybrid. Ex. Bb
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P1 = Represents the parental generation.
F1 = Represents the first filial generation.
- Offspring of the P1 generation.
F2 = Represents the second filial generation.
Offspring of the F1 generation.