Genetics
History
• Genetics is the study of genes.
• Inheritance is how traits/characteristics, are
passed on from generation to generation.
• Genes are passed parents  offspring;
– get one allele for each gene from each parent during Meiosis
cell division
• Chromosomes are made up of genes
– Alleles=diff. versions of a gene
• Gene is made up of DNA.
• Gregor Mendel is considered “The Father of
Genetics“…Used Pea Plants to discover
inheritance.
Mendel Breeding Experiment
P generation (parental
generation)
F1 generation the hybrid
offspring.
Allowing these F1
hybrids to self-pollinate
produces:
F2 generation (second
filial generation).
Mendel’s analysis of this
that lead to an
understanding of genetic
crosses.
Mendelian Genetics
• Dominant traits- traits that are expressed.
• Recessive traits- traits that are covered up.
• Genotype- the types of genes (Alleles) present.
• Phenotype- what it looks like.
• Homozygous- two of the same alleles.
• Heterozygous- two different alleles.
How do Alleles differ?
Dominant allele
Recessive
allele
Recessive allele
Recessive allele
Dominant - a term applied to the trait (allele) that is expressed irregardless of
the second allele. Usually indicated with a Capital Letter (ex. A, L, P)
Recessive - a term applied to a trait that is only expressed when the second
allele is the same (Usually indicated with a lower-case letter (ex. a, l, p)
Probability and Punnett Squares
Punnett square: diagram showing the probabilities of the possible outcomes of a
genetic cross
Genotype versus phenotype.
How does a
genotype ratio differ
from the phenotype
ratio?
Punnett squares - probability diagram illustrating the possible offspring of a
mating.
Ss X Ss
gametes
How Does it Work?
Pedigree analysis reveals patterns in human inheritance
In these family trees, sqaures=male, circles= females. A horizontal line
connecting a male and female (--) indicates a mating, with offspring listed
below in their order of birth, from left to right. Shaded symbols stand for
individuals with the trait being traced.
Incomplete Dominance
• Every genotype has its own phenotype.
– (One allele not completely dominant over the other.)
• Third phenotype that is a blending of the parental traits.
– (2 alleles produce 3 phenotypes.)
• Result: Heterozygous phenotype somewhere inbetween
homozygous phenotype.
Incomplete Dominance
Examples:
• Trait: Flower Color
Expressions: Red x White
 Pink
RR= Red; RW= pink; WW=
white
• straight hair x curly wavy
2. Codominance
• Both alleles contribute to the phenotype.
• In codominance, neither allele are dominant; both
are expressed.
– Example: In some chickens
Black Chicken x White Chicken  Speckled Chicken
YOU tell me which type of
dominance…Incomplete or Codominace?
Codominance!
Type of
Dominance?
Incomplete
Dominance!
Type of Dominance?
Incomplete Dominance!