Download Introduction to Genetics

INTRODUCTION TO
GENETICS
Chapter 10
Genetics
• Genetics: the study of heredity
• Heredity: the passing of characteristics from
parents → offspring
• Characteristics = height, eye color, hair
texture, etc.
• Trait: type of characteristic
• i.e.: tall, blue, curly, etc.
Genes and Alleles
• Gene: a section of DNA that codes for a
particular characteristic
• i.e.: hair color gene, eye color gene
• Alleles: different forms of a gene that
codes for a particular trait
• i.e.: brown hair allele, blue eye allele
Types of Alleles
• 2 Types:
• Dominant: will always be displayed
• Represented by capital letter
• i.e.: “T”, “R”, etc.
• Recessive: will only be displayed if dominant
allele is absent
• Represented by lower-case letter
• i.e. “t”, “r”, etc.
Genotype & Phenotype
• Offspring inherit 1 allele from each parent’s
homologous chromosome
• Genotype: combination of parent’s alleles;
genetic makeup
• Example:
• Mom’s allele → “T” (dominant)
• Dad’s allele → “t” (recessive)
• Offspring’s genotype = “Tt”
• Phenotype: physical appearance;
determined by genotype
Genotype Combinations
• Homozygous: same allele from each parent
is inherited (“True-Breed”)
• i.e.: “TT”, “tt”
• Heterozygous: different allele from each
parent is inherited (“Hybrid”)
• i.e.: “Tt”
• Will usually only show dominant trait
Probability
• Probability: the likelihood that an event will occur
• i.e.: coin flip = ½ or 50%
• Determined by:
• Probability = # times expected to occur
•
total # trials
• Past outcomes do not affect future ones
• Used to predict the outcome of genetic crosses
Punnett Squares
• Punnett Square: use
DAD
probability to predict
traits of offspring
• Based on genotypes of
parents
• Parents lined up on top
& left
• Letters inside represent
allele combinations of
offspring
M
O
M
100% offspring have genotype Tt
100% offspring are tall