Transcript Genetics: The Science of Heredity

Genetics
Genetics Vocab
• Genetics: the scientific study of heredity
• Heredity: passing of traits from generation
to generation
•
• Traits: specific characteristics that vary
from individual to individual
Genetics Vocab
• Genes: segment of DNA that carries the
instructions for making traits
• Alleles: different forms of a trait (we will use letters
to represent the different forms)
– Example:
• Trait: hair color
• Alleles would be:
– Blonde
– Brown
– Black
– Red
– And any combination in between
Genetics Vocab
• Dominant trait: the trait observed when at
least one dominant allele for a
characteristic is inherited
• Recessive trait: a trait that appears only
when 2 recessive alleles for the same
characteristic are inherited
Genetics: The Science of Heredity - Mendel’s Work
Dominant and Recessive Alleles
Mendel studied several traits in pea plants.
Genetics Vocab
• Genotype: the inherited combination of
alleles (TT, tt, or Tt)
• Phenotype: an organisms physical
appearance (Tall, short)
Genetics Vocab
• Homozygous: 2 alleles are the same for a
trait
(TT or tt)
• Heterozygous: 2 alleles are different for a
trait
(Tt)
Mendel
• Austrian monk who studied genetics in
pea plants
• How Mendel did his work:
– By cross-pollinating plants by transferring
pollen from one plant to the egg cells of
another
– He crossed a pair of plants with different
alleles for a trait
Genetics: The Science of Heredity - Mendel’s Work
Crossing Pea Plants
Gregor Mendel crossed pea plants that had different traits.
The illustrations show how he did this.
Genetics: The Science of Heredity - Mendel’s Work
Mendel’s Experiments
In all of Mendel’s crosses, only one form of the trait appeared
in the F1 generation. However, in the F2 generation, the “lost”
form of the trait always reappeared in about one fourth of the
plants.
Punnett Squares
• a table that shows all the combinations
of alleles that might result from a
genetic cross
• Vocab you will need to remember in
order to do a punnett square
– Alleles, dominant, recessive, homozygous,
heterozygous, phenotype, and genotype.
Genetics: The Science of Heredity - Probability and Heredity
A Punnett Square
The diagrams show how to make a Punnett square. In this
cross, both parents are heterozygous for the trait of seed
shape. R represents the dominant round allele, and r
represents the recessive wrinkled allele.
Genetics: The Science of Heredity
Genotypes and Phenotypes
Genotypes:
¼ RR
2/4 or ½ Rr
¼ rr
Phenotypes:
¾ Round
¼ Wrinkled