Download Notes: Genetics

Genetics
Gregor Mendel
The father of Genetics
• Genetics- the study of heredity
• Heredity- the passing of characteristics or
traits from parents to offspring
• Mendel chose pea plants to research. Pea
plants have male and female plants, so each
have sex cells or gametes.
male = pollen
female = egg (in the pistil)
Pollination- transfer of pollen to the pistil
Fertilization- the uniting of male and female
gametes
Mendel’s Peas
• When Mendel crossed 2 plants that
were different in a single trait, he
called that a monohybrid cross.
• The resulting offspring were called the
F1 generation or the first generation. (F
stands for filial which means
son/daughter)
• The F1 generation plants were bred to
give the F2 generation or the second
generation. (the grandkids of the
original plants)
Alleles
Mendel realized that genes
controlled traits.
– Alleles- different forms of the same
gene
– Each organism has 2 alleles for each
trait (1 from mom and one from dad)
on separate chromosomes
Genotype & Phenotype
Some alleles are dominant over others; they are the
ones that show themselves
Dominant = observed trait code (capital letters)
Recessive = hidden trait code (lowercase letters)
• The two allele codes (1 from each parent) make
up the organisms genotype. (Bb)
• Homozygous- the organism has 2 alleles that are
the same for a trait; two capital letters or two
lowercase letters
Ex: TT or tt
• Heterozygous- the organism has 2 alleles that are
different; 1 capital letter and 1 lowercase letter
Ex: Tt
Genotype & Phenotype
• The phenotype of the organism is its
behavior and physical looks. (brown
hair)
Law of Segregation
Law of Segregation- alleles from
the organism separate to produce
2 types of gametes.
Ex: An organism with a Bb
genotype can produce a gamete
carrying the B allele or a gamete
carrying the b allele.
Law of Independent
Assortment
Law of Independent Assortmentgenes for different traits are
inherited independently of each
other.
Ex: just because you have brown
hair you don’t have to be short
Punnett Squares
Punnett Squares- used to predict
possible genotypes and phenotypes of
the offspring.
Monohybrid cross- one trait is crossed
Ex: Tt x TT
Dihybrid cross- 2 traits are crossed
Ex: RrYy x RrYy
Punnett Squares
• Probability of a particular
genotype or phenotype is
determined with punnett squares.
Punnett Squares
Punnett Squares
Cross a pea plant heterozygous yellow
seeds with a green homozygous
recessive pea plant. Yellow seeds are
dominant to green.
Punnett Squares
Cross a pea plant homozygous
dominant for purple flowers with a pea
plant that is homozygous recessive for
white flowers.