Transcript BIO 10 Lecture 2

BIO 10
Lecture 10
REPRODUCTION:
CHROMOSOMES AND HEREDITY
An Introduction to
Mendel and His Peas:
1856-1863
• Research in Brno, Czech Republic
– Observed the inheritance patterns of seven
inherited physical characteristics in several
generations of pea plants and applied
mathematics to discover the two basic laws
that govern their behavior
– Did his work before chromosomes (1880's) or
DNA (1950's) had been discovered
– Was a monk who grew his pea plants in the
monastery garden
Mendel's First Law:
Law of Segregation
-Genetic information is carried by discrete
entities (genes)
– Complex organisms carry two copies of
each gene but pass only one copy to
each gamete
– Each gene controls a single trait (e.g.
seed color) but different forms of the
same gene (alleles) can confer different
expressions of that trait (e.g. yellow vs.
green seeds)
Law of Segregation
continued...
– An individual that carries two of the
same allele for a gene is homozygous.
An individual that carries two different
alleles for a gene is heterozygous.
– In a heteroygote, only one allele is
physically expressed; this allele is
dominant (A) over the unexpressed,
recessive (a) allele.
Genotype vs. Phenotype
• The phenotype of an organism is its
physical appearance or behavior
– This is all Mendel could actually study
– "The mature seed is yellow" = phenotype
• The genotype of an organism is its genetic
make-up
– Mendel inferred how genes behaved based on
his observations of the patterns in which
phenotypes were inherited
– Yy = genotype
Mendel's First Law and Meiosis
YY = yellow
Yy = yellow
yy = green
Punnett Square predicts
3:1 phenotypic ratio
Mendel's Second Law:
Law of Independent
Assortment
- When two genes and their alleles are
followed through a genetic cross, the
alleles of the two different genes are
randomly shed into the gametes without
regard to one another - i.e. independently
– Therefore, a dihybrid will create 4
different types of gametes in equal
proportions: AB, ab, Ab, and aB
Meiosis and the Law of
Independent Assortment
Short Review of Lecture 10
• How many gametes, and what types,
can be produced by a pea plant with the
genotype PP? How about Pp? pp?
• How many gametes, and what types,
can be produced by a pea plant with the
genotype PpTt? How about PPTt?
• How many gametes, and what types,
can be produced by a pea plant with the
genotype PpTtYy? How about PPTtYy?