BIO 10 BIO 10 Lecture 10Lecture 10BIO 10 BIO 10 Lecture 10Lecture 10

REPRODUCTION: REPRODUCTION:

CHROMOSOMES AND HEREDITYCHROMOSOMES 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

-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)

Mendel's First Law: Law of Segregation

– 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.

Law of Segregationcontinued...

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

Punnett Square predicts3:1 phenotypic ratio

YY = yellowYy = yellowyy = green

- 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

Mendel's Second Law: Law of Independent

Assortment

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?