Transcript Unit 6: Mendelian Genetics

Mendelian Genetics
Chapter 9
Gregor Mendel
I love genetics!!
 1843 - entered a
monastery.
 1851 – studied
science & math at the
University of Vienna
 Eventually returned to
the monastery & used
statistics to analyze
the genetics of pea
plants.
Terminology
Inheritance – The passing of traits by
heredity.
Heredity – The transmission of traits from
parents to offspring.
Pure – Always produce offspring with that
trait.
Strain – Describes all plants pure for a
species.
Pollination – Transfer of pollen from anther
to stigma
Mendel’s Experiments
 Grew pure plants
 Produced strains by
allowing plants to selfpollinate.
 Crossed pollinated
parental generation (P1)
 All offspring (F1)
expressed the dominant
trait.
 Self-pollinated the F1
plants & called offspring
F2 generation.
Mendel’s Experiments continued…
Mendel’s Three Principles
 Genes: Chemical factors that determine traits
 Principle of Dominance & Recessiveness
One factor in a pair may mask the other, preventing it
from having an effect.
 Principle of Segregation
Each reproductive cell receives one factor for a trait,
therefore 2 factors separate during egg & sperm
formation.
 Principle of Independent Assortment
Factors for different characteristics are distributed to
reproductive cells independently.
Probability
The likelihood that a specific event will
occur.
The principles of probability can be used
to predict the outcomes of genetic
crosses.
General Terms
 Gene: segment of DNA on chromosomes that
controls a particular hereditary trait.
 Allele: Each of several alternative forms of a
gene.
Represented by lower & upper case letters.
 Genotype: Genetic makeup of organism
 Phenotype: External appearance
 Homozygous: Both alleles of a pair are the
same (ex. TT, tt)
 Heterozygous: Two alleles of a pair are not the
same (ex. Tt)
Genetic Crosses
Monohybrid crosses: A cross between
individuals that involves one pair of
contrasting traits.
Punnet Square: A diagram used to predict
genetic probabilities.
Genetic Crosses – Examples on the
board
Testcross
An cross
between an
individual of
unknown
genotype & a
homozygous
recessive
individual.
Incomplete Dominance
When two or
more alleles
influence the
phenotype,
resulting in an
intermediate
phenotype.
R
RR
W
R
W
WW
RR:RW:WW
Dihybrid Crosses
A cross
between
individuals that
involves two
pairs of
contrasting
traits.