Transcript 1-Intro to genetics - Science-with

Heredity
Biology 30
Chapter 18.1
Early Theories of Inheritance
Aristotle (384-322 B.C.E.)
 proposed the first widely accepted theory of inheritance
• called pangenesis
• egg and sperm consist of particles called pangenes
that come from all parts of the body.
• upon fertilization the pangenes develop into the
parts of the body from which they are derived.
Antony van Leeuwenhoek (1632-1723)
 discovered sperm in semen.
•
•
he believed he thought he saw a complete
miniature person called a homunculus
inside the head of the sperm.
other people of Antony’s time thought
that the egg contained the entire person.
Mendelian Genetics
Gregor Mendel (1822-1884)
 a Augustinian monk in Brunn (Czech
Republic), Austria
 his research laid the foundation for
modern genetics and the science of
inheritance.
 for seven years he bred pea plants
(Pisum sativum) and analyzed the
results.
Gregor Mendel
Mendelian Genetics

Mendel focused on seven different traits of pea plants..
Mendelian Genetics

Mendel let plants self-pollinate to ensure they were true
breeding.
• true breeding plants exhibit the same characteristics
generation after generation.
• Mendel called
• true breeding plants the parental or P generation
• the first offspring first filial or F1 generation
• If the F1 generation were to pollinate the offspring
would be called the second filial or F2 generation
Mendelian Genetics
• because all of Mendel’s initial crosses only involved
•
one trait we call them monohybrid crosses.
Mendel observed that:
• for every trait crossed the F1 generation only
showed one of the two parental traits.
ie. if plants with round seeds were crossed with
plants of wrinkled seeds the F1 generation
would only have plants of round seeds.
Mendelian Genetics
• even though the F1 generation had a copy of both
genes only one was expressed.
• Mendel called this characteristic dominant.
allele: one of alternative forms of a gene.
the gene for wrinkled and the gene for round
peas are alleles.
Mendelian Genetics
dominant trait: a characteristic that is expressed
when one or both alleles in an individual are
the dominant form
~ dominant alleles are indicated by an
uppercase letter (R)
Mendelian Genetics
• Mendel called the characteristic that was not
expressed recessive
recessive trait: a characteristic that is expressed
only when both alleles in an individual are the
recessive form.
• Mendel concluded that one form showed complete
dominance.
• an individual with one dominant and one
recessive (Rr) had the same characteristics as
one with two dominant forms (RR)
Mendelian Genetics
Mendel’s Traits
Trait
Dominant
Recessive
Stem Length
Tall (T)
Short (t)
Pod Shape
Inflated (I)
pinched (i)
Seed Colour
Yellow (Y)
Green (y)
Flower
Position
Axial (A)
Terminal (a)
Flower Colour
Purple (P)
White (p)
Seed Shape
Round (R)
Wrinkled (r)
Pod Colour
Green (G)
Yellow (g)
Mendelian Genetics
Important Definitions
Homozygous: having identical alleles for the same gene
Heterozygous: having different alleles for the same gene.
Genotype: the genetic complement of an organism
Phenotype: the observable characteristics of an organism
Segregation: the separation of alleles during meiosis.
Mendelian Genetics
Law of Segregation


Mendel’s First Law
• All individuals have two copies
of each factor (gene). These
copies segregate (separate)
randomly during gamete
formation, and each gamete
receives one copy of every gene.
in 1909 Danish Botanist Wilhem
Ludwig Johannsen called Mendel’s
“factors” genes
Mendelian Genetics
Analyzing Genetic Crosses
Reginald Punnett (1875-1967)
• devised a visual way to analyze the results of crosses, called a
Punnett’s square.
Mendelian Genetics
Punnett Squares
•are used to predict the genotype and phenotype of potential off-spring
•very useful when producing economically important cattle and plants.
P Generation
♀
♂
Phenotypic Ratio
Genotypic Ratio
Mendelian Genetics
Trait
Dominant
Phenotype
Genotype(s)
Recessive
Phenotype
Genotype(s)
Short
tt (homozygous)
Pinched
ii (homozygous)
Wrinkled
rr (homozygous)
White
pp (homozygous)
TT (homozygous)
Stem Length
Tall
Tt (heterozygous)
II (Homozygous)
Pod Shape
Inflated
Ii (hetorozygous)
RR (Homozygous)
Seed Shape
Round
Rr (Heterozygous)
PP (Homozygous)
Flower Colour
Purple
Pp (herozygous)
In order to see recessive phenotypes the genotype must be homozygous
Now…


Do your ears hang
low activity
Homework: Journal
questions
http://bussongs.com/assets/midi/DoYourEarsHangLow.mp3