Download Genetics - Tenafly Public Schools

Genetics
Really about growth and
development……
Heredity
• Heredity is biological inheritance
– The set of characteristics an organism inherits
form its parents
• Genetics is the study of heredity
Gregor Mendel (1822-1884)
• Studied in Vienna
• Taught in a High School (Brno, in Czech
Republic)
• Worked in a garden
• One of the first to study only one trait at a time
• One of the first to analyze his data systematically
• One of the first to use mathematics to analyze data
• Did about 30,000 experiments
Mendel in the garden
• The true breeding stock of plants
– Always passes its traits to the next generation
• Reproduction in pea plants
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Pollen, male sex cells
Ovum, female sex cells
Seed is produced for new plant
Normal process is self-pollination; one plant is the
parent
• Cross fertilization, two plants as parents
Mendel in the garden
• Seven traits
•
By limiting what traits he followed he
could manage the data
•
These traits are obvious, yes or no traits
•
Look on page 310 of your textbook now
Mendel in the garden
• Crossing (short for cross fertilization)
• Crossed the pollen and eggs of two true
breeding parents
• The result was always the trait of only one
parent
• Look at page 310 again
• Understand the nomenclature P and F-1
generation
Mendel in the garden
• Crossing of the plants from F-1
• If Mendel had not done this he would have
made no discovery
• The trait of the parent that did not show up
in F-1 appeared in ¼ of the F-2
Mendel in the garden
• Merkmal
– Some indivisible unit determined which trait
the plant displayed
– This word is German for character
– We call this a gene today (the unit that
determines traits)
Mendel in the garden
• Alleles
– Mendel figured each plant has two copies of
each “character”
– One from each parent
– Today we say a gene has two alleles
Mendel’s Big Leap
• Dominant and recessive
– Why does a plant with two characters for Tall (each
plant has two copies) grow to the same height as a plant
with one copy of Tall (each plant got one copy of Tall
and one copy of short from the plant with two copies of
short)
• Mendel called the copy (allele) for tall the
dominant character, the copy for short was the
recessive character.
• Today we use the same terminology
Out of the garden
• Phenotype and Genotype
• Phenotype is what you see when you look at
an organism, phenotype of the plants is
what Mendel was looking at
• Genotype is the genetic composition,
genotype is what Mendel was hypothesizing
when he talked about characters and copies
of characters
Out of the garden
• Today we say that an organism with identical
copies of the alleles for a trait is homozygous for
that trait (TT or tt, for Tall and short)
• Organisms with a mixed pair of alleles are
heterozygous for the trait (Tt for tall)
• In modern terms Mendel crossed two plants, one
homozygous for Tall (TT) one homozygous for
short (tt) and the offspring (F-1) were all
heterozygous (Tt) yet were all Tall.
Out of the garden
• Segregation
– Mendel figured out that the two copies of the
characters must separate when the plant
produced pollen and eggs
• Today we call this segregation of alleles
– TT and tt crossed produce Tt
– Tt and Tt crossed produce TT, Tt, Tt and tt
Out of the garden
• Independent assortment
– Mendel followed two traits at the same cross
– The offspring showed distinct ratios of the
different combination so he reasoned that the
characters behave independently
Mendel’s contributions
• Individual units called genes determine biological
characteristics
• For each gene, an organism receives one allele
from each parent.
• The alleles separate form each other (segregation)
when the reproductive cells are formed
• If an organism inherits different alleles for some
trait one allele may be dominant over the other
• Some genes segregate independently