Transcript IntroductiontoGeneticsElizabeth.ppt

Chapter 11
What is genetics?
• The scientific
study of
heredity
Gregor Mendel
• Born in 1822 in
Czechoslovakia.
• Became a monk at a
monastery in 1843.
• Taught biology and
had interests in
statistics.
• Also studied at the
University of Vienna
Mendel continued
• After returning to the
monastery he
continued to teach
and worked in the
garden.
• Between 1856 and
1863 he grew and
tested over 28,000
pea plants
Mendel’s Peas
• Easy to grow.
• Easily identifiable traits
• Can work with large numbers of samples
Mendel’s experiments
• The first thing Mendel did was create a
“pure” generation or true-breeding
generation.
• He made sure that certain pea plants were
only able to self pollinate, eliminating
unwanted traits.
• He did this by cutting away the stamen, or
male part of each flower
Genes and dominance
• Trait : a characteristic displayed.
• Mendel studied seven of these traits
• After Mendel ensured that his truebreeding generation was pure, he then
crossed plants showing contrasting traits.
• He called the offspring the F1 generation
or first filial.
What will happen when pure yellow
peas are crossed with pure green
peas?
• All of the offspring
were yellow.
• Hybrids = the
offspring of
crosses between
parents with
contrasting traits
What did Mendel conclude?
• Inheritance is determined by factors
passed on from one generation to another.
• Mendel knew nothing about
chromosomes, genes, or DNA. Why?
• These terms hadn’t yet been defined.
What were Mendel’s “factors”
• The ‘factors” that Mendel mentioned were
the genes.
• Each gene has different forms called
alleles
• Mendel’s second principle stated that
some alleles are dominant and some are
recessive.
Probability
• The likelihood of a
particular event
occurring. Chance
• Can be expressed as
a fraction or a
percent.
• Example: coin flip.
Punnett Square
• Developed by
Reginald Punnett.
• A diagram used to
show the probability
or chances of a
certain trait being
passed from one
generation to another.
Reading Punnett squares
• Gametes are placed above and to the left
of the square
• Offspring are placed in the square.
• Capital letters (Y) represent dominant
alleles.
• Lower case letters (y) represent recessive
alleles.
Punnett square example
• Homozygous = when an organism
possesses two identical alleles. ex.
– YY or yy
• Heterozygous = when an organism
possesses different alleles. ex.
– Yy
Phenotype vs genotype
• Genotype
 The genetic makeup
 Symbolized with
letters
 Tt or TT
• Phenotype
• Physical appearance
of the organism
• Expression of the trait
• Short, tall, yellow,
smooth, etc.
Probability and statistics
• No one event has a greater chance of
occurring than another.
• You cannot predict the precise outcome of
an individual event.
• The more trials performed, the closer the
actual results to the expected outcomes.
Punnett square review: