Transcript 100975_Mendelian_Genetics_1.pptx

Intro to Mendelian Genetics
1.28.13
What is genetics?
What is genetics?
• The science of heredity
What is genetics?
• The science of heredity
• How traits are passed to offspring
What is genetics?
• The science of heredity
• How traits are passed to offspring
• Gene – A section of DNA that codes for a
specific protein
• Gene – The unit of heredity
Gregor Mendel
• Born in Czech Republic,
settled in Austria
• In 1842, entered
monastery at age of 21,
tended to a garden of
peas
Gregor Mendel
• In 1851 he went to the U.
of Vienna to study science
and statistics
• Returned to monastery to
teach high school and
study heredity through
his peas. (OMG, this is like sooooo
exciting! I can’t wait to hear what happens
next. Seriously, I’m about to pea my pants!)
Current thoughts in 1850
• Blended inheritance
– Offspring are intermediate in appearance
Current thoughts in 1850
• Blended inheritance
– Offspring are intermediate in appearance
• Ex: skin tone in humans
Current thoughts in 1850
• Blended inheritance
– Offspring are intermediate in appearance
• Ex: skin tone in humans
– Ink in water
1. Combined
2. Inseparable
Current thoughts in 1850
• Blended inheritance – (Incorrect)
– Offspring are intermediate in appearance
• Ex: skin tone in humans
– Ink in water
1. Combined
2. Inseparable
Used peas to study inheritance
• Why peas?
Used peas to study inheritance
• Each plant has various
traits to study
• Cheap
• Simple to grow
• Seeds easily stored for
later study
• Short generation time
• Self-pollinators (flowers
have male and female
parts)
• Cloned flowers can
serve as control group
Statistics was the key!
• Used math to explain living systems (one of
the first to do so)
• Published his work in 1866, but mostly
ignored because he didn’t know the
mechanism of heredity (DNA)
Mendel’s 1st Experiment
• Studied 7 characteristics with two traits each
• Plant height, flower color, etc.
Mendel’s 1st Experiment
• Studied 7 characteristics with two traits each
• Plant height, flower color, etc.
– Focus on plant height:
• Tall or short:
Mendel’s 1st Experiment
• Studied 7 characteristics with two traits each
• Plant height, flower color, etc.
– Focus on plant height:
• Tall or short: T or
Mendel’s 1st Experiment
• Studied 7 characteristics with two traits each
• Plant height, flower color, etc.
– Focus on plant height:
• Tall or short: T or t
Mendel’s 1st Experiment
• Studied 7 characteristics with two traits each
• Plant height, flower color, etc.
– Focus on plant height:
• Tall or short: T or t
– All studied traits were heritable, not
environmental
– Used purebreds (clones) achieved through many
generations of self-pollination
Mendel’s 1st Experiment
• Crossed a purebred tall with a purebred short
– Paternal: T x t
– Filial (F1): ??
Mendel’s 1st Experiment
• Crossed a purebred tall with a purebred short
– Paternal: T x t
– Filial (F1): 100% tall (T)
• Same result with all 7 characteristics
• Trait that showed up in F1 generation =
dominant
• Disappearing trait = recessive
Mendel’s 1st Experiment
• Where did the recessive trait go?
Mendel’s 1st Experiment
• Where did the recessive trait go?
• To find out, he self-pollinated the F1 plants
– F1: T x T
Mendel’s 1st Experiment
• Where did the recessive trait go?
• To find out, he self-pollinated the F1 plants
– F1: T x T
– F2: 75% T, 25% t
Law of segregation
• Law of segregation : Traits are discrete units
that occur in pairs and retain their integrity
Law of segregation
• Law of segregation : Traits are discrete units
that occur in pairs and retain their integrity
• Characteristics are now called genes (one or
more genes lead to the appearance of a
certain characteristic)
Mendelian Genetics Continued…
• The location (address) of a gene on a
chromosome is called the locus
• Genes have alternate versions called alleles
• ex: locus for flower color
• Genotype: The collection of alleles in an
individual
– Represented by letters
• Genotype: The collection of alleles in an
individual
– Represented by letters
• P: TT x tt (T = dominant allele –> only one needed for
expression)
• F1:
• Phenotype:
• Phenotype: Physical expression of genotype +
environment
– Represented by
• Phenotype: Physical expression of genotype +
environment
– Represented by descriptive words
• F2 : Tt x Tt
Genotypes:
Phenotypes:
Genotype terminology
• TT = Homozygous dominant or purebred
dominant
• Tt =
• tt =
Genotype terminology
• TT = Homozygous dominant or purebred
dominant
• Tt = Heterozygous dominant or hybrid
• tt = Homozygous recessive or purebred
recessive
• How can you tell the difference between a
homozygous dominant (DD) and a
heterozygous dominant (Dd)?
• How can you tell the difference between a
homozygous dominant (DD) and a
heterozygous dominant (Dd)?
• Test Cross: Breed the unknown with a
homozygous recessive to bring out any hidden
recessive traits
• Test Cross: Breed the unknown with a
homozygous recessive to bring out any hidden
recessive traits
• Law #1: Law of segregation
• Law #2: Law of independent assortment
– Genes located at different loci (locations) on the
same chromosome assort (cross-over)
independently of each other
• Law #1: Law of segregation
• Law #2: Law of independent assortment
– Genes located at different loci (locations) on the
same chromosome assort (cross-over)
independently of each other
• (Whether one gene crosses over during meiosis has no
influence over whether another gene on the same
chromosome crosses over)