Transcript Intro to Mendelian Genetics

Intro to Mendelian Genetics
Gregor Mendel
• Austrian monk and gardener
• Significant work done in
1850’s
• Father of genetics (study of
heredity)
• Heredity = passing on of
traits from parent to
offspring
• Traits = characteristics that
are inherited (ex. eye color)
Mendel’s First Experiment
P (Parent) Generation
X
Purebred tall (≥ 6 ft.)
Purebred short (≤ 2 ft.)
↓ Cross - pollinate
Mendel’s First Experiment
F1 (filial) Generation
all tall
↓ Self - pollinate
Mendel’s First Experiment
F2 Generation
¾ tall
¼ short
Mendel’s life…
• Mendel tried out
different pea plant
traits…
Mendel’s life…
• Thousands of times…
Mendel’s life…
• And got the same results!
– In F1 generation, one trait remained and the other
disappeared.
– In F2 generation, the ratio of plants was ¾ to ¼
What Mendel knew… (1800s)
• Each parent contributes to the traits of a
plant/child.
• Something is passed on from parent to child to
contribute to the traits.
• Some traits were disappearing, then returning
in future generations.
What Mendel didn’t know…
• Chromosomes were being inherited from
parents. (1930s)
• DNA specifically is the molecule being that
gives us our traits. (1920s – 1950s)
• What DNA is made of. (1953)
Mendel’s Rules and Laws
After 1000s of experiments, Mendel came up
with some “rules of heredity”:
1.Rule of Unit Factors
• EACH ORGANISM HAS 2 COPIES OF A GENE
THAT CONTROLS EACH TRAIT; ONE COPY
CAME FROM THE MALE PARENT AND ONE
COPY CAME FROM THE FEMALE PARENT
• each chromosome has genes (a gene is a segment of
DNA that controls a trait – ex. height)
• there can be different forms (versions) of the same
gene; these different forms are called alleles
– ex. for the height gene, the alleles are tall and short
• the offspring get 2 copies of the gene and can inherit
any combination of two alleles from the parents:
Allele from your mom…
Allele from your dad…
tall
tall
short
short
short
tall
short
tall
Mendel’s Rules and Laws
2.Rule of Dominance
• ALLELES CAN BE DOMINANT OR RECESSIVE;
THE DOMINANT ALLELE, IF PRESENT,
COMPLETELY MASKS THE RECESSIVE ALLELE
• Dominant allele - remained in the F1
generation (ex. tall)
• Recessive allele - disappeared in F1 (ex. short)
• So we say that tall is dominant to short
• When writing alleles, follow these rules:
– Use the same letter for different forms of the same
gene.
– Use uppercase letter for dominant allele.
– Use lowercase letter for recessive allele.
– Always write dominant allele first.
• Example: height
T
_______
= tall
_______
= short
t
A plant can be:
tall
TT __________
tall
Tt
__________
short
tt
__________
Important Vocab
PHENOTYPE = written description of appearance or
behavior
Examples: tall and short
BUT, two organisms can look the same but have
different gene (or allele) combinations:
GENOTYPE = 2 – letter gene combination
Examples: TT, Tt, tt
There are 3 different types of genotypes:
Homozygous dominant
____________________________________
Homozygous recessive
____________________________________
Heterozygous
____________________________________
same
Homo- means _______________________
different
Hetero- means _______________________
FYI: homozygous is the same as PUREBRED
heterozygous is the same as HYBRID
(TT)
(tt)
(Tt)
JUST A LITTLE PRACTICE
Description
Red hair
GG
mm
White eyes
Short toe
Dd
Genotype or
Phenotype?
phenotype
genotype
genotype
phenotype
phenotype
genotype
Homozygous or
Heterozygous?
N/A
Homozygous (dominant)
Homozygous (recessive)
N/A
N/A
Heterozygous
Mendel’s Rules and Laws
3.Law of Segregation
THE TWO ALLELES THAT CONTROL EACH TRAIL
WILL SEPARATE DURING GAMETE FORMATION
Explains how two tall plants can give offspring that are ¾
tall and ¼ short!
PLANT 1
Tt
Plant 1’s gametes:
T
t
X
PLANT 2
Tt
Plant 2’s gametes:
T
t
All possible gamete combinations result in the following
TT, Tt, and Tt (3/4 tall)
tt (1/4 short)
offspring:____________________
and ____________
An easier way to determine offspring…
• Reginald Punnett (early
1900s)
• Discovered short-hand way
to solve genetics problems
• Works based on Mendel’s
law of segregation
AND NOW WE…
PRACTICE,
PRACTICE,
PRACTICE!