Gregory Johann Mendel 1822- 1884 Austrian monk Experimented with pea plants He thought that...
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Transcript of Gregory Johann Mendel 1822- 1884 Austrian monk Experimented with pea plants He thought that...
Gregory Johann Mendel
• 1822- 1884• Austrian monk• Experimented with
pea plants• He thought that
‘heritable factors’ (genes) retained their individuality generation after generation
Terms to Know and Use
• Gene - a heritable feature: i.e. flower color coded for on a chromosome
• Trait - variant for a gene: i.e. a purple flower, determined by alleles
• Dominant trait - expressed over recessive trait when both are present
• Recessive trait - not expressed when the dominant trait is present
• Allele - a variation of a gene responsible for different traits, often expressed as A or a
• Locus - location of a gene,or allele, on a chromosome
• Chromosome - strand of DNA that codes for genes
• Haploid - one copy of a chromosome
• Diploid - two copies of a chromosome
• Gamete - a spermatozoa or oocyte (egg) cell, they are haploid
• Zygote – diploid, fertilized egg (2N)
• Genotype - the type of alleles on a chromosome: genetic makeup
• Phenotype - the physical result of a genotype ex. blue eyes
• Hybrid – an organism with two different alleles
Garden Pea Experiments 1856-64
• Mendel disagreed with the “Blending Theory” of inheritance.
• Started with34 kinds peas
Pea Characteristics
Trait on the left is dominant. Trait on the right is recessive.
Dominant Recessive
Mendel Determined that Alleles Separate During Meiosis
Parents:
Assume Round is S and the other form is s.
Punnett Square used to predict
the Genotype of Offspring
S S
S Ss
Smooth
Ss
Smooth
s Ss
Smooth
ss
Smooth
So, cross purebred smooth peas with a plant having the recessive wrinkled form of the peas and see the result
No Blend as
expected!
Mendel’s Hypotheses1. There are alternate forms
of ‘genes’ = alleles
2. For each trait, organisms have 2 genes, one from mom & one from dad
3. Sperm and egg each carry 1 allele/trait because alleles separate
4. Dominant alleles mask the effects or recessive alleles
A A
A
A
AA
AA
AA
AA
Fat
her
cont
r ibu
tes:
Mother contributes:
oror
Pure Breds Crosses – have all dominant traits
a a
A
A
Aa
Aa
Aa
Aa
Fat
her
cont
r ibu
tes:
Mother contributes:
oror
Pure Bred Dominant Father breeds with Pure Bred Recessive
Mother
Purebred Dominant
+ Purebred Recessive
a Hybrid ----> Aa
Describing Alleles Properly
• Aa means the critter is HETEROZYGOUS
It has two different alleles: A & a
The critter is not a purebred but a hybrid
• AA or aa means the critter has the same two alleles, so it is HOMOZYGOUS
Test Cross
Mendel's Laws of Inheritance
1. Genes produce traits (characteristics)
2. Law of Segregation alleles are separated during meiosis into different eggs/sperm
3. Law of Independent Assortment suggested that other alleles do not influence how other alleles come together (how they assort) (demonstrated with a “dihybrid cross”)