Transcript Trait
11 – Introduction to Genetics
The Work of Gregor Mendel
Inheritance other than $$$$
How did things get passed
on?
Genetics – the scientific
study of heredity
Mendel,
peas and his work
Long overlooked
The Role of Fertilization
Male and Female Parts
Fertilization – joining of
reproductive cells
Self-pollination
True breeding
Trait
Cross Breeding
Male parts gone
Hybrids
Genes and Alleles
P1 and F1 generations
Disappearance of traits
Parent to offspring by genes.
Mendel called them factors
Single gene trait (ex. Tall vs.
Short)
Alleles – forms of a gene
Dominant and Recessive Alleles
Principle of Dominance
One dominant allele
Mendel’s second conclusion
Organism shows that trait
Recessive Alleles
Only show when dominant is
not present
SEGREGATION
What happened to the
other trait?
Did an F2 cross
Was it still in the F1?
Trait reappeared
Mendel assumed
Dominance masks
F1 Cross and Gametes
One trait separated from
the other
Segregation
During gamete formation
Follow this chart
11.2 – Applying Mendel’s
Principles
11.2 Applying Mendel’s Principles –
Probability and Punnett Squares
Probability – likelihood that
an event would occur.
Mendel analyzed his data
Found probability
Segregation and Outcomes –
Alleles segregate during
gamete formation (haploid)
Homozygous vs. Heterozygous
Probabilities, Averages, Genotype and
Phenotype
Probabilities predict the
average outcome
Genetic makeup vs.
observable characteristics
Genotype vs. Phenotype
Punnett Squares
Uses math to predict
Independent Assortment
Does segregation of one pair
affect other pairs?
Two factor (dihybrid) cross
Followed two traits
F1
F2
Independent Assortment
Some genes separate
independent of each other
Summary of Mendel
Characteristics are determined by genes and passed from
parents
If there are two or more forms of alleles some may be
dominant or recessive
Most adults have two copies of each gene (one from mom and
one from dad) and the segregate during gamete formation
Alleles usually segregate independent of each other
Summary
Thomas Hunt Morgan
Showed that the same principles apply to animals
Fruit Fly (Drosophila melanogaster)
11.3 – Other Patterns of
Inheritance
Beyond Dominant and Recessive
Incomplete Dominance
Codominance
Both traits show
Multiple Allele
Traits blend
More than two alleles
Polygenic
Several Genes involved
Genes and Environment
Environment can affect gene
expression
Phenotype is determined by
genotype and environment
Western White Butterfly
Pigment changes
Why?
11.4 Meiosis
Chromosome Number
Diploid Cells
Homologous pairs
Diploid (2N)
Inherited from each parent
Segregate during gamete formation
Haploid Cells
Single set of chromosomes
Phases of Meiosis
Meiosis
Chromosome # cut by half
Prophase I
Tetrad
Crossing over
Metaphase I and Anaphase I
Paired homologous
chromosomes line up
Phases of Meiosis
Telophase I and Cytokinesis
Results in 2 daughter cells
Haploid in number
Prophase II
No tetrads
Metaphase II, Anaphase II, Telophase II and Cytokinesis
Similar to Meiosis I but four daughter cells result (gametes) (zygote)
Comparing Meiosis and Mitosis
Replication and Separation of Genetic Material
Mitosis
Replicate once, divide once (single chromosomes lined up, full set
of chromosomes at end
Meiosis
Replicate once, divide twice (pairs lined up), half the number of
chromosomes at end.
Gene Linkage and Gene Maps
Gene Linkage (Thomas Hunt Morgan)
Traits assort independently IF
they are on different chromosomes or
Very far apart on same chromosome
If they are fairly close on the same chromosome, they are LINKED
Distance apart on the chromosome is key
The closer the genes are, the more linked they are
Maps are made based on how often crossing over is observed