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