11 – Introduction to Genetics

The Work of Gregor MendelInheritance other than $$$$

How did things get passed on?Genetics – the scientific

study of heredity

Mendel, peas and his workLong overlooked

The Role of FertilizationMale and Female Parts

Fertilization – joining of reproductive cells

Self-pollination True breeding

Trait Cross Breeding

Male parts gone Hybrids

Genes and AllelesP1 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 AllelesPrinciple of Dominance

Mendel’s second conclusion

One dominant allele Organism shows that trait

Recessive AllelesOnly show when dominant is

not present

SEGREGATIONWhat happened to the

other trait?Was it still in the F1?

Did an F2 crossTrait reappeared

Mendel assumed Dominance masks

F1 Cross and GametesOne trait separated from

the otherSegregationDuring gamete formation

Follow this chart

11.2 – Applying Mendel’s Principles

11.2 Applying Mendel’s Principles – Probability and Punnett SquaresProbability – likelihood that

an event would occur. Mendel analyzed his dataFound probability

Segregation and Outcomes – Alleles segregate during

gamete formation (haploid)Homozygous vs. Heterozygous

Probabilities, Averages, Genotype and PhenotypeProbabilities predict the

average outcome

Genetic makeup vs. observable characteristicsGenotype vs. Phenotype

Punnett SquaresUses math to predict

Independent AssortmentDoes 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 MendelCharacteristics 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

SummaryThomas Hunt Morgan

Showed that the same principles apply to animalsFruit Fly (Drosophila melanogaster)

11.3 – Other Patterns of Inheritance

Beyond Dominant and Recessive Incomplete Dominance

Traits blend

Codominance Both traits show

Multiple Allele More than two alleles

Polygenic Several Genes involved

Genes and EnvironmentEnvironment can affect gene

expressionPhenotype is determined by

genotype and environmentWestern White Butterfly

Pigment changesWhy?

11.4 Meiosis

Chromosome NumberDiploid Cells

Homologous pairsDiploid (2N)

Inherited from each parentSegregate during gamete formation

Haploid CellsSingle set of chromosomes

Phases of MeiosisMeiosis

Chromosome # cut by half

Prophase I Tetrad Crossing over

Metaphase I and Anaphase I Paired homologous

chromosomes line up

Phases of MeiosisTelophase I and Cytokinesis

Results in 2 daughter cellsHaploid in number

Prophase IINo tetrads

Metaphase II, Anaphase II, Telophase II and CytokinesisSimilar to Meiosis I but four daughter cells result (gametes) (zygote)

Comparing Meiosis and MitosisReplication and Separation of Genetic Material

MitosisReplicate once, divide once (single chromosomes lined up, full set

of chromosomes at endMeiosis

Replicate once, divide twice (pairs lined up), half the number of chromosomes at end.

Gene Linkage and Gene MapsGene 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 keyThe closer the genes are, the more linked they are

Maps are made based on how often crossing over is observed