11 – introduction to genetics
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11 – Introduction to Genetics. The Work of Gregor Mendel. Inheritance other than $$$$ How did things get passed on? Genetics – the scientific study of heredity Mendel, peas and his work Long overlooked. The Role of Fertilization. Male and Female Parts - PowerPoint PPT PresentationTRANSCRIPT
11 – Introduction to Genetics
The Work of Gregor MendelInheritance other than $$$$
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