Chapter 11 – Observable Patterns of Inheritance. 11.1 Mendel’s Insight into Inheritance Patterns...
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Transcript of Chapter 11 – Observable Patterns of Inheritance. 11.1 Mendel’s Insight into Inheritance Patterns...
Chapter 11 – Observable Patterns of Inheritance
11.1 Mendel’s Insight into Inheritance Patterns
Monk in Austria
-experimented with pea plants to see how genes are passed on to generation.
-found that sperm and egg cells contain genetic information that play a part in the genes of the offspring.
Gregor Mendel
“Father of Genetics”
Terms to Know:
Gene locus – location of a specific gene
Allele – variations of a gene
Genes
• Units of information about specific traits.
When identical alleles are passed on generation after generation this is called a true-breeding lineage.
When offspring inherit a pair of non-identical alleles for a trait this is called a hybrid offspring.
Homozygous
-when both alleles are identical (TT)
Heterozygous
-when alleles are not identical (Tt)
Genotype and Phenotype
• Genotype – genetic makeup of an individual.
• Phenotype – physical appearance of an individual. Observable traits.
Tracking Inheritance
P = parental generation
F1 = first-generation offspring
F2 = second-generation offspring
11.2 Mendel’s Theory of Segregation
• Mendel tested the idea that a plant inherits two units (genes) of information about a trait.
He performed a Monohybrid Cross
-cross of two parents that are homozygous for different versions of a single trait.
F1 offspring will be hybrid, heterozygous.
TallP Dwarfx
F1All Tall
Phenotype
Monohybrid Cross
Clearly Tall is Inherited…What happened to Dwarf?
F1 x F1 = F2
F23/4 Tall 3:1 ratio1/4 Dwarf
Dwarf is not missing…just masked as “recessive” in a diploid state…
Tall is dominant to tall.
DD dd
Dd
GenotypeHomozygous
DominantHomozygous
Recessive
Heterozygous
Dwarfdd
TallDd
d
TallDd
TallDD
D
dDPunnett Square:
possible gametes
possible gametes
Probability
The chance that an event will occur.
Punnett-square Method
• If half of a plant’s sperm or eggs were a and half were A, then four outcomes would be possible each time a sperm fertilized an egg.
Not precise
Possible event Probable outcome
Sperm A meets egg A ¼ AA offspring
Sperm A meets egg a ¼ Aa
Sperm a meets egg A ¼ Aa
Sperm a meets egg a ¼ aa
Testcrosses
• Fertilizing different genotype plants to see results.
• Test results may reveal whether the organism is homozygous dominant or heterozygous.
Segregation
• Diploid cells have pairs of genes, on pairs of homologous chromosomes.
• The two genes of each pair are separated from each other during meiosis, so they end up in different gametes.
• They do not effect eachother.
11.3 Independent Assortment• Dihybrid Crosses – crossing two traits.
Mendel crosses pea plants with two pairs of genes that were homozygous.
9:3:3:1 ratio