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