How Traits Are Inherited 1.Sex cells with a haploid number of chromosomes are united during fertilization to form a zygote. 2. The new diploid zygote carries half of the genes from each parent. 3. Genes are located on the chromosomes.
GENES vs. ALLELES Genes: The section of DNA on the chromosome that codes for the protein production resulting in a specific trait. Ex. Hair color, Eye color Allele: The different forms of the gene. Ex. Blonde or Brown hair Brown or Blue eyes
Gregor Mendel’s Experiments 1.Mendel crossed a tall pea plant with a short pea plant. - What did the resulting offspring look like? WRONG! They were all tall.
2. When he crossed the resulting 1st generation pea plants… They produced 3 tall pea plants and 1 short pea plant
3. Mendel theorized that the traits (alleles) for tall pea plants were dominant over the traits (alleles) for short pea plants. The traits that did not show up in the first generation were called recessive. Parent Generation 1 st Generation 2 nd Generation
Mendel developed a Punnett Square to predict the outcome of the parent generation cross. TT t t Tt
Here are the results of the 1 st generation cross. T t T t TT Tt tt
T t T t TT Tt tt PHENOTYPE: 3 TALL AND 1 SHORT GENOTYPE: 1 HOMOZYGOUS DOMINANT - TT 1 HOMOZYGOUS RECESSIVE - tt 2 HETEROZYGOUS - Tt
Now try this. TtTt T t TT Tt tt Phenotype:Genotype: Ratio ______X _____Homozygous Dominant ____ % of Tall = ______ %Homozygous Recessive ____ % of Short = ______%Heterozygous _____ Gregor Mendel Tt X Tt