Lecture 13: Mendel, genes, and Inheritance

What were two observations Mendel made as a result of reciprocal crossing?

No evidence of blending and sex of parent did not affect inheritance

What is the first conclusion of Mendel’s experiments?

The adult plants carry a pair of factors that govern the inheritance of each trait (an organism inherits one factor from each parent). Because egg and sperm are haploid, an organism inherits one allele from each parent

What is the second conclusion of Mendel’s experiments?

If an individual’s pair of genes consists of different alleles, one allele is dominant over the other, which is considered recessive

What is the third conclusion of Mendel’s experiments?

The pair of alleles that control a characteristic separate as gametes are formed; half the gametes carry one allele, and the other half carry the other allele

What is Mendel’s principle of segregation?

Haploid egg + haploid sperm = diploid zygote

What are alleles?

Different versions of genes

What is purebred (true-breeding)?

Individuals must be homozygous, which means they must have two of the same allele of a gene. Homozygous dominant = PP and homozygous recessive = pp

What is a hybird?

When an individual has two different alleles of a gene, they are called heterozygous (Pp)

What is a genotype?

Genetic makeup of an organism in terms of genes and alleles (written as two letters: AA, Aa, aa)

What is a phenotype?

Organism’s appearance (written as descriptive words: purple or white flowers)

How can phenotypic differences occur?

Genetic differences, environmental factors, interaction between genetics and the environment

What is a testcross?

A cross between an individual with the dominant phenotype and a homozygous recessive individual. Used to identify if an individual with a dominant trait is heterozygous or homozygous dominant

What is included in a dihybrid cross?

Both parents are heterozygous for both traits and the phenotypic ratio will always be 9:3:3:1 on a 4 × 4 punnet sqaure