11.1 Study Guide Flashcards
Define genotype and phenotype. How are they related?
Genotype is the set of genes/alleles that make up an organism’s genetic code. Phenotype is the organism’s physical traits that are coded for by its genotype.
Explain the difference between homozygous and heterozygous alleles.
Homozygous alleles are allele pairs of the same version of the gene. Heterozygous alleles are allele pairs of two different versions of the gene.
Explain genotypic and phenotypic ratios. What two parent genotypes would produce a genotypic ratio of 1/4 HH : 2/4 Hh : 1/4 hh given that H is a dominant allele and h is a recessive allele?
Genotypic ratios describe how many of all possible offspring genotypes from a cross each specific genotype makes up. Phenotypic ratios describe how many of all possible offspring phenotypes from a cross each specific phenotype makes up. To produce a genotypic ratio of 1/4 HH : 2/4 Hh : 1/4 hh, one would have to make a cross of parents with respective genotypes of Hh and Hh.
Define dominant and recessive genes. Explain how codominant genes differ from the both of them.
Dominant genes are genes that require only one copy to be present for them to be expressed. Recessive genes are genes that require two copies to be present for them to be expressed. Codominant genes are multiple dominant genes that, when both present, are both expressed simultaneously and produce a unique phenotype.
Explain how Mendel’s original experiments on pea plants were organized. How were the generations labeled? What was special about the parent plants? What genotypic and phenotypic ratios consistently appeared in each generation?
Mendel’s original experiments with pea plants were crosses of two ‘true-breeding’ plants, meaning one was entirely homozygous dominant and one was entirely homozygous recessive. These ‘parent plants’ were termed the ‘P’ generation, and their offspring the F1 generation. In Mendel’s experiments, the F1 plants all had identical heterozygous genotypes and dominant phenotypes, and their offspring from self-fertilization were termed the F2 generation. The F2 had a mix of all the possible genotypes and phenotypes, and thus proved that genes are passed on from parent to offspring individually.
Regarding the cross of two parent organisms with genotype AB and AB respectively, explain how the genotypes and phenotypes (plus ratios) of the following two generations differ based on whether the alleles are dominant and recessive or codominant.
If the alleles are dominant (A) and recessive (B), the genotypic ratio will be 1/4 AA : 2/4 AB : 1/4 BB and the phenotypic ratio will be 3/4 Dominant : 1/4 Recessive. If the alleles are codominant, the genotypic ratio will be 1/4 AA : 2/4 AB : 1/4 BB and the phenotypic ratio will be 1/4 A expressed : 2/4 both expressed : 1/4 B expressed.
What is the purpose of a test cross? How is it set up?
A test cross is used to determine the genotype of one organism by crossing it with another with a known genotype. It is done by crossing the mystery organism with a specific other genotype such that the phenotypes of the offspring and the mystery parent will allow for only one possible genotype for the mystery parent.
Regarding the dominant allele P, the recessive allele p, and the codominant alleles Q and R, in the cross of an organism with PpQQ and an organism with ppQR, what will the genotypic ratio of the offspring be?
Genotypic Ratio: 4/16 PpQQ : 4/16 PpQR : 4/16 ppQQ : 4/16 ppQR
Regarding the dominant allele U and the recessive allele u, predict the genotypes of the parent organisms given offspring with genotypes of UU, Uu, Uu, and uu.
The parent organisms will most likely have genotypes of Uu and Uu respectively, as the cross of those genotypes produces a genotypic ratio of 1/4 UU : 2/4 Uu : 1/4 uu.
