11.1 Study Guide Flashcards
What is a genotype?
An individual’s allele combination. Ex: Aa, BB
What does homozygous mean?
Both alleles are the same.
What does heterozygous mean?
Two different alleles.
What is a phenotype?
The visible trait that alleles cause.
What is a genotypic ratio?
The ratio of different allele combinations that are possible in the offspring.
What is a phenotypic ratio?
The ratio of the different phenotype possibilities in the offspring.
Explain dominant vs. recessive.
Dominant: An allele is dominant when it only takes one of that allele to make a protein that causes a certain phenotype, no matter what the other allele is.
Recessive: An allele is recessive when it takes two of that allele to cause a certain phenotype.
What is codominance?
A trait is codominant when both of an individual’s alleles are visible in its phenotype.
How did Mendel set up his genetic experiments?
What were the generations, what did he always start with, what ratios did he consistently see in the F1 and F2?
Mendel cut off pollen portions on male flower parts and painted them onto female flower parts to cross them. Mendel always started with true-breeding (homozygous dominant and homozygous recessive) plants. The first generation was known as the P (parent) generation. The offspring of the P generations is known as the F1 generation. All of the F1 plants would be heterozygous and have the dominant trait visible. The F2 generation would be 1/4 homozygous dominant, 2/4 heterozygous, and 1/4 homozygous recessive. The F2 plants would be 3/4 with the dominant trait visible, and 1/4 with the recessive trait visible.
Contrast genotype and phenotype ratios in traits that are dominant/recessive vs. codominant.
The genotype ratios in the F1 generation in traits that are dominant/recessive are normally all heterozygous. This is the same for the F1 generation involving codominant alleles. However, in the F1 generation in traits that are dominant/recessive, the dominant trait will show in the phenotype. In traits that are codominant, a combination of the dominant and recessive trait will be shown. This is the same for the F2 generation. The genotype ratios are the same, but the phenotypes are different.
Explain how a test cross works.
A test cross mates an unknown genotype with an individual who is homozygous recessive and analyzes the phenotypes of the offspring in order to determine the unknown genotype. A homozygous dominant and a homozygous recessive individual are crossed, and a heterozygous and a homozygous recessive individual are crossed. We can tell if the unknown genotype is homozygous recessive if all of the offspring are homozygous recessive. If some of the offspring show the dominant trait and some of the offspring show the recessive trait, the unknown genotype is heterozygous. If all of the offspring show the dominant trait, then the unknown genotype is homozygous dominant.
Predict genotypic and phenotypic ratios for a trait with a dominant and recessive pattern.
Parents: Ff x Ff
Genotypic ratio: 1/4 FF: 2/4 Ff: 1/4 ff.
Phenotype ratio: 3/4 dominant trait: 1/4 recessive trait
Predict genotypic and phenotypic ratios for a trait that is codominant.
Parents: Cr Cr x Cw Cw
Genotypic ratio: 4/4 Cr Cw
Phenotypic ratio: All the offspring are a mix of the dominant and recessive gene.
Predict genotypic and phenotypic ratios for a trait that has multiple alleles.
Sable= Ay, Wolf grey= aw, Tan points= at, and Black=a.
Parents: at a x aw a
Genotypic ratio: 1/4 aw at: 1/4 aw a: 1/4 at a : 1/4 aa
Phenotype ratio: 2/4 Wolf grey: 1/4 Tan points: 1/4 Black
Predict the parent genotypes based on the phenotypic ratio of offspring.
Y= dominant (yellow)
y=recessive (green)
Offspring: Yellow, Yellow, Yellow, Green
Parent genotypes= Yy x Yy
