Chapter 14: mendel and the gene idea Flashcards
Describe the difference between a character and a trait. Give an example
A character is a heritable feature that varies among individuals, like flower color
The variant for a character is a trait, such as a purple or white flower
What is true breeding?
two parents are homozygous for every trait and produce offspring that are the same phenotype
aaxAA=Aa, all same phenotype
When Mendel crossed the F1 generation of hybrids, what did the F2 generation look like?
a 3:1 ratio of purple to white plants
How did Mendel’s breeding of the plants refute blending theory?
blending theory would produce lighter purple plants, and the white plants would not have reappeared in the F2 generation
How many alleles will an organism inherit from its parent, according to Mendel?
two
What is the law of segregation?
the two alleles for a heritable character separate, or segregate, during gamete formation and end up in different gametes
What are the four points of Mendel’s model?
- alternative versions of genes account for variations in inherited characters (some white, some purple)
- an organism inherits two alleles from each parent
- If the two alleles differ, the dominant trait will be expressed
- law of segregation, the two alleles for a heritable character separate during gamete formation and end up in different gametes
An ___ will help synthesize a dominant allele pigment, leading to its expression
enzyme
Why is a trait dominant?
The enzyme is made that will synthesize the dominant allele
What does a testcross determine?
whether the genotype is heterozygous or homozygous
You perform a testcross between a dominant phenotype and a recessive phenotype and receive a 1/2 offspring dominant and 1/2 offspring recessive. What is the genotype of the dominant parent?
The genotype is heterozygous
What is the law of independent assortment?
Crossing two true-breeding parents differing in two characters produces dihybrids which are heterozygous
a dihybrid cross can determine whether two characters are transmitted to offspring together or separately (think about redheads being allergic to anesthesia. these traits are transmitted together)
What is the multiplication rule?
the probability that two or more INDEPENDENT events will occur together is the product of their individual probabilities
What is the probability that flipping a coin twice will land on heads both times?
25%
50%x50%=25%
What is the addition rule?
the probability that any one of two or more mutually exclusive events will occur is calculated by adding together their individual probabilities
You cross a red rose with a white rose and the F1 generation results in 100% pink, while the F2 generation 50% pink, 25% red, and 25% white. this is an example of
incomplete dominance
Why does incomplete dominance still not support the blending hypothesis?
Because in the F2 generation, dominant and recessive phenotypes are still expressed, while the blending hypothesis would indicate that the mix is present in all generations
Blood type is an example of what kind of dominance
codominance
What is pleiotropy?
When the expression of a single gene has multiple effects on phenotypes
what is epistasis?
the expression of a gene is modified by the expression of one or more other genes
What is polygenic inheritance?
multiple genes independently affect a single trait, ex. skin color
What is a testcross?
breeding of a recessive homozygote with a dominate phenotype (but unknown genotype)
You perform an experiment with a yellow puffle (a recessive trait) and a purple puffle ( a dominant trait) to determine the purple puffle’s genotype. This is an example of-
a testcross
A true-bred offspring is
homozygous for a trait
What does a 3:1 offspring ratio tell us?
It confirms the law of segregation because the alleles for each character segregate during meiosis and end up in different daughter cells
A dihybrid cross can determine whether two characters are
transmitted to offspring together or independently
You cross a blue eyed puffle with a yellow eyed puffle and the F1 generation has green eyes. This is an example of what kind of degree of dominance?
Incomplete.
Explain why incomplete dominance is not “blending”
the traits will appear again in F2. Additionally, the heterozygote is only expressing 50% of the encoded protein, rather than both at the same time
The offspring phenotype must be _____ for codominance to occur
heterozygous
14.3.1 Incomplete dominance and epistasis are both terms that
define genetic relationships. What is the most basic distinction between these terms?
Incomplete dominance describes the relationship between two alleles of a
single gene, whereas epistasis relates to the genetic relationship between two
genes (and the respective alleles of each).
