Chapter 3: Mendelian Genetics Flashcards
inheritance is governed by information stored in discrete unit factors called _____
genes
Genes are transmitted from generation to generate on vehicles called _______
chromosomes
What is transmission genetics?
refers to the study of how genes are transmitted from parents to offspring
What are Mendel’s first three postulates that he derived from his monohybrid cross experiments?
1) genetic characters are controlled by u nit factors existing in pairs in individual organisms; each diploid individual receives one factor from each parent
2) when 2 unlike unit factors responsible for a single characteristic are present in a single individual, one unit factor is dominant to the other, which is said to be recessive
3) during the formation of gametes, the paired unit factors separate, or segregate, randomly so that each gamete receives on or the other with equal likelihood
When both parents are heterozygous, what is the phenotypic and genotypic ratio for the offspring?
phenotypic ratio = 3:1
genotypic ratio = 1:2:1
What is the testcross and how is it useful?
the testcross is a useful way to determine the whether the genotype of a phenotypic dominant individual is homozygous or heterozygous
in a testcross, you cross the phenotypic dominant individual with a homozygous recessive (aka phenotypic recessive) individual. If all offspring are dominant, than the parent is homozygous dominant. If half of the offspring are dominant and half are recessive, the parent is heterozygous dominant.
What is the phenotypic ratio for the dihybrid/two-factor cross for theF1 and F2 generation if one of the P1 parents are homozygous dominant and the other P1 parent is homozygous recessive?
F1 generations will all be heterozygotes and be phenotypic dominant for both traits.
F2 generations will have a 9:3:3:1 ratio
- 9 will be phenotypic dominant for both traits
- 3 will be phenotypic dominant for trait A but recessive for trait B
- 3 will be phenotypic dominant for trait B but recessive for trait A
- 1 will be phenotypic recessive for both traits
This ratio applies to parent generational crosses involving GGWW x ggww or GGww x ggWW
What is the phenotypic ratio for the F1 and F2 generation of a trihybrid cross (assuming the one parent is homozygous dominant and the other homozygous recessive)?
All F1 will be phenotypic dominant, but heterozygotes
F2 ratio = 27:9:9:9:3:3:3:1
27 will be phenotypic dominant (i.e.ABC)
the three 9’s of the ratio are those that have phenotypic dominance for 2 traits and phenotypic recessive for 1 trait
the three 3’s of the ratio are those that have phenotypic recessive for 2 traits and phenotypic dominant for 1 trait
1 will be phenotypic recessive & therefore also homozygous recessive for all three traits (i.e. abc)
What is the Product Law of Probabilities?
When 2 independent events occur simultaneously, the combined probability of the 2 outcomes is equal to the product of their individual probabilities of occurrence.
P(A and B) = P(A) X P(B)
Determine the probability that a plant of genotype CcWw will be produced from parental plants of genotypes CcWw and Ccww
Apply Product law of Probabilities
Calculate the individual probabilities of obtaining the separate outcomes of Cc and Ww first:
Cc x Cc = 1/4 CC, 1/2 Cc, and 1/4 cc. therefore probability of Cc = 50%
Ww x ww = 1/2 Ww and 1/2 ww; therefore probability of Ww = 50%
P(Cc and Ww) = P(Cc) x P(Ww) = (0.5) x (0.5) = 0.25
Probability of an offspring with CcWw is 25%
How many different types of gametes can be formed by the genotype DdEeFF?
Apply Product law of Probabilities:
Dd can produce 2 types of gametes
Ee can produce 2 types of gametes
FF can produce 1 type of gamete
P(Dd + Ee + FF) = P(Dd) x P(Ee) x P(FF) = 2 x 2 x 1 = 4
4 different types of gametes can be formed by the genotype DdEeFF.
What is Mendel’s 4th Postulate?
Independent Assortment will occur between all factors/traits, which results in random segregation. Hence, one pair does not influence the segregation of any other pair and all possible combination of gametes are formed with equal frequency
How many different types of gametes can be produced by an individual with the genotype AABbCCddEeFf?
P(AA + Bb + CC + dd + Ee + Ff) = 1x2x1x1x2x2 = 2^3 = 8
8 different types of gametes can be produced
The following symbols represent what in a pedigree?
a) circle
b) square
c) diamond
d) double line between parents
e) slash through the symbol
f) shaded symbol
g) dot in symbol
a) circle = female
b) square = male
c) diamond = unknown sex
d) double line = consangiuneous parents (parents that are related to one another i.e. first cousins
e) slash through symbol = deceased
f) shaded symbol = affected individual (shows a certain phenotypic trait)
g) dot in the symbol = heterozygous carriers
What is a proband in a pedigree?
refers to the individual that first brought attention to a particular phenotype in the family.
in the pedigree, the proband is indicated by an arrow connected to the designation P
