(2) Th ode Caenorhabditis elegans can reproduce by self-fertilization or cross-f
ID: 196274 • Letter: #
Question
(2) Th ode Caenorhabditis elegans can reproduce by self-fertilization or cross-fertilization. e nemat Hermaphrodites are capable of with normal movement is movement. One of the F1 offspr self-fertilization or cross-fertilization by mating with a male. A wild-type male mated to a paralyzed hermaphrodite. All of the F1 offspring are capable of ing is allowed to self-fertilize to produce an F2 generation. Te a) Create a genetic nomenclature for the gene leading to paralysis. (1 point) b) Which allele is dominant and which is recessive? (1 point) anA :S c) Among the F2 generation worms, what fraction of them do you predict will be paralyzed? (2 points)Explanation / Answer
Ths question is based on Mendel's law of dominance. Before understanding this law. Let us revise some basics of Mendelian genetics. Characters (phenotype) in an organism are directly dependent on the nature of factors (also called genes or genotype). Different forms of genes are termed as the allele. An allele which is responsible for a trait or character is called a dominant allele and the one which is not is called a recessive allele.
During fertilization, an offspring acquire one pair of alleles from his/her father and the other from his/her mother. Thus, the occurrence of a character in an offspring depends on the nature of alleles inherited from parents. Let us take a simple example of height in an offspring. Father is tall and the mother is short. If the tall character is dominant then the young one will also be tall. The allele inherited from the father is called a dominant allele, and the allele inherited from the mother is called a recessive allele. This can be illustrated as follows:
TT x tt (where "TT" are alleles for tall from father and "tt" are alleles for short from mother)
= Tt, Tt, Tt, Tt (Since tall character is dominant, all the offspring will be tall)
So, as per the law of dominance, an offspring express only one character in the first generation and the nature of this character dependent on the dominant allele.
With this background, let us solve the question.
Answer to Question 1
Genetic nomenclature is a way to represent genes for proper understanding. As per the rules of nomenclature
1. the name of the gene must be italicized
2. wild-type or normal genes are represented with the superscript "+" and
3. the mutant gene is represented by the superscript "-".
So, if p is the gene for paralysis, genetic nomenclature for the gene p leading to paralysis will be p-and the gene for normal movement will be p+
Answer to Question 2
All of the offspring in F1 showed movement. This can be possible only when the allele p+is dominant and the allele p- is recessive. This can be explained as follows:
p+p+ X p- p- (Cross between wild-type male p+p+and paralyzed hermaphrodite p- p- )
p+p- , p+p-, p+p-, p+p-(All offsprings in F1 generation showed normal movements and their phenotypic ratio is 1:1:1:1)
Based on the above explanation, the dominant alleles are p+p+ and the recessive alleles are p-p-
The answer to question 3:
In F2 generation 25% would be paralyzed. Reason is as follows:
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.