A snapdragon with pink petals, black anthers, and long stems...

A snapdragon with pink petals, black anthers, and long stems was allowed to self-fertilize. From the resulting seeds, 650 adult plants were obtained. The phenotypes of these offspring are listed here.$$ \begin{array}{rlll} 78 & \text { red } & \text { long } & \text { tan } \\ 26 & \text { red } & \text { short } & \text { tan } \\ 44 & \text { red } & \text { long } & \text { bhek } \\ 15 & \text { red } & \text { short } & \text { black } \\ 39 & \text { pink } & \text { long } & \text { tan } \\ 13 & \text { pink } & \text { short } & \text { tan } \\ 204 & \text { pink } & \text { long } & \text { black } \\ 68 & \text { pink } & \text { short } & \text { black } \\ 5 & \text { white } & \text { long } & \text { tan } \\ 2 & \text { white } & \text { short } & \text { tain } \\ 117 & \text { shite } & \text { long } & \text { black } \\ 39 & \text { white } & \text { short } & \text { black } \end{array} $$ a. Using $P$ for one allele and $p$ for the other, indicate how flower color is inherited. b. What numbers of red : pink: white would have been expected among these 650 plants? c. How are anther color and stem length inherited? d. What was the genotype of the original plant? e. Do any of the three genes show independent assortment? f. For any genes that are linked, indicate the arrangements of the alleles on the homologous chromosomes in the original snapdragon, and estimate the distance between the genes.

A snapdragon with pink petals, black anthers, and long stems was allowed to self-fertilize. From the resulting seeds, 650 adult plants were obtained. The phenotypes of these offspring are listed here.$$
\begin{array}{rlll}
78 & \text { red } & \text { long } & \text { tan } \\
26 & \text { red } & \text { short } & \text { tan } \\
44 & \text { red } & \text { long } & \text { bhek } \\
15 & \text { red } & \text { short } & \text { black } \\
39 & \text { pink } & \text { long } & \text { tan } \\
13 & \text { pink } & \text { short } & \text { tan } \\
204 & \text { pink } & \text { long } & \text { black } \\
68 & \text { pink } & \text { short } & \text { black } \\
5 & \text { white } & \text { long } & \text { tan } \\
2 & \text { white } & \text { short } & \text { tain } \\
117 & \text { shite } & \text { long } & \text { black } \\
39 & \text { white } & \text { short } & \text { black }
\end{array}
$$
a. Using $P$ for one allele and $p$ for the other, indicate how flower color is inherited.
b. What numbers of red : pink: white would have been expected among these 650 plants?
c. How are anther color and stem length inherited?
d. What was the genotype of the original plant?
e. Do any of the three genes show independent assortment?
f. For any genes that are linked, indicate the arrangements of the alleles on the homologous chromosomes in the original snapdragon, and estimate the distance between the genes.

Key Concepts

Gene Mapping

Gene mapping involves determining the relative positions of genes on a chromosome, primarily by analyzing recombination frequencies from genetic crosses. It provides insights into the linear order of genes, their distances, and the likelihood of their co-inheritance.

Recombination Frequency

Recombination frequency is the metric used to estimate the physical distance between linked genes by quantifying the percentage of recombinant offspring in a genetic cross. This value is fundamental for constructing genetic maps and understanding the arrangement of genes on chromosomes.

Independent Assortment

The principle of independent assortment states that alleles of different genes segregate into gametes independently of one another, assuming the genes are on different chromosomes or far apart on the same chromosome. Deviations from independent assortment can suggest genetic linkage.

Genetic Linkage

Genetic linkage refers to the phenomenon where genes located physically close together on the same chromosome tend to be inherited together, resulting in a deviation from the expected independent assortment. Linkage analysis helps to determine which genes are connected and to what degree.

Self-fertilization

Self-fertilization is the process where an organism fertilizes its own gametes, leading to increased homozygosity over generations. In genetic studies, selfing is used to reveal the underlying genotype of traits by producing offspring that segregate according to Mendelian ratios.

Incomplete Dominance

Incomplete dominance is a form of allele interaction in which a heterozygote expresses a phenotype that is intermediate between those of the two homozygotes. This pattern deviates from the classical dominant/recessive relationship and is reflected in a 1:2:1 phenotype ratio in self-fertilized organisms.

Mendelian Inheritance

Mendelian inheritance is the foundational concept detailing how alleles segregate during gamete formation and combine during fertilization. It explains patterns such as dominant and recessive interactions, and in many crosses, yields predictable genotype and phenotype ratios based on simple probability rules.

Phenotypic Ratio Analysis

Phenotypic ratio analysis involves examining the distribution of observable traits in offspring to infer genetic principles such as dominant and recessive interactions, independent assortment, or incomplete dominance. The comparison of observed ratios with expected Mendelian ratios is key to understanding genetic mechanisms.

Transcript

00:02 Hi there.

00:03 In this problem, we are looking at six independently sorting genes, and we have the genotypes of each parent.

00:12 Parent one is big r, little r, big d, little d, little c, little c, big o, little o, big h, little h, and big w, little w.

00:37 And we're crossing that with parent 2.

00:42 Keep these separate here so we know p1 and p2 are not alleles.

00:46 Parent 2 is big r, little r, little d, little d, big c, little c, little c, little o, big h, little h, and little h.

01:04 And little w, all right, and we have a series of questions about these two crosses.

01:11 The first question is referring to parent 1, and wants to know how many different kinds of gametes can be formed.

01:19 So remember we're talking about independent assortment here, where each gene is independent of the next.

01:27 So when we do probability here, it means we need to multiply.

01:32 So for example, when i look at big r, little r, i can get two possible gametes from that.

01:39 When i, i can get a big r or i can get a little r.

01:42 When i look at the next gene, i can have big d, or i can have little d.

01:48 So i need to multiply those two options times the first two options.

01:53 For little c, little c, there's only one option there.

01:57 It can only make little c gametes.

01:59 For big o, little o, we can make a big o gammy or a little o gamete.

02:04 Big h, little h, same thing.

02:07 There are two options.

02:08 And big w, little w, there are again two options.

02:13 Multiplying these together, i get 32.

02:17 There are 32 different gametes that can form from the independent assortment of these alleles.

02:27 All right, moving on to letter b.

02:30 How many genotypes are possible among the progeny, the offspring? so for this cross, we need to look at how many different genotypes are possible.

02:42 Rather than making one huge punnet square, that would be a little bit out of control here with this many different genes, six different ones, we're going to do probability again instead.

02:55 So i'm just going to look at each gene one at a time.

02:58 So at our first cross, we have big r, little r times big r little r.

03:04 And we're talking about genotypes.

03:07 So when we cross big r, little r, big r, little r, we can get big r, big r, big r, big r, big, r, we can get big r, little r, or we can get little r, little r.

03:15 In other words, there are three possible genotypes we can get for that first gene.

03:22 Next, we have big d, little d from parent 1 and little d, little d from parent 2.

03:28 The possible arrangements there would be big d, little d, or little d, little d.

03:34 In other words, there are only two possible genotypes of those offspring.

03:39 Next, we have little c, little c, times big c, little c.

03:43 Looking at all the possible arrangements there, there are only two unique ones.

03:47 There's big c, little c, and there's little c, little c.

03:51 The same thing is going to happen for big o little o times little o.

03:56 There are just two possibilities for genotypes.

04:00 Next we have heterozygous, big h, little h times heterozygous, big h, big h, big h, big h, big h, big h, big h, little h.

04:06 And then finally, for the w, we could have big w, little w, we could have big w little w, or little h, and then finally for the w, w, or little w, little w.

04:20 In other words, two possible arrangements.

04:24 Multiplying these together, we see that there are 144 possible genotypes for the offspring.

04:38 144 different combinations of these six alleles, are these six genes.

04:45 All right, moving on to letter c.

04:47 Letter c wants to know how many phenotypes are possible.

04:50 This is going to be similar to genotypes, except, remember the heterozygous condition, heterozygous dominant is the same as homozygous dominant in terms of phenotype.

05:02 So for big r, big r, little r, rather times big r, little r, we can get big r, big r, we can get big r, little r, those are both going to have the same phenotype.

05:12 The other option, little r, little r is a different phenotype.

05:16 So there are two possible phenotypes here.

05:20 For d, there were two genotypes, and there are going to be two phenotypes...

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