Among Native Americans, two types of earwax (cerumen) are...

Name: Problem 12, Chapter 2: Genetics: From Genes to Genomes
Uploaded: 2023-03-12T00:11:35-08:00
Duration: 4 min 45 s
Channel: Bryan Valdivia
Description: Among Native Americans, two types of earwax (cerumen) are seen, dry and sticky. A geneticist studied the inheritance of this trait by observing the types of offspring produced by different kinds of matings. He observed the following numbers: a. How is earwax type inherited? b. Why are no 3: 1 or 1: 1 ratios present in the data shown in the chart?

Among Native Americans, two types of earwax (cerumen) are seen, dry and sticky. A geneticist studied the inheritance of this trait by observing the types of offspring produced by different kinds of matings. He observed the following numbers: a. How is earwax type inherited? b. Why are no 3: 1 or 1: 1 ratios present in the data shown in the chart?

Among Native Americans, two types of earwax (cerumen) are seen, dry and sticky. A geneticist studied the inheritance of this trait by observing the types of offspring produced by different kinds of matings. He observed the following numbers:
a. How is earwax type inherited?
b. Why are no 3: 1 or 1: 1 ratios present in the data shown in the chart?

Key Concepts

Mendelian Inheritance

This concept involves the transmission of traits from parents to offspring following predictable patterns described by Mendel’s laws. A single gene with two alleles segregates during gamete formation, leading to certain expected genotype and phenotype ratios for traits governed by one gene.

Complete Dominance

Complete dominance refers to the situation where one allele completely masks the expression of another allele in heterozygous individuals. In the case of earwax type, the allele for the dominant phenotype overshadows the recessive allele, meaning heterozygotes exhibit the same phenotype as homozygous dominant individuals.

Inferring Inheritance Patterns from Mating Data

Understanding that only two phenotypes are observed despite different underlying genotypes explains why typical Mendelian ratios like 3:1 or 1:1 might not be evident in the collected data. The inability to distinguish heterozygotes from homozygotes in the dominant phenotype leads to a masking of the underlying genetic ratios in observational studies.

Phenotype and Genotype Distinction

Due to complete dominance, heterozygous and homozygous dominant individuals display the same phenotype. This makes it difficult to distinguish them based solely on outward appearance, which in turn obscures the expected Mendelian genotype ratios (such as 3:1 in a heterozygote cross) when only the phenotype is considered.

Transcript

00:01 In order to answer this question, let's talk about inheritance.

00:03 This question says among native americans, two types of earwarks are seen, drying sticky.

00:08 A geneticist studied the inheritance of this trade by observing the types of offspring produced by different kinds of ratings.

00:15 He observed the following numbers.

00:18 How is earwalks type inherited? and you got the following numbers.

00:23 Okay, here you have sticky with sticky, you're getting in the offspring, you are getting for sticky and for dry, you're getting for sticky 32 and for dry 6.

00:41 In case of sticky with dry, you're getting, you're getting 21 sticky and 9 dry.

00:52 And in a cross with dry with dry, you're getting 0 sticky and 42 dry.

00:59 And it says, how is here was type inherited? so in this case, in this case, remember that, well, let's use here the d .s.

01:09 Okay, that's dominant and the recessive allele.

01:11 So you have a homozygous domino, you have a heterocybolysis, and you have a homozygloid.

01:15 You should know that when you cross two homozygo recessive, like this, the only possibility is going to be to get homozygo -resensive off -pring, because both parents only have recessive alleles.

01:31 So all the off -pring are going to have recessive alleles only.

01:34 Okay.

01:34 But if you cross, two people here with the dominant phenotype, then the dominant phenotype can be homocylus -domin or heterocyclos.

01:45 So you can get, in the off -pring, dominant or recessive off -pring.

01:49 But in this case, what you have to be very sure is that a close between a homocyguiseal recessive and homocygo -recessive, you're going to get only homocyclosive off -pring.

01:58 So in this case, among these crosses, you get that dry with dry is getting only dry off -pring.

02:03 So it means that this is dry, dry is recessive and sticky is dominant.

02:10 Now, this question says, how is earwax type inherited? well, sticky is dominant and dry is excessive.

02:16 Deacon says, why are no 3 to 1 or 1 to 1 ratios present in the data shown in the chart? so as you can see here, you have 6 and you have 3 2...

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