Name: tracking one trait in monohybrid crosses
Uploaded: 2021-04-07T12:11:58.000Z
Duration: 1 min 20 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Biology

heredity-inheritance-and-variation-of-traits

Heredity- Inheritance and Variation of Traits

LS.Bio.7.1

Monohybrid Crosses

Using the pea plant Gregor Mendel originally performed monohybrid crosses. Breeding experiments between organisms that vary by a single trait like pod color.

For example, in the original parental generation, P zero, one parent has all green pods. It&#39;s genotype is homozygous for the green pod color allele represented as upper case G&#39;s . The other parent has only yellow pods and is homozygous for the yellow pod allele indicated with lower case g&#39;s.

Upon crossing the first offspring, the filial or F one generation appear identical expressing the same phenotype of green pods. This result illustrates the Principle of Uniformity and indicates that green is the dominant trait of the two colors.

Now when plants of the F one generation are allowed to self-fertilize, their progeny, F two plants, contain some with green pods and others with yellow ones in a ratio of three to one. Which confirms that yellow is indeed the recessive trait, a hidden form carried down from the initial parents.

monohybrid crosses

<h4>Overview</h4>

In the 1850s and 1860s, Gregor Mendel investigated inheritance by performing monohybrid crosses in pea plants. He crossed two plants that were true-breeding for different traits. Based on his observations, Mendel proposed that organisms inherit two copies of each trait, one from each parent, and that dominant traits can hide recessive traits. These results formed the basis of two fundamental principles in genetics: the Principle of Uniformity and the Law of Segregation.

<h4>Monohybrid Crosses Reveal Dominant and Recessive Traits</h4>

Over eight years spanning the 1850s and 1860s, an Austrian monk named Gregor Mendel carried out seminal breeding experiments with pea plants. These experiments demonstrated the fundamental principles of inheritance, earning him the moniker &ldquo;the father of modern genetics.&rdquo; Mendel&rsquo;s experiments focused on seven pea plant characteristics, each manifesting as one of two traits that are determined by a single gene locus.

Mendel noticed that, when some of his pea plants reproduced by self-fertilization, their progeny always displayed the same trait. In other words, they were true-breeding. For example, some plants with yellow pods only produced offspring with yellow pods. When crossed with other plants that bred true for yellow pods, these plants also produced only progeny with yellow pods. Similarly, Mendel observed true-breeding pea plants that produced only offspring with green pods.

At the time, inherited traits were thought to be some mixture of parental features. Mendel instead observed discrete phenotypes, like green and yellow pods. He proposed that, rather than traits mixing in offspring, discrete factors (now known as genes) are inherited from parents and remain separate in the offspring. In cases where a trait skips a generation, Mendel proposed that the visible trait merely masks the presence of the other inherited trait. In other words, inheritance is particulate, and dominant traits hide recessive traits. To determine which trait was dominant, Mendel conducted monohybrid crosses. Monohybrid crosses combine two true-breeding organisms that differ by a single trait. All offspring of such crosses are monohybrids, or heterozygotes, and display the dominant trait.

For example, Mendel crossed pea plants that bred true for yellow pods with those that bred true for green pods to determine the dominant pod color. This parental generation (P0) produced offspring, the first filial generation (F1), that were all monohybrids with green pods. Repeatedly observing these findings established green pods as the dominant trait and demonstrated Mendel&rsquo;s principle of uniformity: heterozygotes for a single gene trait display the same phenotype.

<h4>Parental Alleles Are Randomly Distributed to Gametes</h4>

Mendel then induced self-fertilization in the F1 plants, producing the F2 generation. F2 pea plants with green pods outnumbered those with yellow pods by a ratio of 3:1. Mendel repeatedly observed this 3:1 inheritance pattern for each of the seven pea plant characteristics.

Mendel&rsquo;s law of segregation explains this recurring ratio. The law of segregation states that an organism distributes one of its two gene copies to each gamete (egg or sperm cell). Importantly, this distribution is random, such that a heterozygote (Gg) is equally likely to produce gametes with dominant (G) and recessive (g) alleles.

If a heterozygote self-fertilizes (Gg x Gg), the parental alleles can combine in four possible ways: paternal G with maternal G (GG), paternal G with maternal g (Gg), paternal g with maternal G (Gg), and paternal g with maternal g (gg). Three outcomes produce green pods (the GG and Gg genotypes) and one produces yellow pods (the gg genotype), a 3:1 ratio. Thus, if all outcomes are equally likely, self-fertilizing heterozygotes will produce three offspring with green pods for every one with yellow pods. This is remarkably close to the phenotypic ratio that Mendel observed, confirming his proposed law of segregation.

<h4>Dominant Traits Are Not Always Common</h4>

Unlike green pods, green peas are recessive, whereas yellow peas are dominant. Why, then, are the peas we regularly encounter green? In short, people prefer green peas over yellow ones. As Mendel&rsquo;s experiments demonstrate, homozygotes produce offspring with the same trait, or phenotype, when self-fertilized or crossed with other homozygotes. If farmers continue to exclude yellow peas from their crop crosses, they will continue producing only green peas. This example illustrates another important point: dominant traits are not necessarily the most common traits. Harmful dominant traits, for example, may be selected against.

Overview

In the 1850s and 1860s, Gregor Mendel investigated inheritance by performing monohybrid crosses in pea plants. He crossed two plants that were ...

Education

JoVE Core

Molecular Biology

Unit 2

Mendelian Genetics

KEY TERMS AND CONCEPTS

tracking one trait in monohybrid crosses

Monohybrid crosses track how one trait is passed from parents to offspring. They are used to study inheritance when only a single characteristic is followed at a time.

A monohybrid cross can compare the possible outcomes for a monogenic trait, which is a trait controlled by one gene. This approach helps show how one gene can shape different inherited forms of the same characteristic.

The method also connects with Mendel's work on genetics. It is a useful way to predict patterns of inheritance and understand how traits are distributed in offspring from a simple genetic cross.

Tracking One Trait in Monohybrid Crosses

punnett squares

Predicting Traits with Punnett Squares

Punnett squares help students predict how traits may be passed from parents to offspring. They are a simple grid used in genetics to organize possible allele combinations. An allele is a version of a gene. The square compares the alleles each parent can give. By filling in the boxes, students can see possible genotypes, which are the genetic makeup of offspring. The results can also help connect those genotypes to traits that may appear in the next generation.

Monohybrid crosses track how one trait is passed from parents to offspring. They are used to study inheritance when only a single characteristic is followed at a time. A monohybrid cross can compare the possible outcomes for a monogenic trait, which is a trait controlled by one gene. This approach helps show how one gene can shape different inherited forms of the same characteristic. The method also connects with Mendel's work on genetics. It is a useful way to predict patterns of inheritance...

dihybrid crosses

Predicting Two-Trait Genetic Crosses

Dihybrid crosses are used to predict how two traits can be passed from parents to offspring. A dihybrid cross tracks two genes at the same time, so it helps students see how different alleles can combine in a genetic pattern. This topic is closely tied to Mendelian genetics and independent assortment. Independent assortment means that allele pairs for different traits can separate into gametes independently of one another. When students work through a dihybrid cross, they can compare the...

trihybrid crosses

Forked Line Method for Trihybrid Crosses

Forked line method for trihybrid crosses helps predict the outcome of three-trait Mendelian crosses. A trihybrid cross studies three pairs of contrasting characteristics. It combines three separate monohybrid crosses. Common examples include plant height, seed shape, and seed color. In a typical trihybrid cross, the F1 plants are heterozygous for all three traits. They can produce eight different gametes. After self-fertilization, these gametes can lead to 64 genotype combinations in the F2...

law of independent assortment

Independent Chromosome Assortment in Meiosis

Independent chromosome assortment in meiosis explains how different gene pairs can be inherited independently. This idea is one of Mendel’s laws of inheritance and is often called the law of independent assortment. The pattern depends on how homologous chromosomes line up during meiosis I. Each chromosome pair orients independently of the others, so the maternal and paternal chromosomes can separate into different gametes in many combinations. This random separation helps create genetic...

chi-square analysis

Chi-Square Test in Genetics

The chi-square test in genetics helps compare expected and observed results. It is a statistical hypothesis test used to see whether a difference between an expected value and an observed value is significant. In genetics, it helps decide whether to accept or reject a hypothesis based on how far the observed data moves from the expected data. The test was developed by Pearson in 1990. The first step is to set up a null hypothesis. This hypothesis says there is no real difference between the...

pedigree analysis

Tracing Traits with Pedigree Charts

Pedigree analysis uses family trees, called pedigrees, to trace how traits and diseases pass from one generation to the next. A pedigree chart helps scientists and students see inheritance patterns clearly across relatives. The chart uses standard symbols to show family members and their relationships. It can reveal whether a trait is likely passed through dominant or recessive inheritance, and it can also help identify patterns linked to sex chromosomes. By studying a pedigree, it is...

multiple allele traits

Multiple Alleles in Trait Inheritance

Multiple alleles can shape how a trait is inherited in a population. A gene may have more than two allele forms, even though each person still carries only two alleles for that gene. These allele combinations can produce traits with more than two possible outcomes. The ABO blood group system is a common example of a multiple allele trait. It shows how different alleles can interact to determine an organism’s phenotype, or observable trait. Multiple allele traits help explain why inheritance...

incomplete dominance

Incomplete Dominance in Traits and Disease

Incomplete dominance is a pattern of inheritance where two alleles both affect a trait in a heterozygous organism. In this case, one allele is not fully dominant over the other. The result is a phenotype that looks like a blend or intermediate form. Gregor Mendel’s pea plant experiments helped explain the usual dominant and recessive pattern. He showed that each gene in a diploid cell has two alleles, one inherited from each parent. In his model, a dominant allele shows its effect with one or...

lethal alleles

When Genes Cause Embryonic Death

Lethal alleles can change inheritance patterns by causing death before birth. In mice, Lucien Cuénot studied the agouti gene, which helps control coat color through an agouti-signaling protein that affects melanin distribution in mammals. The wild-type allele produces a gray-brown coat, while the mutant allele produces a yellow coat. Cuénot also found that the yellow allele was linked to yellow mouse obesity syndrome. This syndrome is associated with early-onset obesity and tumors. When he...

polygenic traits

Traits Shaped by Many Genes

Polygenic traits are characteristics shaped by many genes acting together. This pattern is different from a single-gene trait, where one gene has a larger effect on the outcome. In polygenic inheritance, each gene adds a small contribution to the final trait. Height is a common example of a polygenic trait. Many genes influence human height, so the result can vary across a wide range. These small genetic effects combine to produce differences that are easy to see in a population. Polygenic...

background and environment affect phenotype

background-and-environment-affect-phenotype

How Genes and Environment Shape Traits

Genes and the environment work together to shape phenotype, or the visible traits of an organism. A phenotype can change because of genetic background, environmental conditions, or both. Factors such as temperature, oxygen availability, and mutagens can all influence how a trait appears. Horses show how one gene can affect coat color and how a modifier gene can change that result. The Extension gene controls pigment production in the coat. The wild-type genotype EE produces black pigment,...

x and y chromosomes

Sex Chromosomes in Human Inheritance

Sex chromosomes help determine biological sex in mammals, including humans. Humans have two sex chromosomes, X and Y. Each diploid cell has 22 pairs of autosomes and one pair of sex chromosomes. A female usually has two X chromosomes, while a male usually has one X chromosome and one Y chromosome. Egg and sperm cells carry only half the usual number of chromosomes. They contain 22 autosomes and one sex chromosome. Every egg has an X chromosome. Sperm cells can carry either an X or a Y...

the y chromosome determines maleness

Y Chromosome Structure and Male Traits

The Y chromosome is a sex chromosome that helps guide male development in humans and other vertebrates and mammals. Human males usually have one X chromosome and one Y chromosome, along with 22 pairs of autosomes. In these organisms, the presence or absence of the Y chromosome influences whether male traits develop. The Y chromosome evolved from an autosome about 300 million years ago, when two sex chromosomes began to diverge. Since then, it has lost most of its genes and become much smaller.

the ratio of x chromosome to autosomes

Drosophila Sex Determination by X:A Balance

In Drosophila, sex is determined by the balance between X chromosomes and autosomes, not by the X and Y chromosomes alone. The Y chromosome is active in these flies, but it does not set sex. Instead, it carries genes needed for sperm production in adult males. A normal male Drosophila has one X chromosome and two sets of autosomes. A normal female has two X chromosomes and two sets of autosomes. When this X:A ratio changes, flies can develop different sexual phenotypes, including metamales,...

x-linked traits

X-Linked Inheritance in Families

X-linked inheritance in families explains how traits linked to the X chromosome pass from parents to children. These traits are often tracked through family trees because the pattern can differ between males and females. A male has one X chromosome and one Y chromosome. A female has two X chromosomes. Because of this difference, a trait on the X chromosome can show up in a different way depending on the sex of the child. Family examples often include traits such as color blindness. Studying...

sex linked disorders

Sex-Linked Disorders and Inheritance Patterns

Sex-linked disorders are genetic conditions that follow inheritance patterns tied to the sex chromosomes. These disorders help explain how certain traits can appear more often in one sex than the other. The transcript focuses on examples of sex-linked disorders, including Y-linked infertility, Fragile X syndrome, and Duchenne muscular dystrophy. Y-linked infertility is passed through the Y chromosome, while Fragile X syndrome and Duchenne muscular dystrophy are associated with sex-linked...

dosage compensation

X-Chromosome Balance in Animals

X-chromosome balance in animals helps equalize gene expression between males and females. Sex can be determined by the number and type of sex chromosomes. In humans, females have two X chromosomes and males have one X and one Y chromosome. In C. elegans, one X chromosome is male, while two X chromosomes make a hermaphrodite. The X chromosome carries more than sex-related genes. It also includes genes involved in body functions such as brain development and the immune system. Because males and...

x-inactivation

X-Inactivation and Barr Bodies

X-inactivation is a process that reduces gene activity on one X chromosome. It helps balance gene expression in cells that have more than one X chromosome. A key result of this process is the formation of a Barr body, which is the inactive X chromosome seen in the nucleus. This topic also includes Xist, a gene linked to X-inactivation. Xist produces RNA that coats the X chromosome and helps turn it off. Together, Xist and the Barr body show how cells control X-linked genes during development...

blood types

Blood Types and Transfusion Matching

Human blood types help determine safe blood transfusion matching. Blood is classified by antigens on the surface of red blood cells and antibodies in the plasma. Correct blood typing matters because an unsafe match can affect transfusion success. The International Society of Blood Transfusion has identified 38 human blood types, and ABO, Rh, and MNS are among the most common. The ABO blood group depends on antigens made by genes on chromosome 9. Red blood cells carry a base glycoprotein called...

blood transfusion and agglutination

Matching Blood Types for Safe Transfusion

Blood transfusion is a medical treatment used to restore blood volume after major blood loss from an accident or a medical procedure. It works by taking blood from a suitable donor and giving it to a recipient. Safe transfusion depends on matching blood types and checking for immune compatibility. The history of blood transfusion began in the 17th century, when early experiments were done in animals. In 1818, James Blundell, a British doctor, performed the first successful human blood...

key terms and concepts

Learn how monohybrid crosses track one inherited trait at a time and help explain monogenic traits and Mendelian patterns of inheritance in genetics.

Tracking One Trait in Monohybrid Crosses | JoVE K12

molecular biology

JoVE Core Molecular Biology showcases the molecular processes of the cell through clear and concise animated video lessons. Additionally, in scientist-in-action videos, these concepts' application is demonstrated through real experiments in modern laboratories.

Louisiana Student Standards for Science

High School

Life Sciences

Heredity: Inheritance And Variation Of Traits

HS-LS3-1

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Heredity

Structure and function of DNA in cells

Genetic mechanisms and inheritance

Alabama Course of Study Science

Heredity: Inheritance and Variation of Traits

9-12.B.3.11.a

Florida Department of Education

Life Science

SC.912.L.16

SC.912.L.16.2

Texas Essential Knowledge and Skills

BIO.8

BIO.8.B

myJoVE Corporation

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Use mathematics and computational thinking to predict the variation and distribution of expressed traits based on: Mendelian inheritance, co-dominance, incomplete dominance, multiple alleles, and sex-linked inheritance.

Overview

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Understand genetic mechanisms for variation.

Tracking One Trait in Monohybrid Crosses

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