Name: punnett squares for predicting traits
Uploaded: 2019-03-11T09:21:16.000Z
Duration: 1 min
Channel: JoVE

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Punnett Squares

כיכר פאנט, דיאגרמה פשוטה על שמו של הממציא שלו הוא דרך גרפית כדי לחזות את הסבירות כי צאצאים עשויים לרשת את הגן תכונה, כמו אי סבילות ללקטוז בהתחשב בגנוטיפים ההורים של הפנוטיפ. באמצעות רשת זו התרומות הגנטיות של הורה אחד, אשר במקרה זה הוא הומוזיגסי רצסיבי, עם אללים מסומן כמו שתי אותיות קטנות Ls ממוקמים בחלק העליון. אלה של השני, הטרוזיגי עם אללים מעורבים המיוצגת על ידי האות L יחד עם האות הקטנה L נכתבות בצד שמאל.שילוב של שורות ועמודות אלה בתיבות גורמת לשני גנוטיפים אפשריים בשני פנוטיפים לילד. סיכוי של 50%להיות הטרוזיגיים עם יכולת לעכל לקטוז ו 50%סיכוי להיות הומוזיגסי רצסיבי עם סובלנות ללקטוז.

אדוארדס, א. ו. פ. "רג'ינלד קרונדל פונט: פרופסור ארתור בלפור הראשון לגנטיקה, קיימברידג ', 1912." גנטיקה 192, מס '1 (1 בספטמבר 2012): 3. [<a href="https://doi.org/10.1534/genetics.112.143552" target="__blank">מקור</a>]

ריד, ג'יימס בי וג'ון ג'יי רוס. "הגנים של מנדל: לקראת אפיון מולקולרי מלא". גנטיקה 189, מס' 1 (1 בספטמבר 2011): 3. [<a href="https://doi.org/10.1534/genetics.111.132118" target="__blank">מקור</a>]

ריבוע פַּ֫נֶט

<div style="direction:rtl"><h4>סקירה כללית</h4> ריבוע פנט מציג את הגנוטיפים האפשריים שצאצאים יכולים לרשת משני גנוטיפים הוריים. אם ידוע דפוס הירושה של תכונה (למשל דומיננטית או רצסיבית), ניתן להשתמש בריבועי פנט גם כדי לקבוע את ההסתברות לרשת פנוטיפ. ריבועי פנט ישימים במצבים שבהם תורשת תכונה נקבעת על ידי מיקום גן יחיד ותכונות עוברות בירושה באופן עצמאי. עם זאת, הם אינם יכולים לחזות הסתברויות תכונה עבור תרחישי תורשה גנטית מורכבים יותר. <h4>ריבועי פנט מציגים את הסבירות לירושת תכונה אחת או יותר</h4> ריבועי פנט הם ייצוגים חזותיים המציגים גנוטיפים אפשריים של צאצאים הנובעים מהכלאה בין שני גנוטיפים הוריים. הם יכולים לתאר תורשה של פנוטיפ אחד או תכונות מרובות, אם כי כלים אחרים מתאימים יותר לחקירת תורשה של יותר משתי תכונות. ניתן להשתמש בריבועי פנט כדי לקבוע את הסבירות שצאצאים יורשו גנוטיפ ספציפי, או זוג אללים שיגרום למאפיין מסוים (כלומר, פנוטיפ או תכונה), בתנאי שהפנוטיפ נגרם על ידי לוקוס גן יחיד ומגוונת באופן עצמאי במהלך המיוזה. במילים אחרות, ריבועי פנט שימושיים לקביעת הסתברויות ירושה בתרחישים שבהם הסבירות לרשת תכונה אחת אינה משפיעה על ההסתברות לרשת אחרת. למרות שיש חריגים רבים להנחות אלו (למשל, תכונות המקודדות על ידי גנים סמוכים באותו כרומוזום), מאפיינים אלה מתקיימים לגבי תכונות צמחים ובעלי חיים רבים. <h4>הניסויים של מנדל היוו השראה ליצירת ריבועי פנט</h4> ריבועי פנט נוצרו בתחילת שנות ה-1900 על ידי רג'ינלד פנט, כמה עשורים לאחר שניסויי האפונה פורצי הדרך של גרגור מנדל חשפו את חוקי הירושה הבסיסיים. כיום, ריבועי פנט משמשים לעתים קרובות כדי להמחיש את העקרונות שבבסיס הניסויים של מנדל. מנדל חקר את ההורשה של כמה מאפיינים של צמחי אפונה, כולל צורת וצבע של אפונה ותרמיל, צבע ומיקום הפרחים וגודל הצמח. מנדל בדק גם תכונות תורשתיות לכל מאפיין. לדוגמה, סגול ולבן הם תכונות אפשריות למאפיין צבע הפרח. בצמחי אפונה, פרחים סגולים ולבנים נקבעים על ידי וריאנטים גנים שונים, או אללים, במיקום הגן של צבע הפרח. <h4>ריבועי פנט הם רשתות שמארגנות מידע גנטי</h4> כל תיבה בריבוע של פנט מייצגת אירוע הפריה אפשרי, או גנוטיפ צאצאים, הנובע משתי גמטות הוריות. ריבועי פנט מסודרים בדרך כלל בתצורות של 2x2 או 4x4 כדי לדמיין תורשה של תכונה אחת או שתיים, בהתאמה. לגבי המינוח, אללים מסומנים על ידי האות הראשונה של התכונה הנגרמת על ידי האלל הדומיננטי. לדוגמה, מכיוון שצהוב הוא תכונת צבע האפונה הדומיננטית, אללים המקודדים לצבע האפונה מסומנים באות הנטוי 'y'. אותיות גדולות וקטנות מייצגות אללים דומיננטיים ורצסיביים, בהתאמה. לפיכך, Y מייצג את האלל הצהוב הדומיננטי ו-y מציין את האלל הירוק הרצסיבי. כדי ליצור ריבוע פנט בגודל 2x2 הבוחן תכונה אחת, גנוטיפ הורי אחד רשום מעל התרשים, עם אלל אחד מעל כל עמודה. הגנוטיפ ההורי השני מוצג אנכית משמאל לתרשים, עם אלל אחד ליד כל שורה. כל קופסה מרובעת של פנט מכילה את שני האללים ההוריים (אחד מכל הורה) התואמים לשורה ולעמודה של התיבה, המייצגים תוצאת הפריה אפשרית אחת. ניתן להשתמש בתוכן הריבוע המלא של פנט כדי לקבוע את הסבירות שצאצאים ירשו תכונה מסוימת. <h4>ריבועי פנט הם כלים אינפורמטיביים עבור יועצים ומגדלים גנטיים</h4> למרות שנוצרו לפני יותר מ-100 שנה, לריבועי פנט עדיין יש מספר יישומים רלוונטיים. עבור זוג המקבל ייעוץ גנטי, ריבועי פנט יכולים לעזור לקבוע את הסיכון של ילדם למחלה תורשתית. לדוגמה, אם לאחד ההורים יש סיסטיק פיברוזיס (שני אללים רצסיביים, סיבתיים) ולשני אין או נושא אותה, ילדו יהיה נשא (כלומר, יש לו אלל סיבתי אחד) אך אין לו סיכון לסיסטיק פיברוזיס. ריבועי פנט יכולים גם לעזור למגדלי בעלי חיים וצמחים לבחור אורגניזמים בעלי תכונות ספציפיות להמשך הרבייה. למרות שריבועי פנט שימושיים בהקשרים רבים, הם אינם יכולים לתאר במדויק תורשה גנטית מורכבת. לדוגמה, תכונות המקודדות על ידי גנים שכנים באותו כרומוזום עוברות לרוב יחד מהורה אחד, תופעה הנקראת קישור. תכונות אלו אינן מגוונות באופן עצמאי, ולכן ריבוע פנט אינו יכול לחזות במדויק את דפוסי הירושה שלהם. תכונות מסוימות, כמו גובה, אינן מתאימות לריבועי פנט מכיוון שהן נקבעות על ידי מספר גנים ומושפעות מתנאי הסביבה (למשל, תזונה). ריבועי פנט אינם יעילים גם בניבוי תורשה של תכונות שנרכשו מהורה אחד בלבד.</div>

סקירה

ריבוע פונט מציג את הגנוטיפים האפשריים שצאצאים יכולים לרשת משני גנוטיפים הוריים. אם דפוס ירושה של תכונה...

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KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

punnett squares for predicting traits

Punnett squares help predict which traits offspring may inherit from two parents. They show possible genotypes, which are pairs of alleles, and can also show the chance of a phenotype, or visible trait, when the inheritance pattern is known. These grids work best for traits controlled by a single gene locus and passed on independently during meiosis.

Punnett squares were developed in the early 1900s by Reginald Punnett. His work came after Gregor Mendel’s pea plant experiments revealed the basic laws of inheritance. Mendel studied traits such as pea and pod shape and color, flower color and position, and plant size. For flower color, purple and white are different traits controlled by different alleles at the same gene locus.

A Punnett square organizes genetic information in a grid. Each box represents one possible fertilization event, or one possible offspring genotype, from two parental gametes. These diagrams are often shown as 2x2 squares for one trait or 4x4 squares for two traits. Alleles are usually written with the first letter of the dominant trait. For pea color, Y stands for the dominant yellow allele, and y stands for the recessive green allele.

To build a 2x2 Punnett square, one parent’s genotype is placed across the top and the other parent’s genotype is placed down the side. One allele goes above each column, and one allele goes next to each row. The boxes then combine one allele from each parent. The full square shows the chances of each genotype and helps predict the trait an offspring may show.

Punnett squares still matter in genetics, counseling, and breeding. Genetic counselors can use them to estimate a child’s risk for inherited disease. For example, if one parent has cystic fibrosis and the other neither has nor carries it, the child will be a carrier but will not be at risk for cystic fibrosis. Breeders also use Punnett squares to choose organisms with useful traits for future breeding.

These grids do have limits. They do not work well for complex inheritance patterns, such as linked genes on the same chromosome, because those genes are not independently assorted. They are also not a good fit for traits like height, which can depend on several genes and environmental factors such as diet. Punnett squares are also not useful for traits acquired from only one parent.

Punnett Squares for Predicting Traits

genetic lingo

Genotype, Phenotype, and Inheritance

Genotype, phenotype, and inheritance help explain how traits and disease risk are passed from parents to offspring. In diploid organisms, including humans, most other animals, and many plants, somatic cells carry a duplicate set of chromosomes. These chromosome pairs are homologous, with similar length, centromere position, and gene locations. Diploid organisms inherit two versions of each gene, one from each parent. These versions are called alleles, and they sit at the same relative locus,...

punnett squares

Punnett squares help predict which traits offspring may inherit from two parents. They show possible genotypes, which are pairs of alleles, and can also show the chance of a phenotype, or visible trait, when the inheritance pattern is known. These grids work best for traits controlled by a single gene locus and passed on independently during meiosis. Punnett squares were developed in the early 1900s by Reginald Punnett. His work came after Gregor Mendel’s pea plant experiments revealed the...

monohybrid crosses

Mendel’s Pea Plant Inheritance Ratios

Gregor Mendel used pea plants to study how traits are passed from parents to offspring. His breeding experiments in the 1850s and 1860s showed that inheritance follows clear patterns. He crossed true-breeding plants that differed in one trait and found that dominant traits can hide recessive traits. Mendel focused on seven pea plant traits, and each trait had two forms controlled by a single gene locus. He noticed that true-breeding plants always produced offspring with the same phenotype, or...

dihybrid crosses

Mendel's Law of Independent Assortment

Mendel’s law of independent assortment explains how two traits can be inherited separately. Gregor Mendel tested this idea with pea plants that differed in two characteristics, such as pea color and pea shape. He used true-breeding parents that were homozygous for both traits but showed different phenotypes. In one example, Mendel crossed round, yellow peas with wrinkled, green peas. The parental generation had RRYY and rryy genotypes. Their first-generation offspring were all dihybrids,...

law of segregation

Mendel’s Pea Cross Ratios

Mendel’s pea plant crosses show how traits can disappear in one generation and return in the next. When he crossed plants, one parental trait sometimes seemed to vanish in the F1 generation and reappear in the F2 generation. Mendel used this pattern to explain why some traits are dominant and others are recessive. He proposed that traits are controlled by alleles, which are different versions of a gene. An organism inherits two copies of each gene, one from each parent. In his model, a...

law of independent assortment

Mendel’s Dihybrid Cross and Trait Ratios

Mendel’s dihybrid cross shows how two traits are inherited at the same time. A dihybrid cross is a cross in which both parents are homozygous for two distinct traits, and the F1 generation is heterozygous for both traits. Mendel used pea plants with round yellow peas and wrinkled green peas as an example. One parent had genotype YYRR, and the other had genotype yyrr. In the F1 generation, every plant showed the dominant traits, so the plants were YyRr and had yellow, round peas. The F2...

probability laws

Inheritance Risk with Sum and Product Rules

Inheritance risk can be calculated with the sum rule and the product rule. The sum rule applies to mutually exclusive events, or events that cannot happen at the same time. The product rule applies to independent events, or events that do not affect one another. These rules describe theoretical probability, which is the chance of an event before it happens. Empirical probability is different because it is based on events that have already occurred. These probability rules are useful in...

test cross

Using Test Crosses to Identify Genotypes

Test crosses are used to identify the genotype of an organism with a dominant trait. A genotype is the pair of alleles inherited for a gene, and alleles are different forms of the same gene. In diploid organisms, including humans, each gene usually has two alleles, one from each parent. An allele is recessive when its effect is hidden by another allele at the same gene location. Pea plants provide a clear example with flower color. White flowers are recessive, because one copy of the purple...

polygenic traits

Polygenic Traits in Human Height

Polygenic traits are traits controlled by more than one gene. Human height is a clear example of this kind of inheritance. Because many genes work together, the final trait can vary a lot from person to person. Researchers have found hundreds of loci, or gene locations, that influence height. There are likely many more that have not yet been identified. Many of these genes affect cartilage in the growth plates of the long bones in the arms and legs, either directly or indirectly. Height is...

pedigree analysis

Reading Family Traits in Pedigrees

Pedigrees are family trees used to track how a trait passes through generations. They help scientists and students see whether a trait is dominant or recessive, whether it is autosomal or sex-linked, what genotypes family members may have, and what phenotypes may appear in future generations. For families with a history of inherited disease, this information can be important for family planning. In plants and animals, inheritance is often studied with crosses. Monohybrid crosses can show...

multiple allele traits

Blood Type and Allele Interactions

Multiple alleles can shape traits through blood type, sickle cell anemia, incomplete dominance, and codominance. Multiple allelism means a gene has three or more allelic forms. Diploid organisms, including humans, usually carry only two alleles for each gene, but many human genes exist in multiple forms in the population. Human blood type is a clear example of multiple allelism. The blood type gene has three alleles: I A , I B , and i. These alleles help determine which blood type a person has...

epistasis

Gene Masking in Rabbit Fur Color

Epistasis describes how one gene can mask or change the effect of another gene. In high school genetics, this helps explain why many traits do not follow a simple single-gene pattern. Instead, alleles at different locations can work together to shape the final phenotype. Mendel studied seven unrelated pea traits, but most traits involve multiple gene interactions. Epistasis often happens when one gene interferes with the expression of another gene. It can also occur when genes are part of the...

nature and nurture

Genes and Environment Shape Height

Genes and environment both shape human height and other traits. Genes are the inherited instructions we get from our parents. Environment includes factors such as diet, stress, and social conditions. Many phenotypes, or observable traits, reflect both influences. Some also show up later in life, including cancer and other diseases. Height is a clear example of this interaction. Scientists estimate that 70-90% of height variation comes from genetic differences among people. The remaining 10-30%...

pleiotropy

SOX10 and Multiple Traits in Pleiotropy

Pleiotropy is when one gene affects more than one trait. The SOX10 gene is a clear example because it can influence pigmentation, hearing, and intestinal movement. These traits may seem unrelated, but they can all be linked to the same gene change. In humans, a deleted region in SOX10 can cause Waardenburg Syndrome Type 4, or WS4. WS4 is an autosomal recessive disorder, which means a person usually inherits two altered copies of the gene. Common signs include a white forelock,...

sex-linked disorders

X- and Y-Linked Disorder Patterns

X- and Y-linked disorders come from mutations in genes on the sex chromosomes. These genes, like those on autosomes, are needed for normal body function. When a mutation causes a biological problem, the condition is called sex-linked. Y-linked disorders come from changes in the Y chromosome. They affect only males, because only males carry a Y chromosome. Mutations in this small chromosome can affect male sexual function and secondary sex characteristics. One example is Y-chromosome...

x-linked traits

X-Linked Inheritance in Families

X-linked inheritance explains how traits on the X chromosome are passed through families. In most mammalian species, females have two X sex chromosomes, while males have one X and one Y. A mutation on one X chromosome may be masked in females by a normal allele on the other X. In males, that same mutation is more likely to show because there is no second normal X to balance it. Traits caused by changes on the X chromosome are called X-linked traits. Color blindness is a well-studied example.

x-inactivation

Barr Bodies and X-Chromosome Balance

Barr bodies and X-chromosome balance help explain how female mammalian cells control gene activity from the X chromosome. The human X chromosome carries far more genes than the Y chromosome. Because males usually have one X chromosome and females have two, females would make twice as many of some proteins without a control system. To prevent that imbalance, female mammalian cells inactivate nearly all the genes on one X chromosome during early embryonic development. The inactive X condenses...

non-nuclear inheritance

Maternal DNA in Mitochondria and Chloroplasts

Maternal DNA in mitochondria and chloroplasts explains how some genes are inherited outside the nucleus. Most DNA is in the nucleus, but mitochondria and chloroplasts in the cell cytoplasm also carry their own DNA and can copy it independently of nuclear DNA. Mitochondria are found in both plant and animal cells. They are called the powerhouses of eukaryotic cells because they break down glucose to make energy for cellular activity. Mitochondrial DNA has about 37 genes, and many help with...

chromosomal theory of inheritance

How Genes Map to Chromosomes

Genes map to chromosomes, and this idea explains how Mendel’s inheritance patterns work. Gregor Mendel published his pea plant breeding results in 1866. He showed that physical traits follow predictable patterns. At the time, scientists did not yet know that genes existed. Mendel used the word "factors" for the hereditary units he studied. The details behind Mendel’s laws of segregation and independent assortment were still unknown for many years. In the late 1800s, better microscopes and...

key terms and concepts

Learn how Punnett squares predict offspring genotypes and traits, from Mendel’s pea plants to genetic counseling, breeding, and simple inheritance patterns.

Punnett Squares for Predicting Traits | JoVE K12

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Next Generation Science Standards

High School

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

HS-LS3-1

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New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS3-1.

Georgia Standards of Excellence

9-12

SB3.b

Florida Department of Education

SC.912.L.16

SC.912.L.16.1

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The DNA Helix

Overview

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most ...

DNA Packaging

Overview

Eukaryotes have large genomes compared to prokaryotes. In order to fit their genomes into a cell, eukaryotes must pack their DNA tightly inside ...

Organization of Genes

Overview

The genomes of eukaryotes can be structured in several functional categories. A strand of DNA is comprised of genes and intergenic regions. ...

Replication in Prokaryotes

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DNA replication has three main steps: initiation, elongation, and termination. Replication in prokaryotes begins when initiator proteins bind to ...

Replication in Eukaryotes

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In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high ...

Proofreading

Synthesis of new DNA molecules starts when DNA polymerase links nucleotides together in a sequence that is complementary to the template DNA strand. DNA ...

Mutations

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Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. ...

Transcription

Overview
Transcription is the process of synthesizing RNA from a DNA sequence by RNA polymerase. It is the first step in producing a protein from a gene ...

Translation

Lesson: Translation
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Bacterial Transformation

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What is Gene Expression?

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Gene expression is the process in which DNA&nbsp;directs the synthesis of functional products, that is, proteins. Cells can regulate gene ...

The Central Dogma

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The central dogma of biology states that information encoded in the DNA is transferred to messenger RNA (mRNA), which then directs the synthesis ...

Transcription Factors

Tissue-specific transcription factors contribute to diverse cellular functions in mammals. For example, the gene for beta globin, a major component of ...

RNA Structure

Overview
The basic structure of RNA consists of a five-carbon sugar and one of four nitrogenous bases. Although most RNA is single-stranded, it can form ...

RNA Stability

Intact DNA strands can be found in fossils, while scientists sometimes struggle to keep RNA intact under laboratory conditions. The structural variations ...

Types of RNA

Overview
Three main types of RNA are involved in protein synthesis: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). These RNAs ...

MicroRNAs

MicroRNA (miRNA) are short, regulatory RNA transcribed from introns&mdash;non-coding regions of a gene&mdash;or intergenic regions&mdash;stretches of DNA ...

RNA Splicing

Splicing is the process by which eukaryotic RNA is edited before its translation into protein. The RNA strand transcribed from eukaryotic DNA is called ...

Epigenetic Regulation

Epigenetic mechanisms play an essential role in healthy development. Conversely, precisely regulated epigenetic mechanisms are disrupted in diseases like ...

RNA Interference

RNA interference (RNAi) is a process in which a small non-coding RNA molecule blocks the post-transcriptional expression of a gene by binding to its ...

Operons

Prokaryotes can control gene expression through operons&mdash;DNA sequences consisting of regulatory elements and clustered, functionally related ...

Proteins: From Genes to Degradation

The student will investigate and understand that organisms reproduce and transmit genetic information to new generations. Key ideas include DNA has a role in making proteins that determine organism traits;

LS.10.a

What is Meiosis?

Meiosis is the process by which diploid cells divide to produce haploid daughter cells. In humans, each diploid cell contains 46 chromosomes, half from ...

Meiosis I

Meiosis is a carefully orchestrated set of cell divisions, the goal of which&#x2014;in humans&#x2014;is to produce haploid sperm or eggs, each containing ...

Meiosis II

Meiosis II is the second and final stage of meiosis. It relies on the haploid cells produced during meiosis I, each of which contain only 23 ...

Crossing Over

Unlike mitosis, meiosis aims for genetic diversity in its creation of haploid gametes. Dividing germ cells first begin this process in prophase I, where ...

Nondisjunction

During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed ...

The student will investigate and understand that organisms reproduce and transmit genetic information to new generations. Key ideas include the role of meiosis is to transfer traits to the next generation; and

LS.10.b

Genetic Lingo

Overview

An organism is diploid if it inherits two variants, or alleles, of each gene, one from each parent. These two alleles constitute the genotype ...

Overview

A Punnett square displays the possible genotypes offspring can inherit from two parental genotypes. If a trait&#x2019;s inheritance pattern ...

Monohybrid Crosses

Overview

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

Dihybrid Crosses

Overview

To determine whether traits are inherited together or separately, Gregor Mendel crossed pea plants that differed in two traits. These parental ...

Law of Segregation

When crossing pea plants, Mendel noticed that one of the parental traits would sometimes disappear in the first generation of offspring, called the F1 ...

Law of Independent Assortment

While Mendel&#x2019;s Law of Segregation states that the two alleles for one gene are separated into different gametes, a different question of how ...

Test Cross

Alleles are different forms of the same gene. Humans and other diploid organisms inherit two alleles of every gene, one from each parent.

An allele is ...

Pedigree Analysis

Overview

A pedigree is a diagram displaying a family&#x2019;s history of a trait. Analyzing pedigrees can reveal (1) whether a trait is dominant or ...

X-linked Traits

In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be ...

Sex-linked Disorders

Like autosomes, sex chromosomes contain a variety of genes necessary for normal body function. When a mutation in one of these genes results in biological ...

Nature and Nurture

Many human characteristics, like height, are shaped by both nature&mdash;in other words, by our genes&mdash;and by nurture, or our environment. For ...

The student will investigate and understand that organisms reproduce and transmit genetic information to new generations. Key ideas include Punnett squares are mathematical models used to predict the probability of traits in offspring.

Punnett Squares for Predicting Traits

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