Can you determine the genotype of son 3

Figure 8. To prepare a Punnett square, all possible combinations of the parental alleles the genotypes of the gametes are listed along the top for one parent and side for the other parent of a grid. The combinations of egg and sperm gametes are then made in the boxes in the table on the basis of which alleles are combining. Each box then represents the diploid genotype of a zygote, or fertilized egg.

Because each possibility is equally likely, genotypic ratios can be determined from a Punnett square. If the pattern of inheritance dominant and recessive is known, the phenotypic ratios can be inferred as well. For a monohybrid cross of two true-breeding parents, each parent contributes one type of allele. In this case, only one genotype is possible in the F 1 offspring.

All offspring are Yy and have yellow seeds. When the F 1 offspring are crossed with each other, each has an equal probability of contributing either a Y or a y to the F 2 offspring. The result is a 1 in 4 25 percent probability of both parents contributing a Y , resulting in an offspring with a yellow phenotype; a 25 percent probability of parent A contributing a Y and parent B a y , resulting in offspring with a yellow phenotype; a 25 percent probability of parent A contributing a y and parent B a Y , also resulting in a yellow phenotype; and a 25 percent probability of both parents contributing a y , resulting in a green phenotype.

When counting all four possible outcomes, there is a 3 in 4 probability of offspring having the yellow phenotype and a 1 in 4 probability of offspring having the green phenotype. Using large numbers of crosses, Mendel was able to calculate probabilities, found that they fit the model of inheritance, and use these to predict the outcomes of other crosses.

Observing that true-breeding pea plants with contrasting traits gave rise to F 1 generations that all expressed the dominant trait and F 2 generations that expressed the dominant and recessive traits in a ratio, Mendel proposed the law of segregation. This law states that paired unit factors genes must segregate equally into gametes such that offspring have an equal likelihood of inheriting either factor. For the F 2 generation of a monohybrid cross, the following three possible combinations of genotypes result: homozygous dominant, heterozygous, or homozygous recessive.

The equal segregation of alleles is the reason we can apply the Punnett square to accurately predict the offspring of parents with known genotypes. Beyond predicting the offspring of a cross between known homozygous or heterozygous parents, Mendel also developed a way to determine whether an organism that expressed a dominant trait was a heterozygote or a homozygote. Called the test cross, this technique is still used by plant and animal breeders. In a test cross, the dominant-expressing organism is crossed with an organism that is homozygous recessive for the same characteristic.

If the dominant-expressing organism is a homozygote, then all F 1 offspring will be heterozygotes expressing the dominant trait Figure 8. Alternatively, if the dominant-expressing organism is a heterozygote, the F 1 offspring will exhibit a ratio of heterozygotes and recessive homozygotes Figure 8. The cross between the true-breeding P plants produces F1 heterozygotes that can be self-fertilized.

The self-cross of the F1 generation can be analyzed with a Punnett square to predict the genotypes of the F2 generation. Given an inheritance pattern of dominant—recessive, the genotypic and phenotypic ratios can then be determined. In pea plants, round peas R are dominant to wrinkled peas r.

You do a test cross between a pea plant with wrinkled peas genotype rr and a plant of unknown genotype that has round peas. You end up with three plants, all which have round peas.

From this data, can you tell if the parent plant is homozygous dominant or heterozygous? You cannot be sure if the plant is homozygous or heterozygous as the data set is too small: by random chance, all three plants might have acquired only the dominant gene even if the recessive one is present.

Independent assortment of genes can be illustrated by the dihybrid cross, a cross between two true-breeding parents that express different traits for two characteristics. Consider the characteristics of seed color and seed texture for two pea plants, one that has wrinkled, green seeds rryy and another that has round, yellow seeds RRYY. Because each parent is homozygous, the law of segregation indicates that the gametes for the wrinkled—green plant all are ry , and the gametes for the round—yellow plant are all RY.

Therefore, the F 1 generation of offspring all are RrYy Figure 8. In pea plants, purple flowers P are dominant to white p , and yellow peas Y are dominant to green y. What are the possible genotypes and phenotypes for a cross between PpYY and ppYy pea plants? Computer Programming. Computer Science. Graphic Design. Information Security. Information Technology.

Management Information Systems. Culinary Arts. Art History. Other Fine Arts. Cultural Literacy. Knowledge Rehab. National Capitals. People You Should Know. Sports Trivia. Loading flashcards Rr round c. F 1 generation i. Rr round d. F 2 generation k. What will the phenotypic and genotypic ratio of offspring be a. What is the phenotype of the F 1 generation? What is the genotype of the F 1 generation?

What four types of gametes are formed by F 1 plants? List the phenotypes and ratios found in the F 2 generation. What is the ratio of tall to dwarf plants? Of purple- to white-flowered plants? Note that the alleles for each individual character segregate as in a monohybrid cross.

TtPp c. TP, Tp, tP, tp d , see picture e. What is the probability of offspring that show only one dominant trait? List the possible genotypes for the following blood groups. How many phenotypic classes will there be in the F 2? Is this trait caused by a dominant or recessive allele? How can you tell? Can you determine the genotype of son 3 in the second generation? Why or why not? After obtaining two heads from two tosses of a coin, the probability of tossing the coin and obtaining a head is a.

The probability of tossing three coins simultaneously and obtaining three heads is a. The probability of tossing three coins simultaneoulsy and obtaining two heads and one tail is a. The F 2 generation a. According to Mendel's law of segregation, a. A phenotypic ratio in a testcross indicates that a. Carriers of a genetic disorder a. If both parents are carriers of a lethal recessive gene, the probability that their child will inherit and express the disorder is a.

Which phase of meiosis is most directly related to the law of independent assortment? Which of the following human diseases is inherited as a simple recessive trait? Tay-Sachs disease b. Alzheimer's disease e. Tay-Sachs disease.

A multifactorial disorder a. Human blood type is determined by co-dominant alleles. An allele is one of several different forms of genetic information that is present in our DNA at a specific location on a specific chromosome. There are three different alleles for human blood type, known as I A , I B , and i. Each of us has two ABO blood type alleles, because we each inherit one blood type allele from our biological mother and one from our biological father.

A description of the pair of alleles in our DNA is called the genotype. Since there are three different alleles, there are a total of six different genotypes at the human ABO genetic locus. It is not possible to determine the exact genotype from a blood test result of either type A or type B.

If someone has blood type A, they must have at least one copy of the A allele, but they could have two copies. Their genotype is either AA or AO. A blood test of either type AB or type O is more informative. In comparison, a fly with the genotype BB will only produce B gametes, and a fly with the genotype bb will only produce b gametes. Figure A monohybrid cross between two parents with the Bb genotype.

Figure Detail The following monohybrid cross shows how this concept works. The principle of segregation explains how individual alleles are separated among chromosomes. But is it possible to consider how two different genes, each with different allelic forms, are inherited at the same time?

For example, can the alleles for the body color gene brown and black be mixed and matched in different combinations with the alleles for the eye color gene red and brown? The simple answer to this question is yes.

When chromosome pairs randomly align along the metaphase plate during meiosis I, each member of the chromosome pair contains one allele for every gene. Each gamete will receive one copy of each chromosome and one allele for every gene.

When the individual chromosomes are distributed into gametes, the alleles of the different genes they carry are mixed and matched with respect to one another. In this example, there are two different alleles for the eye color gene: the E allele for red eye color, and the e allele for brown eye color. The red E phenotype is dominant to the brown e phenotype, so heterozygous flies with the genotype Ee will have red eyes. Figure The four phenotypes that can result from combining alleles B, b, E, and e.

When two flies that are heterozygous for brown body color and red eyes are crossed BbEe X BbEe , their alleles can combine to produce offspring with four different phenotypes Figure Those phenotypes are brown body with red eyes, brown body with brown eyes, black body with red eyes, and black body with brown eyes. Consider a cross between two parents that are heterozygous for both body color and eye color BbEe x BbEe. This type of experiment is known as a dihybrid cross.

All possible genotypes and associated phenotypes in this kind of cross are shown in Figure The four possible phenotypes from this cross occur in the proportions Specifically, this cross yields the following:.

Why does this ratio of phenotypes occur? To answer this question, it is necessary to consider the proportions of the individual alleles involved in the cross. The ratio of brown-bodied flies to black-bodied flies is , and the ratio of red-eyed flies to brown-eyed flies is also This means that the outcomes of body color and eye color traits appear as if they were derived from two parallel monohybrid crosses. In other words, even though alleles of two different genes were involved in this cross, these alleles behaved as if they had segregated independently.

The outcome of a dihybrid cross illustrates the third and final principle of inheritance, the principal of independent assortment , which states that the alleles for one gene segregate into gametes independently of the alleles for other genes. To restate this principle using the example above, all alleles assort in the same manner whether they code for body color alone, eye color alone, or both body color and eye color in the same cross. Mendel's principles can be used to understand how genes and their alleles are passed down from one generation to the next.

When visualized with a Punnett square, these principles can predict the potential combinations of offspring from two parents of known genotype, or infer an unknown parental genotype from tallying the resultant offspring.

An important question still remains: Do all organisms pass on their genes in this way? The answer to this question is no, but many organisms do exhibit simple inheritance patterns similar to those of fruit flies and Mendel's peas.

These principles form a model against which different inheritance patterns can be compared, and this model provide researchers with a way to analyze deviations from Mendelian principles. This page appears in the following eBook. Aa Aa Aa. Genes come in different varieties, called alleles.

Somatic cells contain two alleles for every gene, with one allele provided by each parent of an organism. Often, it is impossible to determine which two alleles of a gene are present within an organism's chromosomes based solely on the outward appearance of that organism. However, an allele that is hidden, or not expressed by an organism, can still be passed on to that organism's offspring and expressed in a later generation.

Tracing a hidden gene through a family tree. Figure 1: In this family pedigree, black squares indicate the presence of a particular trait in a male, and white squares represent males without the trait.