Quiz 4

Wild type

-This is usually the dominant allele -The one most likely to be found in the wild -Will usually have at least one dominant letter for each trait/pair of alleles (ex: NnBb) -The non mutant form of a gene, encoding normal genetic function -Sometimes written with a superscript like A + with the plus sign as the superscript if there are mutant alleles present. If there are no mutant alleles present, do not use the + superscript.

Distinguish between a trait, allele (dominant/recessive), and gene.

-Trait- Your phenotype. Includes things like hair color, eye color, and height. Each trait is controlled by alleles (alternate forms of a gene). Alleles occur on the chromosomes at a particular location, called a locus. -Alleles- Forms of genes. Alleles can be the same form of a gene or a different form of a gene (ex: the gene could code for eye color, and the allele would code for a form of the gene, something specific like brown eyes or blue eyes). --In complete dominance, a dominant allele hides a recessive allele and determines the organism's appearance. --Alleles directly specify what traits you have. --Alleles can sometimes result in different phenotypes (observable traits) with certain alleles being dominant (overriding the traits of other alleles). In other cases, multiple alleles can act in a codominant fashion, like blood type AB where both the alleles A and B are expressed. -Each parent contributes one allele, which is a variant of a gene. Gene- Each gene resides at a specific locus on a chromosome. One copy of the gene is inherited from each parent. The copies aren't necessarily the same. When the copies of a gene differ from each other, they are known as alleles.

Explain the meaning and significance of the Law of Segregation

1) Each individual has two factors for each trait. 2) The factors segregate (separate) during the formation of gametes. 3) Each gamete contains only one factor from each pair of factors. 4) Fertilization gives each new individual two factors for each trait. Random fusion of all possible gametes occurred upon fertilization. Which of the parent's two alleles is given is random. If a parent is heterozygous Aa, it will be equally as likely to give either allele ( A) or (a) to its offspring. 50% chance of giving A. 50% chance of giving a. -We know that the segregation of genes occurs during meiosis in eukaryotes, which is a process that produces reproductive cells called gametes. During gametes formation in meiosis I, the alleles from each gene will segregate from each other and each gamete will only carry one of the alleles. Significance- Helps us understand how traits are passed down from one generation to the next. As chromosomes separate into different gametes during meiosis, the two different alleles for a particular gene also segregate so that each gamete acquires one of the two alleles. -In Mendel's experiments, the segregation and the independent assortment during meiosis in the F1 generation give rise to the F2 genotypic ratios. -Mendel proposed the law of segregation after observing that pea plants with two different traits produced offspring that all expressed the dominant trait, but the following generation expressed the dominant and recessive traits in a 3:1 ratio

Identify the purpose of doing a test cross

A test cross may be used to determine whether an organism with a dominant phenotype is homozygous or heterozygous A test cross is used to determine whether an individual with the dominant trait has two dominant factors for a particular trait. This is not possible to tell by observation because an individual can exhibit the dominant appearance while having only one dominant factor.

Recessive trait

Expressed when an organism has two recessive alleles. Recessive alleles are denoted by a lowercase letter. Only individuals with an aa genotype will express a recessive trait. -Offspring must receive one recessive allele from each parent to exhibit a recessive trait. -Phenotypically expressed only in homozygotes. -In Mendel's experiment, the recessive trait was the yellow colored pod plants.

Distinguish between genotype and phenotype

Genotype- Refers to the genetic characteristics of an organism that contributes to its phenotype. The exact versions of alleles you have. Genotype determines phenotype. For example, let's pretend: Ex: Homozygous dominant : HH genotype (tall stem phenotype) Ex: Heterozygous: Hh genotype (tall stem phenotype) Ex: Homozygous recessive: hh genotype (dwarf stem phenotype) Phenotype- Refers to the physical characteristics of an organism. What is expressed, what you see. Big B stands for the phenotype brown eyes, and small b stands for the phenotype blue eyes. B and b are two different alleles, or versions, of the same gene. Bb, bB, and BB all code for the same phenotype (brown eyes). bb codes for the phenotype blue eyes.

Determine the proportion of offspring exhibiting a particular phenotype/genotype for a single trait given the phenotypes/genotypes of the two parents (Monohybrid cross).

Gg x gg: Step 1: separate the pairs of alleles to make gametes Gametes for Gg: G, g Gametes for gg: g, g Step 2: Write the gametes on the punnett square and cross them Gg x gg = Gg, Gg, gg, gg. Genotype: 1/2 Gg, 1/2 gg. Genotype ratio: 2 Gg : 2 gg --> 1 Gg : 1 gg Phenotype: 1/2 green, 1/2 yellow. 50% green, 50% yellow. Phenotype ratio: 2 green: 2 yellow --> simplifies to 1 green: 1 yellow

Differentiate between homozygous (dominant/recessive) and heterozygous genotypes

Homozygous dominant- PP. An organism can be homozygous dominant if it carries two copies of the same dominant allele. (carrying two of the same alleles) Homozygous recessive- pp. An organism can be homozygous recessive if it carries two copies of the same recessive allele (carrying two of the same alleles). Heterozygous- Pp (one dominant one recessive). The presence of two different alleles at a particular gene locus. (carrying two different alleles for that gene).

Determine the proportion of offspring exhibiting a particular phenotype/genotype for two traits given the phenotypes/genotypes of the two parents (Dihybrid cross)

Let's say we are crossing PpRr x pprr STEP 1: First, find the gametes by FOIL: Gametes for PpRr = PR Pr pR pr Gametes for pprr = pr STEP 2: Write the gametes on a punnett square and solve

P1 generation

Mendel called the original parents the P generation. In his experiment, the P generation was the green pod (GG) and the yellow pod (gg). The offspring of the P generation are the F1 generation. He crossed both parents GG x gg.

Dominant trait

Mendel recognized that after combining the parental generation GG x gg, all of the offspring for F1 are Gg. The F1 plants produced green pods (Gg) because the green color was dominant over the yellow color. -A dominant trait is phenotypically expressed in heterozygotes. -Appears in offspring if it is contributed from a parent through a dominant allele. - A dominant allele is identified by an uppercase capital letter.

F1 generation

The first generation of offspring after the P generation. Also called filial 1 generation. Mendel crossed P1 generation GG x gg. As a result, the F1 generation was all Gg. All plants were green. Mendel allowed the F1 generation to self-pollinate (Gg x Gg).

Law of probability

The probability of two independent events occurring together can be calculated by multiplying the individual probabilities of each event occurring alone.

F2 generation

The second generation offspring. Mendel allowed the F1 generation, which was all Gg, to self-pollinate. The F1 generation Gg x Gg made the F2 generation GG, Gg, Gg, and gg. This made a 3:1 phenotype ratio with 3 green: 1 yellow....

1: 2: 1 ratio

This is the genotype ratio after two heterozygotes from the F1 generation self-pollinated (Gg x Gg). The offspring are GG, Gg, Gg, and gg. There is 1 GG: 2 Gg: 1 gg. Genotype ratio 1: 2: 1 -This is the expected genotypic ratio when two heterozygotes are crossed. (1 homozygous dominant): 2 (heterozygous): 1 (homozygous recessive)

3: 1 ratio

This is the phenotype ratio after crossing two heterozygotes (Gg x Gg). You get 3 green: 1 yellow. 3:1 This is the phenotype ratio that Mendel got after crossing the F1 generation Gg x Gg. His F2 generation was phenotypic ratio 3:1 with GG, Gg, Gg, and gg. -This is the phenotype ratio after mating two heterozygotes.

Law of segregation

pg 66 After doing one trait crosses, Mendel arrived at his first law of inheritance, called the law of segregation, which is a cornerstone of the particulate theory of inheritance. 1) Each individual has two factors for each trait. 2) The factors segregate (separate) during the formation of the gametes. 3) Each gamete contains only one factor from each pair of factors. 4) Fertilization gives each new individual two factors for each trait.