Linked Genetics

Meiosis consists of one DNA replication and two nuclear divisions resulting in 4 daughter cells. The process which provides for genetic variation is crossing over. Crossing over occurs in the early stages when homologous chromosomes move together so that their chromatids form a tetrad. This is called synapsis and allows for the exchange of chromosome sections.

parent carried the b allele. The F1 offspring of such a cross would be Bb, and

The likelihood of close relatives sharing the same recessive alleles is greater than in the general population, raising the risks that a child would be homozygous recessive for a trait.

The purpose of this experiment was to measure the T4 reversion rate to wild type combination, and the recombination frequency recombination frequency of the T4 mutants to the wild type. Also to determine the distance between the two mutants, which are T4 rII 29 and T4 rII 31.

Define the term crossing over. (3 points) During meiosis’ prophase the homologous chromatids exchange segments.

Imagine that you are crossing two plants that are heterozygous for flower color and seed shape. The dominant and recessive alleles for these traits are:

Part B: Genes X, Y, and Z are linked. Crossover gametes between genes X and Y are observed

Human cells carry two copies of each chromosome they have two versions of each gene and the different versions are called alleles. Alleles can be either dominant or recessive. Dominant alleles means you have one copy of the gene or your heterozygous. Recessive alleles means you have two copies of the gene or your homozygous.

Imagine DNA as a ladder made of rungs — 3 billion in all — spiraling upward in a double helix. Each step is a base pair, designated by two letters from the nucleotide alphabet of G, T, A, and C. More than 99 percent of these base pairs are identical in all humans, with only about one in a thousand SNPs diverging to make us distinct. For instance, you might have a CG that makes you susceptible to diabetes, and I might have a CC, which makes it far less likely I will get this disease.

The two recessive alleles are both on the same chromosome. Genes A and B completely follow Mendel’s principles of inheritance; genes B and C are physically connected together and never are separated from each other at any time during any cell division cycle or fertilization event. Draw below the gamete genotypes that this individual could produce.

The markers showing linkage are markers B, C, and D since they are more prevalent and highly associated with the mutant allele.

Jumping genes were first introduced to the public in 1951, when Barbara McClintock presented her ideas at the Cold Spring Harbor Laboratory after years of dedicated research. McClintock discovered that mutations were not necessarily “random, rare, and relatively small” (136). She noticed that certain genes moved from one place to another, frequenting certain areas over others. These moves affected other genes, turning them on or off. It also appeared that these movements were “triggered by outside influences … like extreme heat or drought” (137). At first, many people did not believe her, but after more research was done, it became clear that McClintock was correct. Even now, scientists do not know what causes genes to “jump” or how they

Chromosomes line up in different orders (random assortment) so when they go to either new cell on cell might have dominant for one characteristic (e.g. brown eyes), recessive for another (e.g. blond hair), and dominant for a third one (e.g. can roll tongue) whereas the other created cell might be dominant, dominant dominant (brown eyes, brown hair and can roll tongue.

The pairs of alternative traits examined segregated among the progeny of a particular cross, some individuals exhibiting one traits, some the other

During the first stage of meiosis, the chromosomes are replicated and during the stage, it is reported that the genes "may be shuffled from one chromatid to another". (Hartwell, 2006, p.1) During this stage the chromosomes pair up for a brief time and chromosomal crossover occurs in which a gene on one chromosome may be swapped for a gene on the