INVESTIGATING INDEPENDENT ASSORTMENT

INVESTIGATING INDEPENDENT ASSORTMENT

Mendel observed the effects of independent assortment when he carried out his dihybrid crosses. When he crossed two plants that bred true for different versions of two traits, the first-generation offspring all displayed the same phenotype (the dominant phenotype for both traits). However, when these plants were crossed, the second-generation offspring included four different phenotypes.

Mendel carefully recorded the numbers of phenotypes among the offspring of many dihybrid crosses. He found that certain combinations of phenotypes among the second-generation offspring occur in a 9:3:3:1 ratio, on the average. We now know that this pattern occurs because genes on pairs of homologous chromosomes are sorted out for distribution into one gamete or another independently of gene pairs of other chromosomes.

Activity

In this activity, you will first access the meiosis tutorial provided by the University of California, Santa Barbara. The tutorial demonstrates the random assortment of chromosomes into gametes. Next you will complete a tutorial quiz about independent assortment. This is part of The Biology Project from the University of Arizona.

Part 1.

Use your browser to go to the meiosis tutorial at

http://www.sumanasinc.com/webcontent/animations/content/independentassortment.html

Use the tutorial to learn how to determine which allele combinations are possible in two or even three trait crosses.

Part 2.

Use your browser to go to the independent assortment tutorial at

http://www.biology.arizona.edu/mendelian_genetics/problem_sets/dihybrid_cross/dihybrid_cross.html

Go through questions 1-9 of the tutorial. If you answer any question incorrectly, review the tutorial material and try again.

When you have completed this much of the tutorial, answer the questions below:

1. What type of gametes will be produced by a plant of genotype AaBb?

            The gametes produced be a plant with genotype AaBb would be AB or Ab or aB or ab

2. What type of gametes will be produced by a plant of genotype aabb?

            The gametes produced be a plant with genotype aabb would be ab

3. List all the genotypes you would find among the offspring of an AaBb x aabb test cross.

            The genotypes would be AaBb, aaBb, Aabb aabb

4. What is the expected phenotypic ratio of the offspring of an AaBb x aabb test cross?

            The expected phenotypic ratio of the offspring of an AaBb x aabb would be 1:1:1:1

5. List all possible gametes from a trihybrid individual whose genotype is RrSsTt.

            The possible gametes for a trihybrid individual with a genotype RrSsTt would be RST or rst or RsT or RSt or rST or rsT or rSt

In sickness and in health

In Sickness and In health

Autosomal dominant disorders cannot skip generations because they are dominant genes so they will show up if the person has it. They can't just be a carrier. So Greg and his mother can't be carriers of myotonic dystrophy. Greg's aunt or uncle can't be homozygous because their mother is the only one with the disorder. Also Greg's mom and one of his uncles doesn't have it. Greg's cousin has a 50% chance of inheriting the gene. Greg and Olga's children have a 0% chance of inheriting the gene because it is a dominant gene and neither Greg nor Olga have the gene.

There are five hallmarks of autosomal recessive inheritance: The first is Males and females are equally likely to be affected. The second is On average, the recurrence risk to the unborn sibling of an affected individual is 1/4. The third hallmark is The trait is characteristically found in siblings, not parents of affected or the offspring of affected. The forth hallmark is Parents of affected children may be related. The rarer the trait in the general population, the more likely a consanguineous mating is involved. The last hallmark is the trait may appear as an isolated (sporadic) event in small sibships. Consanguineous means the amount of shared (identical) DNA or the genetic material. This concept is important when discussing recessive genetic disorders because it means they have some of the same genetic material so they have more of a chance of inheriting the same genes. The factor VIII deficiency is sex linked and not An autosomal recessive trait because it only effects males.

The characteristics of x linked recessive inheritance are the disease is never passed from father to son. Males are much more likely to be affected than females. If affected males cannot reproduce, only males will be affected. All affected males in a family are related through their mothers. Trait or disease is typically passed from an affected grandfather, through his carrier daughters, to half of his grandsons. A son never inherits his fathers infected X-Chromosome because A son inherets the fathers Y-Chromosome from his father and one of his mothers X-Chromosomes. For a women to display a sex-linked recessive trait she would need to inherit two infected X-Chromosomes. One from her father and one from her mother. It is 1/2 chance that olga is a carrier of Factor VIII deficency. She has a 1/2 chance of passing it off on to her offspring. Male and female childern will be affected differently because a female child will just be a carrier becasue she will inheret a normal gene from her father where a amle child will show the trait because they don't have a spare X-Chromosome. Their is a 0% chance Greg is a carrier of factor VIII defeicy because he would have to show it not just carrie it because males don't have a spare X-chromosome.

The link to the population genetics wont work so i couldn't find the second equation to help figure out the the rest of the questions. If i get the equation i will update this blog and finish it.

Some of the legal risks and benefits of genetic testing are there is a chance you wouldn't be able to get health insurance because of a preexisting conditions or your insurance will be higher because they know you have a disorder but it hasn't showed yet. The benefits are you Know you have it so you can start doing things to try to prevent it. An unintended consequence of genetic testing could be that people would be less liable to seek medical care out of fear that they could later be denied life or health insurance. Privance laws and laws preventing insurance companys from deneying a person because they have a preexising conditing.