genetic disorders and variations on mendel's principles

USE THIS POWERPOINT TO ANSWER QUESTIONS ON PAGES 4-7 OF THE MENDELIAN GENETICS

PACKET

GENE LOCI

P a B

P a b

GENOTYPE:

PHENOTYPE:

Autosomal Recessive Disorders

7. Connection: Many inherited disorders in humans are controlled by a single geneMost such disorders are caused by autosomal recessive alleles.

Examples include and cystic fibrosis and Tay-Sachs Disease

Watch a simple explanation of CF here

Autosomal Recessive Disorders

Tay Sachs

Cystic Fibrosis

Practice Problem

Practice Problem: A couple is planning on having children and they would like to know what is the chance that they will have a child that is deaf. The ability to hear is dominant and deafness is recessive. Both parents are heterozygous dominant. Fill in the punnet square below and the genotypic and phenotypic results.

Autosomal Dominant Disorders

http://images.buddytv.com/userquizimages/q-1/f143fd32-3547-40fb-9104-1197d29085b83.jpg

Fraternal twins

Autosomal Dominant Disorders

Neurofibromatosis

Huntington’s Disease

Practice Problem

Practice Problem: A couple is planning on having children and they would like to know what is the chance that they will have a child that is deaf. The ability to hear is dominant and deafness is recessive. Both parents are heterozygous dominant. Fill in the punnett square below and the genotypic and phenotypic results.

#8: Connection

8. Connection: Fetal testing can spot many inherited disorders early in pregnancy

Two types of tests are amniocentesis and chorionic villus sampling

Chorionic villi sampling Chorionic villus sampling (CVS) is the removal of a small piece of tissue (chorionic villi) from the uterus during early pregnancy to screen the baby for genetic defects.

Interested in learning more about genetic disorders? Check out the Utah Genetics Disorders Library here.

Variations on Mendel

9. The relationship of genotype to phenotype is rarely simple. Mendel’s principles are valid for all sexually reproducing species. However, often the genotype does not dictate the phenotype in the simple way his principles describe.

Practice Problem

Incomplete dominance results in intermediate phenotypes

Practice Problem: A certain type of flower exhibits incomplete dominance. Flowers that are homozygous dominant are red, flowers that are homozygous recessive are white and heterozygous flowers are pink. Complete the punnet square below for a cross between two heterozygous flowers.

#10

11. Codominance

More than one dominant trait is present and both are expressed in their original form.

#12 Pleiotropy

The ability of a single allele to have more than one distinguishable effect. For example the allele responsible for color pattern in Siamese cats.

The Frizzle Effect: an example of pleiotropy

In 1936, researchers Walter Landauer and Elizabeth Upham observed that chickens that expressed the dominant frizzle gene produced feathers that curled outward rather than lying flat against their bodies (Figure 2). However, this was not the only phenotypic effect of this gene — along with producing defective feathers, the frizzle gene caused the fowl to have abnormal body temperatures, higher metabolic and blood flow rates, and greater digestive capacity. Furthermore, chickens who had this allele also laid fewer eggs than their wild-type counterparts, further highlighting the pleiotropic nature of the

frizzle gene. http://www.nature.com/scitable/resource action=showFullImageForTopic&imgSrc=/scitable/content/37535/poncho_MID.jpg

http://www.thecitychicken.com/mainpagemarch24-2011c.jpg

Pleiotropy in Humans

Marfan syndrome is a condition in which your body's connective tissue is abnormal. Connective tissue helps support all parts of your body. It also helps control how your body grows and develops.

Marfan syndrome most often affects the connective tissue of the heart and blood vessels, eyes, bones, lungs, and covering of the spinal cord. Because the condition affects many parts of the body, it can cause many complications. Sometimes the complications are life threatening.

Interested? Read more here.

Marfan Syndrome

http://www.marfan.net.au/images/human_body.jpg

13. A single characteristic may be influenced by many genes. This

situation creates a continuum of phenotypes, an example is height

Typical ‘Bell Curve’ for a polygenic trait

Some scientists suggest this accounts for behavioral traits

Not completely predetermined, but associated with genes

High blood pressure is a polygenic trait.

Food For Thought: What genes could

combine to contribute to high blood pressure?

High blood pressure is a polygenic trait.

The phenotype is an interaction between a person's weight (one or more obesity genes), cholesterol level (one or more genes controlling metabolism), kidney function (salt transporter genes), smoking (a tendency to addiction), and probably lots of others too. Each of the contributing genes can also have multiple alleles.

Environmental Effect on Phenotype

Food for Thought:

What do you think is happening in this picture? Why do you think some phenotypes are effect by the environment? Can you think of other phenotypes that are effected by the environment?

Before watching the video or looking at your notes, see if you can answer the questions on page 6 and 7 about meiosis.

14. Meiosis is a process by which…

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STOP WHEN YOU GET TO:THE CHROMOSOMAL BASIS OF INHERITANCE ON PAGE 7