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You are on page 1of 85 Search inside document Concept of the gene idea, the concepts of genetics Genetic is derived from term genesis which means creation. Today is the branch of biology which study how traits are passed from one generation to next. Briefly genetic is the science which investigates heredity and diversity. Genetic concepts Heredity: passing on traits from parents to their offspring. Trait:charcteristic of an organism Gene: a segment of DNA Allele:one pair of genes, one comming from mother, other from the father.

Alleles is a specific version of genes. Locus is a specific location of a gene. Heterozygote means you have different alleles for a given trait Aa, Bb, Cc. Homozygote means you have same alleles AA, BB, cc, dd. Dominant gene is gene that is always expressed. Recessive is expressed when paired is aa. Phenotype is physical visible characteristic of organism. Genotype is complete set of genes of a living things. Independent genes are alleles for different traits located on different location.

Linked gene is when there is more than one gene on a single chromosome. They can be separated from each other by crossing over in meiosis. Parenteral cross P is mating the father and mother. Filia F : the individuals produced by crossing the father and mother. Round R is dominant to wrinkled r. Yellow Y is dominant to green y. Classify the following as homozygotes or heterozygotes?

What is phenotype? Probability is the branch of matematics that predict chances that a certain event will occure. It is the study of operations of the laws of chance. The law of probability and its applications Law of segregation is also known as Mendels first law. Laws of probability can be used to predict outcomes of genetic crosses. Genetic cross can not be made without knowing the gamete type.

Alleles are different form of genes. Homozygous alleles AA, aa. Heterozygous Aa. When you do crosses you should know how many gametes each person should have. It is due to absence enzyme tyrosinase.

Albinism is autosomal recesive condition. What is the probability of having albino child if the parents are both heterozygous for condition? Huntingtons disease is autosomal dominant. What is the probability of a having child with the disease if one parents is homozygous recesive, other is heterozygous? What Mendel did? The principle of segregation Different pairs of alleles are passed to offspring independently of each other.

The result is that new combinations of genes present in neither parent are possible. The principle of independent assortment Gene is a factor of heritance. Alternative forms are called alleles. Genotype is combination of alleles. Pairs of genes are located on chromosomes and each embryo gets one copy chromosome from the mom other father.

What happens to homologous chromosome in meiosis? Gene pairs are separated because they are located on homologous chromosome segregation-separation. Phenotypes are traits. In summer squash, white fruit color W is dominant over yellow fruit color w and diskshaped fruit D is dominant over sphereshaped fruit d.. If a squash plant truebreeding for white, disk-shaped fruit is crossed with a plant true-breeding for yellow, sphere-shaped fruit, what will the phenotypic and genotypic ratios be for: a.

Write down the cross in terms of the parental P1 genotypes and phenotypes 2. Determine the P1 gametes, place them in a Punnett Square and fill in the resulting genotypes: 3. Determine the genotypic and phenotpic ratios for the F1 generation 4. Write down the cross between F1 progeny 5.

Determine the F1 gametes, place them in a Punnett Square and fill in the resulting genotypes 6. In rabbits, white fur color W is dominant to black, and long ears L are dominant to short. Draw a Punnett square that represents the cross between two rabbits heterozygous for both traits.

What are the phenotype and genotype ratios? In humans, polydactylism having an extra finger on each hand is dominant to the typical 5-finger arrangement. Tongue rolling is dominant to not being able to roll ones tongue. A man who is homozygous for 5fingers and who cannot roll their tongue has children with a woman who is heterozygous for polydactylism and tongue rolling. Draw a Punnett square that represents the cross. What is the probability the couple will produce a polydactyl baby who cannot roll their tongue?

A species of bird is threatened with extinction because its habitat is being destroyed by deforestation.

As a research ecologist, you have been chosen to ensure the genetic diversity of the species. In this species of bird, feathers may be white, black, or white with black spots. In the same species, beaks may be long, medium or short.

A black bird with a medium beak pairs with a spotted bird with a long beak. Make a list of all of the phenotype combinations this pair could possibly produce. A man with a dimple and brown eyes whose father had blue eyes but no dimples marries a woman with a dimple and brown eyes whose father had blue eyes with no dimple. What is the probability their first child will be blue eyed and without dimple?

Traits are inherited trough genes The traits of pea plant are related to its alleles which can be samo or different If the pairs of alleles forming a gene are different, the efects of dominant allele appears in the phenotype Mendel findings: Variety in organism arises from the fact that, during fertilization the gametes combine randomly, allowing the genes for various traits to form new combinations Traits are visible on offspring in predictable ratios, according the principle of probability.

Forked lined method! What are expecting genotype frequency their offspring? Using the forked lined approach in a trihybrid cross involving three traits , where the pigments are both AaBbCc, what is the probability of their producing an offspring recesive for all three traits? What is the probability of producing an offspring with genotype AabbCc?

Always cross the unknown genotype with a homozygous recessive B. Observe count large numbers of offspring to ensure accuracy in determining the unknown genotype.

In fruit flies, red eyes are dominant over sepia brownish eyes. Being the great genetic student that you are, you happen to have a culture of pure red eye and pure sepia eye flies in your laboratory. While working in your lab late one night, a cute, fuzzy, and fantastically friendly, red eyed fruit fly came in for a crash landing on your banana. Wanting naturally to know more about your new friend, you decide to run a test-cross on your little, buzzing buddy. If all of the offspring turn out to be red-eyed all of them!!!

If about of the show up with sepia eyes, what was the actual genotype of your new found friend? Step 2: Figure out what kinds of gametes the parents can produce. Step 3: Set up a Punnett Square for your mating. Step 4: Fill in the offspring inside the table by matching the egg allele at the top of the column with the sperm allele at the head of the row. Step 5: Figure out the genotypic ratio for your predicted offspring.

Step 6: Figure out the phenotypic ratio for your predicted offspring. Incoplete dominance is when two dofferent alleles result in blend phenotype. The trick is to recognize when you are dealing with a question involving incomplete dominance. There are two steps to this: 1 Notice that the offspring is showing a 3rd phenotype. The parents each have one, and the offspring are different from the parents. The color of birds is determined by just two alleles.

The color of fruit for plant "X" is determined by two alleles. What are the genotypes of the parent orange-fruited plants? With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together. A very common phenotype used in questions about codominance is roan fur in cattle. A good example of codominance. Codominance is when two dominan alleles are being expressed in the same time. Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull.


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