Heredity Part Two

Clearly Genetics must involve “Genes”, but where exactly do they fit in to the picture? A gene can be defined as a region of DNA that controls a hereditary characteristic. It usually corresponds to a sequence used in the production of a specific protein or RNA.

- The basic unit of heredity in living things A gene carries biological information in a form that must be copied and transmitted from each cell. - The basic unit of heredity in living things - Hold the info to build and maintain cells - Pass traits to offspring - Are responsible for outward traits, like eye color, and number of limbs - Are also responsible for inward traits like blood type and risk of disease The estimate for the number of genes in humans has decreased as our knowledge has increased. As of 2001, humans are thought to have between 30,000 and 40,000 genes.

An allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome. Organisms have two alleles for each trait. When the alleles of a pair are heterozygous, one is dominant and the other is recessive. The dominant allele is “noticed” and the recessive allele is “hidden”. The opposite, a homozygous pair, has two identical alleles for that trait. In humans, which sex would be considered to have the heterozygous sex allele pair? Any trait, including those less obvious than sex or hair color can be present as either heterozygous or homozygous in an organism.

A Punnett Square is a chart which shows/predicts all possible gene combinations in a cross of parents (whose genes are known). EXAMPLE: We let capital letters represent dominant genes or alleles and lowercase letters represent recessive genes. Using pea plant height as an example of a trait, we know that the dominant gene is for tall plants (T) and the recessive gene is for short plants (t) Therefore: A homozygous pea plant would look like: TT or tt A heterozygous pea plant would look like: Tt First, let’s use a Punnet square to predict what the offspring of a short plant and a tall plant, each homozygous (pure breed) might look like: We must understand what genes each parent can possibly give up to an offspring through reproduction. T T Then we construct and fill in a box with the possible combinations. One parent across the top, and the other along the side T t T t t T t T t t We see that 100% of the offspring will be tall!

Brain Buster: Among one species of animal, different color spots are common. The Dominant spot color is Red (C) while the Recessive spot color is Yellow (c). A male and female have a litter of eight offspring. Using a Punnett square determine how many can we expect to have Red Spots? Important facts: Both parents have Red spots, and both are heterozygous for the gene. Bonus 1: How many offspring will be heterozygous for that gene like their parents? Bonus 2: Why are no offspring born with orange spots? We realize that an animal with red spots will either have the alleles CC or Cc. Although these siblings have the same outward appearance, there remains an underlying genetic difference in their chromosomes. This might not seem significant until a second generation of offspring are produced using these genes. Therefore, scientists need to make a distinction between two such siblings. We would say that these two sibling have the same phenotype but a differing genotype.

The Phenotype of an organism is what it looks like The Phenotype of an organism is what it looks like. This only sometimes represents the dominant gene for that trait coming forward. The Genotype deals with what the pair of alleles is made up of, whether they are dominant or recessive. A Familiar Family: Father, Matt Roloff, and mother, Amy Roloff, are both little. They have two twin boys, Zach and Jeremy, to which Zach is little and Jeremy is normal sized. They, also have one daughter, Molly, and a younger son, Jacob, who are both normal size. Additionally, Matt and Amy’s parents as well as their siblings are all normal size. Given that dwarfism is a recessive gene in this situation, what might the genotypes of each family member look like then?

A change in the environment also can affect the phenotype A change in the environment also can affect the phenotype. Although we often think of flamingos as being pink, pinkness is not encoded into their genotype. The food they eat makes their phenotype white or pink. Can be X or Y related, or both A genetic disorder is a disease that is caused by an abnormality in an individual's DNA or chromosomes. Abnormalities can range from a small mutation in a single gene to the addition or subtraction of an entire chromosome or set of chromosomes. -Most disorders are quite rare and affect one person in every several thousands or millions. -Can be X or Y related (or both) -A mutated gene can be recessive or dominant -Mutations can be present from birth, or can come about from environmental factors -Disorders can be simple or complex

READ ONLY: Codominant alleles occur when rather than expressing an intermediate phenotype, the heterozygotes express both homozygous phenotypes. An example is in human ABO blood types, the heterozygote AB type manufactures antibodies to both A and B types. Blood Type A people manufacture only anti-B antibodies, while type B people make only anti-A antibodies. Codominant alleles are both expressed. Heterozygotes for codominant alleles fully express both alleles. Blood type AB individuals produce both A and B antigens. Since neither A nor B is dominant over the other and they are both dominant over O they are said to be codominant. Incomplete dominance is a condition when neither allele is dominant over the other. The condition is recognized by the heterozygotes expressing an intermediate phenotype relative to the parental phenotypes. If a red flowered plant is crossed with a white flowered one, the progeny will all be pink. When pink is crossed with pink, the progeny are 1 red, 2 pink, and 1 white.

Other Related Terms Cancer – Caused by abnormalities in genetic material, brought on by environmental factors, heredity, or mistakes in DNA replication. Cells that carry this mutation reproduce quickly and attack nearby cells and tissue. The functions of healthy cells are inactivated by cancerous cells. Cloning - The creation of an organism that is an exact genetic copy of another. This means that every single bit of DNA is the same between the two. Identical twins, created naturally, are clones. This process can also be replicated artificially in a lab however. Genetic Engineering - A laboratory technique used by scientists to change the DNA of living organisms. Enzymes can be used to customize DNA Strands to suppress some traits and add or amplify others. This is widely done with foods currently, yet possible human projects are held back by health and ethical concerns.