BIOL 21 - Chapter 19 final exam notes

Set up and analyze a Punnett square for autosomal traits and sex-linked traits.

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Explain the interaction of dominant and recessive alleles.

A dominant allele produces a dominant phenotype in individuals who have one copy of the allele, which can come from just one parent. For a recessive allele to produce a recessive phenotype, the individual must have two copies, one from each parent.

Explain what mutation is and the role of mutation in variation within the human population.

A mutation is a change that occurs in our DNA sequence, either due to mistakes when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke.

Describe how alleles can express phenotypes of complete dominance, incomplete dominance, co-dominance, and polygenic inheritance and give examples.

Complete Dominance: When one allele completely dominates or hides the other allele, it is considered complete dominance. For example, if someone with brown eyes (dominant trait) reproduces with a blue-eyed person (recessive trait) and has brown-eyed children. Incomplete Dominance: Incomplete dominance is when the two alleles work together to create a new phenotype. One example is a red flower and a blue flower being crossed, creating a purple flower. Another example is straight and curly-haired people reproducing and having wavy-haired offspring. Dominance: The inheritance of at least one dominant allele. Co-dominance: When something has both alleles independently expressed. For example, people with the AB blood type have one A allele and one B allele. Because both alleles are expressed at the same time, their blood type is AB.

Explain sex-linked traits and give examples.

Fragile X Syndrome: A genetic disorder that occurs when a single gene on the X chromosome shuts down. A mother can pass down this disorder to BOTH her daughter AND son as she provides an X chromosome to both of them. A father CAN ONLY pass down this disorder to his daughter as he passes an X chromosome to her (XX). Fathers do not provide their son with an X chromosome (XY); the son only receives the Y chromosome from their father, and X from his mother. Hemophilia: Hemophilia is an X-linked recessive hereditary disorder that classically affects males due to the presence of only one X chromosome in males. Females are usually carriers due to the presence of counterpart X chromosome, but many times manifestations of hemophilia are seen in heterozygous carrier females.

Define the terms: gene, allele, dominant, recessive, genotype, phenotype, homozygous, and heterozygous.

Gene: A segment of DNA that carries the code for making one or more proteins. Allele: Alternative versions of genes Dominant (allele or trait): An allele that masks or suppresses expression of its complementary allele / a trait that will appear in the offspring if one of the parents contributes it. Recessive (allele or trait): An allele that does not manifest itself in the presence of a more dominant allele / a trait that tends to be masked by other inherited traits Genotype: A complete set of alleles (has a profound influence on your phenotype) Phenotype: The observable physical and functional traits of an organism Homozygous: Having identical alleles at the same location (on a pair of homologous chromosomes) EX: Bb/bb Heterozygous: Having different alleles at the same location (on a pair of homologous chromosomes) EX: Bb

Explain chromosomal (genetic) disorders and describe those discussed in the lecture and lab including examples of harmless and deleterious mutations and sex-linked disorders.

Klinefelter Syndrome: A condition where boys and men are born with an extra X chromosome. Turner Syndrome: A condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing. Sickle Cell Anemia: You inherit 1 set from your mother and 1 set from your father. To be born with sickle cell disease, a child has to inherit a copy of the sickle cell gene from both their parents. This usually happens when both parents are "carriers" of the sickle cell gene, also known as having the sickle cell trait. Red-Green Colorblindness: To experience color blindness, the genetic mutation for colorblindness must be present on the X chromosome, but for women, this means it must be present on both X chromosomes. Men only need to mutation to be present on their singular X chromosome, making it much easier for them to inherit color blindness.