Biology 102 Exam 2 WSU Carloye Questions And Answers.

Gene vs Allele - Answer-Gene: A section of DNA that controls a certain trait. Example: Eye color. Allele: A specific variation of a gene. Example: Having blue eyes. Dominant vs Recessive - Answer-Dominant: Determines the expression of a trait (visually). Example: Brown eyes, dark hair. Recessive: Much less likely to determine the expression of a trait. Example: Blue eyes, blonde hair. Homozygous vs Heterozygous - Answer-Homozygous: A homozygous trait is when two of the same kind of alleles combine to form a trait. Example: When two tall people have a tall child. Both parents had the same allele and gave it to their child to create a trait. Heterozygous: When two different alleles combine to form a trait. Example: A tall person and a short person have a child who is short. The short allele is dominant so the child grew up to be short. Genotype vs Phenotype - Answer-Genotype: The set of genes that an organism carries. Phenotype: All of an organisms observable characteristics. "True-Breeding" - Answer-When parents product offspring that will carry the same phenotype. This means that the parents are homozygous for every trait. Example: Two purebred labs having purebred puppies with the same traits as them.When doing genetic crosses, what does it mean to be a "carrier" of a trait? - Answer-A carrier is someone who has (carries) a recessive allele for a genetic trait or mutation but doesn't display that trait physically or show symptoms of the trait. Example: Sickle cell anemia. Which process gives rise to gametes - mitosis or meiosis or both? - Answer-Meiosis gives rise to gametes but mitosis does not. Define "Polygeny" - Answer-The theory that humans evolve from several independent pairs of ancestors. Define "Epistasis" - Answer-The idea that traits are often produced through a series of steps. If one step fails, then you don't get to the end result. How does polygeny give rise to such a wide array of skin colors? - Answer-Each dominant allele contributes to 1 increment of pigment. Recessive allele contributes to no pigment. Example: Someone with aabbcc would have very light skin, and someone with AABBCC would have very dark skin. Explain how two blue-eyed parents can have a brown-eyed child. Discuss the two genes involved, what role each plays in creating the pigment of the eyes and what combination of alleles gives rise to blue and brown-eyed phenotypes. - Answer-If the parents are both carriers of the brown eyed gene, it is possible to have a brown eyed baby. A functional gene has pigment, while a non-functional gene has no pigment. Define "sex-linked". - Answer-A trait associated with a gene that is only carried by the male or female parent. What combination of chromosomes is associated with the sex of an individual in humans? - Answer-A female has two X chromosomes (XX) and a male has an X and a Y chromosome (XY). What gene determines the sex of a developing embryo? - Answer-The Y-chromosome carries the SRY gene, which is the "Sex Determining Region of the Y". The SRY gene stimulates testosterone production in growing fetuses. The SRY gene also triggers embryonic gonad gene to become testes.In what way are ovaries and testes the same in a 7-week old embryo? - Answer-At 7 weeks, sex is undetermined. The only areas that can be determined at 7 weeks are the anus, urethra and tail. What are the two ways that you can get a mismatch between the karyotype and the sexual phenotype of an individual? - Answer-1. Loss or gain of the SRY gene. If the SRY-gene is not functional, the male pathway is not initiated. 2. Inability of cells to sense testosterone (Androgen Insensitivity). This can result in normal female sex characteristics, both male and female sex characteristics, or normal male sex characteristics. How does cross-over during Meiosis I result in a mismatch between karyotype and sex of an individual? - Answer-1. Androgen Insensitivity. Receptors on the cells have a mutation and can't detect testosterone. Second way: It is possible during crossover that the SRY gene will accidentally become attached to the X chromosome, resulting in an XY female. How can a person with an XY karyotype be female? Remember that there are two ways this can happen. - Answer-SRY gene can be non-functional, but the chromosomes are still XY. The SRY gene attached to the X chromosome during crossover.