Bio211 Homework #6.docx - Biology 211 Homework#6 Genetics What are genes and what are different versions of genes How are they inherited and when are

Bio211 Homework #6.docx - Biology 211 Homework#6 Genetics...

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Biology 211 Homework#6 Genetics What are genes, and what are different versions of genes? How are they inherited and when are they expressed? Genetics is the study of the outcome of sexual reproduction. Sexual reproduction (the outcome of Meiosis and fertilization), generates diversity in a population. Diversity is generated as a consequence of several important aspects of sexual reproduction, some of which you learned about when we studied the difference between Mitosis (somatic cell division) and Meiosis (generation of eggs and sperm). Because homologous chromosomes segregate from each other during Meiosis randomly, each egg or sperm is essentially unique. This is the big picture of Meiosis, at the chromosome level. While homologous chromosomes are similar in size, and genetic content (the order of the genes in the DNA), they are also different from each other with respect to the exact structure and function of each gene. Some genes may be identical on both chromosomes, if they code for something that all cells have in common (housekeeping genes for example; genes that regulate DNA replication, the cell cycle, essential functions for all cells). But the diploid genome (sum of all genes and DNA) contains two copies of all genes, which combine to result in the phenotype of each organism. Obviously, humans around the world are quite different in appearance from each other, despite the fact that they have many genes in common. Different versions of genes are called “alleles”. A simple example is the one of hair color. There are different alleles for proteins that code for blond hair, brown hair, black hair, and red hair etc. When different alleles combine (like when a blond haired woman has kids with a black haired man), the result may vary depending on the genetics involved. Traits are the outcome of this protein expression. Blond hair is a trait (phenotype), and black hair is a trait. The alleles of genes that combine to create the outcome, or trait, are defined as their genotype. Alleles are found in the same location on different homologous chromosomes. Fertilization results in the mixing of alleles, and some alleles are stronger than others when proteins are being expressed. This is really what genetics is all about. Stronger genes are what we call “dominant”, and weaker genes are what we call “recessive”. When we study genetics, we use capital letters to describe the dominant genes, and lower case letters to define the recessive genes. It can get a little tricky solving problems in genetics, because sometimes different traits start with the same letter. For example if black hair alleles are dominant over brown hair alleles we would use “B” for the black hair allele, and “b” for brown. Same if blond is recessive to black, we would use “b” for blond also. Not because “b” stands for brown or blond, but because they are both recessive to black, which gets the capital “B”. If red hair is recessive to black hair, we would also call it “b”.
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Be sure you understand what the terms homozygous and heterozygous mean.
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  • Spring '16
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