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Genes and DNA

Overview of size and relation to middle school concepts of genetics
by

Jeff Berg

on 14 January 2013

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Transcript of Genes and DNA

Genetics What makes you who you are? your cells Inside the nucleus the genetic information is found, when bunched together it is called the chromosome. Here's a look at what makes up a chromosome The material that contains the genetic code is called DNA Specific sequences of DNA are called genes and are what make up each of our specific traits What color is your hair? Are you tall or short? What decides these things? and your environment Before we look at how cells and the environment combine to make us who we are lets review a little about cells. Each chromosome has MANY genes on it! Each gene contains one unit of information Sexual and Asexual Reproduction Asexual reproduction is when one organism produces one or more organisms identical to itself. A unicellular organism just needs to copy its DNA and split in half to make a new organism through asexual reproduction! Sexual reproduction is when a cell containing genetic material from the father and a cell containing genetic material from the mother combine to become a completely new cell. The male sex cell is called a sperm The female sex cell is called an egg The cells from the male and female that combine are called sex cells. Another name for sex cells is gametes. Sex cells only have HALF of the genetic information that a regular cell has. In a human that means they have all 23 chromosomes present but they are not in pairs. like this not this This means that each parent contributes exactly half of the DNA to the new organism. Heredity Heredity is looking at how parents pass their genes and corresponding traits to their children. People have always noticed that children often look like their parents But other times they do not, why? A trait is something that makes us different from someone else. Like the size of our nose or the way we walk There are different kinds of traits. Inherited traits are traits that we get from the genes we received from our parents Examples are having freckles, eye color, and how long your tongue is. Acquired traits are traits we learn or acquire during life. Examples are the ability to juggle, having your ears pierced, or being able to play the piano. Mendel In the mid 1800s there was a monk in Austria name Gregor Mendel. Mendel was a gardener who made many qualitative observations about the vegetables in his garden especially his pea plants. Mendel noticed that different pea plants had different traits, and wanted to know how these traits were passed on to new plants. Pollen is a flower's male sex cell The ovule in the pistil is the female sex cell Mendel removed the stamen off of the pea plants and pollinated the pea plants by putting pollen from a different plant on the pistil. Mendel wondered if he crossed a tall pea plant with a short pea plant would the new pea plants be tall, short, or somewhere in between? Answer: They were all tall Mendel found that if he crossed plants with yellow seeds and green seeds all of the seeds in the new pea plants that developed were yellow. This pattern of one trait showing up in all of the offspring and the other becoming "lost" happened in all of the traits he tested. Mendel had two hypotheses 1 - Genes occur in pairs. 2 - One gene in a pair may be dominant over another. To keep track of which plants were the parents and which new plants were from which parents Mendel used specific symbols to represent each generation. P1 = The purebred parent generation, the first plants that are crossed

F1 = The offspring of the P1 crossing

F2 = The offspring of the F1 generation crossed together Looking at the F2 generation suddenly some of the short plants were back! Mendel figured out that each gene had two parts called alleles. When sex cells are formed the alleles seperate, each sex cell gets one of the two alleles. If two alleles that code for the same trait are present then that trait is expressed. However if two alleles that code for different traits are present then the allele that is expressed is called dominant and the allele that is hidden is called recessive. Alleles are usually represented by the first letter of the dominant trait. If the allele is dominant it is capitalized. If it is recessive it is lower case. Example - Tall is dominant over short in pea plants

So a pea plant with two tall alleles would be represented as TT

A pure short pea plant would be tt What would a cross between a Tall (TT) and a short (tt) end up growing? A tall plant with one T allele and one t allele How a trait appears is called the phenotype.











Example - the phenotype of the hair on the mouse = white A genotype is the paired symbols that represent the two alleles present for a trait's gene. If white hair is recessive in mice, and a mouse receives an allele for white hair from both its mother and father, then its genotype would be bb. If black fur is the dominant trait for hair in mice then a mouse that receives a black allele from both of its parents would have the genotype BB. What would the phenotype and genotype be of offspring between a BB black mouse and a bb white mouse? Phenotype = Black
Genotype = Bb one from the father one from the mother black is dominant over white If the paired alleles in the genotype are the same (either both dominant or both recessive) then they are homozygous.


If there is one dominant and one recessive allele in the genotype then they are heterozygous. Examples:

HH, gg, QQ, ff are all homozygous




Tt, Mm, Bb, Ee are all heterozygous Sexual Reproduction Asexual Reproduction
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