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Transcript
Name_________________________________________ Date ___________________ Period _______ Make a Face: A genetic simulation of making a baby! Background: We have previously learned that inherited traits vary from acquired traits in that they must be passed from parents to offspring through the molecule known as DNA. DNA can take two forms, chromatin (loosely coiled and easy to read for cell activities) and chromosomes (tightly coiled and easy to move for cell division and reproduction). On each piece of DNA are thousands and thousands of genes which are sections of DNA that code for traits. Before a child is born, father and mother create sex cells (sperm cells or egg cells respectively) that will eventually combine to become the child’s DNA. In the sperm or egg cell there are 23 singular chromosomes rather than 23 pairs of chromosomes. That is because only one out of each pair of chromosomes will be passed to your child (to prevent the child from having double the genes it needs!). 23 singular chromosomes in the sperm cell will combine with 23 singular chromosomes in the egg cell to give the child exactly 23 pairs of chromosomesjust like each parent! However, which singular chromosome within each pair will be present in the sperm or egg cell is completely random/up to chance. The interaction between the combination of genes (genotype) on the chromosomes within each pair (one chromosome from dad + one chromosome from mom = 1 pair of chromosomes for the baby) will determine the phenotypes for each trait or the physical features that we can actually see. Of the 23 chromosome pairs, 22 of them are known as autosomes because they contain genes for traits that are not specific to a gender (ex. Having ten fingers and ten toes regardless of being male or female). The last pair of chromosomes, pair #23 is known as your sex chromosomes. This is either XY genotype for males or XX genotype for females. 1 Name_________________________________________ Date ___________________ Period _______ Since females have XX genotype for sex chromosomes, an X will always be present in each female’s sex cell (egg cell). Males have XY genotype for sex chromosomes, and therefore there is a 50% chance a sperm cell receives an X and a 50% chance a sperm cell receives a Y. Male sperm cells thus technically determine the gender of the child, even though it’s still a 50/50 chance of having a boy or girl. In this lab you will: -Simulate the creation of sex cells (sperm and egg) that have half of the DNA compared to the rest of the cells in the human body -Simulate fertilization of egg by sperm and combination of DNA -Investigate the genotypes and phenotypes of the child to determine its inherited traits Procedure: -Cut chromosomes, fold in half lengthwise and tape or glue (this simulates the 50% chance of any given copy of a chromosome pair to be passed to the offspring via sperm or egg -Place chromosomes randomly on desk and arrange in size/number order -Line up your chromosomes with your partners (be sure to discuss which sex chromosomes to use- pair #23) -Record the genotypes that correspond to each trait in the data table -Look up the phenotypes that each genotype would produce in the lab booklet -Complete the drawing of the child assuming he/she has grown up to age 15 2 Name_________________________________________ Date ___________________ Period _______ Data table Trait Genotype Phenotype Gender Face Shape Chin Shape (round or square) Skin Color* Hair Color* Eye Color* Hair type (curly wavy or straight) Widow’s Peak Eyebrow thickness Eye Shape (almond or round) Eyelashes Dimples Nose size Ear lobes (attached or lobed) Freckles on cheeks *May require more than 1 gene 3 Name_________________________________________ Date ___________________ Period _______ Drawing of child 15 years after birth 4 Name_________________________________________ Date ___________________ Period _______ Analysis Questions: 1. How many chromosome pairs does each human parent have? 2. How many individual chromosomes does each parent give to the next generation via sperm or egg? 3. Are some genes and characteristics expressed over others or do all genes have an equal chance of being expressed? Give evidence from your experience in lab. 4. How is there so much variation in the way children look even if they come from the same parents? 5 Name_________________________________________ Date ___________________ Period _______ Make a Face: Prelab Directions: Write 1 paragraph describing the features your ideal baby would have. Include as many inherited traits as possible. We will compare your ideal baby to the baby you produce during the lab this week. 6