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Human Genetics Introduction The inheritance of human traits is of interest to us all. We carry the genes of our parents and of our grandparents, and when we reproduce, some of our traits will be passed on to our children. At family reunions, it is interesting to theorize where Bobby got his red hair or Diane her brown eyes. A mistake, or mutation in the DNA sequence of a gene, can lead to a variation in the individual. Sometimes these variations are beneficial, but more often they produce an organism that cannot survive or has a genetic disorder. Many genetic disorders are passed on from parent to offspring, and the presence of defective gene can be traced through the use of pedigrees or family histories. Scientists are currently in the process of sequencing the entire human genome in hopes of producing a data bank containing all the human genes. With this knowledge we will be able to pinpoint defects in a person’s genetic makeup and possible provide treatment for diseases that at this time are untreatable. What will be done with this knowledge, who will have access to it, and what will be considered a “normal” person are all issues that an informed public will need to address. Heredity is the passing on of traits, or characteristics, from parent to offspring. The units of heredity are called genes. Different versions of the same gene are called alleles. Genes are found on the chromosomes in a cell. The combinations of genes for each trait occur by chance. When one allele in a pair is stronger than the other allele, the trait of the weaker allele is masked, or hidden. The stronger allele is the dominant allele, and the allele that is masked is the recessive allele. Dominant alleles are written as capital letters and recessive alleles are written as lowercase letters. If both alleles are different, the trait is said to be heterozygous, or hybrid. If both alleles are the same, the trait is said to be homozygous, or purebred. Sometimes alleles are neither dominant nor recessive. The result of such a situation is a blending of traits. The genetic makeup of an individual is known as its genotype. The observable physical characteristics of an individual that are the result of the genotype are known as its phenotype. Part I Introduction Why do people look so different from each other? Even close relatives often look very different from each other. This happens because a very large variety of traits exist in the human population and new variations are created as humans reproduce. During meiosis (the process of producing gametes, sperm and egg) there can be reshuffling and even crossing over of genes between chromosome pairs. In this activity, we will learn why brothers and sisters have different genotypes (genetic messages on their DNA) and phenotypes (physical appearances), even when the share the same parents. So… CONGRATUALTIONS! You are a parent! You and your partner will represent a couple that each have one dominant and one recessive gene for each facial feature illustrated in this lab. Amazing coincidence, huh? As you already know, this means you are heterozygous for each trait. Materials:A partnerA penny Procedure: 1. Obtain a partner and the rest of your materials. Decide which of you will contribute the genes of the mother and with will contribute the genes of the father. 1. Find out the sex of your child. 1. Remember your mom’s genotype is XX and dad’s is XY. The mother provides an X chromosome because that is all she has, and father provides either his X or his Y chromosome. So only Dad flips the coin. 1. Heads = Y sperm, which means the child will be a boy. 1. Tails = X sperm, which means the child will be a girl. 1. Discover the facial features your child will have by flipping the coin as directed by the following pages. For purposes of the rest of the activity: · Heads will represent the dominant trait shown in capital letters. · Tails will represent the recessive trait shown in lowercase letters. 1. On you Face Lab Data Table record the genetic contributions (results from the flips of the coins) in the columns labels Gene(s) from Mother and Gene(s) from Father. Record the actual genetic message in the genotype column, and record the appearance in the phenotype column. 1. Once you have finished determining all facial traits for your child. Try to match these features to an actor or actress. Be sure to identify the name of that person at the end. 1. Please turn this in once you have identified the actor/actress who resembles your offspring and have completed the analysis section of the lab. Facial Features 1. Face Shape Round (RR , Rr) Square (rr) 2. Chin Shape Prominent (PP, Pp) Weak (pp) 3. Chin Shape II – only if your child’s chin is prominent (PP, Pp) Round Chin (RR, Rr) Square Chin (rr) 4. Cleft Chin Present (CC, Cc) Absent (cc) 5. Skin Color: Skin color involves 3 gene pairs. Each parent need to flip the coin 3 times, and record the A, B, and C alleles. For example the result of the first pair of coin flips might be AA, Aa, or aa. Record the first coin flip then do two more alleles B and C. Each capital letter represents an active gene for melanin production (color). 6 capitals 5 capitals 4 capitals 3 capitals 2 capitals 1 capitals 0 capitals Very dark black skin Very dark brown Dark brown Medium brown Light brown Light tan White 6. Hair Color: Like skin color hair color is produced by several genes (polygenic or multiple alleles). For the purpose of this activity we will assume that 4 pairs are involved (more are likely). So, each parent will have to flip the coins 4 times for the A, B, C and D alleles. As before, the capital letters (dominant) represent color while the lower case (recessive) represent little or no color. 8 capitals 7 capitals 6 capitals 5 capitals 4 capitals 3 capitals 2 capitals 1 capitals 0 capitals Black Very dark brown Dark brown Brown Light brown Honey blond Blond Very light blond White 7. Red Hair Color Red hair seems to be caused by a single gene with two alleles: Dark red (RR) Light red (Rr) No red (rr) Red hair is further complicated by the fact that brown hair will mask or hide red hair color. The lighter the hair color the more the red can show through. If your child has 3 or less capitals (for hair color, see number 6), and RR is tossed your child will have flaming red hair. 8. Hair Type: incomplete dominance Curly (CC) Wavy (Cc) Straight (cc) 9. Widow’s Peak: The hair comes to a point…like Eddie Munster Present (WW, Ww) Absent (ww) 10. Eyebrow Color: incomplete dominance Dark (DD) Medium (Dd) Light (dd) 11. Eyebrow Thickness: Bushy (BB, Bb) Fine (bb) 12. Eyebrow Placement: Not connected (NN, Nn) Connected (nn) 13. Eye Color: The genetics of eye color are complex, and there are many variations of eye color among humans. These variations occur because more than one gene controls the expression of the trait, in fact, over 15 different genes have been associated with eye color inheritance. While we may just say that a person has brown eyes, you might notice that there are many shades of brown, all a result of a complex pattern of inheritance. To simplify, this activity will look at three known alleles that affect the basic shade of eye color: brown, green, or blue eyes. These alleles are located on separate chromosomes, so they independently assort during the creation of gametes. Each person then has 4 total alleles that determine their eye color (in this simplified model). The B allele (brown) is always dominant over the G allele (green). The blue eye trait is always recessive. Refer to this chart showing the genotypes and phenotypes BBGG brown BbGG brown BBGg brown BbGg brown BBgg brown Bbgg brown bbGg green bbGG green bbgg blue 14. Eye Distance: Close together (EE) Average (Ee) Far apart (ee) 15. Eye Size: Large (LL) Average (Ll) Small (ll) 16. Eye Shape: Almond (AA, Aa) Round (aa) 17. Eye Tilt: Horizontal (HH, Hh) Upward slant (hh) 18. Eyelashes: Long (LL, Ll) Short (ll) 19. Mouth Size: Long (LL) Average (Ll) Short (ll) 20. Lip Thickness: Thick (TT, Tt) Thin (tt) 21. Lip Protrusion: Very protruding (PP) Slightly protruding (Pp) Absent (pp) 22. Dimples: Present (PP, Pp) Absent (pp) 23. Nose Size: Big (BB) Average (Bb) Small (bb) 24. Nose Shape: Rounded (RR, Rr) Pointed (rr) 25. Nostril Shape: Rounded (RR, Rr) Pointed (rr) 26. Earlobe Attachment: Free (FF, Ff) Attached (ff) 27. Darwin’s Ear Point: Present (PP, Pp) Absent (pp) 28. Ear Pits: Present (PP, Pp) Absent (pp) 29. Hairy Ears: This sex-linked and only occurs in males so if your baby girl skip this. If your baby is a boy, only mom flips. Present (P) Absent (p) 30. Freckles on Cheeks: Present (PP, Pp) Absent (pp) 31. Freckles on Forehead: Present (PP, Pp) Absent (pp) 32. Can roll tongue Dominant Tongue roller (RR, Rr) Recessive: Can’t roll tongue (rr) 33. Straight Thumb Dominant: Straight thumb (TT, Tt) Recessive: Hitchhiker’s thumb (tt) 34. Right thumb on top Dominant: Right thumb on top (TT, Tt) Recessive: Left thumb on top (tt) Parent Names: Baby’s Name: Create A