Heredity Worksheet

Heredity Name _______________ Block ____ Date _________ Recall: the characteristic traits of humans such as hair color or eye color come from a person’s genes. Remember that genes are found in pairs, one from each homologous chromosome. Depending upon the combination of the pair of these 2 genes, this will determine the characteristic “expressed” in the individual. In simple Mendelian genetics, each trait or characteristic is found in only 2 varieties (or alleles). e.g. midfinger hair or no midfinger hair. We can say that there is a gene (or allele) that codes for midfinger hair and one gene (or allele) that codes for no midfinger hair. Since we have a pair of genes for each pair of chromosomes then we can have 3 possible combinations of genes: 1) we could have the 2 genes for midfinger hair 2) we could have the 2 genes for no midfinger hair 3) we could have 1 gene for midfinger hair and 1 gene for no midfinger hair We can represent this idea by using symbols. Let’s use capital H for midfinger hair and lower h for no midfinger hair. So we could represent the above combination as follows: 1) HH 2) hh 3) Hh (rather than hH; we always write the capital letter before lowercase) The combination of genes that an organism possesses is called its GENOTYPE. Each of the three possibilities: HH, hh, Hh are 3 different genotypes. Now, we can guess what we see on a person if their genotype is HH: we expect midfinger hair. Similarly if the person has hh: we expect no midfinger hair. We say that individuals are homozygous for this gene, meaning that both genes are the same. If one of each gene is different in the individual, we say that they are heterozygous for this gene. So what happens if a person’s genotype is Hh? In every case, the person has midfinger hair. We say then, that the gene for midfinger hair is dominant over the gene for no midfinger hair. i.e. H is dominant over h. (this is why the we used capital and lower case letters) Or we could say the gene for no midfinger hair is recessive to the gene for midfinger hair. i.e. h is recessive to H. The trait or characteristic that is expressed, regardless of the genotype, is called the phenotype. So for 2 of the above 3 cases (HH and Hh), the phenotype is midfinger hair. For the other case (hh), the phenotype is no midfinger hair. Your Genetic Makeup Trait or Characteristic Eye color Dominant (phenotype) Dark (brown or black) Recessive (phenotype) Light (blue or grey) Hairline Ear lobe Freckles Thumb Midfinger hair Tongue Cheeks Folding hands # of tendons in wrist Toe Pointed on forehead (widow’s peak) Free lobe Present Bent Present Can be rolled up into “U” Dimpled Left thumb over right Two Second toe longer that all other toes Straight across forehead Attached lobe Absent Straight Absent Cannot be rolled up into “U” No dimples Right thumb over left Three Big toe longer than other toes 1) Determine whether you are “D” dominant or “d” recessive for each of these features. Record them in the “This is me” column. 2) Determine whether your father and/or mother is dominant or recessive for each of these features. Record them in the appropriate column. 3) Now try and figure out what the three “genotype” columns are. Remember that a dominant phenotype can be expressed with “DD” or “Dd”. A recessive phenotype has to be expressed as “dd”. Sometimes, you will not be able to be sure which genotype you or your parents have. In these cases put a question mark (?) there. 4) Now try and determine where you get your traits and characteristics from in the ORIGIN column. You may write MOTHER, FATHER, BOTH, or NED (Not Enough Data). Trait Eye color Hairline Ear lobe Freckles Thumb Midfinger hair Tongue Cheeks Folding hands # of tendons in wrist Toe This is me D/d Phenotype Mother D/d Phenotype Father D/d Origin Phenotype