This is a picture of my children, Caleb is on the left Allison is on the right. Notice any resemblance? Everyone of us is a blond, Caleb has an almost platinum shade and mine is the darkest. All of us have blue eyes, although the color is slightly different. I realized, upon reading the text that my brown-eyed mother must be heterozygous, which explains my own blue eyes. I have always found it amusing that we are the Blond-haired, blue-eyed Rodriguez Family. People always blink when they see us and hear our last name. The truth is the name comes from my husband's adoptive father, however our blond haired blue-eyed family is the result of genotype.
Genotype refers to the genes of a particular person, and genes are segments of chromosomes. Humans have twenty three pairs of chromosomes in each cell. Alleles are alternative forms of a gene that have the same locus on a pair of chromosomes and affect the same trait. Gametes, sperm in males and ovum in females, as a result of meiosis only contain one chromosome for each pair. When the sperm and the egg meet, each gamete contributes its twenty three chromosomes to create a brand new, unique individual. The alleles a child inherits from his parents will determine his phenotype, physical appearance.
Affecting phenotype are dominant and recessive alleles. Alleles are represented by letters, specifying a certain trait. An uppercase letter represents a dominant allele, and the same letter in lower case represents a recessive allele. Individuals usually have two alleles per trait, one from each parent.
An individual with two dominant alleles for a particular trait has a homozygous dominant
genotype. Sometimes a person will have two recessive alleles giving them a homozygous recessive genotype. When an individual inherits one dominant and one recessive allele the resulting genotype is heterozygous.
The Punnet Square below, taken from http://www.mhhe.com/biosci/genbio/virtual_labs/BL_05/BL_05.html illustrates an example of a cross between two heterozygous long winged flies and the different genotypes that could result. The phenotype ratio in this cross is three long-winged off spring and one vestigial-winged.
Taken from the virtual lab at http://www.mhhe.com/biosci/genbio/virtual_labs/BL_05/BL_05.htmlThe dragon lab below shows multiple examples of how genotype affects phenotype. The horns are an example of a heterozygous genotype for this trait. A homozygous dominant genotype is represented in the tail. Lastly, the wings show a homozygous recessive genotype.
Taken from the dragon lab at http://biologica.concord.org/webtest1/web_labs_genophenotype.htmIt is not always possible to determine a person's genotype just by looking at them. However it is possible to get a clue by his/her offspring. I was able to do this in the case of my mother. The Punnet square is also an effective tool.
One question does stick out in my mind in relation to genetic inheritance. Is right and left handedness inherited or not? In high school biology I was told it is, however, both my husband and I are left-handed and both our children are right-handed. This result tells me that it is not an inherited trait. Am I wrong? At least when it comes to their other physical characteristics, it is obvious who Caleb and Allison's parents are.
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