The pioneer of modern day genetics was an Austrian Monk named Gregor Mendel, who established the basic laws of heredity from his studies with pea plants in the late 1800s. Mendel’s fundamental genetic principles may be applied to a variety of traits from many different organisms. Each genetic trait, such as flower color, is regulated by a pair of genes called alleles.
These alleles are found at particular places on the chromosomes called loci. During meiosis, each pair of alleles splits up or segregates so that only one allele from each pair is contained within a gamete (egg or sperm. This is Mendel’s Law of Segregation. In sexual reproduction egg and sperm from parents unite to form a new individual or zygote. Thus, each parent contributes one allele for each genetic locus. Mendel’s Law of Independent Assortment states that during meiosis, each pair of alleles is assorted randomly and inherited independently of the others.
Note that this principle holds true only for genes that are located on different chromosomes. If the two alleles for a trait are different (heterozygous) rather than alike (homozygous), the dominant allele will be expressed over the other (recessive) one.Scientists use an upper case letter to symbolize a dominant allele and a lower case of the same letter to symbolize the recessive allele. For example, in garden peas a purple flower is dominant over a white flower. Thus, A=purple allele, and a=white allele.
In some cases, neither allele is dominant and a blending of the trait results. Other traits are sex-limited and are only expressed in one sex. Observable characteristics of an organism, e. g. , blue eyes or freckles, are referred to as the phenotype while the genes actually regulating a particular phenotype are known as the genotype of the organism.
Although many human traits are regulated by complex genetic principles, Mendel’s Laws can be used to illustrate the inheritance of several visible traits. In this exercise, you will perform a simulation exercise by flipping coins to simulate the independent assortment of chromosomes during gamete formation. Specifically, you will look at inheritance of human facial characteristics. Instructions: Find a partner and if necessary flip a coin to see who will be the father and who will be the mother of the child.
For each trait listed in the table, you will each flip a coin and record the result in the appropriate column (Gene from mother OR Gene from father. ) Heads= Dominant and should be represented as a capital “H. ” Tails= recessive and should be represented as a lower case “h. ” First determine the sex of your child by having dad flip a coin. Heads will represent an “X” (combined with mom’s X) and will result in a girl. Tails will represent a “Y” (combined with mom’s X) and will result in a boy.
In the third column labeled Genotype, you will combine the flips from both Mom and Dad. For example, if dad flipped “H” and mom flipped “h”, then you write heterozygous “Hh” in the column. If both parents flipped “H” then you write homozygous dominant “HH” and if both parents flipped “h” then you write homozygous recessive “hh. ” In the last column, you write the characteristic that is manifested by genotype.
For example, on face shape, if the flips resulted in a genotype of “Hh” then the face shape of the baby would be a phenotype of “round face. ” ?
