Inheritance of Traits Genetics

Genetics: The study of how traits are passed from parents to offspring Chromosomes are long structures found in the nucleus of a cell Chromosomes are actually coiled up DNA molecules Genes are specific sections on chromosomes Each gene determines a specific trait of an organism

Traits Traits are specific characteristics of an organism Examples include: eye color, hair color, shape of body parts, whether one can taste a yucky tasting compound or not, certain chemical processes in the body Organisms have thousands of traits Genetics can also be looked at as the study of how genes control the traits

Genes are arranged on a chromosome, one next to the other Each chromosome has different genes, that control different traits

Passing Traits to Offspring When the sperm fertilizes the egg, DNA from the mother is combined with DNA from the father The offspring now has a complete but unique set of DNA It is a combination of the mother’s and the father’s but it is completely unique compared to both of them

Dominant and Recessive Genes Genes come in pairs (because chromosomes come in pairs) Some genes mask the expression of their counterpart These are called dominant genes Example: If one parent gives the gene for attached earlobes and the other gives the gene for free eat lobes, the child will have free earlobes. The gene for free ear lobes is dominant. It masks the expression of the attached ear lobe gene The gene that gets masked is called recessive

Heterozygous and Homozygous An organism with two dominant genes for a trait is called pure dominant (homozygous dominant) An organism with two recessive genes for a trait is called pure recessive (homozygous recessive) An organism with a dominant gene and a recessive gene is called heterozygous. In this case, the individual will only express the dominant trait even though it carries the recessive trait.

Predicting the Gene Combinations Using a Punnett Square A Punnett square is used to predict the possible gene combinations that offspring may have based on the parent’s genes In the example of the earlobes, free lobes was the dominant trait and attached was the recessive trait. We use one letter to represent these traits. We use the first letter of the dominant trait. Uppercase letters fro dominant and lower case for recessive. So… F = free and f = attached

Example I’ll show you one and you do the rest. Say one parent is pure dominant (homozygous dominant) and the other is heterozygous We set up the Punnett square like this

Then we bring the letters on the left over to the boxes next to them and the letters in the top down. Always right any upper case letters first It should look like this

With this information we can now see that there are only two possible combinations for offspring from these parents So we can say there is a 50% chance of getting an offspring that is pure dominant and a 50% chance of getting an offspring that is heterozygous What kind of earlobes will the offspring have?

Genotype and Phenotype Genotype is just a fancy word for the genetic makeup of something For example, we talked about attached and free earlobes. If your earlobes are free your genotype is Ff or FF. If your lobes are attached your genotype is ff. Phenotype is a fancy word for the actual, physical trait. So, the phenotypes are attached ear lobes or free ear lobes. Genotype controls phenotype!!! (the genes control what traits will be expressed.)

You Try It! Complete Punnett Square for Each of the Following Scenarios Use earlobes again. Both parents are heterozygous Possible outcomes: __________________

Tasting the PTC is dominant to not tasting Parent 1 is heterozygous Parent 2 is homozygous recessive Possible outcomes: ______________________