Genetics and Health Chapter 12

Structures of DNA Can you roll your tongue? Can you bend back your thumb? These are just some of the characteristics that can be inherited from one generation to the next. Diseases and disorders can also be inherited Genetics is the study of how these characteristics or traits are passed from parent to offspring Where is DNA found? Your body contains about 10 trillion cells, each cell has a NUCLEUS that contains CHROMOSOMES, each chromosome contains double-helix shaped molecules called DNA, DNA is divided into segments called GENES, it is these genes that control the traits that you inherit (eye color, hair color, genetic disorders, etc)

Structure of DNA DNA has a double helix shape (‘Twisted latter’) Chemical compounds called BASES attach to 2 sugar-phosphate backbones Only certain bases can pair up with each other: Adenine (A) and Thymine (T) can pair with each other, while Guanine (G) and Cytosine (C) can pair with each other When a cell splits, one half of the DNA goes to the next cell and hence genes are passed on. Different genes have different base pair arrangements/sequences, this is what determines the traits that you inherit

Chromosomes The human body contains 46 chromosomes arranged in 23 pairs that hold all of the genetic information in your body One chromosome of each pair comes from the mother, the other chromosome comes from the father There are two types of sex chromosomes, X and Y: Y chromosome is ONLY found in males. Males are XY Females are XX Does figure 12.2 show the chromosomes from a male or female? How do you know?

A single chromosome A set of 23 paired chromosomes of the body

Inheritance and Genetics Half of your genetic make-up comes from your mother, the other comes from your father BUT, then why don’t you look exactly like your brother, sister, mom or dad? The answer is HEREDITY: the passing of characteristics from parents to offspring In the mid-1800s, Gregor Mendel, an Austrian monk experimented with pea plants to show that traits do not happen by accident. He genetically crossed tall and short pea plants to see how height would be affected. After looking at the results of many generations of pea plants, he found that height was an inherited trait and that tall plants appeared more often because the tallness was a dominant trait (it was more likely to be passed on) compared to shortness, which was a recessive trait (not likely to be passed on)

Mendel’s Experiment Mendel took a tall plant purebred (SS) and short plant purebred (ss) and mated them, he then took the hybrid offspring (Ss) and mated 2 of them. Finally he looked at the offspring produced and found that 75% of the offspring were tall, hence tallness was the dominant trait. Anytime a big ‘S’ was in the genetic makeup the plant came out tall. Only if the plant was ‘ss’ then would it be short

Recording Inherited Traits Chromosomes come in pairs. Genes for traits also come in pairs Many traits are controlled by only one pair of genes, others are controlled by two or more pairs For traits controlled by one pair of genes, geneticist use 2 letters to represent the genotype:combination of genes Capital letters represent the dominant gene Lowercase letters represent recessive genes During reproduction, a chromosome separates and only one chromosome is passed on to the child (from both mother and father), dominant or recessive. The final combination in the child will determine what you inherit Punnett Squares help geneticists determine the probability that offspring will inherit certain traits

Punnett Squares Punnett Squares tell you genotypes: genetic combinations Punnett Squares also tell you phenotypes: appearances For example, all of the offspring will appear RED, since the gene A is dominant, so anytime it is in a pairing it will produce a bird that is RED, the recessive blue trait will only give a blue bird if it is found as ‘aa’ Problem: Do a Punnett Square of two ‘Aa’ birds mating and give the offspring AA aa X

Pedigrees A family tree or pedigree is used to trace traits in a family A pedigree is a diagram that shows the history of a trait from generation to generation Breeders often use pedigree charts to increase the likelihood of breeding an animal with desirable traits Doctors use pedigree charts to determine the likelihood of inheriting deadly diseases from your relatives

Pedigrees

Genetic Changes Most of the time the processes of cell reproduction and copying genes works well, BUT mistakes do happen during reproduction. Most of the time the body cells do a pretty good job of correcting mistakes and errors found in DNA, but occasionally the body cells do not repair the errors and the mistakes are passed on generation to generation Changes in genetic information can result in an abnormal gene called a mutation. Mutations can be due to environmental conditions/factors such as: UV light, chemicals like PCBs (which are found in cigarettes), nuclear radiation, and drugs. These factors that cause mutations are called mutagens Mutations can lead to genetic disorders such as sickle-cell anemia.

Issues in Genetic Research The Human Genome Project: The mapping of the complete set of chromosomes that make up the human body. The genome is the genetic instructions of what makes you who you are Scientists have mapped where each gene belongs on the 46 chromosomes This is truly a powerful thing! BUT, “With Great power comes great responsibility.” Pros: with the new knowledge scientists can transfer out mutated genes from your genome: Genetic Engineering. Genetic disorders can be elimniated. See pg. 223, Table 12.2 on Genetic Research Cons: Its not natural, Ethical concerns arise about who should be able to have genetic alterations done, cloning, Cloning: process of creating an identical copy of an original organism What do you think are some pros and cons of cloning?

Genetic Research Dolly: first animals, what is next, humans? Gene Therapy and Genetic Counseling -Genetic counsellors gather medical information about an individuals’ family and analyzes a his/her chromosomes to help predict the chances of that person developing a particular disorder