3.0 DNA is the inherited material responsible for variation

Captive breeding programs enable scientists to control populations of species at risk of extinction. Using modern technology, geneticists and staff from zoos around the world can analyze the genetic code of the species they are trying to save and use it to introduce variation that will help the species survive when the environment changes. Eg.Bengal tiger

Selective Breeding in Dogs Selective breeding, or breeding organisms for specific features or behaviors, has been done for thousands of years. The Great Pyrenees (#2) is one of the oldest-known dog breeds, bred several thousand years ago to protect sheep herds from wolves(#1) and bears. The dachshund (#3) was bred about 600 years ago to hunt badgers in their underground dens. The toy poodle (#4), a product of the mid-twentieth century, was bred to provide dog lovers with the intelligence and sensitivity of the large poodle in a much smaller form. experiment_shortfilms

3.1 DNA - Transmitter of Genetic Code Characteristics are passed on from one generation to another through the genetic code of the parents. DNA is the genetic code or “blueprint” for all life. All living organisms contain DNA in the nucleus of their cells. Deoxyribonucleic acid (DNA) is the inherited material responsible for variation.

DNA and the Genetic Code 1869: DNA is first identified 1944: Canadian scientist Oswald Avery confirms that DNA is in fact responsible for genetic inheritance and asks the question, “how can the blueprint for so many different organisms be passed on by what seems to be the exact same molecule?”

James Watson and Francis Crick unraveled the structure of DNA, revealing how the same chemical building blocks can carry a wide range of instructions.

Every DNA molecule contains exactly the same chemicals. DNA is like a ladder twisted into a spiral.

The sides of the ladder are the same in all DNA molecules. The rungs are what make the variations. Each rung pairs up two of the following chemicals: guanine (G), cytosine (C), adenine (A), and thymine (T). The arrangement of these four chemicals creates the code that the cells are able to interpret. This is the genetic code of the organism.

Q: Which chemicals always pair up together? A:

Chromosomes DNA contains all the instructions for an organism's characteristics. If the DNA from a single human body cell were stretched out it would be about 2m long! To fit all that DNA into a single cell it is arranged in compact packages called chromosomes. In plants and animals, chromosomes are stored in the cell nucleus.

Every human cell contains 46 chromosomes,containing all the instructions for making a human. In each cell, 23 chromosomes came from their mother’s egg cell, and 23 came from their father’s sperm cell. Not all organisms have the same number of chromosomes ( A dog cell has 78, cats have 38, so dog cells have 39 pairs, cats have 19 pairs). Not all chromosomes from species to species are the same, which accounts for the different characteristics between species.

Sex Chromosomes The 23rd pair of chromosomes are called sex chromosomes because they carry information about sexual characteristics and determine sex of the individual. If the 23rd pair is XX you are female and if it is XY you are male.

Genes A single gene is an uninterrupted segment of DNA containing coded instructions for a particular trait. Genes are located on the chromosomes. Each chromosome has many genes. Genes come in pairs (one from each parent). Both genes in a pair carry instructions for the same trait (eg. hair color, height...) Gene pairs occupy matching locations on the two chromosomes. DNA code may not be exactly the same in both locations. eg. the parents may have different eye colors. Q: How many genes does the DNA found in the 46 chromosomes of each human cell contain? (p. 39)

Offspring inherit genes from both parents. Different forms of a gene are called alleles (eg. straight hairline or widow’s peak hairline) The ultimate combination of the chromosome pair is what makes variation possible.

Two chromosome pairs. Different alleles are marked with uppercase or lowercase letters.

OK, let’s get this straight... DNA is packaged into chromosomes Each chromosome contains many genes Genes are coded instructions for specific traits Different variations of the same gene are called alleles

Much of what we know today about genes comes from research done on fruit flies. Do Check and Reflect p.45 #1-4, and 8 Read the info BIT on p.46 Q: what did scientists believe about reproduction until the 1600’s?

3.2 Cell Division A. Cell Division and Asexual Reproduction Asexual reproduction involves only one parent. All of the offspring are genetically identical to the parent. In single celled organisms, binary fission enables the parent cell to split its contents equally between the two new cells. Prior to division the parent cell duplicates its DNA. When the split takes place each new cell receives a complete exact copy of the parent’s DNA.

Binary Fission in Single Cellular Organisms

We will look at two types of cell division in multicellular organisms: Mitosis and Meiosis

1. Mitosis During mitosis a cell divides into 2 daughter cells, each containing the same number of chromosomes as the parent cell. Q: parent cell - 46 chr; 2 daughter cells - Before division, DNA is replicated (doubled) and then the cell divides. Mitosis occurs during growth and tissue repair. Mitosis Animation

A More Detailed Look at Mitosis

2. Meiosis A type of cell division that produces four daughter cells, each with only half the DNA of the parent cell. Q: parent- 46 chr; 4 daughters- This process involves two cell divisions. Meiosis occurs to produce gametes (sex cells) for sexual reproduction. Q: male gametes = female gametes = Meiosis Animation

Meiosis

Comparison: Mitosis vs. Meiosis

B. Cell Division and Sexual Reproduction in Plants and Animals Sexual reproduction involves joining the gametes of two individual organisms. Offspring produced contain genes from both parents, and are therefore genetically different from either parent. Half the DNA is from one parent and half from the other parent, resulting in a unique offspring. During sexual reproduction, specialized sex cells (gametes) unite to form a zygote, which develops into the new organism.

Gametes contain only half the number of chromosomes that other cells from the organism contain That way when male and female gametes unite, the offspring has the correct number of chromosomes Q: human gametes have ____chromosomes.

Do “Give it a Try” p.48 And Check and Reflect p.48 #1-4,6, and 7

3.3 Patterns of Inheritance Long before the science of genetics, people tried to produce organisms with only the most preferred traits by allowing only the organisms with the most desirable traits to reproduce. (artificial selection) This method was not always successful, but through time (trial and error), this practice of controlled breeding provided scientists with the information to detect certain basic patterns of inheritance.

Gregor Mendel Gregor Mendel was an Augustinian monk and is known as the "father of modern genetics". He used artificial selection to cross pollinate pea plants and was the first person to trace the characteristics of successive generations of a living thing. He established the concept of dominant and recessive traits. Mendel Video Patterns of Inheritance Video Mendel Rap

Between 1856 and 1863, Mendel bred over pea plants and analyzed how traits, or characteristics, were passed from parent to offspring. His work was largely ignored until supporting evidence began to emerge in 1900, about 16 years after his death.

Purebred vs. Hybrid To produce purebred organisms, breeders choose purebred parents (parents whose ancestors have produced only the desired characteristic). Eg. Tall X Tall This is called true-breeding. If a breeder chooses two different 'true- breeds' then a hybrid is produced. eg. Tall X Short

Dominant Traits Crossbreeding two different true-breeds results in all of the offspring having the same characteristic (the dominant trait). Only the DNA instructions for the dominant trait are expressed. Dominant traits are represented by an upper case letter, and recessive by the lowercase of the same letter. Crossing round (R ) and wrinkled (r) plants produce all round plants because the round trait is dominant over wrinkled.

Dominant Traits Mother (Pure Bred White) Father (Pure Bred Black) Offspring (Hybrid Black) Q: Which trait is dominant?

Recessive Traits When crossbreeding hybrids, the average results will produce 75% of the offspring with the dominant trait and 25% of the offspring with the recessive trait. A recessive trait only appears in the offspring if two recessive alleles are inherited.

Recessive Traits Father (Hybrid Black) With one black and one white allele Mother (Hybrid Black) With one black and one white allele Offspring 75% Black 25% White

The gametes of parents only have one allele for a trait, so offspring receive 2 alleles for any trait in four possible combinations.

Pea plants: dominant trait recessive trait

The Punnet Square: a diagram that is used to predict the outcome of a particular cross or breeding experiment. Note: Capital letters represent dominant traits

What fur color will the four offspring have? Punnet Square Calculator: Click Here!

Other Patterns of Inheritance Incomplete dominance When the alleles are neither dominant, nor recessive both alleles are expressed as an intermediate form of the trait (a combination of the two traits). Eg. red X white = pink 4 o’clock flower

Co-dominance Both alleles are equally dominant so both traits are expressed. Eg. red X white = roan coat color (white and red hairs) Red shorthorn bullWhite shorthorn cow Roan shorthorn heifer

Offspring unlike Either Parent. More than one gene location or set of alleles may be responsible for some traits. eg. Hair color, eye color, skin color The complex mixing of the possible combinations for that particular trait may account for the variation of traits an offspring has.

The effect of polygenic traits is sometimes additive and sometimes subtractive. Skin color is a good example of a trait that is affected by two genes with an additive effect: The effect of polygenic traits is sometimes additive and sometimes subtractive. Skin color is a good example of a trait that is affected by two genes with an additive effect: Black SkinAABB Dark SkinAABb or AaBB Intermediate AaBb or AAbb or aaBB Light SkinAabb or aaBb White Skinaabb The more dominant genes present, the darker the phenotype.

Environmental Factors can also have a bearing on how DNA is interpreted and developed. Fetal alcohol syndrome is a result of alcohol consumption during the developing stages of the offspring. The alcohol affects the DNA and the fetus may not develop normally. Taking drugs can also affect the DNA and defects in the organism can occur. Eg.Thalidomide use resulted in children being born without limbs

Do Check and Reflect P.54 #1-4, and 6 Do Section Review P.55 # 2,4,5,6,8, and 10

Here’s a cool genetics link: Science Museum Link Science Museum Link line/genes/index.asp

To review for Unit A Exam: P.84 S1 2,6,7,9 S2 11, S S , 32,39 Use exambank or quest a+, KEY booklet, and do the practice test in your booklet!