Genetics 11 1 Learning Targets I can explain

Genetics 11. 1

Learning Targets �I can explain how genes pass traits from parents to offspring � I can describe the role of chromosomes in heredity � I can identify patterns of heredity in humans � I define genetics, dominant gene, recessive gene, genotype, and phenotype

Genetics Experiments Human Heredity Twins Mendel Applied Genetics Genetic Diseases Morgan Environment Selective Breeding Genetic Engineering

Genetics and Heredity � Genetics � What is the study of heredity is heredity? › The passing on of traits from parents to offspring › All organisms pass information (DNA) about traits to their offspring

Mendel � More than 100 years ago, a scientist named Gregor Mendel made important discoveries about heredity � He took seeds from tall pea plants and planted them. � Some plants were tall, but some were short. WHY? ?

Mendel’s Studies � Mendel decided to study pea plants and their seeds � He wanted to grow only tall pea plants � Since the flowers of pea plants have both male and female sex organs, Mendel tried self-pollination � Self-pollination occurred when Mendel moved pollen from the male sex organs to the female sex organs on the same plant

Mendel’s Studies (cont. ) � After self-pollination occurred, each flower produced seeds � Mendel planted the seeds and then selfpollinated the plants that grew from those seeds � He did this again and again � Finally, Mendel had seeds that produced only tall pea plants (pure tall seeds)

The “P” Generation � Using the same self-pollination process, Mendel grew only short plants as well (pure short seeds) � Mendel �P called these plants the P Generation. stands for the parent generation

Cross-Pollination � Eventually, Mendel wanted to know what type of offspring two different pure parent plants would make � He used the process cross-pollination to find out. � Cross pollination is the movement of pollen from the male sex organs to the female sex organs of a different plant

The F 1 Generation � So Mendel moved the pollen from pure tall pea plants to the female sex organs of pure short pea plants (and vice versa) � When the seeds produced plants, Mendel took the seeds from those flowers and planted them. � He called these plants the F 1 Generation � F stands for filial (son or daughter)

Results of F 1 Plants � Mendel found that all F 1 Generation plants were tall � He crossed hundreds of pure short plants with pure tall plants � All the results were similar…tall plants � What happened to the short trait? ?

Punnett Squares Short pure P generation T T t Tt Tt (tall) Tall pure P generation F 1 Generation All tall

Punnett Squares � Mendel used these to explain his crosses �A gene is the information that a parent passes to its offspring for a trait �A pea plant inherits two genes for height (one gene received from each parent)

Genes �A gene that is hidden when it is combined with another gene is called a recessive gene (lower case letter) � The gene that shows up is called the dominant gene (capital letter) � All pea plants were tall, so the dominant gene is tallness

Genotypes and Phenotypes � An organism’s combination of genes for a trait is called its genotype � For example, the genotype of the F 1 pea plants is Tt � What an organism looks like as a result of its genes is its phenotype � The phenotype of the F 1 pea plants was tall

The F 2 Generation � Mendel then self-pollinated the F 1 Generation plants � Mendel found that short plants started showing up again (25% of the time) � This F 2 Generation always included short plants � Short plants reappeared because in the F 2 Generation, the plants inherited two recessive genes for shortness

Punnett Square T T t TT Tt (tall) F 2 Generation F 1 Generation (Tt) t F 1 Generation (Tt) Tt tt (tall) (short) ¾ Tall ¼ Short

Mendel’s Conclusions � Mendel concluded that there was information in a plant that caused it to have certain traits � The dominant genes hid the appearance of recessive genes � The offspring receive half their genes from one parent and half from the other

Vocabulary � Genetics � Self-pollination � Cross-pollination � Dominant � Self Gene Genotype Phenotype Gene Recessive Gene Check questions, pg. 238 #1 -5 � COMPLETE SENTENCES

What are Chromosomes? 11. 2

What are Chromosomes? � Rod-shaped structures made of proteins and a chemical called DNA � Found �A in the nucleus of the cell chromosome can contain hundreds of genes, which determine all the traits of an organism

Mitosis Review � Basic › › steps to Mitosis: Chromosomes make a copy of themselves Nuclear membrane dissolves The two sets of chromosomes separate A nucleus forms around each set of chromosomes › RESULT: Two new identical cells each with a nucleus and set of chromosomes

Mitosis and Cell Division � Following mitosis, the entire cell divides � Each new cell gets one nucleus with a complete set of chromosomes � Each set of chromosomes is identical to the parent’s (new cell is identical to parent cell)

Sexual Reproduction � Two gametes (sex cells) join to form one complete cell � Each gamete has only half of the chromosomes of other cells in the body � When gametes join, they form a cell that has a complete set of chromosomes

How Many Chromosomes? � Most human have 46 chromosomes in their body cells � Sperm cells and egg cells only have 23 chromosomes each � Sperm and egg join to form a cell called a zygote with 46 chromosomes total � Together, the 46 human chromosomes carry 50, 000 -100, 000 genes

Meiosis Review � Basic › › steps to Meiosis: Chromosomes make a copy of themselves The cell divides into two new cells Each new cell then divides again RESULT: One parent cell results in four new sex cells › **Each sex cell contains half the number of chromosomes of the parent cell

Sex Chromosomes � Humans have 46 chromosomes; they consist of 23 pairs � Each chromosome that makes up a pair comes from a different parent � For 22 of the pairs, the two chromosomes look alike � However, the chromosomes that make up the 23 rd pair look different from each other these are sex chromosomes

Sex Chromosomes (cont. ) � These two chromosomes determine a person’s sex � There are two types of sex chromosomes › X and Y › Females have two X chromosomes › Males have one X and one Y chromosomes

How are sex chromosomes passed? � Parents pass one of their sex chromosomes on to their offspring �A male can pass an X or a Y chromosome to its offspring �A female can only pass an X chromosome to its offspring

Human offspring � Human offspring have a 50% chance of being male or female Male Parent X Y X X XX XX (female) XY XY (male) Female parent Offspring 50% chance of being female (XX) 50% chance of being male (XY)

Thomas Morgan � Morgan used fruit flies rather than pea plants to learn about chromosomes and genes � Fruit flies are easy to study because: › › Their cells have only 4 pairs of chromosomes The chromosomes are large; easy to see Fruit flies reproduce quickly It’s easy to tell the female fly from the male

Sex-Linked Traits � Traits that are linked to the sex of an organism are called sex-linked traits � Fruit flies usually have red eyes � Morgan noticed one male fly with white eyes � He mated the white-eyed male with a red-eyed female

Results � This resulted in the F 1 Generation and all flies had red eyes (dominant trait) � Morgan found that when he mated flies from his F 1 Generation to produce an F 2 Generation, some flies had white eyes and some had red � However, all white-eyed flies were male

Results (cont. ) � Morgan concluded that the white eye color in fruit flies is linked to the sex of the fly �A female fruit fly has two X chromosomes �A male has one X and one Y chromosome

� Morgan found that the gene for eye color in fruit flies is on the X chromosome � There is no gene for eye color on the Y chromosome � This explains why eye color in fruit flies is a sex-linked trait

Vocabulary � Sex Chromosome � Sex-linked Trait � Carrier � Self-Check questions, pg. 245 � COMPLETE SENTETCES!!

How is Heredity studied in Humans? 11. 3

Human Genetics � Human genetics is the study of how humans inherit traits � Humans have more chromosomes, do not reproduce quickly, and cannot be used in experiments � Scientists study heredity in humans by studying identical twins

Different kinds of Twins � Identical Twins › Sperm and egg join, form one zygote › Zygote divides into two cells that separate › Cells have identical genes � Fraternal Twins › Form from two different zygotes › Zygotes develop into offspring with different sets of genes

Heredity and Environment � Your genes determine your skin color, eye color, body shape, and other characteristics � But your environment can also affect your characteristics � Scientists study identical twins who have been separated since birth � Both twins have identical genes, but grew up in different environments

The Influence of Environment � Food, sunlight, air and other parts of the environment can affect characteristics �A person who doesn’t have good nutrition may not grow tall, even though they have the gene for tallness � X-rays and some types of chemicals cause changes in genes, called mutations

DNA � DNA in chromosomes is the material that contains an organism’s genes � DNA passes the genes from one cell to another during cell division � DNA is a large molecule shaped like a twisted ladder � The rungs of the ladder are made of four different kinds of molecules called bases

Bases � The order of the bases in the DNA of a cell provides a code for all the information that the cell needs to live � Different organisms have different orders of bases � The greater the difference between organisms, the greater the difference in order of bases � The four bases are abbreviated as: › T, A, C, and G

Difference of Bases � The order of bases in a frog’s DNA is very different from the order of bases in human DNA � But, the difference in the order of bases between your DNA and your friend’s DNA is not as great � The order of bases in a gene for hair color, for example, determines whether the hair will be black, red, brown, or blonde

DNA Replication � DNA can replicate, or copy, itself � DNA molecules are held together at the rungs of the ladder � The bases pair up in certain ways � When DNA replicates, it first splits down the middle of its rungs � The paired bases separate, then new bases pair with the separated bases

� The result is two identical copies of the original DNA molecule � DNA replication occurs every time a cell divides normally � Pairing of Bases: › Base A pairs with Base T › Base C pairs with Base G

Mutations � Sometimes there is a change in the order of bases in a DNA molecule � Parts of the environment and chemicals can cause mutations � Mutations cause changes in genes � Genes determine traits, so any mutation can affect the traits of an organism

Genetic Diseases � Mutations can be harmful, helpful, or have no effect to the organism � A genetic disease is a disease that results from the genes a person inherits � Recessive genes cause most genetic diseases � That means a person must inherit the recessive gene from both parents in order to have the disease

Inbreeding �A gene pool is all the genes that are found within the population � The larger the population, the larger the gene pool � People living in a small population, often mate others who may have the same or similar genes � Sexual reproduction among people in a small gene pool is called inbreeding

Diseases � Inbreeding can cause a disease called hemophilia � This disease causes the blood to not have a certain protein that it needs to clot or clump � People who have hemophilia bleed excessively when slightly injured � Hemophilia was known as the “Royal Disease” WHY? ?

Human Sex-linked Traits �A number of human traits are sex-linked � The gene for color blindness in sex-linked � Color blindness is more common in males because the recessive gene is found on the X chromosome � Hemophilia and muscular dystrophy are also sex-linked � Both are found on the X chromosome, so they are both more common in males

Vocabulary � Mutation � Base � Genetic Disease � Self-Check Replicate Gene Pool Inbreeding Questions, pg. 251 � COMPLETE SENTENCES!!

What is Applied Genetics? 11. 4

Applied Genetics � Farmers use breeding techniques to grow hardier and better-tasting crops � Animal breeders use breeding techniques to make prizewinning horses � These are examples of people affecting the traits that organisms inherit

Useful Mutations �A mutation that results in an animal with white fur would be helpful to that animal in a snowy region � Over long periods of time, mutations may lead to changes in population � This is one way that new species are formed

Selective Breeding � Farmers and scientists use their knowledge of genetics to produce new varieties of plants and animals � Selective breeding is selecting useful mutations and breeding organisms so the mutation shows up again � Examples: Short legged sheep, cows that produce large amounts of milk, pink grapefruits and navel oranges

Breeding Racehorses � Selective breeding is used to produce great race horses � The breeder will select two parents with desirable genes � The will also select parents that have good temperaments � An animal’s genes also affect its behavior

Genetic Engineering � The process of introducing new genes into an organism is genetic engineering � Began in the 1970’s when scientists transferred genes from one species of bacteria to another species of bacteria � Today, scientists transfer genes between entirely different organisms � Used to treat certain diseases or conditions of plants and animals

Vocabulary � Applied Genetics � Selective Breeding � Genetic Engineering � Self-Check questions, pg. 256 � COMPLETE SENTENCES!!