Chapter: The Role of Genes in Inheritance

2. Table of Contents Chapter: The Role of Genes in Inheritance Section 1: Continuing Life Section 2: Genetics—The Study of Inheritance

3. Continuing Life 1 Reproduction—The Importance of Reproduction • Organisms produce offspring through the process of reproduction. • Hereditary material is passed from parent to offspring during reproduction. • This material is found inside cells. It is made up of the chemical deoxyribonucleic (dee AHK sih rib oh nook lay ihk) acid, called DNA.

4. Continuing Life 1 Reproduction—The Importance of Reproduction • DNAcontrols how offspring will look and how they will function by controlling what proteins each cell will produce. • The DNA that all living things pass on determines many of their offspring’s characteristics. • Reproduction always involves the transfer of hereditary information.

5. Continuing Life 1 Life’s Code • DNA is found in all cells in structures called chromosomes. • All of the information that is in your DNA is called your genetic information. • You can think of DNA as genetic blueprint that contains all of the instructions for making an organism what it is.

6. Continuing Life 1 Life’s Code • If you could look at DNA in detail, you would see that it is shaped like a twisted ladder. • The two sides of the ladder form the backbone of the DNA molecule. • The sides support the rungs, which hold all the genetic information.

7. Continuing Life 1 Life’s Code • Each rung of the ladder is made up of a pair of chemicals called bases. • There are only four bases in DNA, and they pair up very specifically. • The sequence forms a code. From this DNA code the cell gets instructions about what substances to make, how to make them, and when to make them.

8. Continuing Life 1 Cell Division • Cell division has two big steps. First, DNA in the nucleus is copied. • Then the nucleus divides into two identical nuclei. • Each new nucleus receives a copy of the DNA. • Division of the nucleus is called mitosis (mi TOH sus). Click box to view movie.

9. Continuing Life • After mitosis has taken place, the rest of the cell divides into two cells of about equal size. 1 Cell Division • Almost all the cells in any plant or animal undergo mitosis.

10. Continuing Life • Cell division results in growth and replaces aging, missing, or injured cells. 1 Cell Division

11. Continuing Life 1 Reproduction by One Organism • Reproduction in which a new organism is produced from a part of another organism by cell division is called asexual (ay SEK shoo ul) reproduction. • In asexual reproduction, all the DNA in the new organism comes from one other organism.

12. Continuing Life 1 Reproduction by One Organism • Some one-celled organisms, such as bacteria, divide in half, forming two cells. • Before the one-celled organism divides, its DNA copies itself. • After it has divided, each new organism has an exact copy of the first organism’s DNA. • The two new cells are alike.

13. Continuing Life 1 Budding and Regeneration • Many plants and species of mushroom, and even a few animals reproduce asexually. • When an organism reproduces asexually, and a new individual grows on it, the process is called budding. • The bud has the same shape and characteristics as the parent organism. • The bud matures and eventually breaks away to live on its own.

14. Continuing Life 1 Budding and Regeneration • Many plants and species of mushroom, and even a few animals reproduce asexually. • When an organism reproduces asexually, and a new individual grows on it, the process is called budding.

15. Continuing Life 1 Budding and Regeneration • The bud has the same shape and characteristics as the parent organism. • The bud matures and eventually breaks away to live on its own.

16. Continuing Life • In a process called regeneration (rih je nuh RAY shun), some organisms are able to replace body parts that have been lost because of an injury. 1 Budding and Regeneration • Sea stars can grow a new arm if one is broken off. • Lizards, such as chameleons, can grow a new tail if theirs is broken off.

17. Continuing Life 1 Cloning • Making copies of organisms is called cloning. • The clone receives DNA from just one parent cell. • In the past, most cloning was done with plants. • Gardeners clone plants when they take cuttings of a plant’s stems, leaves, or roots. • They can grow many identical plants from one.

18. Continuing Life 1 Cloning • Only since the 1990s has cloning large animals become possible. • In 1997, it was announced that an adult Finn Dorset sheep had been cloned. • The new sheep, named Dolly, was the first successfully cloned mammal.

19. Continuing Life 1 Sex Cells and Reproduction • Humans, as well as many other organisms, are the products of sexual (SEK shoo ul) reproduction. • In sexual reproduction a new organism is produced from the DNA of two cells. Sexcells are the specialized cells that carry DNA and join in sexual reproduction.

20. Continuing Life 1 Production of Sex Cells • When a skin cell, a bone cell, or another body cell divides, it produces two new cells by cell division. • Each cell has DNA that is identical to the original cell. • A human body cell has 46 chromosomes arranged in 23 pairs. • Each chromosome of a pair has genetic information about the same things.

21. Continuing Life 1 Production of Sex Cells • Instead of being formed by cell division like body cells are, sex cells are formed by meiosis (mi OH sus). • Only certain cells in reproductive organs undergo the process of meiosis.

22. Continuing Life 1 Production of Sex Cells • Before meiosis begins, DNA is duplicated. • During meiosis, the nucleus divides twice. • Four sex cells form, each with half the number of chromosomes of the original cell. Click box to view movie.

23. Continuing Life • Human eggs and sperm contain only 23 chromosomes each—one chromosome from each pair of chromosomes. 1 Production of Sex Cells • When a human egg and sperm join in a process called fertilization,the result is a new individual with a full set of 46 chromosomes.

24. Continuing Life 1 Sex Cells in Plants • Plants can reproduce sexually. • Flowers contain structures for reproducing. • Male flower parts produce pollen, which contains sperm cells. • Female flower parts produce eggs.

25. Continuing Life 1 Sex Cells in Plants • When a sperm and an egg join, a new cell forms. • In most flowers, rapid changes begin soon after fertilization. • The cell divides many times and becomes enclosed in a protective seed. • The petals and most other flower parts fall off. • A fruit that contains seeds soon develops.

26. Section Check 1 Question 1 _______ controls how offspring will look and how they will function by controlling what proteins each cell will produce.

27. Section Check 1 Answer The answer is DNA. All the information in your DNA is called your genetic information.

28. Section Check 1 Question 2 Which of the following best describes the process occurring in picture one? A. budding B. sexual reproduction C. regeneration D. fission

29. Section Check 1 Answer The answer is A. Budding is a type of asexual reproduction made possible by cell division which results in an exact copy of the adult.

30. Section Check 1 Question 3 _______ always involves the transfer of hereditary information. Answer The answer is reproduction. Without reproduction, species could not continue.

31. Genetics—The Study of Inheritance 2 Heredity • Heredity (huh REH duh tee) is the passing of traits from parents to offspring. • Eye color, hair color, skin color, nose shape, and many other features, including those inside an individual that can’t be seen, are traits that are inherited from a person’s parents.

32. Genetics—The Study of Inheritance 2 Heredity • A trait is a physical characteristic of an organism. • The study of how traits are passed from parents to offspring is called genetics(juh NE tihks).

33. Genetics—The Study of Inheritance 2 Genes • All traits are inherited. • Half of your genetic information came from your father, and half came from your mother. • This information was contained in the chromosomes of the sperm and egg that joined and formed the cell that eventually became you.

34. Genetics—The Study of Inheritance 2 Genes • Inherited traits, such as hair and eye color, are controlled by genes on chromosomes. • Characteristics such as manners are called acquired skills. • Acquired skills are not determined by genes.

35. Genetics—The Study of Inheritance 2 Genes • All chromosomes contain genes (JEENZ). • A gene is a small section of DNA on a chromosome that has information about a trait. • Humans have thousands of different genes arranged on 23 pairs of chromosomes.

36. Genetics—The Study of Inheritance 2 Genes • Genes control all of the traits of organisms—even traits that can’t be seen, such as the size and shape of your stomach and your blood type. • Genes provide all of the information needed for growth and life.

37. Genetics—The Study of Inheritance 2 What determines traits? • One pair of chromosomes can contain genes that control many different traits. • Each gene on one chromosome of the pair has a similar gene on the other chromosome of the pair. • Each gene of a gene pair is called an allele (uh LEEL)

38. Genetics—The Study of Inheritance 2 What determines traits? • The genes that make up a gene pair might or might not contain the same information about a trait. • If a pair of chromosomes contains different alleles for a trait, that trait is called a hybrid (HI brud). • When a trait has two identical alleles, it’s called pure.

39. Genetics—The Study of Inheritance 2 Dominant and Recessive Alleles • The combination of alleles in a gene pair determines how a trait will be shown, or expressed, in an organism. • Dominance (DAH muh nunts) means that one allele covers over or masks another allele of the trait.

40. Genetics—The Study of Inheritance 2 Dominant and Recessive Alleles • For instance, if a pea plant has one purple-flower allele and one white-flower allele or two purple-flower alleles, its flowers will be purple. • Purple is the dominant flower color in pea plants.

41. Genetics—The Study of Inheritance 2 Dominant and Recessive Alleles • The dominant allele is seen when the trait is hybrid or dominant pure. • White flowers, the masked allele, are said to be recessive. • Recessive alleles are seen only when a trait is recessive pure.

42. Genetics—The Study of Inheritance 2 Dominant and Recessive Alleles • Humans also have traits that are controlled by dominant and recessive alleles. • To show a dominant allele, a person can have either one or two alleles for the trait. Click image to view movie.

43. Genetics—The Study of Inheritance 2 Expression of Traits • The environment can play an important role in the way that a trait is shown, or expressed. • Human hair color and skin color are traits that are coded for by genes, but the environment can change the way that the traits appear. • The environment can affect the expression of traits in every kind of organism, including bacteria, fungi, plants, and animals.

44. Genetics—The Study of Inheritance 2 Expression of Traits • Sometimes the effect of the environment allows adaptations that aid a species survival. • For example, in the winter months, the arctic fox does not produce fur pigment, and its fur appears white. As a result, the fox blends with the snow, helping it to avoid predators.

45. Genetics—The Study of Inheritance 2 Passing Traits to Offspring • The traits that an organism will inherit depend upon which genes are carried in each plant’s sex cells. • In sex cell formation, pairs of chromosomes duplicate, then separate as the four sex cells form. • Gene pairs also separate. As a result, each sex cell contains one allele for each trait.

46. Genetics—The Study of Inheritance 2 Passing Traits to Offspring • In fertilization, one sperm will join with one egg. Many events, such as flipping a coin and getting either heads or tails, are a matter of chance. In the same way, chance is involved in heredity.

47. Genetics—The Study of Inheritance • Suppose a hybrid purple-flowered pea plant (one with two different alleles for flower color) is mated with a white-flowered pea plant. 2 Passing Traits to Offspring

48. Genetics—The Study of Inheritance • Because the purple flowered plant is a hybrid, half of its sex cells contain the purple-flower allele and half contain the white-flowered allele. 2 Passing Traits to Offspring

49. Genetics—The Study of Inheritance 2 Differences in Organisms • The inherited genes from his or her parents determine hair color, skin color, eye color, and other traits. • Variations (vayr ee AY shuns) are the different ways that a certain trait appears. • They result from permanent changes in an organism’s genes. • Some gene changes produce small variations, and others produce large variations.

50. Genetics—The Study of Inheritance 2 Differences in Organisms • Flower color in pea plants shows a simple pattern of inheritance. • Sometimes, though, the pattern of inheritance of a trait is not so simple. • Many traits in organisms are controlled by more than two alleles. • For example, in humans, multiple alleles A, B, and O control blood types A, B, AB, or O.