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Classical Genetics Gregor Mendel.

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Presentation on theme: "Classical Genetics Gregor Mendel."— Presentation transcript:

1 Classical Genetics Gregor Mendel

2 The Work of Gregor Mendel
Genetics: the scientific study of heredity, or how traits are passed from one generation to the next Gregor Mendel’s Peas - Mendel was an Austrian monk who is credited as the “father of genetics.”

3 The Work of Gregor Mendel
- Mendel began working with pea plants that were true-breeding, meaning that if allowed to self pollinate, they would only produce offspring identical to themselves -ex. Tall plants produce tall plants, green seeded plants produce green seeded plants

4 The Work of Gregor Mendel
Genes and Dominance - Mendel studied 7 different plant traits. Traits are characteristics such as height or flower color.

5 The Work of Gregor Mendel
Seed Shape Seed Color Seed Coat Color Pod Shape Flower Position Pod Color Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall

6 The Work of Gregor Mendel
- Mendel called the original plants the P (parent) generation. The offspring were the F1 (first filial) generation . - the offspring of crosses between parents of different traits are called hybrids

7 The Work of Gregor Mendel
Mendel's F2 Generation F1 Generation F2 Generation P Generation Tall Tall Tall Short Tall Tall Tall Short

8 11-1 The Work of Gregor Mendel
From his experiments, Mendel drew two conclusions 1) biological inheritance is determined by factors that are passed from one generation to the next. Today we call these factors genes. - the different forms of a gene are called alleles

9 The Work of Gregor Mendel
ex. gene (trait) is eye color alleles (forms) are blue, brown, green, etc. 2) the second conclusion is called the principle of dominance - the principle of dominance states that some alleles are dominant and others are recessive

10 The Work of Gregor Mendel
Segregation - Mendel saw that some forms of traits would disappear during the F1 generation, but reappear during the F2 generation - he explained this by showing that the alleles segregated during the formation of gametes, or sex cells.

11 The Work of Gregor Mendel

12 Section Quiz Gametes are also known as genes. sex cells. alleles.

13 Section Quiz The offspring of crosses between parents with different traits are called alleles. hybrids. gametes. dominant.

14 Section Quiz In a cross of a true-breeding tall pea plant with a true-breeding short pea plant, the F1 generation consists of all short plants. all tall plants. half tall plants and half short plants. all plants of intermediate height.

15 Section Quiz If a particular form of a trait is always present when the allele controlling it is present, then the allele must be mixed. recessive. hybrid. dominant.

16 Probability and Punnett Squares
Genes and Probability - the likelihood that an event will occur is called probability ex. a coin landing on heads has a probability of 50% - the principle of probability can be used to predict the outcome of genetic crosses

17 Probability and Punnett Squares
- the gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square

18 Probability and Punnett Squares

19 Probability and Punnett Squares
Organisms that have two identical alleles for a particular trait are called homozygous. ex. TT Organisms that have two different alleles for a particular trait are called heterozygous ex. Tt

20 Probability and Punnett Squares

21 Probability and Punnett Squares
The physical characteristics of an organism are called its phenotype ex. tall plant The genetic makeup of an organism is its genotype ex. TT or Tt

22 Section Quiz Probability can be used to predict
average outcome of many events. precise outcome of any event. how many offspring a cross will produce. which organisms will mate with each other.

23 Section Quiz Compared to 4 flips of a coin, 400 flips of the coin is
more likely to produce about 50% heads and 50% tails. less likely to produce about 50% heads and 50% tails. guaranteed to produce exactly 50% heads and 50% tails. equally likely to produce about 50% heads and 50% tails.

24 Section Quiz Organisms that have two different alleles for a particular trait are said to be hybrid. heterozygous. homozygous. recessive.

25 Section Quiz Two F1 plants that are homozygous for shortness are crossed. What percentage of the offspring will be tall? 100% 50% 0% 25%

26 Exploring Mendelian Genetics
Independent assortment - the principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes ex. Seed color does not depend on seed shape

27 Exploring Mendelian Genetics

28 Exploring Mendelian Genetics
Beyond dominant and recessive alleles - some alleles are neither dominant nor recessive , and many traits are controlled by multiple alleles or multiple genes

29 Exploring Mendelian Genetics
Incomplete dominance or Codominance - the heterozygous phenotype is somewhere between the two homozygous phenotypes ex. red flower + white flower = pink Punnett square animation

30 Exploring Mendelian Genetics

31 Exploring Mendelian Genetics
Multiple alleles - multiple alleles contribute to the phenotype ex. Blood type (i, IA, IB) Type O = i i Type A = IA IA or IA i Type B = IB IB or IB i Type AB = IA IB

32 Exploring Mendelian Genetics

33 Exploring Mendelian Genetics
Polygenic traits - two or more genes control the outcome of a particular trait ex. Skin color in humans is controlled by the combinations of 4 different genes

34 Exploring Mendelian Genetics

35 Section Quiz In four o'clock flowers, the alleles for red flowers and white flowers show incomplete dominance. Heterozygous four o'clock plants have pink flowers. white flowers. half white flowers and half red flowers. red flowers.

36 Section Quiz Mendel's principles apply to pea plants only.
fruit flies only. all organisms. only plants and animals.

37 Human Heredity Human Chromosomes
A typical human body cell contains 46 chromosomes - 44 autosomes and 2 sex chromosomes Chromosomes are arranged in a karyotype, a picture of the chromosomes

38 Human Heredity

39 Human Heredity Males and females differ in the sex chromosomes they contain - males are XY - females are XX All egg cells carry a single X chromosome. However, half of all sperm cells carry a X chromosome while half carry a Y chromosome.

40 Human Heredity

41 Human Heredity Human Traits
Scientists use a pedigree to help study how traits are passed from one generation to the next. Pedigree: a chart which shows the relationships within a family Pedigree animation

42 Human Heredity Square = Male Circle = Female Parental line
Marriage line carrier of the trait not shaded = does not express the trait shaded = express the trait

43 Human Heredity Since most human traits are polygenic (many genes), they can not be traced to a single parent Many genes have been discovered through the study of genetic disorders - they can be dominant or recessive

44 Human Heredity In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder

45 Human Heredity Cystic Fibrosis
- caused by a recessive allele on chromosome 7 - causes digestive and respiratory problems - only half of people with CF live into their 20s

46 Human Heredity

47 Human Heredity Sickle Cell Disease
- causes hemoglobin to be less soluble - changes the shape of red blood cells; become bent into the sickle-shape

48 Human Heredity Malaria and the Sickle Cell Allele
Regions where malaria is common Regions where the sickle cell allele is common

49 Section Quiz A chromosome that is not a sex chromosome is know as a(an) autosome. karyotype. pedigree. chromatid.

50 Section Quiz An individual with a blood type phenotype of O can receive blood from an individual with the phenotype O. A. AB. B.

51 Human Chromosomes Human genes and chromosomes
- on each chromosome there is the information for several hundred genes ex. Gene for ALS is on 22nd chromosome

52 Human Chromosomes Sex-linked genes: genes located on the X or Y chromosome ex. colorblindness, hemophilia, muscular dystrophy Males have only 1 X chromosome and cannot be heterozygous for the trait. Females can be carriers (heterozygous).

53 Human Chromosomes Father (normal vision) Normal vision Colorblind Male
Female Daughter (normal vision) Son (normal vision) Mother (carrier) Daughter (carrier) Son (colorblind)

54 Human Chromosomes Chromosomal disorders
The most common error occurs when homologous chromosomes fail to separate during meiosis. This is called nondisjunction.

55 Homologous chromosomes fail to separate
Human Chromosomes Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II

56 Human Chromosomes

57 Human Chromosomes If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may result. - Down syndrome results from a nondisjunction of the 21st chromosome - Turner’s syndrome (XO) and Klinefelter’s syndrome (XXY)


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