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Genetics: The Science of Heredity

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1 Genetics: The Science of Heredity
Lesson 1 A Priest-Scientist Gregor Mendel

2 Who was Gregor Mendel? Gregor Mendel was an Austrian monk.
He lived between 1822 to 1884. He was a teacher & a botonist He did experiments on hundreds of pea plants. Why Pea Plants? Simple genetic make up Traits are easily observed Can cross-pollinate or self-pollinate

3 Heredity Father of Genetics
Mendel’s work with pea plants has become the basis of genetics, the study of heredity. Heredity is the passing of traits from parents to offspring.

4 Mendel’s Pea Experiments
He crossed plants with two different traits, for example purple flowers with white flowers. He started his experiments with purebred plants known as True Breeders. Purebred plants ALWAYS produce offspring with the same trait as the parent. For example, if the parent is tall, all offspring will be tall. If the parent is short, all offspring will be short.

5 Some Pea Traits that Mendel Studied

6 F1 Generation Mendel called the parent plants the P generation.
He called the offspring from the parents the F1 generation. F is from the Latin word, filial, which means son. When Mendel crossed pure pea plants with purple flowers with pure pea plants with white flowers, all the F1 generation had purple flowers. P Generation (Parent Plants) F1 Generation, Offspring of the Parent Plants

7 F2 Generation When he crossed the F1 generation peas with one another, only some of the offspring had purple flowers. These formed the F2 generation. Mendel found that in the F2 generation, ¾ of the plants had purple flowers and ¼ of them had white flowers (3:1 ratio). F1 Generation, offspring of Parent Plants F2 Generation, offspring of F1 Generation

8 Lesson 1 Review 1. Who was Gregory Mendel?
2. Why did he choose peas for his experiments? 3. What is heredity? 4. What is genetics? 5. What is a purebred plants? 6. What is the P generation? 7. What is the F1 generation? 8. What is the F2 generation?

9 Understanding Mendel’s Experiments
Lesson 2 Understanding Mendel’s Experiments

10 Dominant and Recessive Traits
It seemed to Mendel, that for each characteristic in peas, one trait was stronger than the other. He called the “stronger” one, the dominant trait. He called the “hidden” one, the recessive trait. This has become known as “Mendel’s Principle of Dominance”

11 Genes and Alleles The traits of peas (and yours) are controlled by factors that scientists call genes. You inherit your genes from your parents. The different forms of a gene are called alleles. You inherit a combination of two alleles from your parents.

12 Dominant and Recessive Traits in Peas
For each of the 7 traits that Mendel studied in peas, there is a dominant allele and a recessive allele. If a plant inherits both a dominant allele and a recessive allele, the dominant allele masks the recessive allele.

13 Understanding Mendel’s Experiments Part I
2 alleles for purple PP 1 allele for purple. 1 allele for white Pp 2 alleles for white pp

14 Understanding Mendel’s Experiment Part II
1 allele for purple 1 allele for white Pp Pp 2 alleles for purple PP 2 alleles for white pp 1 allele for purple 1 allele for white Pp

15 Principle of Segregation
Based on the outcome of his experiment, Mendel developed his “Principle of Segregation” that states that when forming sex cells, the paired alleles separate so that each egg or sperm only carries one form of the allele. The two forms of the allele come together again during fertilization.

16 Lesson 2 Review 16. What did Mendel find to be the same with all 7 traits of the pea plant that he studied? 17. What are genes? 18. What are dominant alleles? 19. What are recessive alleles? 20.What happens if a pea plant inherits two dominant allele of the same gene? 21. What happens if a pea plant inherits a dominant allele and a recessive allele of the same gene? 22. What happens if the pea plant inherits two recessive alleles of the same gene?

17 Probability and Genetics
Lesson 3 Probability and Genetics

18 Probability Probability is the likelihood that a particular event will occur. The laws of probability determine what is likely to occur, not what does occur. Mendel was the first scientist that applied the principles of probability to genetics.

19 Punnett Square Punnett square is a table that shows all the possible combinations of alleles that can result when two organisms cross. Using Punnett square, geneticists can predict the probability of occurrence of a particular trait. The allele that each parent will pass to its offspring is based on chance, just like tossing a coin.

20 Genotypes and Phenotypes
Genotype: Indicates the alleles that the organism has inherited regarding a particular trait. Phenotype: The actual visible trait of the organism. Genotype

21 Homozygous and Heterozygous
Homozygous: An organism with two identical alleles for a trait (a purebred organism). Heterozygous: An organism that has two different alleles for a trait (a hybrid organism).

22 Review 16. What it probability? How is it related to genetics?
17. What is the Punnett Square? How is it helpful to geneticist? 18. What is a genotype? 19. What is a phenotype? 20. What is a homozygous organism? 21. What is a heterozygous organism?

23 Lesson 4 Alleles

24 Genetics Alleles 1. Alternative forms of genes.
2. Homozygous alleles are exactly the same. 3. Dominant alleles – capitalized (TT - tall pea plants) a. Homozygous dominant 4. Recessive alleles - lowercase (tt - dwarf pea plants) a. Homozygous recessive 5. Heterozygous (different) (Tt - tall pea plants)

25 Phenotype Outward appearance Physical characteristics Examples:
1. tall pea plant 2. dwarf pea plant

26 Genotype Arrangement of genes that produces the phenotype Example:
1. tall pea plant TT = tall (homozygous dominant) 2. dwarf pea plant tt = dwarf (homozygous recessive) 3. tall pea plant Tt = tall (heterozygous)

27 Practice! Practice! Practice!!!
In pea plants the Tall (T) allele is dominant over the dwarf (t) allele.

28 Practice! Practice! Practice!!!
In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 1. What is the genotype of a homozygous tall plant?

29 Practice! Practice! Practice!!!
In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 2. What is the genotype of a homozygous short plant?

30 Practice! Practice! Practice!!!
In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 3. What is the genotype of a heterozygous tall plant?

31 Practice! Practice! Practice!!!
In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 4. A plant has a genotype of Tt. What is its phenotype?

32 Practice! Practice! Practice!!!
In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 5. A plant has a genotype of tt, what is its phenotype?

33 Practice! Practice! Practice!!!
In pea plants the Tall (T) allele is dominant over the dwarf (t) allele. 6. What are the two alleles for the height of a pea plant?

34 Answers: 1. TT 2. tt 3. Tt 4. Tall 5. short 6. T (tall) and t (short)

35 Lesson 5 Mono-Hybrid Crosses

36 Monohybrid Cross A breeding experiment that tracks the inheritance of a single trait. Mendel’s “principle of segregation” pairs of genes separate during gamete formation (meiosis) & reform during ferlization.

37 Homologous Chromosomes
Paternal Maternal eye color locus B = brown eyes eye color locus b = blue eyes This person would have brown eyes (Bb)

38 Monohybrid Cross Example: Cross between two heterozygotes for brown eyes (Bb) BB = brown eyes Bb = brown eyes bb = blue eyes B b Bb x Bb male gametes female gametes

39 Monohybrid Cross B b Bb x Bb 1/4 = BB - brown eyed
1/4 = bb - blue eyed 1:2:1 genotype 3:1 phenotype BB Bb bb

40 Practice! Practice! Practice!!!!
In cocker spaniels black (B) is dominant to red (rust) (b). 1. What would be the phenotypic ratio of a cross between a true breeding black crossed with a true-breeding rust?

41 Step 2 – List the possible gametes from each parent
BB bb B B b b

42 Step 3 Draw punnett square and place the gametes on the sides.
BB bb b b B B b b B B

43 Step 4 Fill in the punnett square to find the possible zygotes
BB bb b b B B b b B b B b B B b B B b

44 Step 5 Determine the genotypic and Phenotypic ratios
BB bb b b B B b b Phenotype B b B b B 100% Black Genotype B b B B b 100% Bb

45 Practice Problems Complete a Punnett Square for each of the following:
T = tall plant t = short plant P = purple flowers p = white flowers PP x pp Pp x pp Tt x TT 5. tt x TT Pp x PP Tt x tt

46 Lesson 6 Dihybrid Cross A breeding experiment that tracks the inheritance of two traits. Mendel’s “principle of independent assortment” a. during Metaphase I, each pair of alleles seperates independently b. formula: 2n (n = # of heterozygotes)

47 Independent Assortment
Question: How many gametes will be produced for the following allele arrangements? Remember: 2n (n = # of heterozygotes) 1. RrYy 2. AaBbCCDd 3. MmNnOoPPQQRrssTtQq

48 Answer: 1. RrYy: 2n = 22 = 4 gametes RY Ry rY ry
2. AaBbCCDd: 2n = 23 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD 3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametes

49 Dihybrid Cross Example: cross between round and yellow heterozygous pea seeds. R = round r = wrinkled Y = yellow y = green RrYy x RrYy RY Ry rY ry x RY Ry rY ry possible gametes produced

50 Dihybrid Cross RY Ry rY ry RY Ry rY ry

51 Dihybrid Cross RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy
Round/Yellow: 9 Round/green: wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy

52 Lesson 7 Exceptions

53 Incomplete Dominance F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. Example: snapdragons (flower) red (RR) x white (rr) RR = red flower rr = white flower R r

54 Incomplete Dominance R produces the Rr F1 generation r All Rr = pink
(heterozygous pink) produces the F1 generation Rr

55 Codominance In codominance, the alleles are neither dominant, nor recessive. Neither allele is masked by the other. Roan Cow Is both white and red

56 Lesson 8 Mutations

57 MUTATIONS Mistakes that occur during the duplication of the chromatin material GERM CELL MUTATIONS - occur in gametes, passed on to offspring without affecting parent SOMATIC MUTATIONS - occur in body cells, not usually passed on to offspring

58 Mutations Chromosomal Mutations affect the entire chromosome
Occur during the Crossing Over period of Meiosis Duplication Mutations – one chromosome carries two copies of a gene or set of genes Deletion Mutations – post cell division, the new cell will lack the genes that were carried by the piece that broke off

59 Chromosomal Mutations, cont.
Inversion Mutations – the segment that breaks off reattaches itself but in the backwards position Translocation Mutations – a chromosome segment attaches itself to a non-homologous chromosome

60 Chromosome Mutations, cont.
NONDISJUNCTION-failure of a chromosome to separate from its homologue during meiosis *one gamete will receive an extra copy of a chromosome while the other gamete will not have the chromosome Results in: *DOWN SYNDROME (TRISOMY 21)-an extra copy of the 21st chromosome

61 Mutations Gene Mutations affect individual genes on a chromosome.
Occur by: Insertion of a nucleotide or Deletion of a nucleotide

62 The Number of Chromosomes
Humans that have even one missing or one extra chromosome usually die before birth or have serious defects. Down Syndrome happens when a person is born with an extra copy of chromosome number 21.

63 Chromosomes Males are XY and females are XX
Genes found on sex chromosomes…SEX LINKED Genes on an X chromosome are X-LINKED. Genes on a Y chromosome are Y-LINKED. Eye color in fruit flies is X-Linked. Only male fruit flies have white eyes.

64 Sex linked traits Examples of sex linked traits are
1. Blood clotting factor – this factor is located on the X chromosome and the dominant allele allows your blood to clot normally. The recessive form does not allow your blood to clot. Two recessive alleles causes the disease hemophilia. Boys are more likely to get the disease because they only have one X.

65 2. Red-green color vision is another sex-linked trait
2. Red-green color vision is another sex-linked trait. The dominant allele allows you to see reds and greens. The recessive allele prevents seeing red or green. Boys are most often affected because of having only 1 X chromosome.


67 Sex Influenced Traits Influenced by male or female sex hormones

68 Multiple Alleles Traits that are determined by 2 or more alleles & produce different colorations based on the original traits. Include: blood type Hair color Eye color

69 Polygenic Traits The results of the interaction of multiple genes
Example: hypertension Caused by the interaction of one’s: Weight Ability to process fats Cholesterol count Ability to process salts Lifestyle - i.e. Smoking, drinking, exercise

70 Mutagens Environmental factors that can cause mutations Include:
Radiation exposure via X-rays or UV light Natural or made-made chemicals Pollutants Extremely high temperatures Viruses

71 Human Karyotype showing homologous chromosome pairs
This individual has inherited three copies of chromosome 21 and has a condition called Down syndrome.

72 Nondisjunction, cont. KLINEFELTER’S SYNDROME- (XXY)-feminine characteristics, mentally impaired, infertile TURNER’S SYNDROME- (XO)- female appearance, no sexual maturity, infertile

73 Human Genetic Disorders
Cystic fibrosis-(CF)-difficulties with breathing and digestion Sickle cell anemia -forms sickle shaped RBCs because of a defective protein called hemoglobin, leads to lack of O2 & circulatory problems

74 Fig , p. 183

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