Presentation on theme: "10.1 Genetics developed from curiosity about inheritance"— Presentation transcript:
1 10.1 Genetics developed from curiosity about inheritance
2 I. The Blending Hypothesis of Inheritance A trait is a variation of a particular characteristic such as for red flowers or yellow flowersIn the early 1800’s many biologists believed in the blending hypothesis, which stated that offspring would be a blend of their parents traits. A red and yellow flower would produce and orange flower
3 II. Mendel’s Plant Breeding Experiments Mendel’s work gave rise to the branch of Biology called genetics, the study of heredityMendel developed the particulate hypothesis which states that parents pass on separate and distinct factors, or genes
4 Mendel’s Plant Breeding Experiments To test this hypothesis, Mendel crossed true-breeding plants that had distinct and contrasting traits such as purple and white flowersMendel cross-fertilized all his pea plants by hand to control which traits he wanted to control
7 I. Mendel’s Principle of Segregation The offspring of two different true-breeding varieties are called hybridsB. When Mendel crossed plants that differed in only one-trait it was called a mono-hybrid cross
8 C. From these results Mendel developed the following hypothesis There are alternative forms of a gene called alleles.For each inherited trait, an organism has two alleles for the gene controlling that character, one from each parent. If both alleles are the same the individual is homozygous, and if the alleles are different the individual is heterozygous.
9 Mendel developed the following hypothesis 3. When only one of the alleles in a heterozygous individual appears to affect the trait, that allele is called the dominant trait. The allele that does not appear to have an affect on the individual is called the recessive trait
12 Mendel developed the following hypothesis 4. The two alleles for a character separate during the formation of gametes, so each gamete carries only one allele for each character. This is known as Mendel’s Principle of Segregation
13 II. Probability and Punnett Squares The inheritance of alleles follows the laws of probabilityIf you were to flip two pennies the probability of flipping a head or a tail on one does not affect the probability of the other oneA diagram that shows all the possible outcomes of a genetic cross is the Punnett Square
15 Punnett SquareEye colorHomozygousBrown male XBlue femaleBbBb
16 III. Genotypes and Phenotypes The way an organism looks is not the same as its genetic make-upAn observable trait is called a phenotype while the genetic make-up of alleles is called the genotype
17 IV. The TestcrossA testcross breeds individuals of unknown genotypes, but the dominant phenotype with a homozygous recessive individualDepending on the ratios of the offspring, the genotype of the unknown can be determined
19 V. Mendel’s Principle of Independent Assortment Mendel also did crosses between plants that differed in two traits called a dihybrid crossFrom this he developed his Law of Independent Assortment which states that during gamete formation the way in which one allele is inherited does not affect the way another is inherited if they are on separate chromosomes
20 Problem: Monohybrid 11. An allele for brown eyes B is dominant over that for blue eyes b. A blue-eyed man, both of whose parents were brown-eyed, marries a woman. They have one child who is blue-eyed. What are the genotypes of all the individuals mentioned?
21 Problem 1Man’s parents: BbDad: bbMom: BbKids: Bb or bbbBBbbb
22 Problem: Monohybrid 22. The ability to taste the chemical PTC is determined by a single gene in humans with the ability to taste given by the dominant allele T and inability to taste by the recessive allele t. Suppose two heterozygous tasters (Tt) have a large family.
23 Problem: Monohybrid 2Predict the proportion of their children who will be tasters and nontasters. Use a Punnett square to illustrate how you make these predictions.What is the likelihood that their first child will be a taster? What is the likelihood that their fourth child will be a taster?What is the likelihood that the first three children of this couple will be nontasters?
26 Dihybrid Cross- FOILFirstOutsideInsideLastRrYy x RrYy
27 Problem 3: Dihybrid3. In pepper plants, green (G) fruit color is dominant to red (g) and round (R) fruit shape is dominant to square (r) fruit shape. These two genes are located on different chromosomes.
28 3. Dihybrida. What gamete types will be produced by a heterozygous green, round plant?b. If two such heterozygous plants are crossed, what genotypes and phenotypes will be seen in the offspring and in what proportions?
29 #3 Types of gametesFOILFirst- GROutside- GrInside- gRLast- gr
32 10.3 There are many variations of inheritance patterns
33 I. Intermediate Inheritance When an organism has two alleles and neither is dominant the phenotype is intermediate between the two allelesThis pattern of inheritance is called intermediate inheritance
35 Problem: Intermediate Inheritance 4. A hybrid pink CRCW snapdragon was crossed with a pure white one CWCW. Red flower color is incompletely dominant.Make a diagram and list the genotypic and phenotypic ratios of the F1 generation
36 Problem 41:1CR CW :CW CWPink:WhiteCRCWCR CWCW CW
37 II. Multiple AllelesMany genes have several alleles for each trait which expands the number of genotypes and phenotypesCodominance is when a heterozygous individual expresses both traits equally.
39 Problem: Multiple Alleles 5. Paul is blood type O. His father was blood type A and his mother was blood type B. What were the genotypes of his parents and what are the possible blood types and ratios expected for crosses involving these parental genotypes?
40 Problem 5IAi and IBi1:1:1:1AB:A:B:OIAiIBIA IBIBiIAiii
41 III. Polygenic Inheritance When multiple genes affect a character the variation in phenotypes can become even greater.When two or more genes affect a single character, it is called polygenic inheritanceExamples of polygenic inheritance would include skin color, and height
42 Problem: Polygenic6. Melanin is coded for when the gene L, M, or N is present. The more of these genes are present, then the darker the skin the individual. Number the following genotypes in order of the darkest to lightest skin color phenotypes.
44 IV. The Importance of Environment An individuals phenotype depends on environment as well as on geneIn humans, nutrition influences height, exercise affects build, and exposure to sunlight darkens the skin
46 I. Chromosome Theory of Inheritance A. Biologists worked out the processes of mitosis and meiosis in the late 1800s and observed the parallels between the behavior of chromosomes and the behavior of Mendel’s heritable factors
47 Chromosome TheoryB. The chromosome theory of inheritance states that genes are located on chromosomes, and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patternsC. The alleles for a gene reside at the same location or gene locus
49 II. Genetic Linkage and Crossing Over Mendel’s principles only work when for genes that are located on separate chromosomesThe tendency for the alleles on one chromosome to be inherited together is called genetic linkageC. The closer the two genes are on a chromosome, the greater the genetic linkage
55 II. Sex-Linked Disorders A. A number of human conditions, including red-green color blindness and hemophilia are inherited as sex linked recessive traitsB. It takes two copies of the allele to be present in females for them to show signs of the disorder while it only takes one in males
56 Problem: Sex-linked7. A color blind father and a mother who carries the color blind trait (b) have a boy and a girl. What are the percent chances of the children being color blind? A carrier for color blindness?
57 Color blindness: Sex-linked children25% carrierXbYXBXB XbXBYXb XbXbY
58 12.2 Accidents Affecting Chromosomes can Cause Disorders
59 I. Down SyndromeA. Trisomy 21 results in having three number 21 chromosomesB. In most cases, a human embryo with an abnormal number of chromosomes results in a miscarriageC. People with trisomy 21 have Down syndrome, named after John Langdon Down
60 II. Nonseparation of Chromosomes A. Nondisjunction is when homologous fail to separateB. A woman’s age will have an effect on the possibility of nondisjunction occurringC. This is due to the time line of egg cell development
62 III. Damaged Chromosomes A. Duplication is when part of a chromosome is repeatedB. Deletion is when a fragment of a chromosome is lostC. Inversion involves reversing a fragment of the original chromosomeD. Translocation occurs when a fragment of one chromosome attaches to a non-homologous chromosome
66 IV. Jumping GenesA. Single genes may move from one location to another in a chromosome or to a different chromosomeB. This was discovered by Barbara McClintock in the 1940’sC. These genes can land in the middle of other genes and disrupt themD. These genes are called transposons
71 II. Disorders Inherited as Recessive Traits A. There are over one thousand genetic disorders that are inherited as a dominant or recessive trait controlled by a single geneB. Most human genetic disorders are recessiveC. A carrier is an individual who has a copy of the recessive disorder but does not show symptoms
73 Pedigree #9Is the attached ear lobe trait a dominant or recessive trait? How do you know?Recesssive, only those ff colored.What two terms could be used to describe the Ff genotype?Heterozygous, or carrier
74 Problem 9: Pedigree F f FF Ff ff What are the percent chances? 75% Unattached25% attachedFfFFFfff
75 III. Disorders inherited as Dominant Traits A. Dominant alleles that are lethal are more common than lethal recessivesB. Usually, the person with the dominant disorder dies before the allele can be passed on
77 IV. Sex-Linked Disorders A. Sex-Linked alleles are usually located on the X Chromosome in humansB. A male only needs to inherit one copy of the allele to exhibit the traitC. A female must inherit two copies of the allele to exhibit the trait
81 V. Predicting and Treating Genetic Disorders A. A genetic counselor is trained to collect and analyze data about inheritance patternsB. This information is used by couples to determine the risks of passing on genetic disorders to their childrenC. Genetic tests are done before and after the baby is born