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Intro to Genetics.

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Presentation on theme: "Intro to Genetics."— Presentation transcript:

1 Intro to Genetics

2 Background Vocabulary
True-breeds: pure gene lines – offspring match parent Self-pollination: pollen from flower fertilizes the same plant Cross-pollination: pollen will fertilize a different plant Hybrid: Cross between organisms with different traits (blonde hair & brown hair) Trait: Physical characteristics

3 Gregor Mendel Austrian monk “Father of Modern Genetics”
Famous for his work with peas

4 Mendel’s Peas

5 Cross-Pollinating

6 Mendel’s Crosses TRAIT 1: Seed Shape P Cross: Round v. Wrinkled
F1 Phenotype: Round

7 Mendel’s Crosses TRAIT 2: Seed Color P Cross: Green v. Yellow
F1 Phenotype: Yellow

8 Mendel’s Crosses TRAIT 3: Flower Color P Cross: Purple v. White
F1 Phenotype: Purple

9 Mendel’s Crosses TRAIT 4: Pod Shape P Cross: Inflated v. Pinched
F1 Phenotype: Inflated

10 Mendel’s Crosses TRAIT 5: Pod Color P Cross: Green v. Yellow
F1 Phenotype: Green

11 Mendel’s Crosses TRAIT 6: Flower Position P Cross: Axial v. Terminal
F1 Phenotype: Axial

12 Mendel’s Crosses TRAIT 7: Plant Height P Cross: Tall v. Short
F1 Phenotype: Tall

13 Mendel’s Conclusions Biological inheritance is determined by chemical factors passed from one generation to the next (Particulate hypothesis) Geneticists now refer to these factors as genes Genes can come in more than one form, each form is an allele ex. B or b (The “B” gene w/ 2 alleles)

14 The Principle of Dominance
Certain alleles will be expressed over others The expressed alleles are dominant to the unexpressed recessive alleles

15 The F1 Cross Mendel’s experiment: The results:
Allow the F1 plants to self pollinate The results: The dominant trait was expressed 75% of the time The recessive trait was expressed 25% of the time

16 The Explanations: 1. The recessive allele was still present in the F1 plants 2. Principle of Segregation: Each individual inherits two alleles for each gene.

17 Probability The likelihood of an event happening How is it determined:
Likelihood of rolling heads = 50% (1 of 2 possibilities) Rolling heads twice? 50% x 50% = 25% To predict outcomes of genetic crosses we use punnett squares

18 More genetics vocabulary…
Homozygous: two identical alleles (AA or aa) Heterozygous: two different alleles (Aa) Phenotype: Physical appearance Genotype: Genetic make-up Homozygous dominant (AA) Homozygous recessive (aa) Heterozygous (Aa)

19 The Test Cross In order to determine whether an individual expressing a dominant trait is homozygous or heterozygous, it can be crossed with an organism expressing the recessive trait. If R = round seeds and r = wrinkled seeds, show how the results of a test cross for seed shape will differ for homozgygous v. heterozgous genotypes for round seeds.

20 Monohybrid (1-factor) Cross Practice
KEY: G = green pods, g = yellow pods P = purple flowers, p = white flowers T = tall plants, t = short plants Show a cross a plant heterozygous for green pods with a plants with yellow pods. What are the expected genotype and phenotype ratios? Show a cross of a homozygous tall plant with a heterozygous tall plant. What are the expected genotype and phenotype ratios? Show a cross of two heterozygous purple flowered plants. What are the expected genotype and phenotype ratios?

21 Exploring Mendelian Genetics
Does segregation of one set of alleles influence the segregation of another pair of alleles? Mendel’s Two Factor Crosses Followed two traits at a time. Same method as his original single-factor crosses Cross-pollinated to produce the F1 and allowed them to self-pollinate

22 The Parental Cross _________________________________

23 The F1 Cross _________________________________

24 A Summary of Mendel’s Principles
Dominance: a recessive allele will be masked by a dominant allele Segregation: alleles for each trait segregate (separate) during gamete formation Independent Assortment: Alleles for different traits do not influence each other’s segregation

25 Mendel’s Peas were ideal for learning about inheritance, but they do not represent the norm…
Traits in pea plants are determined by just two alleles In peas, one allele is clearly dominant & the other is clearly recessive However, things aren’t always this clear-cut and simple in the world of genetics.

26 What if Mendel looked at mice?
If a female black mouse and a male white mouse were crossed, what will the offspring look like? - 100% are GREY If the F1 offspring were crossed, what will there offspring look like? - 25% black - 50% grey - 25% white

27 Incomplete Dominance A cross between two organisms with different traits results in an offspring with a third phenotype that is a blending of the parental traits. It’s like mixing paints: Red + White = Pink Red does not totally block (dominate) white, we end up with something in-between.

28 Inheritance in Snapdragons

29 Let’s try crossing snapdragons…
What will the genotype and phenotype ratios be if a red plant is crossed with a pink plant? (Use the following allele symbols: CR & CW) G: P:

30 What does the prefix “Co-” mean?
Consider the meaning of the following words: - Cooperate - Coexist - Cohabitat What about “Codominance”?

31 This is called ‘roan’ fur; red & white fur together.
Let’s look at cattle…. This cow resulted from a cross between a cow with red fur and a cow with white fur. This is called ‘roan’ fur; red & white fur together.

32 Codominance Similar to incomplete dominance in that there is a 3rd phenotype In COdominance, the “recessive” and “dominant” alleles appear together in the phenotype of hybrid organisms. Red x White = red & white

33 Let’s try crossing cattle….
What will the gentype and phenotype ratios be if a red cow is crossed with a white cow? G: P:

34 Polygenic (Multifactorial) Traits
Phenotype is determine by more than one gene Often results in gradations, where each gene has an additive effect Ex) If 10 gene loci are turned on plant will be 20cm tall, if only 5 loci are turned on plant will be 10cm tall Results in a bell-shaped curve Skin color & Height are examples in humans

35 Phenotype Distribution:Polygenic Traits

36 Multiple Alleles More than 2 alleles for a particular trait KEY
C = full color; dominant to all other alleles cch = chinchilla; partial defect in pigmentation; dominant to ch and c alleles ch = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles Coat color in rabbits is determined by a single gene that has at least four different alleles. Different combinations of alleles result in the four colors you see here. photo credits: 1. ©John Gerlach/Visuals Unlimited 2.Animals Animals/©Richard Kolar 3. ©Jane Burton/Bruce Coleman, Inc. 4. ©Hans Reinhard/Bruce Coleman, Inc. AIbino: cc Chinchilla: cchch, cchcch, or cchc Himalayan: chc, or chch Full color: CC, Ccch, Cch, or Cc

37 ABO Blood Types In addition to having multiple alleles, ABO blood type also exhibits codominance ‘IA’ & ‘IB’ are codominant ‘i’ is recessive

38 ABO Blood Typing Genotype Blood Type IA IA or IA i IB IB or IB i IAIB

39 What does your ABO blood type mean?
Remember the ‘flags’ on our cell membranes? They help cells to recognize each other. Some of those flags ‘announce’ your blood type. We call these flags antigens Blood Type Antigen A B AB O

40 ABO Blood Transfusions
Type Can receive: A B AB* O*

41 Summary of ABO Blood Types

42 Rh Factor Blood can also be categorized as + or –
This refers to the presence (dominant) or absence (recessive) of the Rh antigen Phenotype Genotype(s) Antigen Rh+ Rh-

43 Rh Factor & Pregnancy

44 Rh Disease Mother's antibodies cross the placenta to fight the
Rh positive cells in the baby's body. As the antibodies destroy the red blood cells, the baby can become anemic. The anemia can lead to other complications including jaundice and organ enlargement With amniocentesis, the amniotic fluid may have a yellow coloring and contain bilirubin. Ultrasound of the fetus shows enlarged liver, spleen, or heart and fluid build up in the fetus' abdomen.

45 Gene Linkage & Mapping Chromosomes
Genes on the same chromosome are more likely to be inherited together Crossing over helps to increased variation, but the closer two genes are on a chromosome the more likely they are to be “linked”

46 Sex Chromosomes & Autosomes
Two of the 46 human chromosomes are known as sex chromosomes, because they determine the individual’s sex. Females have two copies of an X chromosome. Males have one X chromosome and one Y chromosome. The remaining 44 chromosomes are known as autosomal chromosomes or autosomes.

47 Sex-Linked Genes Located on one of the sex chromosomes (X or Y)
Since the X chromosome is longer, it has many genes not found on the Y chromosome. Most sex-linked genes are X-linked genes.

48 Sex-Linked Genes

49 Possible Inheritance of Colorblindness Allele

50 Calico/Tortioseshell Cats
There is a fur color gene located on the X chromosome in cats. For tortoiseshell there are two possible alleles, orange and black, which are codominant in a heterozygote For calico there are also codominant black and orange alleles, but they code for blotches on a white background. Are these cats male or female? Explain.

51 Complete the following sex-linked crosses:
Laura and Steve are expecting their first child. They are concerned about the chances their child might be hemophiliac because both Steve and Laura’s father are hemophiliac. What is the probability of Laura and Steve having a hemophiliac child? Eva and Paul just had a son, Michael. Paul is has normal color vision, but Eva’s father was colorblind. What is the likelihood that Michael is colorblind?

52 Pedigree Analysis of Traits

53 Sex-Linked Pedigree Analysis

54 Complete the following pedigrees. Which is for a sex-linked trait
Complete the following pedigrees. Which is for a sex-linked trait? How do you know?

55 Chromosomal Disorders
The most common error in meiosis occurs when homologous chromosomes fail to separate. This is known as nondisjunction, which means “not coming apart” If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes and a disorder of chromosome numbers may occur. A monosomy results if an entire chromosome is missing and a trisomy results if there is an additional copy of a chromosome

56 Other Chromosomal Mutations

57 Jumping Genes In the 1940’s, while studying corn, Barbara McClintock discovered that sometimes genes could move from one location to another in a chromosome or even to other chromosomes. The movement could result in the genes landing in the middle of another gene and disrupting them. These “jumping genes” are now called transposons.

58 Amniocentesis: Detecting Chromosomal Disorders

59 Karyotypes: Detecting Monsomies, Trisomies & Translocations

60 Down Syndrome Trisomy 21 Produces mild to severe mental retardation
Characterized by: Increased susceptibility to many diseases Higher frequency of some birth defects.

61 Turner Syndrome Monosomy X Result of nondisjunction in females
Characteristic physical abnormalities, such as short stature, broad chest, low hairline, low-set ears, and webbed neck

62 Klinefelter Syndrome Karyotype 47, XXY
Extra X chromosome interferes with meiosis and usually prevents these individuals from reproducing Most common sex chromosome disorder, second most common disorder due to the presence of an extra chromosome

63 Genes & The Environment
Many of your personal traits are only partially governed by genetics. Environmental factors can have an effect on gene expression. Epigenetics is the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence.

64 Epigenetics NOVA Video (13min)

65 The Genetic Basis of Cancer
You already know that cancer results when controls on the cell cycle do not work properly and cells grow and divide too quickly. Two classes of genes direct the production of proteins that regulate cell growth and division: one produces growth factors to initiate cell division (can mutate to an oncogene & result in too much growth factor) the other produces proteins to stop cell division (tumor suppressor genes) Cancer is always a genetic disease in that it results from changes in DNA: Since the mutations do not usually arise in gametes, cancer is not usually passed from parent to child However some mutations do arise in the ovaries or testes which can give rise to gametes and result in the inheritance of cancer genes.

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