Genetics Notes Gregor Mendel (by Teachers Pet 5 min) Video https://youtu.be/cWt1RFnWNzk Genetics study of how traits are passed from parent to offspring. Traits are the expressions of genes that we see or observe in living organisms. Traits are determined by the genes on the chromosomes. A gene is a segment of DNA that determines a trait.
Chromosomes come in homologous pairs, thus genes come in pairs. Homologous pairs matching genes one from female parent and one from male parent Example: Humans have 46 chromosomes or 23 pairs. One set from dad 23 in sperm One set from mom 23 in egg One pair of Homologous Chromosomes: Gene for eye color (blue eyes) Homologous pair of chromosomes
Gene for eye color (brown eyes) Alleles different genes (possibilities) for the same trait ex: blue eyes or brown eyes Ill take genetics for $500, Please Alex. This Austrian Monk known as the Father of Genetics was also a high school math teacher. He used the pea plant to study genetics because he could control pollination, it
had several easy to identify traits and it was easy to grow. You wrote Who is Gregor Mendel? That is correct, choose again. Gregor Mendels Principles of Genetics Principle of Segregation Each parent carries two alleles that separate during gamete formation. Principle of Independent Assortment Alleles separate independently of other alleles. Inheritance of one trait has no effect on the inheritance of another trait. Hair and eye
color are independent of each other. Principle of Dominance Some forms of genes or traits are dominant over other traits which are called Recessive. Recessive traits are only seen when there is no dominant allele. Freckles are dominant to no freckles. Dominant and Recessive Genes Gene that prevents the other gene from showing dominant Gene that does NOT show even though it is present recessive Symbols Dominant gene upper case letter, ex. T Recessive gene lower case letter, ex. t
Dominant color Recessive color Parent alleles can be; Heterozygous identical to the other ex. Both brown eyes Or Homozygous different from each other ex. Brown eyes vs Blue eyes
Example: Straight thumb is dominant to hitchhiker thumb T = straight thumb t = hitchhikers thumb (Always use the same letter for the same alleles No S = straight, h = hitchhikers) Straight thumb = TT Straight thumb = Tt Hitchhikers thumb = tt * You must have 2 recessive alleles for a recessive trait to show. Genotype - Combination of genes an organism has
(actual gene makeup) Ex: TT, Tt, tt Phenotype - Physical appearance resulting from gene make-up Ex: hitchhikers thumb or straight thumb Both genes of a pair are the same homozygous or purebred TT homozygous dominant tt homozygous recessive One dominant and one recessive gene heterozygous or hybrid Tt heterozygous BB Black
Bb Black w/ white gene bb White Punnett Square and Probability Used to predict the possible gene makeup of offspring Example: Black fur (B) is dominant to white fur (b) in mice 1. Cross a heterozygous male with a homozygous recessive female. Black fur (B) Heterozygous male
White fur (b) White fur (b) Homozygous recessive female White fur (b) How to Use a Punnett Square 1. First Simple 4 square video https://youtu.be/prkHKjfUmMs 2. If you are making mistakes this video can fix it. https://youtu.be/Y1PCwxUDTl8 3. Advanced Punnett Squares
https://youtu.be/Qcmdb25Rnyo Cross 2 hybrid mice and give the genotypic ratio and phenotypic ratio. B b B BB
Bb b Bb bb Bb X Bb Genotypic ratio = 1 BB : 2 Bb : 1 bb 25% BB : 50% Bb : 25% bb Phenotypic ratio = 3 black : 1 white
75% black : 25% white Example: A man and woman, both with brown eyes (B) marry and have a blue eyed (b) child. What are the genotypes of the man, woman and child? Bb X Bb Man = Bb B b
B BB Bb b Bb bb Woman = Bb
Crossing involving 2 traits Dihybrid crosses Example: In rabbits black coat (B) is dominant over brown (b) and straight hair (H) is dominant to curly (h). Cross 2 hybrid rabbits and give the phenotypic ratio for the first generation of offspring. Possible gametes: BbHh X BbHh BH BH Gametes Bh Bh bH bH BH bh bh
Phenotypes - 9:3:3:1 9 black and straight 3 black and curly 3 brown and straight 1 brown and curly BH Bh bH bh
BBHH BBHh BbHH BbHh Bh BBHh
BBhh BbHh Bbhh bH BbHH BbHh bbHH
bbHh bh BbHh Bbhh bbHh bbhh
Polygenic Inheritance Polygenic traits, or continuous traits, are governed by alleles at two or more loci. Ex. Hair, eye and skin color, Stature, height, Shape of face, Fingerprint patterns Medium Traits Codominance and Incomplete Dominance
a) Birds can be blue, white, or white with blue-tipped feathers. b) Flowers can be white, pink, or red. c) A Hoo can have curly hair, spiked hair, or a mix of both curly and spiked. d) A Sneech can be tall, medium, or short. e) A Bleexo can be spotted, black, or white. Can you figure out in the above list, which of the letters represent codominant traits and which are incomplete. Codominant _____________ Incompletely Dominant ________________ Incomplete dominance and Codominance When one allele is NOT completely dominant over another (they blend) incomplete dominance
Example: In carnations the color red (R) is incompletely dominant over white (W). The hybrid color is pink. Give the genotypic and phenotypic ratio from a cross between 2 pink flowers. RW X RW R R W RR RW W RW WW
Genotypic = 1 RR : 2 RW : 1 WW Phenotypic = 1 red : 2 pink : 1 white When both alleles are expressed Codominance Example: In certain chickens black feathers are codominant with white feathers. Heterozygous chickens have black and white speckled feathers. Multiple Alleles (Amoeba Sisters ABO Blood types https://youtu.be/9O5JQqlngFY) 3 or more alleles of the same gene that code for a single trait In humans, blood type is determined by 3 alleles A, B, and O
BUT each human can only inherit 2 alleles 1. Dominant A and B (codominance) Recessive O 2. Blood type A = AA or AO B = BB or BO AB = AB O = OO Example: What would be the possible blood types of children born to a female with type AB blood and a male with type O blood? (Amoeba Sisters ABO Blood types https://youtu.be/9O5JQqlngFY) AB X OO
A O AO B BO O AO BO Children would be type A or B only Sex linked Traits
Genes for these traits are located only on the X chromosome (NOT on the Y chromosome) X linked alleles always show up in males whether dominant or recessive because males have only one X chromosome Amoeba Sisters Sex Linked traits https://youtu.be/h2xufrHWG3E Sex Determination People 46 chromosomes or 23 pairs
22 pairs are homologous (look alike) called autosomes determine body traits 1 pair is the sex chromosomes determines sex (male or female) Females sex chromosomes are homologous (look alike) label XX Males sex chromosomes are different label XY Male = Bb X Female = bb b Male gametes - N (One gene in sperm) b
B Bb Bb b bb bb
Female gametes N (One gene in egg) Possible offspring 2N Write the ratios in the following orders: Genotypic ratio = 2 Bb : 2 bb 50% Bb : 50% bb Phenotypic ratio = 2 black : 2 white 50% black : 50% white Genotypic ratio homozygous : heterozygous : homozygous dominant
recessive Phenotypic ratio dominant : recessive What is the probability of a couple having a boy? Or a girl? Chance of having female baby? 50% male baby? 50% X X X
XX XX Y XY XY Who determines the sex of the child? father
Examples of recessive sex-linked disorders: 1. colorblindness inability to distinguish between certain colors You should see 58 (upper left), 18 (upper right), E (lower left) and 17 (lower right). Color blindness is the inability to distinguish the differences between certain colors. The most common type is red-green color blindness, where red and green are seen as the same color.
2. hemophilia blood wont clot Example: A female that has normal vision but is a carrier for colorblindness marries a male with normal vision. Give the expected phenotypes of their children. N = normal vision n = colorblindness XN Xn X XN Y XN Xn
XN XNXN XNXn Y XNY XnY Phenotype: 2 normal vision females 1 normal vision male
1 colorblind male Pedigrees Graphic representation of how a trait is passed from parents to offspring Tips for making a pedigree 1. Circles are for females 2. Squares are for males 3. Horizontal lines connecting a male and a female represent a marriage 4. Vertical line and brackets connect parent to offspring 5. A shaded circle or square indicates a
person has the trait 6. A circle or square NOT shaded represents an individual who does NOT have the trait 7. Partial shade indicates a carrier someone who is heterozygous for the trait Example: Make a pedigree chart for the following couple. Dana is color blind; her husband Jeff is not. They have two boys and two girls. HINT: Colorblindness is a recessive sex-linked trait. XnXn
Has trait XNY Can pass trait to offspring What if DNA Gets Damaged? http://ed.ted.com/lessons/what-happenswhen-your-dna-is-damaged-monica-menesini Mutations Mutation sudden genetic change (change in base pair sequence of DNA)
Can be : Harmful mutations organism less able to survive: genetic disorders, cancer, death Beneficial mutations allows organism to better survive: provides genetic variation Neutral mutations neither harmful nor helpful to organism Mutations can occur in 2 ways: chromosomal mutation or gene/point mutation Detecting Genetic Disorders picture of an individuals chromosomes karyotype
amniotic fluid surrounding the embryo is removed for analysis amniocentesis Female with Downs syndrome Chromosomal mutation: less common than a gene mutation more drastic affects entire chromosome, so affects many genes rather than just one caused by failure of the homologous chromosomes to separate normally during meiosis chromosome pairs no longer look the same too few or too many genes, different shape
Examples: Downs syndrome (Trisomy 21) 47 chromosomes, extra chromosome at pair #21 Turners syndrome only 45 chromosomes, missing a sex chromosome (X) Girls affected short, slow growth, heart problems Klinefelters syndrome 47 chromosomes, extra X chromosomes (XXY) Boys affected low testosterone levels, underdeveloped muscles, sparse facial hair
Having an extra set of chromosomes is fatal in animals, but in plants it makes them larger and hardier. Hardier Gene or Point Mutation most common and least drastic only one gene is altered Examples: Recessive gene mutations:
Sickle cell anemia red blood cells are sickle shaped instead of round and cannot carry enough oxygen to the body tissues heterozygous condition protects people from malaria Cystic fibrosis mucous builds up in the lungs Tay-Sachs Disease deterioration
of the nervous system early death Mutated genes produce enzymes that are less effective than normal at breaking down fatty cell products known as gangliosides. As a result, gangliosides build up in the lysosomes and overload cells. Their buildup ultimately causes damage to nerve cells. Phenylketonuria (PKU) an amino acid common in milk cannot be broken down and as it builds up it causes mental retardation
newborns are tested for this Dominant gene mutations: Huntingtons disease gradual deterioration of brain tissue, shows up in middle age and is fatal Dwarfism variety of skeletal abnormalities Electrophoresis DNA Fingerprinting DNA is extracted from
samples of victims and suspects or parents and children. A restriction enzyme breaks the DNA into lengths based on cutting at specific code sequences. Then the pieces are placed in a machine that uses chromatography to separate them by size.
Epigenetics Gene expression can also be altered by environmental chemicals. This short video will help you to understand how this can happen. https://youtu.be/ ujLppvMqUOI Watch the videos and answer the Questions. Where did genes come from? http://
ed.ted.com/lessons/where-do-genes-come-from-carl-zimmer# watch What is a Gene and what is a genetic modification? https://youtu.be/5MQdXjRPHmQ What is Genetic Engineering? Selective Breeding? https ://youtu.be/_ZbnfjLoDSY I might have bad genes now what can I do about it? http:// ed.ted.com/lessons/your-genes-are-not-your-fate-dean-ornish What do you think about industrial GMOs?
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