Genetics Study Guide with Examples

Genetics Study Guide ❖ Traits: Characteristics or attributes of an organism that are expressed by genes. ❖ Genes: Information (genetics) transferred from a parent to offspring, combined with another parent, to determine all characteristics of the offspring. ❖ Alleles: An alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome, responsible for variation, inherited from the parents, inheriting two alleles. ❖ Genotype: The genetic “makeup” of an individual organism. (Gg) ❖ Phenotype: The physical appearance of an organism, distinguished from its genetic makeup. Can be altered physically, is a color/trait. Ex. Red Hair or No Bobtail. ❖ Homozygous Dominant: Purebred - means homozygous. Simply is a genotype of two dominant traits, ex. BB, GG, TT. Parents could be BB x BB, Bb x BB, Bb x Bb, or Bb x Bb. ❖ Homozygous Recessive: Purebred - means homozygous. Simply is a genotype of two recessive traits, ex. bb, gg, tt. Parents could be Bb x Bb, Bb x bb, bb x Bb, or bb x bb. ❖ Heterozygous: A genotype composed of both a dominant allele, and recessive allele, with the result being the dominant, ex. Bb, Gg, Tt. Parents could be Bb x Bb, Bb x bb, bb x Bb, or BB x bb. ❖ Generations ➢ P-Generation: The Parent Generation, the first generation mentioned in the scenario. ➢ F1-Generation: The offspring of the P-Generation members. ➢ F2-Generation: The offspring of the F1-Generation members. ❖ Law of Segregation: (hypothesized by Gregor Mendel) When the genes for a specific trait all break up into individual gametes. So, by definition, it is when the alleles split up, leaving them all separately for all options. The genes for the same trait are then crossed, with the possibilities being based on the specific genes. The segregation Bb BB part of The Law of Segregation (Par (Par is since they are all split up, e e t individually. 1) 2) ❖ Independent Assortment: B B (hypothesized by Gregor Mendel) B B b B B b When chromosomes of a cell line up, in random order, which leads to variation in gene combinations. This basically means that the composition, better words combination, of the genetic info can be completely altered because simply of how the chromosomes line up, and split. Meiosis ❖ Haploid vs. Diploid ➢ Haploid: only one set of chromosomes - 23 chromosomes (egg or sperm) ➢ Diploid: two sets of chromosomes - 46 chromosomes (egg and sperm, fertilized egg) H ap loi d 23 Chromos 1 omes Allel e of ever y gen e Di 46 pl Chromos oi omes d H ap loi d 23 Chromos 1 omes Allel e of 2 ever Allel y esgen of e ever y e Rules of Probability Multiplication: The probability that independent events will occur simultaneously is the product of their individual probabilities. Example: What is the outcome that 2 pennies will both land heads up? Answer: ½ x ½ = ¼ Example: If each parent is Nn (Nn x Nn), what is the probability that their offspring will be nn? Answer: ½ N x ½ N = ¼ NN, ½ N x ½ n = ¼ Nn, ½ n x ½ N = ¼ Nn, ½ n x ½ n = ¼ nn. Addition: The rule of or, probability of an event can occur in two or more alternative ways is the sum of the separate probabilities. Example: What is the probability a 6-sided die would roll to a 1 or a 2? Answer: ⅙ + ⅙ = 2/6 = ⅓ Example: If each parent is heterozygous (Bb), what is the probability their offspring will be Bb? Answer: B could be sperm, or b could be sperm. Same with egg. ½ B x ½ b = ¼ Bb ½ b x ½ B= ¼ Bb ¼ Bb + ¼ Bb = ½ Bb Crosses Monohybrid Cross: A genetic cross between homozygous parents that differ in the alleles they possess for one characteristic (meaning one has to be RR, the other has to be rr) with all of the offspring being heterozygous. Dihybrid Cross: A genetic cross between the parents, that are identically hybrid for two traits, with all of the possible gametes, to see the possibilities of the offspring. Sex-Linked Cross: Only the X chromosome is involved with sex-linked diseases/illnesses, so the Xs can either be affected with a lowercase letter (h) or not affected with an uppercase letter (H). Depending on the alleles inherited, males have a higher chance of being affected with sex-linked diseases than women, as they have an extra X chromosome to try and stop it. XhY = Male, Affected XHY = Male, Not Affected XHXH = Female, Not Affected H h X X = Female, Not Affected, Carrier XhXh = Female, Affected Multiple Alleles: When more than two different alleles exist for the same trait. Humans can have two alleles from a set of three possible alleles, A and B, A and O, or B and O. Six possible genetic combinations - genotypes, four possible types of blood - phenotypes. A and B exhibit codominance, forming AB blood. Multiple Alleles and Dominance Incomplete Dominance: One allele isn’t completely dominant over another, creating a heterozygote which expresses both conditions of the two parents. In this case, the red flower and the white flower cross, but form a pink flower by taking the red and white and “mixing” them. FW FW F RF R FW FR Codominance: Both alleles contribute to the phenotype of the organism. They are both present, and do not mix, but are both seen. Polygenic Inheritance: (Traits controlled by two or more genes) Ashley Madekwe, fashion blogger and actress, has roots from Nigeria, Switzerland, and Great Britain. Her mixed father comes from a white grandmother and a black grandfather, as her mother comes from a white British line. With her parents varying in backgrounds, their skin colors acting as a real-life example for polygenic inheritance as for one, skin color is an example of this revelation, but also because by using Ashley’s parents, it shows a great example for the polygenic inheritance and how skin color comes together with the different combinations. Ashley Epistasis Epistasis is an interaction between two or more genes to control a single phenotype. Example: With labrador retrievers, Black (Bb) is dominant to Chocolate (bb). Yellow is recessive epistatic. Ee or EE is dominant, meaning not yellow. ee is recessive, meaning yellow. Any dog with “ee” will be yellow. BB Bb bb EE BBEE BbEE bbEE Ee BBEe BbEe bbEe ee BBee Bbee bbee This is a great example of epistasis as it requires two or more genes to react, so the genes for coat color and the yellow recessive epistatic both react to determine the coat’s color. Pedigrees Autosomal Recessive: The black circles and squares (females and males) represent those whom contract whatever the trait is. To use Autosomal Recessive, the black is always bb. The whites can then be determined off of the blacks to see if they are BB or Bb. Autosomal Dominant: The black circles and squares (females and males) represent those whom contract whatever the trait is. To use Autosomal Dominant, the white is always bb. The blacks can then be determined off of the whites to see if they are BB or Bb. Sex/X -Linked Recessive: The black circles and squares (females and males) represent those whom contract whatever the trait is. To use SexLinked Recessive, the black squares are always XhY, and the white are XHY. This can then determine the rest of the pedigree. Sex/X -Linked Dominant: The black circles and squares (females and males) represent those whom contract whatever the trait is. To use Sex-Linked Dominant, the black squares are always XHY, and the white are XhY. This can then determine the rest of the pedigree. Hardy-Weinberg Problems Allele Frequency: p + q = 1, (p < 1, q < 1) Genotype Frequency: p2 + 2pq + q2 = 1 Key to These Problems Symbol Definition Example p Frequency of Dominant A q Frequency of Recessive a Frequency of Homozygous Dominant AA 2pq Frequency of Heterozygous Aa q2 Frequency of Homozygous Recessive aa p 2 Meiosis Review Meiosis Highlights ❖ Each somatic (body) cell had 46 chromosomes, 23 pairs. ❖ Homologous chromosomes carry genes controlling the same inherited characteristics. ❖ Homologous chromosomes can also be called homologs. ❖ Autosomal: 22 pairs, 44 chromosomes, Sex: 1 pairs, 2 chromosomes. ❖ Karyotype: a display of magnified images of the individual’s chromosomes (pictured to right). ❖ Abnormal chromosome count is a result of nondisjunction. ➢ Chromosomes can fail to separate in Meiosis I. ➢ Chromatids can fail to separate in Meiosis II. Punnett Squares! Codominance Table Incomplete Table R Dominance R W RR RW W RW WW “What is difference between codominance and incomplete dominance?”: Codominance: The genes mix genotypically, as well as phenotypically, but they don’t mix completely in color, their offspring are commonly checked with both colors. Incomplete Dominance: The genes mix phenotypically and genotypically, like the red and white flowers, to make pink flowers. Incomplete dominance, is the two work together to mix their genes. Hardy-Weinberg cont. 1. Mating must be random. 2. Population size must be LARGE. 3. No gene flow. 4. No mutations. 5. No natural selection. *Can NOT occur in nature* Equations p + q = 1 (Allele Frequency) p2 + 2pq + q2 = 1 (Genotype Frequency) Practice Problems (answers below in white - highlight when done) 1. 204 out of the 9056 people of Chatham have an extra 1,000 taste buds compared to the others of Chatham, being a recessive trait. How many people are homozygous dominant and heterozygous? ----2. 872 of the 946 toucans in Santa Clara, Costa Rica have black feathers, a dominant trait, with the recessive feathers being dark blue. How many toucans are homozygous dominant, heterozygous, or recessive? ----3. In a small town, Friday Harbor, off the Washington coast, no citizens have B blood. A blood is dominant with 2,203 out of the 2,277 citizens having it, and the rest having O blood. How many people are homozygous dominant, heterozygous or recessive? Highlight Below for Hardy-Weinberg Practice Problem Answers (here) Answers: #1 = 2309 (25.5%) heterozygous, 6543 (72.25%) homozygous dominant. #2 = 491 (51.84%) homozygous dominant, 381 (40.32%) heterozygous, 74 (7.84%) homozygous recessive). #3 = 1528 (67.07%) homozygous dominant, 675 (29.65%) heterozygous, 74 (3.27%) recessive. (to here) Scenario Practice Problems Corine and Ben Blackshaw are planning on having four children over the next few years. Corine has red hair, and Ben’s mother, Angie, had red hair, while he has brown hair, and his father, Colton, did not have red hair. What is the chance that all of their four children they plan to have will have red hair? (Hint: Red hair is recessive!) Answer: (highlight) 1/16 After seven years, Corine and Ben have four children: (Oldest to Youngest): Delancey, Deirdre, Donal and Davidson. What was the probability of them having kids in this order? (Girl, Girl, Boy, Boy) Answer: (highlight) 1/16 Delancey and Donal have red hair, while Deirdre and Davidson have brown hair. What is the probability of this occurring? Answer: (highlight) 1/16 Ben’s sister, Saoirse, has red hair. Saoirse’s son with Will, Maxwell, has black hair. What is his genotype for hair? Answer: (highlight) Bb Over time, Davidson, Corine and Ben’s son, who has brown hair, marries a girl named Sierra. Sierra has brown hair as well, but they have their first child, Lily, and her hair is red. How is this possible? Answer: (highlight) Sierra’s mother or father has red hair. Leela, Donal’s wife, has black wavy hair. Their first child, Georgia, has black wavy hair as well. How is this possible? (Hint: wavy hair is recessive!) Answer: (highlight) Leela’s parents both had wavy hair, same with Donal. Georgia marries a man named Beckett, who has blonde, curly hair. Her hair is black and his is blonde. They have two children named Anais and Niobe. Anais and Niobe both have black hair. What were their chances for getting blonde hair like their father? Answer: (highlight) 0% Lily has a son named Jacob. His hair is brown. What color is her husband’s, Xander, hair? Answer: (highlight) Brown Family Tree of everyone mentioned in this problem/scenario for reference is on the next page for better understanding if you are confused! Mendel’s Hypotheses There are alternate forms of genes. For each inherited characteristic, an organism has 2 alleles (one from each parent). A sperm or egg carries only ONE allele for each trait. When two genes of a pair are different alleles, and one is fully expressed, while the other has no noticeable effect. (Recessive and Dominant) Mendel soon went on to study seven characteristics of pea plants. He controlled whether they self-pollinated or cross-pollinated, always knowing the parents. Tetrahybrid Example Venti: Gg Green Tea: bb Lemonade: Aa Sweetened: tt Grande: gg Passion Tea: Bb No Lemonade: aa Sweetened: Tt Gg x gg = ½ Gg, ½ gg x bb x Bb = ½ Bb, ½ bb ¼ GgBb + ¼ Ggbb + ¼ ggBb + ¼ ggbb X Aa x aa = ½ Aa, ½ aa x tt x Tt = ½ Tt, ½ tt ¼ AaTt, ¼ Aatt, ¼ aaTt, ¼ aatt ¼ GgBb + ¼ Ggbb + ¼ ggBb + ¼ ggbb x ¼ AaTt + ¼ Aatt + ¼ aaTt + ¼ aatt 1/16 GgBbAaTt + 1/16 GgBbAatt + 1/16 GgBbaaTt + 1/16 GgBbaatt + 1/16 GgbbAaTt + 1/16 GgbbAatt + 1/16 GgbbaaTt + 1/16 Ggbbaatt + 1/16 ggBbAaTt + 1/16 ggBbAatt + 1/16 ggBbaaTt + 1/16 ggBbaatt + 1/16 ggbbAaTt + 1/16ggbbAatt + 1/16 ggbbaaTt + 1/16 ggbbaatt