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Unit 3 Heredity Heredity Word Meanings • Mono - One • Di – Two • hybrid - A combination of two or more different things • Hetero – Greek "heteros“; meaning "different." • -zygous – The type of genes that an organism has • Pheno– Prefix; physical appearance • Geno– Prefix; genetic appearance I. Genetics a. What is Genetics? i. b. the branch of biology that studies heredity What is Heredity? i. c. The passing on of characteristics from parents to offspring through GAMETES (See Unit 4) What are Traits and where are they found? i. d. Characteristics that are inherited from the chromosomes you receive from each parent. (Review Meiosis) Who was Gregor Mendel? i. ii. iii. 19th century Austrian Christian Monk Worked with pea plants to see how traits were passed from generation to generation. His research is the basis for our modern day notion of heredity. II. Monohybrid Crosses= (Creates hybrids) a. 1 trait that differs between parents I. II. III. Offspring will have a combination of traits from the parents. Example: Height One parent tall and One parent short Monohybrid = 1 trait that differs P1 (parents) short pea plant X tall pea plant F1(generation 1 = all tall) F2 (generation 2 = 3 tall: 1 short) b. What are Alleles? i. Alleles are found directly on chromosomes. ii. They are different forms (types) of the same gene (trait) • Ex. Gene for height= H/h iii. You have Two alleles for each physical trait • 1 from mother and 1 from father iv. 3 different allele combinations can be possible: HH / hh / Hh Alleles b. The Law of Segregation i. ii. iii. Every individual has 2 alleles for each gene (trait) When offspring are produced they receive one allele from each parent Law of segregation example (each gamete receives one copy of each allele): Father :Hh x Mother: Hh Monohybrid Punnet Square Set Up Possible Alleles individual Sperm cells have from Father Possible Alleles individual Egg cells have from Mother H h H HH Hh h Hh hh F1 (generation) HH=1/4 =25% Hh=2/4= 50% Yellow = Children Possible and the Alleles each child could receive. hh=1/4=25% d. What does it mean to be Dominant? i. ii. e. Trait that shows up and will hide the recessive allele Examples: HH & Hh = Tall What does it mean to be Recessive? i. ii. iii. f. Trait that can be hidden by the dominant allele Must have two recessive allele to show recessive trait Examples: hh = short Phenotype i. g. What the organism looks like. Genotype i. h. The allele combination an organism contains. [HH or Hh or hh] Homozygous Dominant a. i. Having 2 dominant alleles Example: HH Heterozygous a. j. Having 1 dominant allele and 1 recessive allele Homozygous Recessive a. Having 2 recessive alleles Example: hh Example: Hh III. Dihybrid Crosses= (Creates more varied hybrids) a. b. 2 traits that differ between parents Example Traits: Height and Color i. ii. One parent is heterozygous tall and heterozygous red (Hh and Rr) One parent is homozygous short and homozygous blue (hh and rr) Dihybrid Punnet Square Set Up 1. 2. Each trait gets one letter [Height = H/h & Color =R/r] Figure out the parents genotype if not given and set up cross. a. b. 3. Father = HhRr Mother = hhrr The cross is – HhRr x hhrr NOTICE: I Put all possible combinations the father and mother could provide to the offspring, and each top box gets one of each trait! HR Hr hR hr hhrr hr Hhrr hr hr hr hhRr HhRr hhrr IV. Pedigree a. b. V. A graphic representation of genetic inheritance Different symbols represent different traits. Mendelian Inheritance of Traits a. Simple recessive heredity i. ii. iii. b. Most genetic disorders are caused by recessive alleles examples: Cystic fibrosis and Tay- Sachs Recessive allele must be inherited from both parents for trait to show. Simple dominant heredity i. ii. one single dominant allele can be inherited from one parent to show dominant trait Example: widows peak, hanging earlobes, Huntington's disease b. Codominance 1. 2. 3. both alleles are dominant both alleles are expressed equally Example: Yellow four-o’clock flower = YY (Father-Yellow) x Pink four o’clock flower Spotted Cattle = PP (Mother-Pink) P P Y Y YP YP YP YP X YP = Yellow and Pink at same time = Blood Type – Codominance example • • • Blood type is determined by three different alleles A, B, and i. These three alleles give rise to the ABO blood types in humans Both A and B result in the creation of specific proteins that appear on the surface of the red blood cell. • These proteins on the RBC are ID passes to let the body know that these blood cells belong to that body • i is an allele that does not produce proteins on the surface of the RBC. A B O O d. Incomplete dominance 1. Neither alleles are dominant or recessive 2. Neither alleles are expressed but a fusion shows up 3. Example: Pink Roses= Red x White (RR x WW) R R W RW = Pink W Phenotype Genotype Phenotype Genotype Phenotype Genotype Green B1B1 Steel Blue B2B2 Royal Blue B1B2 X = Skin color – Polygenic Trait/Incomplete dominance example • • skin color is determined by alleles at several different genes, and so is a polygenic trait. The alleles though, do behave in a sort of incomplete dominant manner. Did you know we are all the same skin color? • BROWN – We have packets of melanin in our skin that is the color brown. • Some of us have more melanin or less. • The more melanin you have, the darker you are. • DNA – Your DNA is 0.2% different from the person sitting next to you. – The genes that make up your physical characteristics are 0.01% different from the person sitting next to you • Genetics • The gene for skin color is represented by many alleles. Looking at just three alleles Aa, Bb and Cc we get many different combinations – AABBCC = very dark color – AaBbCc = middle shade color – aabbcc = very light color – Father :AaBBCc x Mother: aaBbcc V. Sex-linked Inheritance 1. Sex Chromosomes (The 23rd chromosomes) determine sex of offspring (XX or XY) 2. Traits controlled by genes located on sex chromosomes 3. Written as superscripts of the X and Y (Ex. Xr and Yr) 4. If trait is a X-linked trait the mother and father can both pass the trait on 5. If the trait is a Y-linked trait only the father can pass it on 6. Ex: Disorders on the X chromosome 1. red-green color blindness- recessive allele 2. Male pattern baldness Baldness Red-Green Color Blindness Sex-Linked Punnet Square Set Up 1. You will be dealing with only two chromosomes: X and Y a. Females = X X Males = X Y 2. The trait in question gets written as a superscript. a. Hemophelia = homozygous X-linked recessive disease b. XH / Xh 3. Figure out the parents genotype if not given and set up cross. a. Father = XHY Mother = XHXh h X Y b. The cross is – XHY x XHXh XH Y XH Xh Male Hemophelic = Xh Y