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QOD Who is considered to be the father of genetics? Gregor Mendel 1 Genetics The field of Biology devoted to understanding how characteristics are passed from parents to offspring 2 Gregor Mendel Mendel studied heredity- which is the transmission of characteristics from parent to offspring Mendel is most famous for studying pea plants He studied what he called “factors” in pea plants – 3 Factors would be height, pod color, flower color, etc Gregor Mendel 4 What were Mendel’s factors in reality? – We call these traits today – These traits are caused by genes on DNA – Genes are segments of DNA that code for one protein – Mendel also used the word “factor” to describe alleles, or alternate forms of genes – Alleles for height would be short or tall – Alleles for flower color would be white or purple Some of Mendel’s Traits 5 Gregor Mendel 6 First, Mendel grew true-breeding plants – According to Mendel true-breeding plants are plants that will always produce offspring with the same traits – So a true-bred pea plant with purple flowers will only produce plants with purple flowers because it only has the genes for purple (not white). P Generation (true-breeding parents) F1 Generation (hybrids) F2 Generation 7 Purple White flowers flowers All plants had purple flowers Mendel then considered: Phenotype- physical appearance – Genotype- genetic makeup – 8 For example purple, wrinkled, tall, etc This is usually abbreviated with letters like Gg, FF, of hh Gregor Mendel- P generation 9 What he did not know: – Purple flower color was dominant – Dominant alleles mask recessive alleles – White Flower Color was recessive – We symbolize the dominant alleles with upper case letters, like F – We symbolize the recessive alleles with lower case letters, like f Gregor Mendel- P generation – 10 Mendel’s P generation had the genotypes FF (for purple) and ff (for white) When the genotype has only one type of allele it is called homozygous FF is homozygous dominant ff is homozygous recessive Gregor MendelF1 generation 11 All of the offspring of the P generation (which he called the F1 generation) turned out purple Mendel called purple flower color the dominant factor He hypothesized that when the dominant factor was present, the recessive factor (white color) did not show. Gregor Mendel- F1 generation 12 What Mendel did not know: – All of F1 pea plant flowers heterozygous (two different alleles), or Ff – That is why they were all purple – Remember dominant alleles mask recessive alleles – Heterozygous organisms are also considered called hybrids (two different alleles… one dominate & one recessive)… the dominate allele will show. Let’s Review Phenotype – physical appearance (purple flower) Genotype – genetic makeup (alleles) (Letters: Bb) Dominate Allele – Will show over recessive allele – Recessive Allele – Will not show with dominate allele – 13 (Lower Case Letter- b) Homozygous – One type of allele (either both dominate or both recessive) – (Capitol Letter- B) (BB – homozygous dominate or bb – homozygous recessive) Heterozygous – Two different alleles (one dominate & one recessive) – (Bb) Let’s Practice If red flowers (RR) are dominate over yellow (rr) flowers then… 14 RR – What is the phenotype? Is it homozygous or heterozygous? Rr - What is the phenotype? Is it homozygous or heterozygous? rr - What is the phenotype? Is it homozygous or heterozygous? Last slide QOD The offspring receives traits from its parents this is called? heredity 15 Mendel’s Experiments P F1 F2 16 Remember that Mendel performed experiments over three generations. Genetics have a tool that can predict the outcome of genotypes and phenotypes. It is called a Punnett Square. 17 Gregor MendelF1 generation 18 Punnett Square: – Shows possible genetic combinations in the zygotes – All offspring are Ff and will therefore be purple color leaves F F f Ff Ff f Ff Ff Gregor MendelF2 generation 19 Next, Mendel crossed the offspring from the F1 generation (he called this the F2 generation) – He observed that about 75% of the flowers were purple and about 25% were white – This is equal to about a 3:1 ratio Gregor MendelF2 generation 20 Punnett Square: – 3 of the 4 squares (or zygotes) would have purple flowers – 1 of the 4 squares (or zygotes) would have white flowers – Phenotypic ratio= 3 purple:1 white F f F FF Ff f Ff ff Gregor Mendel- F2 generation Punnett Square: – The genotypic ratio: FF=1 F f F FF Ff f Ff ff Ff=2 ff=1 So, 21 1:2:1 Predicting the Results of Heredity 22 Punnett Squares are used to predict the outcome of genetic crosses – The outcomes are often expressed as percents and ratios Let’s do a Punnett square for BB x Bb B = black fur in bunnies b = white fur in bunnies Predicting the Results of Heredity 23 Phenotypic ratio: – 100% black bunnies Genotypic ratio: – 2BB:2Bb:0bb= 2:2:0 What are the chances of a white bunny? – 0% B B B BB BB b Bb Bb Predicting the Results of Heredity Let’s look at a heterozygous cross – Bb 24 x Bb Predicting the Results of Heredity 25 Phenotypic ratio: – 3 black :1 white = 3:1 Genotypic ratio: – 1BB:2Bb:1bb = 1:2:1 What are the chances of a white bunny? – 25% (1 in 4) What are the chances of a black bunny? – 75% (3 in 4) B b B BB Bb b Bb bb Predicting the Results of Heredity 26 In a monohybrid cross (only one trait is considered) When writing ratios: – Phenotypic, the dominant # goes first (that’s why it is 3:1 in the last example and not 1:3) – Genotypic, it goes homozygous dominant (BB), heterozygous (Bb), then homozygous recessive (bb) ( in the last example 1:2:1) – Numbers will always add up to 4 in monohybrid cross!! Predicting the Results of Heredity What do these ratios and percents mean? – If we flip a coin, there is a 50% chance that it will land on heads. But it is still possible to get 5 tails in a row (although it is highly UNLIKELY!) – The more times you flip it, the more likely your results will be 50:50 – If Bb and Bb bunnies mate, there is a 1:4 chance the offspring will be white (this does NOT mean that they will or will not have white bunnies) – If they have LOTS of children, about 25% of them will be white Last slide 27 QOD What are the different forms of a particular gene called? Alleles 28 29 Mendel’s Laws 30 Keep in mind that Mendel knew nothing of Punnett squares, genes, alleles, or even DNA!!! All he could do was observe phenotypes and record ratios and other statistics He came up with 2 important laws as a result of his observations: – Law of Segregation – Law of Independent Assortment Mendel’s LawsLaw of Segregation 31 Mendel concluded that each plant gets two factors (alleles) for a characteristic and when the plant reproduces, these two factors separate or segregate. So… – Each gamete (sex cell) gets one factor (allele) AND therefore… – Each offspring gets one factor from each parent Law of Segregation is shown in Punnett Squares 32 Notes on Mendel 33 The reason alleles come in pairs is because chromosomes come in pairs!! – One allele on each chromosome! – WHAT A COINCIDENCE!!! Is inheritance always this simple? – NOOOOO! There are many other types of inheritance besides monogenic complete dominance That would be a trait controlled by only one gene, where one allele is dominant over another Mendel’s LawsLaw of Independent Assortment 34 Mendel looked at 14 plant traits in total He even did experiments using more than one trait (like height and seed color) He noticed that one trait did not influence the inheritance of another trait In other words, different factors separate independently of each other during the formation of gametes Mendel’s LawsLaw of Independent Assortment 35 Examples: – Pea plants can be short or tall – Their seeds can be green or yellow – Short plants can have green or yellow seeds – Tall plants can have green or yellow seeds – So the inheritance of one does not affect the inheritance of the other. – Mendel noticed this with all the traits he studied 36 Notes on Mendel Independent Assortment is not always true– – – 37 If different genes are located on the same chromosome, then they will most likely be inherited together These are called Linked Genes The only way to separate linked genes is through crossing over during meiosis. Last slide Predicting the Results of Heredity Dihybrid Cross- a cross in which two characteristics are tracked – Remember… Monohybrid Cross- a cross in which only one characteristic is tracked – 38 For example- if we crossed two pea plants and were concerned with the flower color and plant height For example- if we crossed two pea plants and were only concerned with the flower color 39 Test Cross 40 When genotypes are not know, a testcross can be performed to figure it out – The organism with an unknown genotype is crossed with a homozygous recessive individual. – In the bunny example, if a Bb crossed with bb, white bunnies are produced – BUT if a BB crossed with bb, no white bunnies are produced – If a testcross produces white bunnies, we know the unknown genotype is Bb; if not the genotype is BB 41 QOD The inheritance of 1 trait having no effect on the inheritance of another is known as the? Law of independent assortment 42 Complex Inheritance It’s not usually that simple…. 43 Other Types of Inheritance Incomplete Dominance – – 44 The phenotype of the heterozygote is intermediate between phenotypes of the dominant and recessive traits Example: when a homozygous red carnation is crossed with a homozygous white carnations, then pink carnations are produced Incomplete Dominance 45 RR = Red Rr = pink rr = white Other Types of Inheritance 46 Codominance – Occurs when both alleles for a trait are expressed in heterozygous offspring – Codominant alleles are often symbolized with different letters – For example, human blood types have 3 alleles A, B, and O. O is recessive to A and B: Genotype AO or AA = A blood Genotype BO or BB = B blood Genotype OO = O blood Genotype AB = AB blood (both alleles expressed) Codominance BB = Brown BW = Roan WW = White Notice both brown and white are present in the heterozygote 47 Other Types of Inheritance 48 Multiple Alleles: – Genes with 3 or more alleles (or variations) – Not only does human blood type show codominance, it also has multiple alleles- A, B, and O Blood Type Last slide 49 QOD What would be the blood type of a person who inherited a B allele from one parent and an O allele from the other? B Type Blood 50 Other Types of Inheritance 51 Sex-Linked Genes and Traits – Remember sex chromosomes are the chromosomes that determine the sex of an organism – So these are traits/genes carried on sex chromosomes – These traits are symbolized using a superscript on the X or Y, such as Xr or XR 52 Other Types of Inheritance Sex-Linked Genes and Traits Examples: – 53 The Y chromosomes on males carries a gene that codes for a protein that causes the gonads (reproductive organ) to develop as testes instead of ovaries Other Types of Inheritance Sex-Linked Genes and Traits Examples: – In fruit flies, the gene for eye color is on the X chromosome. Red (XR) is dominant, white (Xr) is recessive. – To have white eyes, females must have the genotype Xr Xr , or in other words TWO white alleles – To have white eyes, males must have the genotype Xr Y, or in other words ONE white allele – This is why sex-linked traits are more common in 54 males Other Types of Inheritance Sex-Linked Genes and Traits Examples: – – – 55 Other examples of sex-linked traits: 1. Color Blindness 2. Hemophilia – blood doesn’t clot Other Types of Inheritance 56 Polygenic Inheritance: – Traits that are controlled by more than one gene – Most human traits are polygenic – Examples are height, skin color, eye color, and hair color 57 Other Types of Inheritance 58 Complex Characters: – Characters that are influenced by genetics AND the environment – Skin color and height are examples Other Types of Inheritance 59 Sex-Influenced Traits: – Traits in which males and females show different phenotypes even though they have the same genotypes – Baldness is an example- it is dominant in men, but recessive in women – The differences are mainly due to males and females producing different hormones (chemical signals) Other Types of Inheritance 60 Single Allele Traits – traits where there is only one allele – If you have the allele you have the traitthere is no recessive – Huntington’s disease is an example Last slide QOD Skin color, eye color, and height are examples of which type of traits? Polygenic Inheritance 61 Pedigrees Another way to show heredity…. 62 Pedigree is a chart or “family tree” that tracks which members of a family have a particular trait. 63 Pedigrees 64 In pedigrees carriers have one copy of the recessive allele – So they CARRY the trait, but they do not show it Pedigrees can be used to make predictions about – Future offspring – The genotype of individuals in the pedigree #63 Ww ww ww First generation Ww (grandparents) 1 Ww ww ww Ww Ww ww 2 3 WW or Ww Widow’s peak Second generation (parents plus aunts and uncles) Third generation (two sisters) ww No widow’s peak Dominant trait (widow’s peak) 65 ww= no widow’s peak WW= widow’s peak LE 14-14b 1 First generation (grandparents) Second generation (parents plus aunts and uncles) Ff Ff ? 3 FF or Ff ff ff Third generation (two sisters) Attached earlobe Recessive trait (attached earlobe) 66 ff Ff Ff ff FF or Ff ff 2 Free earlobe