5 Alleles An allele is a distinct form of a gene. Every person has 2 alleles for a gene 1 from the father and 1 from the mother
6 AllelesLetters of the alphabet are used to represent an allele of interest.Every person has two copies of an allele, so they will have two letters.TPAYR
7 AllelesDominant alleles are symbolized with a capital letter. Dominant alleles will mask a recessive alleles in cases of simple dominance/recessiveness.Recessive alleles are symbolized with lower case letters.Aa
8 Homozygous Alleles AA aa If an organism has two like copies of an allele, it is homozygous (homo = same).If the two alleles are dominant, the organism is homozygous dominant.If the two alleles are recessive, the organism is homozygous recessive.AAaa
9 Heterozygous Alleles Aa If an organism has two different copies of an allele, it is heterozygous (hetero = different).Aa
10 Genotype and Phenotype The letters an organism has represent the organism’s genotype - what alleles the organism has.As a result of the alleles present, a trait is expressed. The phenotype is the expressed trait.
11 Genotype and Phenotype Example: In a plant species, there are two alleles for flower color: R and r.R is dominant, and codes for red flowersr is recessive and codes for white flowers
12 Genotype and Phenotype The genotype is the combination of alleles: either RR, Rr, or rr.The phenotype is what is expressed: either red or white flowers.
13 Genotype and Phenotype RR -Homozygous dominantRed flowersRr -Heterozygous dominantrr -Homozygous recessiveWhite flowersIn cases of simple dominance, an organism must have two copies of the recessive alleles to express the recessive trait.
14 Purebreds and HybridsPurebred - an organism that receives the same genetic traits from both of its parentsHybrid - an organism that receives different forms of a genetic trait (different alleles) from each parent
15 Contributions of Gregor Mendel Mendel’s LawsContributions of Gregor Mendel
16 Law of DominanceThe dominant alleles is expressed and may mask a recessive allele. The recessive form of a trait is only shown in a homozygous recessive organism.Ex. R is allele for round, r is allele for square.RR - roundRr - roundrr - square
17 Parent: Dd Parent: dd D d d d Gametes Gametes Law of Segregation Gene pairs separate when gametes are formed.Parent:DdParent:ddDdddGametesGametes
18 Law of Independent Assortment Genes segregate randomly and independently. This means that if there are 2 or more traits, every combination of those traits is possible.AbCAbcabCabcAabbCc
19 Probability and Punnett Squares Predicting the genotypes and phenotypes of offspring
20 ProbabilityProbability - the likelihood that a particular event will occur (what are the odds?)What is the probability that a single coin flip comes up heads?50% or 1/2
21 ProbabilityTrue or False? The past outcomes of coin flips greatly affects the outcomes of future coin flips.False.There’s still a 50% chance of heads and 50% chance of tails!
22 ProbabilityThe way in which alleles separate is random, like a coin flip. (Mendel’s Law of Segregation)From a mother who is heterozygous for an allele, there is a 50% chance she passes on the dominant allele and a 50% chance she passes on the recessive allele.
23 Punnett SquaresPunnett squares show probabilities for genotypes and phenotypes of offspring of two parent organisms.Example:In Mendel’s pea plants, the plants had either purple (P) or white (p) flowers.
24 Punnett Squares Step 1. Make the grid. If there is 1 trait, it is a 2x2 grid.If there are 2 traits, it is a 4x4 grid.Because we are only looking at 1 trait (flower color), a 2x2 grid is needed.
25 Punnett SquaresPpStep 2: Determine the parents’ genotypes and possible gametes.Example: a heterozygous pea plant and a homozygous dominant pea plant.PpPPPP
26 Punnett SquaresPpStep 3: Fill in the squares by combining what is on top of the column and to the left of the row.PpPPPPpPPPPPpP
27 Punnett SquaresPpStep 4: Use the Punnett square to determine probabilities and ratios.PpPPPPpPPPPPpP
29 Punnett SquaresWhat is the probability of an offspring plant having purple flowers?100%What is the probability of an offpsring plant being heterozygous?2/4 = 1/2 = 50%PPPpPPPp
30 Punnett SquaresIf there are 2 traits, the Punnett square will be a 4x4 grid.Example: Cross a pea plant that is heterozygous for both flower color and seed shape with a plant that has white flowers and is heterozygous for seed shapeP - purple; p - whiteR - round, r - wrinkled
31 Punnett Squares PpRr ppRr PR, Pr, pR, pr pR, pr, pR, pr Cross a pea plant that is heterozygous for both flower color and seed shape with a plant that has white flowers and is heterozygous for seed shapePpRrppRrPR, Pr, pR, prpR, pr, pR, pr
39 Intermediate Inheritance There are 3 types of intermediate inheritance, genetic patterns that don’t follow the simple dominant-recessive rules.Incomplete dominanceCodominanceMultiple alleles
40 Incomplete DominanceIncomplete dominance - neither allele is completely dominant over the otherThe heterozygous form is a “blended” form of the two alleles.
41 Incomplete DominanceExample: In snapdragon flowers, there is an allele that codes for red (r), and allele that codes for white (w).rr - redww - whiterw - pink
42 Incomplete Dominance r w rr rw r r Ex. Cross a red and a pink snapdragon.rwrrrwrr
43 Incomplete DominanceSometimes two like capital letters are used, but one gets a prime sign (‘).Ex: Human hairCurly hair HHStraight hair H’H’Wavy hair HH’
44 CodominanceCodominance - both alleles are dominant and get expressed equallyIn the heterozygous has some of each phenotype, but they are not blended.
45 CodominanceExample - in a type of cattle, red hair (R) and white hair (W) are codominant.RR - redWW - whiteRW - roanSome red, some white, but not pink!
46 CodominanceEx. Cross a red parent and a white parent.RRRWWW
47 Multiple AllelesMultiple alleles - there are more than 2 alleles for a trait.Ex. Fur color - gray, black, stripedEx. Human blood types
48 Sex-linked, sex-limited, and sex-influenced traits Sex LinkageSex-linked, sex-limited,and sex-influenced traits
49 Human ChromosomesHumans have 23 homologous pairs of chromosomes, for a total of 46.22 pairs are called autosomes , which are all of the non-sex chromosomesThe 23rd pair is the sex chromosomes - X and Y.
50 Sex Chromosomes X and Y Females - XX All eggs have an X Males - XY Sperm have either an X or Y
51 Sex-Linked TraitsTraits controlled by genes on the sex chromosomes are sex-linked traits.Examples of sex-linked traits: hemophilia, color blindness, male pattern baldnessMost are “attached” to the X chromosome.Therefore, females have 2 copies of these alleles and males only have one
52 Example - Hemophilia Hemophilia - a blood clotting disorder Hemophilia is X-linked.XH = normalXh = hemophiliaY is still just a Y
53 Example - Hemophilia Females could be: XHXH - don’t have hemophilia, not a carrierXHXh - don’t have hemophilia, is a carrierXhXh - have hemophilia
54 Example - Hemophilia Males can be: XHY - does not have hemophilia XhY - has hemophiliaMales cannot be carriers - they either have it or they don’t!
55 Example - Hemophilia XH Y XHXH XHY XHXh XhY XH Xh Draw a Punnett square for cross between a carrier female and an unaffected male.Female: XHXh Male: XHYXHYXHXHXHYXHXhXhYXHXh
56 Example - Hemophilia XH Y XHXH XHY XHXh XhY XH Xh What is the percent chance that a child of theirs will have the disorder?25%XHYXHXHXHYXHXhXhYXHXh
57 Example - Hemophilia XH Y XHXH XHY XHXh XhY XH Xh What is the percent chance that a child of theirs will have the disorder?25%XHYXHXHXHYXHXhXhYXHXh
58 Example - Hemophilia XH Y XHXH XHY XHXh XhY XH Xh What is the percent chance that a a son would have the disorder?50%XHYXHXHXHYXHXhXhYXHXh
59 Example - Hemophilia XH Y XHXH XHY XHXh XhY XH Xh What is the percent chance that a daughter would be a carrier?50%XHYXHXHXHYXHXhXhYXHXh
60 Example - Colorblindness Color blindness is also X-linked.X = normalXc = colorblind
61 Example - Colorblindness Cross a colorblind male and a carrier female.XcYXXcXYXcXcXcYXXc
62 Sex-limited traitsSex-limited traits are only expressed in the presence of sex hormones, or are only observed in one sex or the other.Ex. Beard growth
63 Sex-influenced traits Sex-influenced traits are expressed in both sexes, but they are expressed differently.Ex. Baldness is dominant in men, recessive in women