CHAPTER 6, SECTIONS 3, 4, & 5 CHAPTER 7 UNIT 7: GENETICS TOPIC 1: TERMINOLOGY FOR GENETICS TERMS Gene: a segment of DNA with coded information for a particular trait or characteristic. Because animals are diploid (i.e., chromosomes in homologous pairs), there are 2 genes for each traitone inherited from each parent. Gene
TERMS Allele: Actual DNA letters or N-base codes found in the chromosome One allele is inherited from each parent for each genetic trait Ex: Gene = repair enzyme; Alleles = broken vs normal purple P white p TERMS
Gene Notation: letters are used to represent traits Rule: 1 letter for each trait Dominant allele: alleles which hide or mask the information carried by recessive alleles. Dominant allele is expressed when 2 different alleles are present Notation = capital letters Ex: R = normal repair enzyme allele TERMS
Recessive allele: alleles which are only expressed or observed when NOT paired with a dominant allele Recessive alleles are only expressed when there are 2 copies present Notation = lowercase letters Ex: r = broken repair enzyme allele TERMS Genotype: the 2 alleles inherited for each genetic trait the actual genetic info.
Homozygous: 2 copies of the same allele for a trait. Ex: RR or rr Heterozygous: 2 different alleles for a trait Ex: Rr Phenotype: physical appearance of the expressed trait which can be seen. Ex: have the disease or are normal and symptom free? (i.e., sick or healthy?) LETS REVIEW Homozygous or heterozygous?
Homozygous LETS REVIEW Homozygous or heterozygous? heterozygous LETS REVIEW What is this flowers genotype? Ff (heterozygous) LETS REVIEW What is this flowers phenotype?
purple LETS REVIEW What is this flowers phenotype?. white LETS REVIEW What is this flowers genotype? ff LETS REVIEW
Is this flower homozygous or heterozygous? heterozygous TOPIC 2: CRACKING THE CODE OF HEREDITY Genetics The study of heredity, how traits are passed from parent to offspring or x = or 6.3: MENDEL & HEREDITY
Heredity was a mystery for a long time It was thought that parents traits blended in the next generationlike red and white blend to make pink Are there any traits that are NOT inherited this way? GREGOR MENDEL Austrian monk The Father of Genetics The first person to start unraveling the mystery of heredity in the 1800s
EXPERIMENTAL GENETICS BEGAN IN AN ABBEY GARDEN Modern genetics began with Gregor Mendels experiments with pea plants Stamen Carpel Figure 9.2A, B MENDELS EXPERIMENTS Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation Mendel studied seven pea traits for several
years and discovered they were each inherited in a similar math pattern. He hypothesized that these traits were shaped by alternative forms of genes --the units that determine heredity FLOWER COLOR Purple White Axial Terminal
SEED COLOR Yellow Green SEED SHAPE Round Wrinkled POD SHAPE Inflated Constricted
POD COLOR Green Yellow STEM LENGTH Tall Dwarf FLOWER POSITION MENDELS LAW OF SEGREGATION DESCRIBES THE INHERITANCE OF A SINGLE TRAIT
Parents have two alleles for every trait, but only give one allele to a gamete (sex cell) In the offspring, one allele comes from each parent Ex. The F1 purple flower received 1 allele for purple and 1 for white from each parent P GENERATION (true-breeding parents) Purple flowers
White flowers All plants have purple flowers F1 generation Fertilization among F1 plants (F1 x F1) F2 generation /4 of plants have purple flowers 3 /4 of plants have white flowers 1
Why did the white color disappear in the F1 generation but reappear in the F2 generation? Mendel suggested that many traits have two opposite forms that are determined by dominant or recessive alleles (i.e., dominant purple recessive hides Only when two white) recessive alleles are inherited in the F2 generation will the recessive trait show
P GENERATION (true-breeding parents) Purple flowers White flowers F1 generation All plants have purple flowers Fertilization among F1 plants (F1 x F1) /4 of plants have white flowers
1 F2 generation /4 of plants have purple flowers 3 TOPIC 3: GENETIC CROSSES (ONE & TWO-TRAIT) The inheritance of many human traits follows Mendels principles and the rules of probability PUNNETT SQUARES
Punnett square: a box like diagram used to predict all possible genotypes that result from a cross Punnett square Quick Tips: Define your dominant & recessive letter symbols: make a key Write each parents genotype Fill in Moms egg and Dads sperm varieties along the PS sides Complete the PS boxes to see all the possible genetic cross outcomes or kids genotypes LAYOUT OF PUNNETT SQUARES Kids Genotypes Symbol Key
Parent Genotypes Dad 's Spe rm vari etie s (All Mom's Egg Varieties (alleles) PUNNETT SQUARES: ONE TRAIT CROSSES MONOHYBRID CROSSES
Example 1: Having freckles is dominant trait. What is the chance that a child will have freckles if DAD is homozygous for freckles and 4/4MOM does not have freckles? ______ f f F Ff Ff F Ff Ff
Gene Notation Symbols F = freckles f = no freckles Parent Genotypes: MOM: ff DAD: FF ONE TRAIT CROSSES CONT Example 2: If two offspring from the F1 generation in Example 1 are 3/4 crossed, what is the chance that a child will have freckles? ____ F f
F FF Ff f Ff ff Gene Notation Symbols F = freckles f = no freckles Parent Genotypes: MOM: Ff DAD: Ff ONE TRAIT CROSSES CONT
Example 3: Widows peak is a dominant trait. What is the chance that a child will have a straight hairline if DAD is heterozygous for widows peak 2/4MOM has a straight hairline? and _______ Gene Notation h h Symbols H = widows peak h = straight Parent Genotypes: hairline MOM: hh DAD: Hh H
Hh Hh h hh hh PUNNETT SQUARES: TWO TRAIT CROSSES DIHYBRID CROSSES Dihybrid crosses involve two genes (traits)this means that four alleles are involved.
Punnett squares for dihybrid crosses have 16 boxes instead of 4 Law of Independent assortment: allele pairs separate independently of each other during gamete formation (meiosis) Different traits appear to be inherited TWO TRAIT CROSSES CONT Example 1: In pea plants, yellow color is dominant to green color, and round pods are dominant to wrinkled pods. If two parents are crossed who are both heterozygous for both traits, what is the phenotypic ratio of the F1 Parent Genotypes: Gene Notation
generation? Symbols Y = yellow color y = green color R = round pods r = wrinkled pods MOM: YyRr DAD: YyRr TWO TRAIT CROSSES EXAMPLE 1 CONT When you have a dihybrid cross involving 4 alleles, above each column and row should have 2 alleles, one for each trait: Mom: Y y R r
1st column: YR, 2nd: Yr, 3rd: yR, 4th: yr Dad: YyRr 1st row: YR, 2nd: Yr, 3rd: yR, 4th: yr TWO TRAIT CROSSES, EXAMPLE 1 CONT YR Yr yR yr YR
YYRR YYRr YyRR YyRr Yr YYRr YYrr YyRr Yyrr yR YyRR
YyRr yyRR yyRr yr YyRr Yyrr yyRr yyrr TWO TRAIT CROSSES, EXAMPLE 1 CONT The following genotypes result in yellow
round pea pods (phenotype): The following genotypes result in yellow, wrinkled pea pods (phenotype): YYrr, Yyrr The following genotypes result in green, round pea pods (phenotype): YYRR, YYRr, YyRR, YyRr yyRR, yyRr
The following genotypes result in green, wrinkled pea pods (phenotype): yyrr TWO TRAIT CROSSES, EXAMPLE 1 CONT To get the phenotypic ratio for the F1 generation, count how many of each phenotype there is Therefore, the phenotypic ratio is: 9:3:3:1
9 yellow, round: 3 yellow, wrinkled: 3 green, round: 1 green, wrinkled TWO TRAIT CROSSES CONT Example 2: If you take two offspring from the F1 generation: YYRr & Yyrr, what will the F2 phenotypic and genotypic ratios be? Gene Notation Symbols Y = yellow color y = green color R = round pods Moms alleles: r = wrinkled
podsYR, Parent Genotypes: MOM: YYRr DAD: Yyrr Yr, YR, Yr Dads alleles: Yr, Yr, yr, yr TWO TRAIT CROSSES, EXAMPLE 2 CONT YR Yr YR Yr Yr YYRr
YYrr YYRr YYrr Yr YYRr YYrr YYRr YYrr yr YyRr Yyrr
YyRr Yyrr yr YyRr Yyrr YyRr Yyrr TWO TRAIT CROSSES, EXAMPLE 2 CONT F2 Genotype ratio:
4 YYRr: 4 YYrr: 4 YyRr: 4 Yyrr F2 Phenotype ratio: 8 yellow, round: 8 yellow, wrinkled TOPIC 4: COMPLEX INHERITANCE PATTERNS INCOMPLETE DOMINANCE, CODOMINANCE AND SEX-LINKED TRAITS VARIATIONS ON MENDELS PRINCIPLES The relationship of genotype to phenotype is rarely simple The inheritance of some traits is more complex than Mendels principles can explain
INCOMPLETE DOMINANCE RESULTS IN INTERMEDIATE PHENOTYPES Sometimes the 2 alleles for a trait BLEND together creating an intermediate phenotype = incomplete dominance Neither allele is dominant P GENERATION White rr
Red RR Gametes R r Pink Rr F1 GENERATION R /2 1 /2 1
Eggs 1 /2 /2 r 1 R /2 R 1 Red RR r Pink Rr
Figure 9.12A F2 GENERATION /2 r 1 Pink rR White rr Sperm INCOMPLETE DOMINANCE CONT Heterozygotes show an intermediate phenotype RR = red flowers
rr = white flowers Rr = PINK flowers make 50% less color INCOMPLETE DOMINANCE CONT P X true-breeding red flowers true-breeding white flowers 100% pink flowers 100% Rr F1
generation (hybrids) self-pollinate 25% red F2 generation 50% pink 25% white 1:2:1 RR:Rr:rr INCOMPLETE DOMINANCE CONT
Example 1: In betta fish, green color is homozygous, steel blue is also homozygous, and the heterozygous trait is royal blue. What is the genotypic and phenotypic ratio of the F1 generation if a steel blue fish is crossed with a royalParents blue genotypes fish? Gene Notation Symbols BB = green color bb = steel blue color Bb = royal blue MOM = bb DAD = Bb
INCOMPLETE DOMINANCE, EXAMPLE 1 CONT b B b Bb bb b Bb bb F1 genotypic ratio: 2Bb : 2bb F1 phenotypic ratio: 2 steel blue: 2 royal blue
CODOMINANCE Codominance is when both traits are fully and separately expressed Both alleles express themselves Example: blood type AB blood type MANY GENES HAVE MORE THAN TWO ALLELES IN THE POPULATION = MULTIPLE ALLELES
Human ABO blood types are determined by 3 alleles in the human gene IA pool: IB i The alleles for A and B blood types are codominant, and have the following IA I B symbols: i The O allele is recessive = This means that there are two dominant alleles and one recessive allele, but if the two dominant alleles are together, then they are both expressed BLOOD DONATION BLOOD TYPE genotype
phenotype phenotype status I I I i type A type A oligosaccharides on surface of RBC I I I i type B type B oligosaccharides on surface of RBC
__ type AB both type A & type B oligosaccharides on surface of RBC universal recipient type O no oligosaccharides on surface of RBC universal donor A A A
B B B I I A B ii __ CODOMINANCE CONT Example 1: List all the possible blood genotypes and phenotypes and their ratios for children conceived from a male heterozygous for type A blood with a woman with homozygous type B blood.
Gene Notation Symbols IAIA or IAi= Type A blood IBIB or IBi= Type B blood A B Parents genotypes MOM = IBIB DAD = IAi CODOMINANCE, EXAMPLE 1 CONT IB IB IA
IAIB IAIB i I i IB i Genotypes IA IB IB i B fractions 2/4 =1/2 1/2
Phenotypes fractions Type AB blood 1/2 Type B blood 1/2 SEX CHROMOSOMES AND SEX-LINKED GENES Chromosomes determine sex in many species
A human female =XX A human male =XY A babys gender depends on whether Dads sperm delivers a X or Y chromosome So, should Henry the 8th have executed all of his wives for not giving him sons? SEX CHROMOSOMES autosomal chromosomes Sex chromosome GENES ON SEX CHROMOSOMES Y chromosome
SRY: sex-regulation gene master gene for maleness & male hormones X chromosome other traits beyond sex determination HUMAN X CHROMOSOME Sex-linked traits have genes on the X chromosome more than 60 diseases traced to genes on X chromosome, including: Hemophilia Duchenne muscular dystrophy color-blindness
SEX-LINKED TRAITS All genes that are carried on the X chromosome are considered to be sexlinked In many organisms, the X chromosome carries many genes unrelated to gender Fruit fly eye color is a sex-linked characteristic CONNECTION: SEX-LINKED DISORDERS AFFECT MOSTLY MALES Most sex-linked human disorders are due to recessive alleles
Examples: hemophilia, red-green color blindness A male receives a single X-linked allele from his mother, and will have the disorder, while a female has to receive the recessive X allele from both parents to be affected A C B D E Color blind testing
Color blind pictures F SEX-LINKED TRAITS CONT Example 1: Color-blindness is a sex-linked trait. Jim is not colorblind and neither is his wife, Mary. However, because Marys dad WAS colorblind, she is heterozygous for redgreen colorblindness. What are the chances that a daughter will be colorblind? What about a son? What are the chances that a daughter will be a carrier? Gene Notation Symbols XBXB = female noncarrier XBXb = female carrier
XbXb = female colorblind B Parents genotypes MOM = XBXb DAD = XBY SEX-LINKED TRAITS, EXAMPLE 1 CONT XB Xb XB XBXB XBXb
F1 phenotypes: females will be normal, females will be carriers, males will be normal, males will be colorblind Y XBY XbY The chance of having a colorblind child is .
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Thank you!Email: [email protected] This project was funded by the National Institute for Health Research (NIHR) Public Health Research (NIHR PHR) Programme (project number 09/3005/12). The views and opinions expressed therein are those of the authors and do not .
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