Mendel and the Gene Idea Chp 14 Mendel and the Gene Idea

Blending Model vs. Particulate Model genetic material mixes like paint Parent’s traits inseparable Discreet inheritable units Traits retain separate identities

Web Lab: Mendel and his Peas Figure 14-01 Gregor Mendel Austrian Monk Did not know about DNA, genes, or chromosomes! Tried to prove particulate model of inheritance using pea plants Web Lab: Mendel and his Peas

Advantages of working with pea plants: Many different varieties Character = inheritable feature (GENE) Trait = variation of that character (ALLELE) Can control plant matings (paintbrush)

LE 14-2 Removed stamens from purple flower Transferred sperm- bearing pollen from stamens of white flower to egg- bearing carpel of purple flower Parental generation (P) Stamens Carpel Pollinated carpel matured into pod Planted seeds from pod Examined offspring: all purple flowers First generation offspring (F1)

Started with true-breeding varieties = HOMOZYGOUS If allowed to self-pollinate, all offspring had the same traits as their parent plant Then, cross-pollinated two different true-breeding varieties = HYBRIDIZATION

Hybridization

Monohybrid Cross – tracks a single character/gene P Generation Appearance: Purple flowers PP White flowers pp Genetic makeup: Gametes: P p F1 Generation hybrid Appearance: Genetic makeup: Purple flowers Pp Monohybrid Cross – tracks a single character/gene

Mendel’s Law of Segregation: Parental alleles separate (segregate) during gamete formation occurs in Metaphase I of Meiosis I only one allele per gamete

Punnett Square shows possible offspring after fertilization gametes P Generation Appearance: Purple flowers PP White flowers pp Genetic makeup: Gametes P p F1 Generation Appearance: Genetic makeup: Purple flowers Pp gametes Gametes: 1 2 P 1 2 p F1 sperm P p F2 Generation Punnett Square shows possible offspring after fertilization P PP Pp gametes F1 eggs p Pp pp 3 : 1

Phenotype Genotype PP (homozygous Purple 1 Pp (heterozygous 3 Purple 2 White 1 Ratio 3:1 Ratio 1:2:1

R r F1 Rr F2 R r Rr Rr rr 3 round: 1 wrinkled 1 RR : 2 Rr : 1 rr

Law of Dominance: The dominant allele (trait) is fully expressed and the recessive allele has no noticeable effect Recessive ≠ Bad

Test Cross Used to determine the genotype of an individual with a dominant phenotype Cross it with a homozygous recessive and observe offspring ratios

100% tall 100% Tt 1 tall : 1 dwarf 1 Tt : 1 tt T T T t Tt Tt tt t t Tt Tt Tt Tt tt t t

Law of Independent Assortment: Each allele pair segregates independently of other allele pairs during Meiosis (Metaphase I).

Dihybrid Cross: tracks two genes (characters)

9 tall purple 3 dwarf purple 3 tall white 1 dwarf white 12:4 or 3:1 TP Tp tP tp TP TTPP TTPp TtPP TtPp Tall purple Tp TTPp TtPp TTpp TtPp Ttpp tP TtPP TtPp ttPP ttPp TP Tp tP tp tp TtPp Ttpp ttPp ttpp 9 tall purple 3 dwarf purple 3 tall white 1 dwarf white 12:4 or 3:1 12:4 or 3:1

Rules of Probability & Genetics Probability ranges from 0 – 1 Rule of Multiplication: Used to determine the chance of two or more independent events occurring together Determine probability of each independent event Multiply probabilities together Ex: What is the probability (chance) that when 2 coins are flipped they will both end up heads? ½ x ½ = ¼ (or .25)

½ ½ ½ ¼ ¼ ½ ¼ ¼

Multiplication Rule Probability Problems What is the probability (chance) that 2 dice will both show a 4 when rolled? 1/6 x 1/6 = 1/36

Ex (F1): T t P p x T t P p F2: t p t p ½ x ½ x ½ x ½ = 1/16 t t p p ½

Rule of Addition What is the probability (chance) that the sum of the numbers shown on 2 dice will equal 5? Rule of Addition: used to determine the probability of an event that can occur in two or more different ways/combinations Calculate probability for each possible combination/way using Rule of Multiplication Add the probabilities for each separate combination to get the total probability

Rule of Addition What is the probability (chance) that the sum of the numbers shown on 2 dice will equal 5? Possible combinations: 1 + 4 2 + 3 3 + 2 4 + 1 1/6 x 1/6 1/6 x 1/6 1/6 x 1/6 1/6 x 1/6 1/36 + 1/36 + 1/36 + 1/36 = 4/36 ( 1/9 )

= 3/8 x 1 ¾ ½ x A a AA Aa aa b B Bb bb C c Cc

A__ B__ C__ = A__ B__ c c = A__ b b C__ = a a B__ C__ = A a AA Aa aa b

A__ B__ C__ = 3/8 A__ B__ c c = 0 A__ b b C__ = 3/8 a a B__ C__ = 1/8 Sum = 7/8 A a AA Aa aa b B Bb bb C c Cc

Text book: pages 272 - 273 All problems (#1-17) due on Tonight, work on problems: # 2, 3, 4, 7, 8, & 10

Types of Dominance Complete Dominance – one allele complete masks the other; the heterozygous (Rr) and homozygous dominant (RR) have the same phenotype The dominant allele usually codes for some protein/enzyme and the recessive allele codes for a defective protein/enzyme. Both are “expressed”, but only the dominant allele is functional and observable

Types of Dominance Codominance = two alleles expressed separately & both affect phenotype Ex: Red & White rhododendron “Roan” color in cattle CR CW CR CW

Types of Dominance Incomplete Dominance = F1 hybrids (heterozygotes) have an intermediate phenotype Results in a THIRD phenotype NOT the same as blending (F2 show all phenotypes) 1:2:1 phenotypic and genotypic ratios in F2

Fill in Interactive Question 14.6 Multiple Alleles = more than two alleles/varieties IA & IB are codominant over i Fill in Interactive Question 14.6

Blood Type practice… Suppose a father of blood type B and a mother of blood type A have a child of type O. What are the chances that their next child will be: Type O? Type B? Type A? Type AB?

Blood Type practice… Suppose a father of blood type B and a mother of blood type A have a child of type O. What are the chances that their next child will be: Type O? ¼ Type B? ¼ Type A? ¼ Type AB? ¼ IB i IA IAIB IAi IBi ii

Pleiotropy Pleiotropy = one gene has multiple phenotypic effects Ex: cystic fibrosis & sickle-cell disease

Epistasis = (“force upon”) one gene affects the expression of another gene Ex: coat color in mice BbCc BbCc Sperm 1 BC 1 bC 1 Bc 1 4 4 4 4 bc 1 BC 4 BBCC BbCC BBCc BbCc 1 bC BbCC 4 bbCC BbCc bbCc 1 BBCc BbCc BBcc Bbcc 4 Bc 1 bbcc bc BbCc bbCc Bbcc 4 9 3 4 16 16 16

M__B__ ¾ * ¾ = 9/16 brown ¾ * ¼ = 3/16 white mm __ __ ¼ * 1 = 4/16 (¼)

# alleles + 1 = # phenotypes Polygenic = additive effect of 2 or more genes on one phenotype Ex: skin color height AaBbCc AaBbCc aabbcc Aabbcc AaBbcc AaBbCc AABbCc AABBCc AABBCC 20/64 15/64 Fraction of progeny 6/64 # alleles + 1 = # phenotypes 1/64

Seven (6 alleles + 1 = 7 phenotypes) AaBbCc = 25 cm Seven (6 alleles + 1 = 7 phenotypes)

Nature vs. Nurture…. Acidic soil Basic soil

Pedigree Family tree showing relationships between family members and the pattern of inheritance across the generations

Figure 14-16

No – either he or his wife is AA, but can’t be certain Aa Aa AA aa aa Aa A_ A_ A_ Aa Aa Aa Aa aa Aa Aa A_ A_ A_ A_ A_ Aa Aa AA Aa Aa No – either he or his wife is AA, but can’t be certain

Recessive Disorders Carriers = heterozygotes (Aa) have the defective allele, but are not affected by disorder “carry” allele, but do not express it Can pass it on to offspring (50% chance) ¼ A a AA Aa aa 2/3

Recessive Disorders Cystic Fibrosis Tay-Sachs Disease Sickle-cell Disease

? 2/3 Aa x 2/3 Aa x ¼ aa = 4/36 = 1/9 A a AA Aa aa Aa Aa Aa Aa aa A_

Dominant Disorders RARE – nature will weed out (no carriers!) Achondroplasia Dwarfism Huntington’s Disease

LE 14-17a Amniocentesis Amniotic fluid withdrawn A sample of amniotic fluid can be taken starting at the 14th to 16th week of pregnancy. Fetus Centrifugation Placenta Uterus Cervix Fluid Fetal cells Biochemical tests can be performed immediately on the amniotic fluid or later on the cultured cells. Biochemical tests Several weeks Fetal cells must be cultured for several weeks to obtain sufficient numbers for karyotyping. Karyotyping

LE 14-17b Chorionic villus sampling (CVS) A sample of chorionic villus tissue can be taken as early as the 8th to 10th week of pregnancy. Fetus Suction tube inserted through cervix Placenta Chorionic villi Fetal cells Biochemical tests Karyotyping and biochemical tests can be performed on the fetal cells immediately, providing results within a day or so. Several hours Karyotyping