2 Gregor Mendel… Father of Genetics Augustinian monkworked with garden peasstudied pea’s characteristicsformulated 2 basic laws of geneticsgoverning nature of inheritance50 yrs before we knew of chromosomes; 100 yrs before genes and DNA
3 Mendel chose to study one character at a time. Character=feature(like flower color);Trait = variant of a character (purple, white)
4 Each cell has 2 genes for a character One gene for a character is on each chromosome in a homologous pair.One chromosome /gene comes from the mother, while other chromosome /gene comes from the father.Flower ColorGenes
5 The variants (different genes for the same character) are called alleles. Flower ColorGenesPurple and white are the 2 alleles (variants) for flower color in peas.Mendel found these alternative genes are responsible for variations in inherited characters.
6 PRINCIPLE OF DOMINANCE Some alleles always show themselves…they are said to beDominant AllelesOther alleles only show themselves if they are found in pairs…they areRecessive AllelesThis is called thePRINCIPLE OF DOMINANCE
7 Dominant genes are shown as a capital letter (P) Recessive genes are shown as a small letter (p)This gives 3 possible genotypes…PPPppp
8 PPis known as pure purple orhomozygous dominantPpis known as hybridorheterozygousppis known as pure white orhomozygous recessive
9 The physical appearance that results from this pair of genes is called the PHENOTYPEPP and Pp both have at least one dominant allele so they produce purple flowers.pp has two recessive alleles so they produce white flowers.
10 Mendel’s 1st Law The Law of Segregation The two alleles for a character segregate randomly into gametes. Each gamete contains one allele.Remember…Gametes are haploid.PpP p
21 LAW OF INDEPENDENT ASSORTMENT F TtBb x TtBbTbTBTbTBtBtbtBtbEach pair of alleles segregated into gametes independent of the other pair.This is Mendel’s 2nd LawLAW OF INDEPENDENT ASSORTMENT
22 Let’s look at why this happens… BbEach character’s genes are on a different pair of homologous chromosomes, so each pair assorts independent of the other pair.Is there any time when this would not be true?
23 And the answer is….YES!If both pairs of alleles are on the same pair of homologous chromosomeTbtBGenes on the same chromosome are said to beLINKED GENESThey are inherited together (red hair/freckles)
24 How many different gametes? AaBBCcDDEeff2 · 1 · 2 · 1 · 2 · 1Multiply the # of different alleles in each pair to get the answer.Answer= 8 combinations(Examples: ABcDef, aBCDEf, etc.)Note: each gamete has one of each pair.
25 Incomplete Dominance (Blending or Partial Dominance) Some alleles aren’t completely dominant, they are partially dominant.Example: Flower color in snapdragonsR = red (incomplete dominant)r = white
27 And with Roan cattle…No, there are no pink cows…
28 Multiple AllelesSome characters have more than 2 alleles…they have multiple alleles.The ABO blood groups are an exampleof multiple alleles…the alleles areA = codominantB = codominantO = recessive
29 Genotype PhenotypeAA Type A bloodAO Type A bloodAB Type AB bloodBB Type B bloodBO Type B bloodOO Type O blood
30 P AO x BO AB AO BO OO gametes A O B O B O A O What is probability offspring will be Type A blood?
31 The ABO blood groups used to be used in cases of disputed paternity. DNA fingerprinting has replaced ABO blood grouping in these cases.
32 Autosomes & Sex Chromosomes As you recall, humans have 23 pairs of chromosomes in each cell.22 pairs are autosomes1 pair is sex chromosomes(They also have a chromosome in their mitochondria in each cell.)
33 Sex Chromosomes There are two sex chromosomes… X – required for life Y – determines sexNote that the X and Yare not homologous.Do you know why?
34 XX XY XX XY X Y What is the probability of having a son? X Who determines the child’s sex?XXXYX
35 In somatic (body) cells of females, one of the two X chromosomes is inactivated. It coils up in the corner of nucleus. It is called a Barr body.
36 Nondisjunction and Aneuploidy Things can go wrong during meiosis and a gamete can wind up with more than one of a pair of chromosomes or with no chromosome from a pair.This is abnormal segregation is called nondisjunctionThe abnormal # of chromosomes it produces is calledaneuploidy
37 Monosomy – one chromosome instead of a pair Types of AneuploidyMonosomy – one chromosome instead of a pairTrisomy – three chromosomes instead of a pair
59 Phenylketonuria is a recessive genetic disease that causes retardation Phenylketonuria is a recessive genetic disease that causes retardation. It can be controlled with diet.A “heel stick” is done at birth to detect PKU.
60 Chromosomal Mutations Deletion(whole or part of chromosome)Inversion(piece breaks off/reattaches wrong)Translocation(piece breaks off/moves to anotherchromosome)
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