Presentation on theme: "GREGOR MENDEL Austrian monk Studied at the University of Vienna Discovered the basic principles of heredity Worked with breeding garden peas –Self pollinating."— Presentation transcript:
GREGOR MENDEL Austrian monk Studied at the University of Vienna Discovered the basic principles of heredity Worked with breeding garden peas –Self pollinating –Perfect flowers –Artificially cross pollinated
Mendel’s Pea Plants True breeding – all offspring same variety Hybridization – crossing 2 contrasting true breeding varieties P generation – parental generation (true breeding) F 1 – first filial (hybrids) F 2 – second filial (from self pollinating F 1 s)
Mendel tracked heritable characters for 3 generations
MENDEL’S LAWS 1.Alternative versions of genes (alleles) account for variations in inherited characters. 2.For each character, an organism inherits two alleles, one from each parent. 3.If the 2 alleles differ, then one, the dominant allele is fully expressed in the organism’s appearance; the recessive allele has no noticeable effect on the organism’s appearance 4.The 2 alleles for each character segregate during gamete production.
Law of Segregation Letters represent alleles (upper case for dominant alleles & lower case for recessive alleles) P generation – true breeding plants, matching alleles (PP or pp) Gametes contain only one allele Fusion of gametes → hybrid F 1 s
When hybrids produce gametes, the 2 alleles segregate Half the gametes receive the P allele and half receive the p allele Punnett squares show possible combinations of alleles in gametes Each square is a possible offspring
PROBABILITY LAWS 1.CHANCE HAS NO MEMORY 2.RULE OF MULTIPLICATION: the chance of 2 independent events occurring together is the product of their individual probabilities. 3.RULE OF ADDITION: the probability of an event that can occur in 2 or more different ways is the sum of the separate probabilities.
PROBABILITY PRACTICE 1)If a coin is tossed 7 times and lands heads all seven times, what is the chance of getting heads again? 2)A couple has 3 girls; what is the chance that their fourth child will be another girl? 3)In a deck of 52 cards, what is the chance of drawing: a)Any red card? b)Any ace? c)Any heart?
PROBABILITY PRACTICE 1.From a normal deck of cards, what is the chance of drawing the Jack of Hearts? 2.When tossing 2 dice, what is the probability of getting a “6” up on both? 3.What is the probability of 2 parents, with genotypes AabbCc x AaBBCc, having a child with the genotype AaBbCc?
AaBbRr x Aabbrr What fraction of the offspring will have the following genotypes? –aabbrr- AaBbRr- aaBbrr What fraction of the offspring will have at least two recessive phenotypes? a) list all possible genotypes b) calculate probabilities (rule of multiplication) c) pool probabilities (rule of addition)
Incomplete Dominance Alleles for red and white, neither is dominant. Hybrids are a blend of the two alleles and are phenotypically pink There is NO allele for pink, therefore NO true breeding pink flowering plants. Codominance: both alleles equally expressed. Human blood type, cow coloring
EPISTASIS Gene at one locus alters the phenotypic expression of a gene at a second locus Gene for fur color: (B) black (b) brown 2 nd gene deposition of pigment: (C) color (c) white
Polygenic Traits Skin color and height in humans Additive effect of 2 or more genes on 1 phenotype Quantitative characters – variation along a continuum Dots represent “units” of darkness
NATURE and NURTURE The product of a genotype is a range of phenotypic possibilities over which there may be variation due to environmental influence. Norm of reaction - Hydrangea flower color and pH (blue-pink) - Human bloodtyping: little range (genotype mandates phenotype. - Human blood counts: vary with altitude, fitness, infectious agents Norms of reaction broadest for polygenic traits like skin color. Multifactorial characters: both genetic & environmental influences.
The Chromosomal Basis of Mendel’s Laws Segregation R & r alleles Segregate Only one long chromosome In each gamete Fertilization recombines the R & r alleles Independent Assortment Long and short chromosomes; Arranged in 2 equally likely ways They assort independently Fertilization 9:3:3:1 ratio
THOMAS HUNT MORGAN Worked with Drosophila Wild type – phenotype most common in the wild. Red eyes, gray, normal wings Mutant phenotypes – white eyes, ebony, vestigial wings Discovered sex linkage Sex linked genes – on sex chromosomes
Sex Linked Inheritance Sex linked genes: on the X or Y chromosome X & Y NOT homologous X-linked genes: males being XY have only one copy/allele, females XX have two copies/alleles X-Linked recessive – more common in males X-Linked dominant – more common in females
SEX DETERMINATION Humans – sex determined by presence or absence of Y chromosome; XX-female; XY-male Fruit flies – # of X chromosomes; XX- female; XY-male; XXY-female Birds – females are heterogametic
Transmission of Sex-Linked Recessive Traits Father w/ trait Carrier passes Carrier w/ afflicted transmits to all trait to ½ sons male; 50% of daughters ½ daughters children afflicted Sons afflicted
LINKAGE Law of Linear Order: genes on the same chromosome are linked and are inherited in a block. Drosophila – 2 linked genes; inherited together –body color (G gray, g ebony) – wing size (L long, l vestigial) Test cross by Morgan produced unexpected results
MAPPING Linkage map – genetic map based on recombination frequencies Map units – one map unit = 1% recombination frequency Cytological maps – locate genes with respect to chromosomal features like stained bands
Recombination frequencies: used to construct genetic map The probability of a crossover between 2 loci is proportional to the distance separating the loci
Human Chromosomal Disorders Down Syndrome (Trisomy 21) Turner Syndrome (XO, monosomy X) Klinefelter syndrome (XXY) XYY, XXX Cri du chat (cry of the cat) deletion in #5 CML (chronic myeloid leukemia) translocation of # 22 Down Syndrome due to translocation of #21
Genomic Imprinting Prader-Willi Syndrome: –Mental retardation, obesity, short stature, small hands & feet (father) Angelman Syndrome: –Spontaneous laughter, jerky movements, other motor and mental symptoms (mother) Same cause – partial deletion of chromosome #15 Genomic Imprinting – gene on one chromosome silenced