UNIT VI - MENDELIAN GENETICS Baby Campbell – 11,12 Big Campbell – Ch 14, 15

I. MENDEL Mendel Mendel’s Principles Alternative versions of genes known as ______________ account for variations in inherited characters. Organisms inherit _____ alleles for each trait If alleles at a locus differ; that is; if the genotype is _______________, the allele that shows is known as the ________________ allele. Law of Independent Assortment Law of Segregation

II. ANALYZING PROBABILITIES Test Cross Punnett Square Multiplication Rule States the probability of 2 or more independent events occurring together can calculated by multiplying individual probabilities For example, Determine the probability of a homozygous recessive short plant produced from F1 X F1 Cross = Probability of tt offspring =

II. ANALYZING PROBABILITIES, cont Addition Rule States that the probability of 2 or more mutually exclusive events occurring can be calculated by adding together their individual probabilities For example, Determine the probability of a heterozygous plant produced from F1 X F1

II. ANALYZING PROBABILITIES, cont Crosses Involving Multiple Characters Determine the genotype ratio of the offspring for the cross BbCCDD X BBccDd

II. ANALYZING PROBABILITIES, cont Determine the expected phenotypes of the offspring for the cross YyRrSS X yyRrss

II. ANALYZING PROBABILITIES, cont In the cross, PpYyRr X Ppyyrr, what is the probability of offspring that are purple, green, & round? P= purple, p = white Y = yellow, y = green R = round, r = wrinkled

III. VARIATIONS IN INHERITANCE Co-Dominance Both alleles affect phenotype in separate & distinguishable ways Incomplete Dominance Neither allele is dominant; heterozygotes show a blend of two homozygous phenotypes

III. VARIATIONS IN INHERITANCE, cont Epistasis Gene at one locus alters phenotypic expression of a gene at a second locus For example, A dominant allele, P causes the production of purple pigment; pp individuals are white. A dominant allele C is also required for color production; cc individuals are white. What proportion of offspring will be purple from a ppCc x PpCc cross?

III. VARIATIONS IN INHERITANCE, cont Phenotype Genotype A B AB O Multiple Alleles Many genes have more than 2 alleles Example, ABO blood groups in humans Three alleles Rh Factor A woman with O positive blood has a child with Type A negative blood. The man she claims is the father has AB positive blood. Is it possible that he is the father of this child?

III. VARIATIONS IN INHERITANCE, cont Polygenic Inheritance For example, AABBCC = very dark skin; aabbcc = very light skin. Intensity based on units; in other words, AaBbCc and AABbcc individuals would have the same pigmentation

III. VARIATIONS IN INHERITANCE, cont Pleiotropy

III. VARIATIONS IN INHERITANCE, cont Environmental Impact on Phenotypes

IV. SEX-LINKED INHERITANCE First recognized by Thomas Hunt Morgan Drosophila melanogaster Fruit flies Excellent organism for genetic studies Prolific breeding habits Simple genetic make-up; 4 pairs of chromosomes → 3 pairs of autosomes, 1 pair of sex chromosomes Crossed true-breeding wild-type females with true-breeding mutant males Mutant trait showed up in ½ male F2 offspring ; was not seen in F2 females Determined mutant allele was on X-chromosome; thus inherited differently in males versus females In females, In males,

IV. SEX-LINKED INHERITANCE, cont The gene for amber body color in Drosophila is X-linked recessive. The dominant allele produces wild type body color. The gene for black eyes is autosomal recessive; the wild type red eyes are dominant. If males with amber bodies, heterozygous for eye color are crossed with females heterozygous for eye color and body color, calculate the expected phenotype ratios in the offspring.

IV. SEX-LINKED INHERITANCE, cont X Inactivation in Females During embryonic development, one X chromosome in female cells is inactivated due to addition of methyl group to its DNA Dosage compensation Inactive X chromosome condenses; known as Barr body

IV. SEX-LINKED IN INHERITANCE, cont Occurs randomly Females will have some cells where “Dad’s copy” of X is inactivated, some where “Mom’s copy” is inactive Therefore, females are a mosaic of cells Preserved in mitosis In ovaries, Barr body chromosome is reactivated for meiosis and oogenesis

V. PEDIGREE ANALYSIS

V. PEDIGREE ANALYSIS, cont

VI. CHROMOSOMAL BASIS OF INHERITANCE Chromosomal Theory of Inheritance States genes occupy specific loci on chromosomes During meiosis, chromosomes undergo segregation & independent assortment Linked Genes During Thomas Morgan’s work with Drosophila, he recognized Two genes located on same chromosome were linked; that is, inherited together However, offspring phenotypes showed this wasn’t always true

VI. CHROMOSOMAL BASIS OF INHERITANCE, cont Linked Genes, cont In fruit flies, normal wild-type phenotype is gray body, normal wings – both genes are located on same chromosome G = wild-type (gray) body; g = black body W = wild-type wings; w = mutant wings True-breeding wild type flies X true-breeding mutants F1 showed all F1 X test cross Counted 2300 offspring Should have counted

VI. CHROMOSOMAL BASIS OF INHERITANCE, cont Linked Genes, cont Instead Morgan counted 965 GWgw 944 gwgw 206 Gwgw 185 gWgw Morgan realized variation in probabilities due to Linkage Maps In crossing over, the further apart two genes are …

VI. CHROMOSOMAL BASIS OF INHERITANCE, cont Linkage Maps, cont Recombination Frequency = # recombinants_ total # offspring One map unit = 1% recombination Morgan’s Data … F1 X test cross GW/gw X gw/gw Counted 2300 offspring Should have counted 965 GWgw 944 gwgw 206 Gwgw 185 gWgw

VI. CHROMOSOMAL BASIS OF INHERITANCE, cont In a genetics experiment with fruit flies, P generation true-breeding flies are crossed. The female parent is brown and wingless while the male parent is black with normal wings. All of the F1 flies are brown with normal wings. In the next cross, F1 females are test-crossed with black, wingless males. The following offspring are counted: 85 brown winged flies 728 black winged flies 712 brown wingless flies 75 black wingless flies How many map units apart are the two genes?

VI. CHROMOSOMAL BASIS OF INHERITANCE, cont The genes for vestigial wings, black body color, and cinnabar eyes are linked genes. In controlled crosses … The gene for vestigial wings (vg) and body color (b) have a 17% crossover rate. The gene for eye color (cn) and vestigial wings have a 9% crossover rate. The gene for eye color and body color have an 8% crossover rate. Draw the chromosome.

VII. MUTATIONS Change in the nucleotide sequence of DNA May be spontaneous mistakes that occur during replication, repair, or recombination May be caused by mutagens; for example, x-rays, UV light, carcinogens Classification Gene Chromosomal

VIII. INHERITED GENETIC DISORDERS Most often due to gene mutations Classified according to type of chromosome on which affected gene is located Autosomal Disorders X-linked Disorders Grouped according to path of inheritance

VIII. INHERITED GENETIC DISORDERS Autosomal Recessive Disorders Albinism Cystic Fibrosis PKU Tay Sachs

VIII. INHERITED GENETIC DISORDERS, cont Autosomal Co-Dominant Disorders Sickle Cell Anemia Autosomal Dominant Disorders Huntington’s Disease Marfan Syndrome Achondroplasia Hypercholesteremia

VIII. INHERITED GENETIC DISORDERS, cont X-Linked Disorders Hemophilia Colorblindness Duchenne Muscular Dystrophy

IX. CHROMOSOMAL MUTATIONS Abnormal Chromosome Structure Often due to mistakes in

IX. CHROMOSOMAL MUTATIONS, cont Abnormal Number of Chromosomes Most commonly due to nondisjunction Results in aneuploid gametes Detected with ________________________

IX. CHROMOSOMAL MUTATIONS, cont Chromosomal Number Disorders Examples Down Syndrome

IX. CHROMOSOMAL MUTATIONS, cont Turner Syndrome

IX. CHROMOSOMAL MUTATIONS, cont Klinefelter Syndrome

X. GENETIC TESTING Identification of Carriers/Genetic Counseling Gene testing is available for Tay-Sachs, sickle cell, cystic fibrosis, Huntington’s, PKU, & many others Fetal Testing Gene Testing Amniocentesis Chorionic Villus Sampling (CVS) Karyotype Newborn Screening PKU PGD Pre-Implantation Genetic Diagnosis