Biol 1411 1st Edition Lecture 19 Outline of Last Lecture I. Genetic LinkageOutline of Current Lecture I. More Geneticsa. Genetic Mapsb. Sex Chromosomesc. X-linkedd. Probabilities Current Lecture- What is the relationship between genes and chromosomes?o All of the loci on a chromosome form a linkage groupo Recombinant frequencies can be used to make genetic maps showing the arrangement of genes along a chromosomeo Distance between genes= map unit = 100 x recombinant frequencyo Map unit also called a centimorgan (cM)- Genetic map anchored at one end of the linkage group, the Zero position. Since map units are additive, the total map length represents the summation of smaller intervals. - Sex Chromosomeso Sex determination varies among specieso In most dioecious organisms (two separate sexes), sex is determined by a gene orgeneso The gene(s) with primary control of sexual development are present on the sex chromosomeso Other chromosomes are called autosomes- Human Chromosomeso Human Karyotype: 23 pairs of homologous chromosomes (2n=46), 22 pairs of autosomes, a single pair of sex chromosomeso Mammals in general Female have 2 X chromosomes Male has an X and Y chromosome Male produce two types of gametes (heterogamic) which determine the sex of the zygoteThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. The SRY gene (sex-determining region on the Y) encodes a protein that initiates male development - In other animals, sex determination by Chromosomes is different from mammals (Bees, fruit flies, birds (ZW), mammals) - Human Sex Chromosomeso Genes on sex chromosomes exhibit sex-linked inheritanceo The Y chromosome carries few genes; the X chromosome carries many genes involved in a variety of functionso Thus, males have only one copy of the genes on the X- hemizygous- and express the phenotype of the allele- Reciprocal Crosses: white x wild type (male and female) - X-linked recessive phenotypes:o Appear much ore often in males than females; heterozygous females are carrierso Mutant phenotype can skip a generation if it passes from a male to his daughter and then grandson - X chromosomeso Females inherit the single X chromosome of their fathero Females and males inherit a single X chromosomes from their mother - Nondisjunction of sex chromosomeso Sex chromosome abnormalities can result from nondisjunction in meiosis Pair of homologous chromosomes fail to separate in meiosis I  Pair of sister chromatids fail to separates in meiosis IIo Result in aneuploidy- abnormal number of chromosomes XO- the individual has only one sex chromosome- Turner syndrome XXY- Klinefelter syndrome, affects males and results in sterility and overlong limbs - Probability Ruleso Probability (p) is a measure of the likelihood of an event occurring, with a value between 0 and 1 o Probability of 2 independent events happening together- apply the multiplication rule Tossing 2 coins- probability both outcomes are heads: .5 x .5 = .25o Probability of an event that can occur in 2 different (mutually exclusive) ways is the sum of the individual probabilities- apply the addition Rule Tossing 2 coins and getting 1 head and 1 tail: 2 different ways so .24 + .25 = .5o Application of the rules of probability to genetic crosses Probabilities of F2 genotypes from a monohybride cross- Example: Ss x Ss- Probability of getting two dominant alleles (SS) = p(S) from sperm x p(S) from egg = .5 x .5 = .25 (multiplication)- Probability of getting two recessive alleles (ss) also .25- There are 2 mutually exclusive ways to get a heterozygote: S form sperm, s from egg or inverse- P= (.5x.5) + (.5x.5) =.5 ( multiplication then addition)- Mendelian inheritance in humanso Single gene disorders Most are rare Caused by a mutant allele of a single gene This genetic change alone results in a change in phenotypeo Some well studied examples Recessive Disorders (both alleles have to be mutant) Dominant