Biol 1411 1st Edition Lecture 19 Outline of Last Lecture I Genetic Linkage Outline of Current Lecture I More Genetics a Genetic Maps b Sex Chromosomes c X linked d Probabilities Current Lecture What is the relationship between genes and chromosomes o All of the loci on a chromosome form a linkage group o Recombinant frequencies can be used to make genetic maps showing the arrangement of genes along a chromosome o Distance between genes map unit 100 x recombinant frequency o 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 Chromosomes o Sex determination varies among species o In most dioecious organisms two separate sexes sex is determined by a gene or genes o The gene s with primary control of sexual development are present on the sex chromosomes o Other chromosomes are called autosomes Human Chromosomes o Human Karyotype 23 pairs of homologous chromosomes 2n 46 22 pairs of autosomes a single pair of sex chromosomes o 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 zygote These 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 Chromosomes o Genes on sex chromosomes exhibit sex linked inheritance o The Y chromosome carries few genes the X chromosome carries many genes involved in a variety of functions o 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 carriers o Mutant phenotype can skip a generation if it passes from a male to his daughter and then grandson X chromosomes o Females inherit the single X chromosome of their father o Females and males inherit a single X chromosomes from their mother Nondisjunction of sex chromosomes o 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 II o 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 Rules o 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 25 o 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 5 o 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 humans o Single gene disorders Most are rare Caused by a mutant allele of a single gene This genetic change alone results in a change in phenotype o Some well studied examples Recessive Disorders both alleles have to be mutant Dominant disorders
View Full Document
Unlocking...