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Chromosomes and Inheritance. Chapter 12-1. Objectives. Distinguish among inheritance patterns D ominant , recessive, codominant , sex-linked, polygenic, incomplete dominance, multiple alleles Explain how mutations in the DNA sequence can sometime result in change of an organism

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  • Distinguish among inheritance patterns
    • Dominant, recessive, codominant, sex-linked, polygenic, incomplete dominance, multiple alleles
  • Explain how mutations in the DNA sequence can sometime result in change of an organism
  • Explain how mutations in gametes can result in change in the offspring
  • Amniocentesis
  • Carrier
  • Chromosome map
  • Deletion
  • Frame shift mutation
  • Genetic disorder
  • Germ-cell mutation
  • Inversion
  • Lethal mutation
  • Monosomy
  • Nondisjunction
  • Pattern of inheritance
  • pedigree
  • Point mutation
  • Polygenic trait
  • Sex-influenced trait
  • Sex linkage
  • Single-allele trait
  • Somatic mutation
  • Substitution
  • Translocation
  • Trisomy
sex determination
Sex Determination
  • X is female and Y is male (smaller chromosome)
  • After meiosis II, one cell gets X and one get Y (from male parent)
  • 50% chance of being male or female
sex linkage
Sex Linkage
  • Sex linkage is on sex chromosome
  • More genes on X chromosome than on Y
  • When on X, called X-linked genes
  • When on Y, called Y-linked genes
linkage groups
Linkage Groups
  • Genes located on one chromosome and are inherited together
  • Crossing over is the exchange of genes
    • Causes new gene combinations
chromosome mapping
Chromosome Mapping
  • The farther apart on the chromosome, the likelier crossover will happen
  • Chromosome map shows the linear sequence of genes on the chromosome through breeding experiments
  • One map unit are 2 genes separated by crossing over 1% of the time (closer together, less likely to be seperated)
  • Change in DNA of an organism
  • Germ mutation- no affect, in gametes (offspring?)
  • Somatic mutations- in body cells, do not affect offspring
  • Lethal mutations- cause death usually before birth
  • Some mutations are beneficial
chromosome mutations
Chromosome Mutations
  • Deletion is the loss of a piece of chromosome
  • Inversion is when a piece breaks off and reattaches backwards
  • Translocation is when a breaks off and reattaches to another nonhomologous chromosome
  • Nondisjunction is when the chromosome doesn’t separate and the gamete gets an extra
gene mutations
Gene Mutations
  • Point mutation-substitution, addition, or removal of a nucleotide
  • Substitution- one nucleotide is replaced with another and makes a new codon
    • Sickle cell anemia- adenine is substituted for thymine
  • Insertion is when a nucleotide is added and deletion is when one is lost
    • Both are serious and cause frame shift mutation (all codons moved)
human genetics


Chapter 12-2

studying human inheritance
Studying Human Inheritance
  • Geneticists focus on disease
  • Usually study phenotype of members of the same family and make a pedigree
  • Patterns of inheritance are predictable patterns throughout generations
  • Carriers do not express allele but can pass it on to offspring (recessive)
genetic traits and disorders
Genetic Traits and Disorders
  • Genetic disorders are diseases or debilitating conditions that have genetic basis
traits controlled by a single allele
Traits Controlled by a Single Allele
  • Single allele traits controlled by a single allele of a gene
  • Huntington’s Disease controlled by a dominant allele
    • Most people do not know they have the disease until after they have children (in their 30s or 40s)
    • Discovered genetic marker (short section of DNA that is known to have association with nearby gene)
  • Others are controlled by homozygous recessive traits
    • Cystic fibrosis and sickle-cell anemia
traits controlled by multiple alleles
Traits Controlled by Multiple Alleles
  • 3 or more alleles of the same gene for a single trait
    • ABO blood type (IA, IB, i)
      • A has A antigen, B has B antigen, AB has both, O has none
      • A person with Rh- blood cannot receive Rh+ blood

Blood Typing

polygenic traits
Polygenic Traits
  • Controlled by 2 or more genes
  • Show many degrees of variation
  • Also influenced by environment (ex: height)
x linked traits
X-Linked Traits
  • Found on the X chromosome
  • Colorblindness, Hemophilia, Duchenne muscular dystrophy
  • Not all are diseases, mostly code for protein
sex influenced traits
Sex-Influenced Traits
  • The presence of male or female sex hormones influence traits
  • Ex: male pattern baldness
    • Both male and female homozygous will lose hair
    • Heterozygous males will lose hair, female will not
disorders due to nondisjunction
Disorders Due to Nondisjunction
  • Usually causes death
  • Monosomy -1, trisomy +1chromosome
    • Down Syndrome (trisomy-21) has an extra chromosome 21
    • Klinefelter’s Syndrome (XXY) has feminine characteristics, mental retardation, infertile
    • Turner’s Syndrome (X) is female but does not mature, infertile
      • Just Y does not survive
detecting human genetic disorders
Detecting Human Genetic Disorders
  • Genetic screening examines the genetic make-up through karyotype or blood tests (+ or – proteins)
  • Genetic counseling is medical guidance for people at risk

Can also test fetus

    • Amniocentesis removes fluid from around fetus
    • Chorionic villi sampling removes tissue from between the uterus and placenta
  • Or immediately after birth
    • Some babies have phenylketonuria (PKU) which prevents the digestion of phenylananine and can cause brain damage
      • Can be prevented by removing from the diet