Chromosomes and Inheritance Chapter 12-1

Objectives 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

Vocabulary Amniocentesis Lethal mutation Single-allele trait Carrier Monosomy Somatic mutation Chromosome map Nondisjunction Substitution Pattern of inheritance Deletion Translocation Frame shift mutation pedigree Trisomy Point mutation Genetic disorder Polygenic trait Germ-cell mutation Sex-influenced trait Inversion Sex linkage

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 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 Genes located on one chromosome and are inherited together Crossing over is the exchange of genes Causes new gene combinations

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)

Mutation 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 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 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 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)

Pedigree Chart

Genetic Traits and Disorders Genetic disorders are diseases or debilitating conditions that have genetic basis

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 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 Controlled by 2 or more genes Show many degrees of variation Also influenced by environment (ex: height)

X-Linked Traits Found on the X chromosome Colorblindness, Hemophilia, Duchenne muscular dystrophy Not all are diseases, mostly code for protein

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 Usually causes death Monosomy -1, trisomy +1 chromosome 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 Genetic screening examines the genetic make-up through karyotype or blood tests (+ or – proteins) Genetic counseling is medical guidance for people at risk

Or immediately after birth 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