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Mendel’s Legacy Chapter 9-1 Heredity • Heredity is the transmission of characteristics from parents to offspring • Mendel observed pea plants and wanted to explain variations (performed experiments) • Concluded that Conclusions • There is a dominant (masking, capital letter) and recessive (masked but can reappear, lowercase letter) factors – Called alleles • Offspring receives 1 allele from each parent • Law of segregation- alleles for same trait are separated in gametes (sex cells aka egg and sperm) – Mom and dad gene go in different directions • Law of independent assortment- alleles for different traits are separated randomly – Have different genes from both mom and dad in gamete Genetic Crosses Chapter 9-2 Genotype and Phenotype • Genotype is the genetic makeup – Represented by letters: PP, Pp, pp • Phenotype is the appearance: purple, white • Homozygous is when both alleles are the same (pp or PP) • Heterozygous is when alleles are different (Pp) Predicting Results of Monohybrid Crosses • Monohybrid cross is a cross with one pair of traits • Dihybrid cross is a cross with two pairs of traits – Use a Punnett Square to predict offspring rryy b b B Bb Bb B Bb Bb RRYY ry ry ry ry RY RrYy RrYy RrYy RrYy RY RrYy RrYy RrYy RrYy RY RrYy RrYy RrYy RrYy RY RrYy RrYy RrYy RrYy Predicting Results of Monohybrid Crosses • Complete dominance heterozygous and homozygous dominant look the same • Incomplete dominance is when both alleles (heterozygous) influence appearance – Ex: Red allele and white allele make pink • Codominance is when both alleles (heterozygous) are expressed but do not blend – Ex: Brown and black coat on dog Incomplete Dominance R r R RR Rr r Rr rr Codominance R R r Rr Rr r Rr Rr Chromosomes and Inheritance Chapter 12-1 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 linked traits on X or Y chromosome Linkage Groups • Genes located on one chromosome and are inherited together • Crossing over is the exchange of genes – Causes new gene combinations Cell Mutations • Change in DNA of an organism • Germ mutation- only affects 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 • Study phenotype of members of the same family and make a pedigree • Carriers do not express allele but can pass it on to offspring (recessive) Genetic Traits and Disorders • Genetic disorders are diseases or debilitating conditions that have genetic basis Traits Controlled by a Single Allele • Huntington’s Disease is dominant – Most people find out in their 30s or 40s (after kids) – Discovered genetic marker • Others are controlled by homozygous recessive – 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) 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 proteins 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) – Klinefelter’s Syndrome (XXY)- feminine characteristics, mental retardation, infertile – Turner’s Syndrome (X)- female but does not mature, infertile • Just Y does not survive Detecting Human Genetic Disorders • Genetic screening uses karyotype or blood tests (+ or – proteins) • Genetic counseling is medical guidance • Test Fetus – Amniocentesis – Chorionic Villi Sampling • Or Child (after birth) – Test for phenylketonuria (PKU) which prevents the digestion of phenylananine. Can cause brain damage