Genetic Abnormalities

Mutation: any mistake or change in DNA sequence

Point mutation: change in one nitrogen base in DNA; Ex: albinism

Silent: results in same aa (or one that does not negatively impact protein) Nonsense: premature STOP (sickle cell) Missense: codes for different aa

Frameshift Mutation

Frameshift THE FAT CAT ATE THE RAT Insert “H” in “THE” (at the beginning) THH EFA TCA TAT ETH ERA… Delete “H” from “THE” (at the beginning) TEF ATA ATA TET HER T…

Insertion vs. Deletion

Crossing Over Occurs naturally during Meiosis I Two homologous chromosomes overlap Some genes cross over and switch places

Crossing Over Chromosomal crossover (or crossing over) is the exchange of genetic material between homologous chromosomes that results in recombinant chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis during a process called synapsis.

Crossing Over

Describe common mutation types. Chromosomal mutation: part of a chromosome is lost, added, or moved to another chromosome; usually not passed on because zygote dies Crossing over: occurs when chromosomes exchange genes. (This is supposed to happen, but mistakes can occur.)

Chromosomal Mutations

Nondisjunction Nondisjunction: occurs when a chromosome pair fails to separate properly during meiosis Results in gamete with abnormal number of total chromosomes

Types of nondisjunction Monosomy: when gamete has one less chromosome than it should; if it joins with another gamete the zygote would have only 45 chromosomes Ex: Turner syndrome Missing a sex chromosome

Types of nondisjunction Trisomy: when gamete has one more chromosome than it should; if it joins with another gamete, the zygote would have 47 chromosomes Ex: Down’s syndrome, extra #21

Nondisjunction

Trisomy

Trisomy

Monosomy

Karyotype vs . Pedigree Karyotype: a photo of an individual’s chromosomes Pedigree: a family tree (usually tracing the occurrence of a particular trait or disease)

Karyotype A picture of an organism’s chromosomes Can be used to determine if there are genetic abnormalities

Karyotyping: pictures of chromosomes are matched up according to size

Pedigree symbols

Pedigree

Pedigree chart

Pedigree Generations Individuals

Sex Linked Trait Pedigree

Describe methods of detection Ultrasound: sound waves are used to generate an image of the unborn child. Used to detect abnormalities of limbs, organs, etc. Also called sonogram

Amniocentesis: fluid surrounding the fetus is drawn out by needle, fetal cells are collected and grown in a lab. Chromosomes can be then karyotyped

Chorion villi sampling: a sample of the chorion (membrane surrounding fetus) is taken, chemical tests and karyotyping are performed

Quiz 1 A ___ mutation occurs when part of a chromosome is lost. a. chromosomal b. crossing over c.point In ___ a gamete has one less chromosome than it should . a. disomy b. monosomy c. trisomy ___ occurs when chromosomes overlap and genes change places. a. chromosomal b. crossing over c. point In ___ a needle withdraws a small amount of fluid from around the fetus for testing. a. amniocentesis b. chorion villi sampling c. ultrasound In ___ pictures of chromosomes are cut out and matched up in pairs. a. DNA fingerprint b. karyotyping c. ultrasound

Interpret testcrosses Testcross: way of determining genotype Cross individual of unknown genotype with homozygous recessive If all offspring resemble “unknown” then it is homozygous dominant If some offspring resemble homozygous recessive parent, unknown is a hybrid Testcrosses are used in breeding plants and animals if a certain offspring is needed

Interpret pedigrees Pedigrees: graphic representation of family tree Symbols identify sex, if they are carriers, if they have a certain trait, etc. May be used if testcross cannot be made