Science 300:31 April 2003 Chromosome number error (aneuploidy) rose from 1-2% to 40% in mouse eggs! Reason- bisphenol A (BPA), a component of plastic.. ….. results in meiosis errors in mouse eggs normal BPA treated Meiosis Environment-induced disruptions in meiosis

Chromosomes and Human Genetics Chapter 11 Chromosomes and Cancer Genes on chromosomes drive ___________ __________ is uncontrolled cell division Philadelphia Chromosome First abnormal chromosome to be associated with a cancer Associated with a chronic ________ Overproduction of white blood cells Due to _____________________

Genes Units of information about _______________ Each has a particular __________ –Location on a _______________ _______________ are identical in length, size, shape, and gene sequence Different __________ forms of a gene Arise through _____________ Alleles

Fig. 11.4, p. 173 _______________- display of chromosomes

Sex Chromosomes Discovered in late ______ Mammals, fruit flies –XX is _______, XY is _________ In other groups XX is male, XY female Sex determination

The Y Chromosome < ____ genes Includes ____ gene- dictates ______ phenotype > ______ genes Most genes - _______ traits Genes expressed in both males and females The X Chromosome

Effect of Y Chromosome 10 weeks Y present Y absent 7 weeks birth approaching appearance of structures that will give rise to external genitalia appearance of “uncommitted” duct system of embryo at 7 weeks Y present Y absent testis ovary testesovaries

Thomas Hunt Morgan - first to associate a specific gene with a specific chromosome in the early 20th century. Morgan’s model-Drosophila melanogaster, a fruit fly - have three pairs of __________ and a pair of _____________ chromosomes (XX in females, XY in males). Normal is called “_________” Red eyesWhite eyes Non-normal is called “______”

Morgan’s experiments- Red eye X White eye F1 3:1 Red:white But- all __________were white, all females red All Red eye F2 Morgan concluded that a fly’s eye color was linked to the _ _____________ ___. = _ _____ _ = _______ _ Know these symbols Conclude- classic _ ________ _ genetics Fig. 15.3

Chromosome- 1.5 x 10 8 base pairs containing about _ _____ genes Genes located on the same chromosome,___ ______ ______ _, tend to be inherited together because the chromosome is passed along as a unit. Linked genes tend to be inherited together because they are located on the same chromosome 0.4% of a chromosome, containing 10 genes Results of crosses with linked genes deviate from those expected according to __ _____________________ __.

Linkage Groups Genes on one type of chromosome Fruit flies –__ homologous chromosomes –__ linkage groups -____________to the distance that separates genes ABCD Crossing over will disrupt linkage between _________ more often than _________ Crossover Frequency Frequencies can be used to construct a _______________

Incomplete Linkage Parents: F1 offspring Unequal ratios of four types of gametes: All AaCc x meiosis, gamete formation ACac A C A C A C a c a c A c a C a c Most gametes have parental genotypes A smaller number have recombinant genotypes

Linkage Mapping in Humans Chart that shows _____________ connections among individuals Knowledge of probability and Mendelian patterns used to suggest basis of a trait Called a “________” Pedigree for __________ Unusual number of toes or fingers

Genetic Disorders Autosomal _________ _________ conditions that cause mild to severe medical problems Autosomal __________ Trait typically appears in _______ generation Most of these ________ from population. WHY? Many people are _________ Heterozygous parents-- child will have a _____ chance of being affected

1. Huntington Disorder Causes involuntary movements, nervous system deterioration, death Symptoms don’t usually show up until person is past age ___ People often pass allele on before they know they have it Autosomal dominant diseases In homozygous form usually leads to _______ Heterozygotes display a type of _________ Have short arms and legs relative to other body parts 2. Acondroplasia

X-Linked Recessive Inheritance Males show disorder _________ females Son _______ inherit disorder from his father 1. Color blindness- 2. _________, Blood-clotting disorder; 1/7,000 males 3. ________- Allele has repeated segments of DNA; causes mental retardation 4. ____________________ - Appears to be dominant; spontaneous mutation; premature aging effect, early death Examples

Usually due to ________________ n + 1 n - 1 chromosome alignments at metaphase I nondisjunction at anaphase I alignments at metaphase II anaphase II The wrong number of chromosomes is bad

Nondisjunction results in too many or to few chromosomes termed ______________. – some gametes receive two of the same type of chromosome and another gamete receives no copy. –_______ cells - three copies of a particular chromosome type and have _______ total chromosomes. –_________ cells - one copy of a particular chromosome type and have 2n - 1 chromosomes. Normally results in embryonic death, but some survive Organisms with more than two _______ _sets of chromosomes, have undergone _________, e.g. 3n or 4n (rare in ____________) Polyploids are more nearly normal in phenotype than ___________.

Other chromosome problems An inversion - a chromosomal fragment ________ to the original chromosome but in the reverse orientation. In_ _______, a chromosomal fragment joins a _________ chromosome. Fig c & d Some translocations are ___________ others are not. A ________- a chromosome fragment lacking a ________ is lost during cell division A ___________- a fragment becomes attached as an extra segment to a sister chromatid

Homozygous embryos with a large ________ normally die A deletion in the X chromosome is _ ______ in males A __ ________________ can alter phenotype because a gene’s expression is influenced by its location. Results of chromosome errors Example- Leukemia is due to a growth gene being placed next to an active region resulting in cancer Approx. _____ of human embryos are aneuploid and die early in development Some are viable- Chromosome 15 trisomy- die at birth Chromsome 21 trisomy- ________ syndrome

Down syndrome- trisomy 21. –One in 700 children born in the United States. –result from ___________________ during gamete production Fig correlates with the age of the mother. Karyotype Phenotype

Extra sex chromosomes are allowed _____________________ _an XXY male, occurs once in every 2000 live births. –Male sex organs, but are_ ________. –Feminine characteristics; normal intelligence. Males with an extra Y chromosome (XYY) tend to somewhat _______ than average. Trisomy X (XXX), which occurs once in every 2000 live births, produces _ ________ _ females. Monosomy X or _____________ (X0), which occurs once in every 5000 births, produces phenotypic, but immature females. XYY and XXYY- males often found in _________.

In utero testing for genetic screening. 1. _____________ - beginning at the 14 th to 16 th week of pregnancy to assess the presence of a specific disease. Fig a Fetal cells extracted from amniotic fluid are cultured and __________. 2. _____________ ________(CVS)- performed as early as the eighth to tenth week of pregnancy. –Extracts a sample of fetal tissue from the chrionic villi of the placenta are karyotyped. Fig b

Other techniques- ____________________________ allow fetal health to be assessed visually in utero. –usually reserved for cases in which the risk of a genetic disorder or other type of birth defect is relatively great. If fetal tests reveal a serious disorder, the parents face the difficult choice of terminating the pregnancy or preparing to care for a child with a genetic disorder.