Unit 4: Genetics C HAPTER 11: C HROMOSOMES AND H UMAN I NHERITANCE

H UMAN C HROMOSOMES  Most animals have a _________number of chromosomes: _____  Humans have ____ pairs of chromosomes  All (except one) of those pairs are called _______________  Same length, shape, and centromere location  Humans have ___  ______ _______________ are the last pair

S EX C HROMOSOMES  Sex chromosomes determine ________  Males : ___  Females: ____  X and Y chromosomes differ in length, shape, and the genes they carry

___ __________  Each egg contains 22 autosomes + an X chromosome  Sperm will contain 22 autosomes + either an X chromosome OR a Y chromosome  Egg and sperm combine  either XX (female) or XY (male)  Reference figure 11.2, pg. 170

S EX D ETERMINATION : Y C HROMOSOME  Fewer than two dozen genes identified  The Y chromosomes carries the ____ ______  Master gene for male sex determination  Expression of SRY gene triggers formation of ________, which are the primary male sex organs (or gonads)  These secrete ________________, which is responsible for the male secondary sex traits

S EX D ETERMINATION  Absence of the male-determining SRY gene in females results in the formation of ovaries  Mutations in the SRY gene causes individuals who are XY to develop as females  The X chromosome codes for sexual traits but ALSO carries many genes for nonsexual traits  X chromosome carries over ______ genes  Males only have one copy of these genes Reference figure 11.2

K ARYOTYPING  A _____________ is a diagnostic tool that is a preparation of an individual’s metaphase chromosomes  Mitosis is arrested in _________  Chromosomes are photographed, and then cut out and arranged by pairs according to size, shape, and length  Array can be compared to a normal standard and analyzed for extra or missing chromosomes

K ARYOTYPING Figure 11.3, pg. 171

H UMAN GENETIC ANALYSIS  Humans are difficult to study genetically due to long life spans (compared to a fruit fly or a garden pea) and small families  Data on human inheritance is displayed in _________________  A pedigree is a chart that shows genetic connections among individuals  Analysis of family pedigrees provides data on inheritance patterns through several generations

P EDIGREES  Knowledge of ______________ and ________________________________ is used in analysis of pedigrees to yield clues to a trait’s genetic basis  Conclusions most accurate when drawn from large number of pedigrees  Can be used to predict the risk of disease in future offspring in a family (genetic counseling)

P EDIGREES  Uses standardized symbols:  Squares = ________, Circles = ______  Shaded squares/circles = those who carry trait of interest  Horizontal line between male/female = __________________  Number generations from oldest (top) to youngest (bottom) with Roman numerals  Number individuals within a generation from oldest (left) to youngest (right) with Arabic numerals

E XAMPLE P EDIGREE

A PEDIGREE FOR POLYDACTYLY Polydactyly: An unusual number of fingers of toes Figure 11.17, pg. 180

G ENETIC DEVIATIONS  Genetic ________________ is a term applied to a genetic condition that is a deviation for the usual (or average) and is not life-threatening  Rare or less common version of a trait  Genetic ______________ is used to describe conditions that cause medical problems  ______________ is a recognized set of symptoms that characterize an abnormality or disorder  A disease is an illness caused by infection or environmental factors  A genetic _____________ is a term used only when factors alter previously workable genes in a way that disrupts body functions

A UTOSOMAL I NHERITANCE P ATTERNS  Some alleles on autosomes are inherited in simple Mendelian patterns  Certain mutated forms of alleles give rise to genetic abnormalities or genetic disorders

______________________ Figure 11.4a, pg. 172

A UTOSOMAL D OMINANT I NHERITANCE  The dominant allele is nearly always expressed, even in heterozygotes  If one parent is heterozygous and the other homozygous recessive, there is a 50% chance that their child will be heterozygous  If the gene (and its resulting disorder) reduces the chance of surviving or reproducing, its frequency should decrease  However, it may not due to:

E XAMPLES : A UTOSOMAL D OMINANT  Acondroplasia (dwarfism)  A benign abnormality that does not affect persons’ ability to reproduce  Adults have abnormally short arms and legs  Huntington disease  A serious degeneration of the nervous system with an onset from age 40 onwards  At this point, the gene has typically been passed from parent to offspring unknowingly

____________________ Figure 11.4b, pg 172

A UTOSOMAL RECESSIVE INHERITANCE  Either parent can carry the recessive allele on an autosome  Heterozygotes are symptom-free; homozygotes are affected  Two heterozygous parents have a 50% chance of producing heterozygous children and a 25 percent chance of producing a homozygous- recessive child  When both parents are homozygous, all children can be affected

E XAMPLE : A UTOSOMAL R ECESSIVE  Galactosemia: the inability to metabolize lactose  A single gene mutation prevents the manufacture of an enzyme needed in the conversion pathway  Lactose  galactose  glucose-6- phosphate, which can be converted to glycogen or enter glycolysis

N UEROBIOLOGICAL DISORDERS  Nuerobiological disoders (NBDs) include:  Changes in genes contribute to the abnormal biochemistry in NBDs  Most NBDs involve multiple genes and environment factors – not just a single allele  Some mutated alleles are linked to these disorders and can predispose a person

H UTCHINSON -G ILFORD P ROGERIA SYNDROME  Premature aging is caused by a mutated allele  In one of 8 million newborn humans, a mutated gene will cause accelerated aging  Observable symptoms arise by age two  Their skin thins, skeletal muscles weaken, bone growth ceases, hair loss occurs, and they “look old”  Most progeriacs expect to die in their teens

______ I NHERITANCE PATTERNS  Certain dominant and recessive alleles on the X chromosome are inherited in Mendelian patterns  Approximately _________ of all genes are located on the X chromosome  Mutated alleles on the X chromosome contribute to more than 300 known genetic disorders  Males can’t transmit X-linked alleles to sons:

X- LINKED INHERITANCE  In X-linked recessive inheritance, the mutated gene occurs only on the X chromosome  Males are more often affected because a single recessive allele on the X chromosome cannot be masked by a dominant gene on another chromosome  Heterozygous females are phenotypically normal

X- LINKED INHERITANCE Figure 11.7, pg. 174

X- LINKED INHERITANCE  A normal male mated with a female heterozygote (or carrier):  Homozygous recessive female and a normal male:

H EMOPHILIA A  Hemophilia is a serious X-linked recessive condition that prevents blood from clotting properly  The blood cannot clot because the genes do not code for the necessary clotting agent or agents  Today, hemophilia affects about 1 in 7,500 people  This number may be increasing because hemophilia is now treatable Reference Figure 11.8 (pg 174)

R ED -G REEN C OLOR B LINDNESS  Color blindness is the inability to distinguish colors  Mutated genes change the light-absorbing capacity of sensory receptors in the eyes  Normal people can distinguish among 150 colors  People with red-green color blindness can only see 25 colors (or fewer)  Males are 12 times more likely than women to be affected by color blindness

D UCHENNE MUSCULAR DYSTROPHY  Duchenne Muscular Dystrophy (DMD) affects about 1 in 3,500 boys  It’s characterized by a rapid degeneration of muscles  A recessive allele encodes for dystrophin, a structural protein in muscle fibers  Abnormal or absent dystrophin causes the muscle degeneration