Chromosomes, Mapping, and the Meiosis-Inheritance Connection
Chapter 12 Chromosomes and Human Inheritance. Objectives 1. Describe how an understanding of...
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Transcript of Chapter 12 Chromosomes and Human Inheritance. Objectives 1. Describe how an understanding of...
Chapter 12Chapter 12
Chromosomes and Human Chromosomes and Human InheritanceInheritance
ObjectivesObjectives
1. Describe how an understanding of chromosomes helps to account for events that compose mitosis and meiosis.
2. Name some ordinary and extraordinary chromosomal events that can create new phenotypes (outward appearances).
3. Understand how changes in chromosome structure and number can affect the outward appear ance of organisms.
4. Distinguish autosomal recessive inheritance from sex-linked recessive inheritance.
ObjectivesObjectives
5. Give examples of each of the above types of inheritance.
6. Discuss how fruit fly experiments have helped us understand chromosomal behavior.
7. Explain how changes in chromosomal number can occur and present an example of such a change.
8. List examples of phenotypic defects and describe how each can be treated.
ObjectivesObjectives
9. Explain how knowing about modern methods of genetic screening can minimize potentially tragic events.
Neurobiological disorders (NBDs) include Neurobiological disorders (NBDs) include schizophrenia, depression, bipolar schizophrenia, depression, bipolar disorder, and autism.disorder, and autism.
Schizophrenia is a neurobiological Schizophrenia is a neurobiological disorder (1 of every 100 people)disorder (1 of every 100 people)
Symptoms: delusions, hallucinations, Symptoms: delusions, hallucinations, disorganized speech, abnormal social disorganized speech, abnormal social behaviorbehavior
12.0 12.0 Strange Genes, Tortured Strange Genes, Tortured MindsMinds
Emotionally healthy people who show Emotionally healthy people who show creative brilliance tend to have personality creative brilliance tend to have personality traits in common with the mentally traits in common with the mentally impairedimpaired (p186) (p186)
Altered gene expression in certain brain Altered gene expression in certain brain regions may boost creativity as well as regions may boost creativity as well as invite illness (p187)invite illness (p187)
Strange Genes, Richly Tortured Strange Genes, Richly Tortured MindsMinds
12.1 Human Chromosomes 12.1 Human Chromosomes
Some genes on chromosomes control cell Some genes on chromosomes control cell growth and divisiongrowth and division
If something affects chromosome structure If something affects chromosome structure at or near these loci, cell division may at or near these loci, cell division may spiral out of controlspiral out of control
This can lead to cancerThis can lead to cancer
Genes Genes
Units of information about heritable traitsUnits of information about heritable traits
In eukaryotes, distributed among In eukaryotes, distributed among
chromosomes chromosomes
Each has a particular locus Each has a particular locus Location on a chromosomeLocation on a chromosome
Homologous ChromosomesHomologous Chromosomes
Homologous autosomes are identical in Homologous autosomes are identical in length, size, shape, and gene sequencelength, size, shape, and gene sequence
Sex chromosomes are nonidentical but Sex chromosomes are nonidentical but still homologous (Human X & Y)still homologous (Human X & Y)
Homologous chromosomes interact, Homologous chromosomes interact, then segregate from one another during then segregate from one another during meiosismeiosis
AllelesAlleles
Different molecular forms of a geneDifferent molecular forms of a gene
Arise through mutationArise through mutation
Diploid cell has a pair of alleles at each Diploid cell has a pair of alleles at each
locuslocus
Alleles on homologous chromosomes may Alleles on homologous chromosomes may
be same or differentbe same or different
Sex ChromosomesSex Chromosomes
Discovered in late 1800sDiscovered in late 1800s
Mammals, fruit fliesMammals, fruit flies XX is female, XY is maleXX is female, XY is male
In other groups XX is male, XY femaleIn other groups XX is male, XY female
Human X and Y chromosomes function as Human X and Y chromosomes function as
homologues during meiosishomologues during meiosis
12.2 Karyotype Preparation - 12.2 Karyotype Preparation - Stopping the Cycle Stopping the Cycle
Cultured cells are arrested at metaphase Cultured cells are arrested at metaphase by adding colchicine – a poison that by adding colchicine – a poison that prevents microtubules from forming.prevents microtubules from forming.
This is when cells are most condensed This is when cells are most condensed and easiest to identifyand easiest to identify
Karyotype PreparationKaryotype Preparation
Arrested cells are broken openArrested cells are broken open Metaphase chromosomes are fixed Metaphase chromosomes are fixed
and stainedand stained Chromosomes are photographed Chromosomes are photographed
through microscopethrough microscope Photograph of chromosomes is cut Photograph of chromosomes is cut
up and arranged to form karyotype up and arranged to form karyotype diagramdiagram
Fig. 12-3f, p.189
Karyotype DiagramKaryotype Diagram
Philadelphia ChromosomePhiladelphia Chromosome
First abnormal chromosome to be associated First abnormal chromosome to be associated
with a cancerwith a cancer (Spectral Karyotype using (Spectral Karyotype using
colored fluorescent dyes.colored fluorescent dyes.
Reciprocal translocationReciprocal translocation
Causes chronic myelogenous leukemia Causes chronic myelogenous leukemia
(CML)(CML)
12.3 Autosomal 12.3 Autosomal Dominant InheritanceDominant Inheritance
Trait typically Trait typically appears in appears in every every generationgeneration
Fig. 12-10a, p. 190
Huntington DisorderHuntington Disorder
Autosomal dominant alleleAutosomal dominant allele Causes involuntary movements, nervous system Causes involuntary movements, nervous system
deterioration, deathdeterioration, death Symptoms don’t usually show up until person is Symptoms don’t usually show up until person is
past age 30past age 30 People often pass allele on before they know People often pass allele on before they know
they have itthey have it
AchondroplasiaAchondroplasia
Autosomal dominant alleleAutosomal dominant allele In homozygous form usually leads to In homozygous form usually leads to
stillbirthstillbirth Heterozygotes display a type of dwarfismHeterozygotes display a type of dwarfism Have short arms and legs relative to other Have short arms and legs relative to other
body partsbody parts
Autosomal Recessive Autosomal Recessive Inheritance PatternsInheritance Patterns
If parents are If parents are
both both
heterozygous, heterozygous,
child will have a child will have a
25% chance of 25% chance of
being affected being affected
Fig. 12-10b, p. 191
GalactosemiaGalactosemia
Caused by autosomal recessive alleleCaused by autosomal recessive allele Gene specifies a mutant enzyme in the Gene specifies a mutant enzyme in the
pathway that breaks down lactose – may lead pathway that breaks down lactose – may lead to death if not treated.to death if not treated.
galactose-1-phosphate
enzyme 2
lactose galactose
enzyme 1
+glucose
galactose-1-phosphate
enzyme 3
intermediatein glycolysis
12.4 Hutchinson-Gilford 12.4 Hutchinson-Gilford ProgeriaProgeria
Mutation causes accelerated agingMutation causes accelerated aging
No evidence of it running in familiesNo evidence of it running in families
Appears to be dominant (1 out of 8 million Appears to be dominant (1 out of 8 million
births.)births.)
Seems to arise as spontaneous mutationSeems to arise as spontaneous mutation
Usually causes death in early teens Usually causes death in early teens
Sex determination: The Y Sex determination: The Y ChromosomeChromosome
Carries 255 genes, one is the master Carries 255 genes, one is the master
gene for male sex determination gene for male sex determination SRY gene (sex-determining region of Y)SRY gene (sex-determining region of Y)
SRY present, testes formSRY present, testes form
SRY absent, ovaries formSRY absent, ovaries form
The X ChromosomeThe X Chromosome
Carries 1,141 genesCarries 1,141 genes
Most genes deal with nonsexual traits, ex. Most genes deal with nonsexual traits, ex. Blood clotting factors.Blood clotting factors.
Genes on X chromosome can be Genes on X chromosome can be expressed in both males and femalesexpressed in both males and females
x
x
eggs sperm
diploidgerm cellsin female
diploidgerm cellsin male
meiosis, gameteformation in bothfemale and male:
sex chromosomecombinations
possible in newindividual
Fertilization:
XX XX
X
X
Y
X
XX
X
X XY XY
Fig. 12-8a, p.192
Sex Sex Determination Determination
Thomas Morgan Embryologist – Thomas Morgan Embryologist – discovered sex-linked outcomes of discovered sex-linked outcomes of hemophilia in males.hemophilia in males.
DrosophilaDrosophila, fruit fly’s X chromosome has , fruit fly’s X chromosome has the gene for eye color and another gene the gene for eye color and another gene for body color (p193)for body color (p193)
Reciprocal crossesReciprocal crosses
12.6 X-linked Inheritance12.6 X-linked Inheritance
Discovering Discovering Linkage Linkage
homozygous dominant female
recessive male
Gametes:
XX X Y
All F1 have red eyes
x
1/4
1/4
1/4
1/4
1/2
1/2 1/2
1/2
F2
generation:
XX X Y
xGametes:
12.7 X-Linked Recessive 12.7 X-Linked Recessive InheritanceInheritance
Males show Males show disorder more disorder more than femalesthan females
Son cannot inherit Son cannot inherit disorder from his disorder from his fatherfather
Fig. 12-10, p.194
Examples of X-Linked TraitsExamples of X-Linked Traits
Color blindness (Red-Green)Color blindness (Red-Green) Inability to distinguish among some of all Inability to distinguish among some of all
colorscolors
HemophiliaHemophilia Blood-clotting disorderBlood-clotting disorder 1/7,000 males has allele for hemophilia A1/7,000 males has allele for hemophilia A Was common in European royal familiesWas common in European royal families
Fig. 12-12, p.195
Color BlindnessColor Blindness
Fig. 12-11, p.194
HemophiliaHemophilia
Father with Hemophilia and Mother Carrier Genetics
Fragile X SyndromeFragile X Syndrome
An X-linked recessive disorderAn X-linked recessive disorder
Causes mental retardationCauses mental retardation
Mutant allele for gene that specifies a Mutant allele for gene that specifies a
protein required for brain developmentprotein required for brain development
Allele has repeated segments of DNAAllele has repeated segments of DNA
12. 8 Duplication12. 8 Duplication
Gene sequence that is repeated several to Gene sequence that is repeated several to
hundreds of times hundreds of times
Duplications occur in normal Duplications occur in normal
chromosomeschromosomes
May have adaptive advantageMay have adaptive advantage Useful mutations may occur in copyUseful mutations may occur in copy
DuplicationDuplication
normal chromosome
one segment repeated
three repeats
DeletionDeletion
Loss of some segment of a chromosomeLoss of some segment of a chromosome Most are lethal or cause serious disorderMost are lethal or cause serious disorder
DeletionDeletion
Cri-du-chatCri-du-chat
Fig. 12-13, p.196
InversionInversion
A linear stretch of DNA is reversed A linear stretch of DNA is reversed
within the chromosomewithin the chromosome
segments G, H, I become inverted
In-text figureIn-text figurePage 196Page 196
TranslocationTranslocation
A piece of one chromosome becomes A piece of one chromosome becomes attached to another nonhomologous attached to another nonhomologous chromosomechromosome
Most are reciprocalMost are reciprocal Philadelphia chromosome arose from a Philadelphia chromosome arose from a
reciprocal translocation between reciprocal translocation between chromosomes 9 and 22chromosomes 9 and 22
In-text figurePage 206
TranslocationTranslocation
one chromosome
a nonhomologouschromosome
nonreciprocal translocation
In-text In-text figurefigure
Page 196Page 196
Chromosome StructureChromosome Structure
Alterations to chromosome structure are Alterations to chromosome structure are usually badusually bad
Duplications are adaptive: one gene Duplications are adaptive: one gene functions normally - the other is free to functions normally - the other is free to mutatemutate
Chromosome structure evolvesChromosome structure evolves
Chromosome StructureChromosome Structure
Human body cells have 23 pairs of Human body cells have 23 pairs of chromosomeschromosomes
Chimpanzees, gorilla, or orangutan body cells Chimpanzees, gorilla, or orangutan body cells have twenty-four pairs of chromosomeshave twenty-four pairs of chromosomes
During human evolution, two chromosomes in During human evolution, two chromosomes in an early ancestor fused to form chromosome 2 an early ancestor fused to form chromosome 2 (p197)(p197)
Fig. 12-15, p.197
chimpanzeehuman gorilla orangutan
Chromosome Chromosome StructureStructure
12.9 Aneuploidy12.9 Aneuploidy
Individuals have one extra or less Individuals have one extra or less chromosome chromosome
(2(2nn + 1 or 2 + 1 or 2nn - 1) - 1) Major cause of human reproductive Major cause of human reproductive
failurefailure Most human miscarriages are Most human miscarriages are
aneuploids aneuploids
PolyploidyPolyploidy
Individuals have three or more of each Individuals have three or more of each type of chromosome (3type of chromosome (3nn, 4, 4nn))
Common in flowering plantsCommon in flowering plants Lethal for humansLethal for humans
99% die before birth99% die before birth Newborns die soon after birthNewborns die soon after birth
NondisjunctionNondisjunction
n + 1
n + 1
n - 1
n - 1chromosome alignments at metaphase I
nondisjunction at anaphase I
alignments at metaphase II anaphase II
Figure 12.16Page 198
Down SyndromeDown Syndrome
Trisomy of chromosome 21Trisomy of chromosome 21 Mental impairment and a variety of Mental impairment and a variety of
additional defectsadditional defects Can be detected before birthCan be detected before birth Risk of Down syndrome increases Risk of Down syndrome increases
dramatically in mothers over age 35dramatically in mothers over age 35
Fig. 12-17, p.199
Down SyndromeDown Syndrome
Turner SyndromeTurner Syndrome
Inheritance of only one X (XO)Inheritance of only one X (XO) 98% spontaneously aborted98% spontaneously aborted Survivors are short, infertile femalesSurvivors are short, infertile females
No functional ovariesNo functional ovaries Secondary sexual traits reducedSecondary sexual traits reduced May be treated with hormones, surgeryMay be treated with hormones, surgery
Klinefelter SyndromeKlinefelter Syndrome
XXY conditionXXY condition Results mainly from nondisjunction in Results mainly from nondisjunction in
mother (67%)mother (67%) Phenotype is tall malesPhenotype is tall males
Sterile or nearly soSterile or nearly so Feminized traits (sparse facial hair, somewhat Feminized traits (sparse facial hair, somewhat
enlarged breasts)enlarged breasts) Treated with testosterone injectionsTreated with testosterone injections
XYY ConditionXYY Condition
Taller than average malesTaller than average males Most otherwise phenotypically normalMost otherwise phenotypically normal Some mentally impairedSome mentally impaired Once thought to be predisposed to Once thought to be predisposed to
criminal behavior, but studies now criminal behavior, but studies now discreditdiscredit
12.10 12.10 Pedigree Pedigree Symbols Symbols
male
female
marriage/mating
Individual showing trait being studied
sex not specified
generationI, II, III, IV...
offspring in order of birth, from left to right
Fig. 12-19a, p.200
Pedigree for PolydactylyPedigree for Polydactyly
I
II
III
IV
V
6 7
12
5,5 6,6
5,5 6,6
5,5 6,6
5,5 6,6
5,5 6,6
5,5 6,6
6,6 5,5
6,6 5,5
5,6 6,7
6,6 6,6*Gene not expressed in this carrier.
*
malefemale
Fig. 12-9b, p. 200
Genetic AbnormalityGenetic Abnormality
A rare, uncommon version of a traitA rare, uncommon version of a trait
PolydactylyPolydactyly
Unusual number of toes or fingersUnusual number of toes or fingers
Does not cause any health problemsDoes not cause any health problems
View of trait as disfiguring is subjectiveView of trait as disfiguring is subjective
Genetic DisorderGenetic Disorder
Inherited conditions that cause mild to Inherited conditions that cause mild to
severe medical problemssevere medical problems
Why don’t they disappear?Why don’t they disappear? Mutation introduces new rare allelesMutation introduces new rare alleles
In heterozygotes, harmful allele is masked, so In heterozygotes, harmful allele is masked, so
it can still be passed on to offspring it can still be passed on to offspring
Genetic Disorders and Genetic AbnormalitiesGenetic Disorders and Genetic Abnormalities
12.11 Phenotypic Treatments12.11 Phenotypic Treatments
Symptoms of many genetic disorders can Symptoms of many genetic disorders can
be minimized or suppressed bybe minimized or suppressed by Dietary controlsDietary controls
Adjustments to environmental conditionsAdjustments to environmental conditions
Surgery or hormonal treatmentsSurgery or hormonal treatments
Genetic ScreeningGenetic Screening
Large-scale screening programs detect Large-scale screening programs detect affected persons affected persons
Newborns in United States routinely Newborns in United States routinely tested for PKUtested for PKU Early detection allows dietary intervention Early detection allows dietary intervention
and prevents brain impairmentand prevents brain impairment
Prenatal DiagnosisPrenatal Diagnosis
AmniocentesisAmniocentesis
Chorionic villus samplingChorionic villus sampling
FetoscopyFetoscopy
All methods have some risksAll methods have some risks
Preimplantation DiagnosisPreimplantation Diagnosis
Used with in-vitro fertilizationUsed with in-vitro fertilization
Mitotic divisions produce ball of 8 cellsMitotic divisions produce ball of 8 cells
All cells have same genesAll cells have same genes
One of the cells is removed and its genes One of the cells is removed and its genes
analyzedanalyzed
If cell has no defects, the embryo is If cell has no defects, the embryo is
implanted in uterusimplanted in uterus