Download ppt - Chapter 12 Chromosomes & Human Inheritance

Chapter 12Chapter 12Chromosomes & Human Chromosomes & Human

InheritanceInheritanceOCC BIO-114OCC BIO-114

In this chapter…In this chapter…

you will learn how biologists use their you will learn how biologists use their knowledge of DNA & chromosome knowledge of DNA & chromosome behavior to study how traits are inherited & behavior to study how traits are inherited & expressed.expressed.

Sex-determining Chromosomes and Sex-determining Chromosomes and LinkageLinkage

sex chromosomessex chromosomes autosomesautosomes

Sex ChromosomesSex Chromosomes

It’s all about the “X” It’s all about the “X” and the “Y”and the “Y”

Sex determination and Inheritance Sex determination and Inheritance of Sex-linked genes:of Sex-linked genes:

Mammals/ many insects= male/female same number of Mammals/ many insects= male/female same number of chromosomeschromosomes-one pair= -one pair= sex chromosomessex chromosomes

different appearance and genetic compositiondifferent appearance and genetic composition XX= femaleXX= female

XY= maleXY= male

Humans: Humans:

Autosomes = # 1-22Autosomes = # 1-22

Sex chromosome = #23Sex chromosome = #23

sex chromosome carried by sperm determines sex of offspring ( X or Y sex chromosome carried by sperm determines sex of offspring ( X or Y sperm)sperm)

Sex-LinkageSex-Linkage

In 1910, Thomas Hunt Morgan - Studied In 1910, Thomas Hunt Morgan - Studied inheritance patterns of fruit fly, inheritance patterns of fruit fly, Drosophila Drosophila melanogastermelanogaster, discovered presence of a , discovered presence of a white eye in certain individuals. white eye in certain individuals.

Since this was a distinctive feature, Since this was a distinctive feature, Morgan decided to study the inheritance Morgan decided to study the inheritance pattern for this recessive eye color.pattern for this recessive eye color.


Morgan made several crosses using a Morgan made several crosses using a white-eyed male, expecting the standard white-eyed male, expecting the standard Mendelian results. He did not get them.Mendelian results. He did not get them.

While the ratio of 3:1 was obtained, all of While the ratio of 3:1 was obtained, all of the white-eyed second generation the white-eyed second generation offspring were male flies. offspring were male flies.

All females had red eyes (and 25% of the All females had red eyes (and 25% of the males also had red eyes).males also had red eyes).

Sex-LinkageSex-Linkage Morgan did a series of reciprocal crosses of white-eye Morgan did a series of reciprocal crosses of white-eye

males with red-eye females and red-eye males with males with red-eye females and red-eye males with white-eye females. white-eye females. He concluded that the gene for eye color was located on the X He concluded that the gene for eye color was located on the X

chromosome.chromosome. Males passed the trait their daughters (on their solitary Males passed the trait their daughters (on their solitary

X chromosome) & mothers passed the trait sons.X chromosome) & mothers passed the trait sons. White eyed females could also pass the white eye allele White eyed females could also pass the white eye allele

to their daughters, but if the father fly had red eyes, the to their daughters, but if the father fly had red eyes, the eye color of the daughters would be red, while the eye eye color of the daughters would be red, while the eye color of the sons of white-eyed females would always be color of the sons of white-eyed females would always be white.white.


Morgan concluded that eye color was Morgan concluded that eye color was related to sex, & that the sex-determining related to sex, & that the sex-determining chromosomes also had genes that were chromosomes also had genes that were unrelated to gender determination. unrelated to gender determination.

Prior to Morgan's discovery, no one knew Prior to Morgan's discovery, no one knew that genes unrelated to gender were also that genes unrelated to gender were also located on these chromosomes.located on these chromosomes.


These other traits are said to be sex-linked These other traits are said to be sex-linked because they are inherited along with the sex of because they are inherited along with the sex of the individual. the individual.

Because the X and Y chromosome are not Because the X and Y chromosome are not exactly matching, the X chromosome can have exactly matching, the X chromosome can have genes that are not located on the Y genes that are not located on the Y chromosome, and vice-versa. chromosome, and vice-versa.

Some of these genes are unrelated to the sexual Some of these genes are unrelated to the sexual characteristics, but are inherited with the sex-characteristics, but are inherited with the sex-determination. This is referred to as determination. This is referred to as sex-sex-linkagelinkage..

sex-linked (X-linked)sex-linked (X-linked) genes on one sex chromosome; not on other genes on one sex chromosome; not on other Y= carries relatively few genesY= carries relatively few genes

X= many genes; some not specifically related to female traitsX= many genes; some not specifically related to female traits

Ex: genes for: Ex: genes for: color vision;color vision;

blood clotting; structural proteinsblood clotting; structural proteins

female XX= homozygous or hybrid (dominant/recessive)female XX= homozygous or hybrid (dominant/recessive)

male XY= fully expresses all alleles on single X (whether dominant male XY= fully expresses all alleles on single X (whether dominant or recessive)or recessive)

Ex: color blindness; hemophilia; muscular dystrophyEx: color blindness; hemophilia; muscular dystrophy

Some human sex-linked traits areSome human sex-linked traits are

Hemophilia (X)Hemophilia (X)Hairy ear rims (Y)Hairy ear rims (Y)Red-green color blindness (X) (fig.12.9)Red-green color blindness (X) (fig.12.9)Duchene muscular dystrophy (X)Duchene muscular dystrophy (X)

X-LinkedX-Linked

Only found on X chromosomeOnly found on X chromosomeColorblindnessColorblindness – red/green, most common – red/green, most common

in males (8%)in males (8%)HemophiliaHemophilia – blood clotting, affects males – blood clotting, affects malesDuchene Muscular DystrophyDuchene Muscular Dystrophy – weakens & – weakens &

destroys muscle tissuedestroys muscle tissue

*Not all X-Linked traits are diseases = Only a *Not all X-Linked traits are diseases = Only a few of hundereds of genes on X chrom. few of hundereds of genes on X chrom. Others code for normal functioning proteinsOthers code for normal functioning proteins

The Effect of Recombination on Gene Linkage and The Effect of Recombination on Gene Linkage and InheritanceInheritance

Meiosis results in exchange of bits & pieces of Meiosis results in exchange of bits & pieces of DNA between homologous pairs of DNA between homologous pairs of chromosomes at the chromosomes at the chiasmatachiasmata during during prophase I of meiosis.prophase I of meiosis.

This process of recombination results in This process of recombination results in gametes (or meiotic products) that are not gametes (or meiotic products) that are not identical; some of the linkage groups have been identical; some of the linkage groups have been changed by the crossing-over. changed by the crossing-over.

As a result of recombination, new allele As a result of recombination, new allele combinations are formed, and we have combinations are formed, and we have more more genetic variationgenetic variation..

crossing overcrossing over

segments of homologous chromosomes segments of homologous chromosomes are exchanged w/ each other at site called are exchanged w/ each other at site called chiasmatachiasmata during meiosis I during meiosis I

forms new gene combinations on both forms new gene combinations on both homologous chromosomes homologous chromosomes

gene combinations for daughter cell gene combinations for daughter cell different from parent cell different from parent cell

Crossing Over and Recombination

Cell MutationsCell Mutations

Germ-cell mutationGerm-cell mutation – gametes, passed – gametes, passed on to offspringon to offspring

Somatic mutationsSomatic mutations – body cells, affect – body cells, affect organism. Not passed on to offspring. i.e. organism. Not passed on to offspring. i.e. leukemialeukemia

Lethal mutations – cause death. Are they Lethal mutations – cause death. Are they beneficial???beneficial???

Chromosome mutations(12.5)Chromosome mutations(12.5)

DeletionDeletion – piece of chrom breaks off & is lost – piece of chrom breaks off & is lost (end); due to virus, radiation, chemicals, or envir (end); due to virus, radiation, chemicals, or envir factors. Most are lethalfactors. Most are lethal Ex:ABCDEFG becomes ABCFG, Cri-du-chat Ex:ABCDEFG becomes ABCFG, Cri-du-chat

syndrome (p.192)syndrome (p.192) InversionInversion – breaks off & reattaches in reverse – breaks off & reattaches in reverse

Ex: ABCDEFG becomes ABGFEDCEx: ABCDEFG becomes ABGFEDC TranslocationTranslocation – breaks off & reattaches to – breaks off & reattaches to

different (non-homologous chrom)different (non-homologous chrom) Ex: ABCDEFG becomes ABCDLMNOPEx: ABCDEFG becomes ABCDLMNOP

Changes in Chrom #Changes in Chrom #

NondisjunctionNondisjunction – chrom fail to separate – chrom fail to separate during Anaphase (gamete formation) during Anaphase (gamete formation) (p.192)(p.192)

AneuploidyAneuploidy – 1 extra or less chrom – 1 extra or less chromMonosomic-1 less, Turner syndrome (XO)Monosomic-1 less, Turner syndrome (XO)Trisomic-1 moreTrisomic-1 more

PolyploidyPolyploidy – 3 or more of each type of – 3 or more of each type of chrom; lethal for humanschrom; lethal for humans

Inheritance of Recessive AllelesInheritance of Recessive Alleles

Any alteration of a gene, called a Any alteration of a gene, called a mutationmutation, has the , has the potential to inhibit the formation of a needed enzyme. potential to inhibit the formation of a needed enzyme. With diploid organisms, however, a mutation most likely With diploid organisms, however, a mutation most likely affects just one of the homologues, and the second can affects just one of the homologues, and the second can still code for the appropriate enzyme with little or no still code for the appropriate enzyme with little or no phenotypic effect on the individual. phenotypic effect on the individual.

Gene alterations that affect health are called Gene alterations that affect health are called genetic genetic disordersdisorders (Table 12.1, p.196) (Table 12.1, p.196). .

Those that are just "abnormal" but do not affect Those that are just "abnormal" but do not affect physiological health, are called genetic physiological health, are called genetic abnormalities abnormalities i.e. 6 toesi.e. 6 toes

When the genetic alteration causes a host of symptoms, When the genetic alteration causes a host of symptoms, it may be called a it may be called a syndromesyndrome..

DiseaseDisease –illness caused by infections, not by inheritance –illness caused by infections, not by inheritance

Single Allele TraitsSingle Allele Traits

Controlled by a single allele of a gene.Controlled by a single allele of a gene.>200 human traits governed by single >200 human traits governed by single

dominant allele.dominant allele.Ex: Huntington’s Disease (HD) caused by Ex: Huntington’s Disease (HD) caused by

dominant allele located on an autosome = dominant allele located on an autosome = autosomal dominant pattern of inheritanceautosomal dominant pattern of inheritance

Read description of HD on p.196, Table Read description of HD on p.196, Table 12.112.1

HD continuedHD continued

Geneticists discovered a Geneticists discovered a genetic markergenetic marker for for HD allele.HD allele.

Genetic markerGenetic marker is a short section of DNA is a short section of DNA known to have a close association w/ a known to have a close association w/ a particular gene located nearby. Easy to I.D. particular gene located nearby. Easy to I.D. the HD allele.the HD allele.

If marker is present = 96% chance of dev HDIf marker is present = 96% chance of dev HDParents can be tested for marker before Parents can be tested for marker before

conceiving a child.conceiving a child.

Other Single-Allele Traits Other Single-Allele Traits (Table 12.1)(Table 12.1)

Homozygous recessive (must have 2 Homozygous recessive (must have 2 copies of recessive allele):copies of recessive allele):Cystic FibrosisCystic FibrosisSickle Cell AnemiaSickle Cell Anemia

*these are recessive alleles located on *these are recessive alleles located on autosomes = autosomes = Autosomal RecessiveAutosomal Recessive

pattern of inhertiancepattern of inhertiance

polygenic inheritance polygenic inheritance Trait that is controlled by 2 or more Trait that is controlled by 2 or more

genes = many different variationsgenes = many different variations Ex: Skin Color-influenced by additive effects of 3 to Ex: Skin Color-influenced by additive effects of 3 to

6 genes. Each gene results in certain amount of 6 genes. Each gene results in certain amount of melaninmelanin (brownish-black pigment) (brownish-black pigment)

More melanin=darkerMore melanin=darker Ex: eye color. Light blue eyes=very little melaninEx: eye color. Light blue eyes=very little melanin Human height – polygenic, but influenced by Human height – polygenic, but influenced by

environmental factors, such as disease & nutritionenvironmental factors, such as disease & nutrition

Disorders due to NondisjunctionDisorders due to Nondisjunction

Occurs during meiosis causes gametes to Occurs during meiosis causes gametes to lack a chromosome or have an extra one lack a chromosome or have an extra one (fig 12-10, p. 231)(fig 12-10, p. 231)

A zygote w/ 45 chrom. = monosomyA zygote w/ 45 chrom. = monosomy47 chrom. = trisomy47 chrom. = trisomyOften lethalOften lethalTrisomy 21 = Trisomy 21 = Down SyndromeDown Syndrome – mild to – mild to

severe mental retardation…severe mental retardation…

Nondisjunction cont.Nondisjunction cont.

Males w/ 1 extra X chrom. = Males w/ 1 extra X chrom. = Klinefelter’s Klinefelter’s syndrome (XXY)syndrome (XXY). Some feminine . Some feminine characteristics, mentally retarded & infertilecharacteristics, mentally retarded & infertile

Turner’s SyndromeTurner’s Syndrome – Have a single x – Have a single x chrom. (XO) = female appearance, but do chrom. (XO) = female appearance, but do not mature sexually & remain infertile. What not mature sexually & remain infertile. What happens if zygote only receives a Y chrom.?happens if zygote only receives a Y chrom.?

Detection (fig.12.21, 12.22)Detection (fig.12.21, 12.22)

Genetic ScreeningGenetic Screening = = KaryotypeKaryotype (picture of (picture of person’s chrom.person’s chrom.

AmniocentesisAmniocentesis – procedure removes – procedure removes amniotic fluid from fetus & tested (14amniotic fluid from fetus & tested (14thth-16-16thth week of pregnancy)week of pregnancy)

Chorionic Villi SamplingChorionic Villi Sampling – Removes fetal – Removes fetal cells from chorion fluid (between mothers cells from chorion fluid (between mothers uterus & fetus)uterus & fetus)

Ultrasound Ultrasound – Sound waves to observe – Sound waves to observe fetusfetus

Detection Cont.Detection Cont.

In U.S. 1 out of 10,000 babies is afflicted In U.S. 1 out of 10,000 babies is afflicted w/ w/ phenylketonuria (PKU) – phenylketonuria (PKU) – body cannot body cannot metabolize amino acid phenylalanine = metabolize amino acid phenylalanine = brain damage.brain damage.

Genetic CounselingGenetic Counseling – medical guidance – medical guidance for couples at riskfor couples at risk

12-10 Human Genetics12-10 Human Genetics

Humans have up to 20 times as many Humans have up to 20 times as many genes as genes as DrosophilaDrosophila, & our 23 pairs of , & our 23 pairs of chromosomes & are made up of about chromosomes & are made up of about 100,000 genes.100,000 genes.

Geneticists focus on disease-causing Geneticists focus on disease-causing genes b/c of concern for human pop.genes b/c of concern for human pop.

Pedigree AnalysisPedigree Analysis

PedigreePedigree – a family record that shows – a family record that shows how a trait is inherited over several how a trait is inherited over several generations (fig 12-19).generations (fig 12-19).

Certain phenotypes are usually repeated Certain phenotypes are usually repeated in predictable patterns from 1 generation in predictable patterns from 1 generation to the next = to the next = patterns of inheritancepatterns of inheritance..

CarriersCarriers – individuals who have 1 copy of – individuals who have 1 copy of a recessive allele, but can pass it along to a recessive allele, but can pass it along to their offspring.their offspring.

How to read a PedigreeHow to read a Pedigree

Human pedigreesHuman pedigrees Before we consider human Mendelian Before we consider human Mendelian

inheritance it is convenient to consider the inheritance it is convenient to consider the symbols used to draw pedigrees. symbols used to draw pedigrees.

Generations are numberered from the top of the Generations are numberered from the top of the pedigree in uppercase Roman numerals, I, II, III pedigree in uppercase Roman numerals, I, II, III etc. Individuals in each generation are etc. Individuals in each generation are numbered from the left in arab numberals as numbered from the left in arab numberals as subscripts, III1 , III2, III3 etc.subscripts, III1 , III2, III3 etc.

Hemophilia pedigree of the Hemophilia pedigree of the European Royal FamiliesEuropean Royal Families

Practice ProblemsPractice Problems

Glencoe

ReferencesReferences

http://www.scidiv.bcc.ctc.edu/rkr/http://www.scidiv.bcc.ctc.edu/rkr/Biology101/lectures/pdfs/Biology101/lectures/pdfs/HumanInheritance101.pdfHumanInheritance101.pdf