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Chromosomal Inheritance Chapter 12

Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

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Page 1: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Chromosomal InheritanceChromosomal

Inheritance

Chapter 12Chapter 12

Page 2: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Drosophila ChromosomesDrosophila Chromosomes

Page 3: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Chromosomal InheritanceChromosomal Inheritance

Humans are diploid (2 chromosomes of each type) Humans have 23 different kinds of chromosomes Arranged in 23 pairs of homologous chromosomes Total of 46 chromosomes (23 pairs) per cell

One of the chromosome pairs determines the sex of an individual (the sex chromosomes)

The other 22 pairs of chromosomes are autosomes.

Autosomal chromosomes are numbered from smallest (#1) to largest (#22)

The sex chromosomes are numbered as the 23rd pair

Humans are diploid (2 chromosomes of each type) Humans have 23 different kinds of chromosomes Arranged in 23 pairs of homologous chromosomes Total of 46 chromosomes (23 pairs) per cell

One of the chromosome pairs determines the sex of an individual (the sex chromosomes)

The other 22 pairs of chromosomes are autosomes.

Autosomal chromosomes are numbered from smallest (#1) to largest (#22)

The sex chromosomes are numbered as the 23rd pair

Page 4: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Sex Determination in Humans

Sex Determination in Humans Sex is determined in humans by

allocation of chromosomes at fertilization.

Both sperm and egg carry one of each of the 22 autosomes

The egg always carries the X chromosomes as number 23

The sperm may carry either and X or Y If the sperm donates an X in fertilization, the zygote will be female.

If the sperm donates a Y in fertilization, the zygote will be male.

Therefore, the sex of all humans is determined by the sperm donated by their father.

Sex is determined in humans by allocation of chromosomes at fertilization.

Both sperm and egg carry one of each of the 22 autosomes

The egg always carries the X chromosomes as number 23

The sperm may carry either and X or Y If the sperm donates an X in fertilization, the zygote will be female.

If the sperm donates a Y in fertilization, the zygote will be male.

Therefore, the sex of all humans is determined by the sperm donated by their father.

Page 5: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

X-linked AllelesX-linked Alleles Genes carried on autosomes are said to be autosomally linked

Genes carried on the female sex chromosome (X) are said to be X-linked (or sex-linked)

X-linked genes have a different pattern of inheritance than autosomal genes have The Y chromosome is blank for these genes Recessive alleles on X chromosome:

Follow familiar dominant/recessive rules in females (XX)

Are always expressed in males (XY), whether dominant or recessive

Males said to be monozygous for X-linked genes

Genes carried on autosomes are said to be autosomally linked

Genes carried on the female sex chromosome (X) are said to be X-linked (or sex-linked)

X-linked genes have a different pattern of inheritance than autosomal genes have The Y chromosome is blank for these genes Recessive alleles on X chromosome:

Follow familiar dominant/recessive rules in females (XX)

Are always expressed in males (XY), whether dominant or recessive

Males said to be monozygous for X-linked genes

Page 6: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Eye Color in Fruit Flies

Eye Color in Fruit Flies Fruit flies (Drosophila melanogaster)

are common subjects for genetics research

They normally (wild-type) have red eyes A mutant recessive allele of a gene on the X chromosome can cause white eyes

Possible combinations of genotypes and phenotypes

Fruit flies (Drosophila melanogaster) are common subjects for genetics research

They normally (wild-type) have red eyes A mutant recessive allele of a gene on the X chromosome can cause white eyes

Possible combinations of genotypes and phenotypes

Genotype Phenotype

XRXR Homozygous Dominant Female Red-eyed

XRXr Heterozygous Female Red-eyed

XrXr Homozygous Recessive Female White-eyed

XRY Monozygous Dominant Male Red-eyed

XrY Monozygous Recessive Male White-eyed

Page 7: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

X-linked InheritanceX-linked Inheritance

Page 8: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Human X-linked Disorders: Red-Green

Color Blindness

Human X-linked Disorders: Red-Green

Color Blindness Color vision in humans: Depends three different classes of cone cells in the retina

Only one type of pigment is present in each class of cone cell The gene for blue-sensitive is autosomal The red-sensitive and green-sensitive genes are on the X chromosome

Mutations in X-linked genes cause RG color blindness

All males with mutation (XbY) are colorblind Only homozygous mutant females (XbXb) are colorblind

Heterozygous females (XBXb) are asymptomatic carriers

Color vision in humans: Depends three different classes of cone cells in the retina

Only one type of pigment is present in each class of cone cell The gene for blue-sensitive is autosomal The red-sensitive and green-sensitive genes are on the X chromosome

Mutations in X-linked genes cause RG color blindness

All males with mutation (XbY) are colorblind Only homozygous mutant females (XbXb) are colorblind

Heterozygous females (XBXb) are asymptomatic carriers

Page 9: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Red-Green Colorblindness Chart

Red-Green Colorblindness Chart

Page 10: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

X-linked Recessive Pedigree

X-linked Recessive Pedigree

Page 11: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Human X-linked Disorders:Muscular Dystrophy

Human X-linked Disorders:Muscular Dystrophy

Muscle cells operate by release and rapid sequestering of calcium

Protein dystrophin required to keep calcium sequestered

Dystrophin production depends on X-linked gene

A defective allele (when unopposed) causes absence of dystrophin Allows calcium to leak into muscle cells Causes muscular dystrophy

All sufferers are male Defective gene always unopposed in males Males die before fathering potentially homozygous recessive daughters

Muscle cells operate by release and rapid sequestering of calcium

Protein dystrophin required to keep calcium sequestered

Dystrophin production depends on X-linked gene

A defective allele (when unopposed) causes absence of dystrophin Allows calcium to leak into muscle cells Causes muscular dystrophy

All sufferers are male Defective gene always unopposed in males Males die before fathering potentially homozygous recessive daughters

Page 12: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Human X-linked Disorders:Hemophilia

Human X-linked Disorders:Hemophilia

“Bleeder’s Disease” Blood of affected person either refuses to clot or clots too slowly Hemophilia A -due to lack of clotting factor X Hemophilia B - due to lack of clotting factor VIII

Most victims male, receiving the defective allele from carrier mother

Bleed to death from simple bruises, etc. Factor VIII now available via biotechnology

“Bleeder’s Disease” Blood of affected person either refuses to clot or clots too slowly Hemophilia A -due to lack of clotting factor X Hemophilia B - due to lack of clotting factor VIII

Most victims male, receiving the defective allele from carrier mother

Bleed to death from simple bruises, etc. Factor VIII now available via biotechnology

Page 13: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Hemophilia PedigreeHemophilia Pedigree

Page 14: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Human X-linked Disorders: Fragile X

Syndrome

Human X-linked Disorders: Fragile X

Syndrome Due to base-triplet repeats in a gene on the X chromosome

CGG repeated many times 6-50 repeats -- asymptomatic 230-2,000 repeats -- growth distortions and mental retardation

Inheritance pattern is complex and unpredictable

Due to base-triplet repeats in a gene on the X chromosome

CGG repeated many times 6-50 repeats -- asymptomatic 230-2,000 repeats -- growth distortions and mental retardation

Inheritance pattern is complex and unpredictable

Page 15: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Gene LinkageGene Linkage

Page 16: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Gene LinkageGene Linkage When several genes of interest exist on the same chromosome

Such genes form a linkage group Tend to be inherited on same chromosome: Gametes of parent likely to have exact allele combination as gamete of either grandparent

Independent assortment does not apply If all genes on separate chromosomes:

Allele combinations of grandparent gametes will be shuffled in parental gametes

Independent assortment working

When several genes of interest exist on the same chromosome

Such genes form a linkage group Tend to be inherited on same chromosome: Gametes of parent likely to have exact allele combination as gamete of either grandparent

Independent assortment does not apply If all genes on separate chromosomes:

Allele combinations of grandparent gametes will be shuffled in parental gametes

Independent assortment working

Page 17: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Linkage GroupsLinkage Groups

Page 18: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Constructing a Chromosome MapConstructing a Chromosome Map Crossing over can disrupt a blocked allele pattern on a

chromosome Affected by distance between genetic loci Consider three genes on one chromosome:

If one at one end, a second at the other and the third in the middle

Allelic patterns of grandparents will likely to be disrupted in parental gametes with all allelic combinations possible

If the three genetic loci occur in close sequence on the chromosome Crossing over very Unlikely to occur between loci Allelic patterns of grandparents will likely to be preserved in parental gametes

Rate at which allelic patterns are disrupted by crossing over: Indicates distance between loci Can be used to develop linkage map or genetic map of chromosome

Crossing over can disrupt a blocked allele pattern on a chromosome

Affected by distance between genetic loci Consider three genes on one chromosome:

If one at one end, a second at the other and the third in the middle

Allelic patterns of grandparents will likely to be disrupted in parental gametes with all allelic combinations possible

If the three genetic loci occur in close sequence on the chromosome Crossing over very Unlikely to occur between loci Allelic patterns of grandparents will likely to be preserved in parental gametes

Rate at which allelic patterns are disrupted by crossing over: Indicates distance between loci Can be used to develop linkage map or genetic map of chromosome

Page 19: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Crossing-OverCrossing-Over

Page 20: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Complete vs. Incomplete Linkage

Complete vs. Incomplete Linkage

Page 21: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Chromosome Number: Polyploidy

Chromosome Number: Polyploidy Polyploidy

Occurs when eukaryotes have more than 2n chromosomes

Named according to number of complete sets of chromosomes

Major method of speciation in plants Diploid egg of one species joins with diploid pollen of another species

Result in tetraploid species that is self-fertile but isolated from both “parent” species

Ofen lethal in higher animals

Polyploidy Occurs when eukaryotes have more than 2n chromosomes

Named according to number of complete sets of chromosomes

Major method of speciation in plants Diploid egg of one species joins with diploid pollen of another species

Result in tetraploid species that is self-fertile but isolated from both “parent” species

Ofen lethal in higher animals

Page 22: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Chromosome Number: Aneuploidy

Chromosome Number: Aneuploidy Monosomy (2n-1)

Diploid individual has only one of a particular chromosome

Caused by failure of synapsed chromosome to separate at Anaphase (nondisjunction)

Trisomy (2n+1) occurs when an individual has three of a particular type of chromosome Diploid individual has three of a particular chromosome

Also caused by nondisjunction This usually produces one nonsomic daughter cell and one trisomic daughter cell in meiosis I

Down syndrome is trisomy 21

Monosomy (2n-1) Diploid individual has only one of a particular chromosome

Caused by failure of synapsed chromosome to separate at Anaphase (nondisjunction)

Trisomy (2n+1) occurs when an individual has three of a particular type of chromosome Diploid individual has three of a particular chromosome

Also caused by nondisjunction This usually produces one nonsomic daughter cell and one trisomic daughter cell in meiosis I

Down syndrome is trisomy 21

Page 23: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

NondisjunctionNondisjunction

Page 24: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Trisomy 21Trisomy 21

Page 25: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Chromosome Number: Abnormal Sex Chromosome

Number

Chromosome Number: Abnormal Sex Chromosome

Number Result of inheriting too many or too few X or Y chromosomes

Caused by nondisjunction during oogenesis or spermatogenesis

Turner Syndrome (XO) Female with single X chromosome Short, with broad chest and widely spaced nipples

Cam be of normal intelligence and function with hormone therapy

Result of inheriting too many or too few X or Y chromosomes

Caused by nondisjunction during oogenesis or spermatogenesis

Turner Syndrome (XO) Female with single X chromosome Short, with broad chest and widely spaced nipples

Cam be of normal intelligence and function with hormone therapy

Page 26: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Chromosome Number: Abnormal Sex Chromosome

Number

Chromosome Number: Abnormal Sex Chromosome

Number Klinefelter Syndrome (XXY)

Male with underdeveloped testes and prostate; some breast overdevelopment

Long arms and legs; large hands Near normal intelligence unless XXXY, XXXXY, etc.

No matter how many X chromosomes, presence of Y renders individual male

Klinefelter Syndrome (XXY) Male with underdeveloped testes and prostate; some breast overdevelopment

Long arms and legs; large hands Near normal intelligence unless XXXY, XXXXY, etc.

No matter how many X chromosomes, presence of Y renders individual male

Page 27: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Turner & Klinefelter Syndromes

Turner & Klinefelter Syndromes

Page 28: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Chromosome Number: Abnormal Sex Chromosome

Number

Chromosome Number: Abnormal Sex Chromosome

Number

Ploy-X females XXX simply taller and thinner than normal

Some learning difficulties Many menstruate regularly and are fertile

More than 3 Xs renders severe mental retardation

Jacob’s syndrome (XYY) Tall, persistent acne, speech and reading problems

Ploy-X females XXX simply taller and thinner than normal

Some learning difficulties Many menstruate regularly and are fertile

More than 3 Xs renders severe mental retardation

Jacob’s syndrome (XYY) Tall, persistent acne, speech and reading problems

Page 29: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Abnormal Chromosome Structure

Abnormal Chromosome Structure

Deletion Missing segment of chromosme Lost during breakage

Translocation A segment from one chromosome moves to a non-homologous chromosome

Follows breakage of two homologous chromosomes and improper re-assembly

Deletion Missing segment of chromosme Lost during breakage

Translocation A segment from one chromosome moves to a non-homologous chromosome

Follows breakage of two homologous chromosomes and improper re-assembly

Page 30: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Deletion, Translocation, Duplication, & InversionDeletion, Translocation, Duplication, & Inversion

Page 31: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Abnormal Chromosome Structure

Abnormal Chromosome Structure

Duplication A segment of a chromosome is repeated in the same chromosome

Inversion Occurs as a result of two breaks in a chromosome The internal segment is reversed before reinsertion

Genes occur in reverse order in inverted segment

Duplication A segment of a chromosome is repeated in the same chromosome

Inversion Occurs as a result of two breaks in a chromosome The internal segment is reversed before reinsertion

Genes occur in reverse order in inverted segment

Page 32: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Inversion Leading to Duplication & DeletionInversion Leading to

Duplication & Deletion

Page 33: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Abnormal Chromosome Structure

Abnormal Chromosome Structure

Deletion Syndromes Williams Syndrome -- loss of segment of chromosome 7

Cri du chat syndrome (cat’s cry) -- loss of segment of chromosome 5

Translocation Alagille syndrome Some cancers

Deletion Syndromes Williams Syndrome -- loss of segment of chromosome 7

Cri du chat syndrome (cat’s cry) -- loss of segment of chromosome 5

Translocation Alagille syndrome Some cancers

Page 34: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Williams SyndromeWilliams Syndrome

Page 35: Chromosomal Inheritance Chapter 12. Drosophila Chromosomes

Alagille SyndromeAlagille Syndrome