AP Bio Ch 12 Power Point

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Published on September 19, 2007

Author: MrDPMWest

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Patterns of Inheritance

Patterns of Inheritance

Genetics Field founded by Gregor Mendel, monk in a monastery in Brno (now in Czech Republic) in late 1800s Worked with sweet pea Knew nothing of cells, chromosomes, etc.; also interested in math. Was unappreciated by peers, Work was rediscovered after Charles Darwin , after Mendel’s death

Field founded by Gregor Mendel, monk in a monastery in Brno (now in Czech Republic) in late 1800s

Worked with sweet pea

Knew nothing of cells, chromosomes, etc.; also interested in math.

Was unappreciated by peers, Work was rediscovered after Charles Darwin , after Mendel’s death

Inheritance Inheritance is the process by which the characteristics of individuals are passed to their offspring Genes encode these characteristics A gene is a unit of heredity that encodes information for the form of a particular characteristic The location of a gene on a chromosome is called its locus

Inheritance is the process by which the characteristics of individuals are passed to their offspring

Genes encode these characteristics

A gene is a unit of heredity that encodes information for the form of a particular characteristic

The location of a gene on a chromosome is called its locus

Alleles Homologous chromosomes carry the same kinds of genes for the same characteristics Genes for the same characteristic are found at the same loci on both homologous chromosomes

Homologous chromosomes carry the same kinds of genes for the same characteristics

Genes for the same characteristic are found at the same loci on both homologous chromosomes

Alleles Genes for a characteristic found on homologous chromosomes may not be identical Alternate versions or forms of genes found at the same gene locus are called alleles

Genes for a characteristic found on homologous chromosomes may not be identical

Alternate versions or forms of genes found at the same gene locus are called alleles

Alleles Each cell carries two alleles per characteristic, one on each of the two homologous chromosomes If both homologous chromosomes carry the same allele (gene form) at a given gene locus, the organism is homozygous at that locus If two homologous chromosomes carry different alleles at a given locus, the organism is heterozygous at that locus (a hybrid )

Each cell carries two alleles per characteristic, one on each of the two homologous chromosomes

If both homologous chromosomes carry the same allele (gene form) at a given gene locus, the organism is homozygous at that locus

If two homologous chromosomes carry different alleles at a given locus, the organism is heterozygous at that locus (a hybrid )

Genes, Alleles, Loci, and Chromosomes Chromosome from One Parent Homologous Chromosome from Other Parent M locus has gene that controls leaf color . Plant homozygous for this gene D locus has gene that controls plant height . Plant homozygous for this gene Bk locus has gene that controls fruit shape . Plant heterozygous for this gene 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Loci: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Loci:

The Secrets of Mendel’s Success Important aspects of pea plants Pea flowers have male structures that produce pollen (male gametes) by meiosis Pea flowers have female structures that produce eggs (female gametes) by meiosis Pea flower petals enclose both male and female flower parts and prevent entry of pollen from another pea plant

Important aspects of pea plants

Pea flowers have male structures that produce pollen (male gametes) by meiosis

Pea flowers have female structures that produce eggs (female gametes) by meiosis

Pea flower petals enclose both male and female flower parts and prevent entry of pollen from another pea plant

Seeds & Flowers of Edible Pea Intact pea flower Flower dissected to show reproductive structures Stamens (male) produce pollen Carpel (female) produces eggs

The Secrets of Mendel’s Success Mendel experimental design was simple and methodical He studied characteristics that have unmistakably different forms (like purple versus white) He only studied one trait (characteristic) at a time

Mendel experimental design was simple and methodical

He studied characteristics that have unmistakably different forms (like purple versus white)

He only studied one trait (characteristic) at a time

Definitions 1 Must know these!!! Trait —A variable characteristic of organism Gene —A segment of chromosomal DNA controlling a specific trait Locus —Chromosomal position where DNA for a specific gene lives Genome —Refers to all standard loci for a species

Must know these!!!

Trait —A variable characteristic of organism

Gene —A segment of chromosomal DNA controlling a specific trait

Locus —Chromosomal position where DNA for a specific gene lives

Genome —Refers to all standard loci for a species

Definitions 2 Must know these!!! Alleles —Different forms of a gene “Flower color” is a gene; “Purple” is one flower-color allele “White” is another flower-color allele Genotype —List of alleles for an individual at specific genes Familiar organisms are diploid One or two alleles per individual

Must know these!!!

Alleles —Different forms of a gene

“Flower color” is a gene;

“Purple” is one flower-color allele

“White” is another flower-color allele

Genotype —List of alleles for an individual at specific genes

Familiar organisms are diploid

One or two alleles per individual

Definitions 3 Homozygous —Maternal & paternal alleles same Father donates purple-flower allele Mother donates purple-flower allele Heterozygous —Maternal & paternal alleles differ Father donates purple-flower allele Mom donates white-flower allele

Homozygous —Maternal & paternal alleles same

Father donates purple-flower allele

Mother donates purple-flower allele

Heterozygous —Maternal & paternal alleles differ

Father donates purple-flower allele

Mom donates white-flower allele

Definitions 4 Phenotype : List of traits exhibited by individual Doesn’t always represent genotype Dominant —Allele that is expressed 100% in heterozygote Recessive —Allele is not expressed in heterozygote Incomplete dominance —heterozygote displays intermediate trait

Phenotype :

List of traits exhibited by individual

Doesn’t always represent genotype

Dominant —Allele that is expressed 100% in heterozygote

Recessive —Allele is not expressed in heterozygote

Incomplete dominance —heterozygote displays intermediate trait

Genetic Symbolism Often use initial letter of dominant allele Capital letter represents dominant Lower case of same letter represents recessive If purple flower dominant to white… “P” represents allele for purple “p” represents allele for white

Often use initial letter of dominant allele

Capital letter represents dominant

Lower case of same letter represents recessive

If purple flower dominant to white…

“P” represents allele for purple

“p” represents allele for white

Cross Fertilization of Parents True-breeding Purple-flowered Parent True-breeding White-flowered Parent Cross-Fertilize All Purple-flowered Offspring Pollen Pollen P P F 1

Self-fertilization of F 2 F 1 Self-Fertilize F 2 F 2 F 2 F 2 75% Purple 25% White

Genotype vs Phenotype Phenotype is how we look/behave Purple flowers White flowers Genotype is what our genes say White Flowers / White Flowers White Flowers / Purple Flowers Purple Flowers / Purple Flowers

Phenotype is how we look/behave

Purple flowers

White flowers

Genotype is what our genes say

White Flowers / White Flowers

White Flowers / Purple Flowers

Purple Flowers / Purple Flowers

Genotype vs Phenotype 2 Genotypes PP = homozygous for purple flower pp = homozygous for white flower Pp = heterozygous for flower color Phenotype from genotype: PP = purple flower Pp = purple flower pP = purple flower pp = White flower

Genotypes

PP = homozygous for purple flower

pp = homozygous for white flower

Pp = heterozygous for flower color

Phenotype from genotype:

PP = purple flower

Pp = purple flower

pP = purple flower

pp = White flower

How Meiosis Separates Genes The two alleles for a characteristic separate during gamete formation (meiosis) Homologous chromosomes separate in meiosis anaphase I Each gamete receives one of each pair of homologous chromosomes and thus one of the two alleles per characteristic The separation of alleles in meiosis is known as Mendel’s Law of Segregation

The two alleles for a characteristic separate during gamete formation (meiosis)

Homologous chromosomes separate in meiosis anaphase I

Each gamete receives one of each pair of homologous chromosomes and thus one of the two alleles per characteristic

The separation of alleles in meiosis is known as Mendel’s Law of Segregation

Gametes of Homozygotes A A Homozygous Parent Gametes All gametes identical regarding this gene A A

Gametes of Heterozygotes A a Heterozygous Parent Gametes Gametes 50/50 regarding this gene A a

Homozygous Dominant X Homozygous Recessive pp homozygous recessive P p P p Purple Parent PP homozygous dominant White Parent sperm nuclei egg nuclei sperm nuclei egg nuclei

P Sperm + p Eggs same as p Sperm + P Eggs Pp pP Purple F 1 Purple F 1 P p sperm nucleus egg nucleus + p P egg nucleus sperm nucleus +

Pp X Pp Cross Purple homozygous dominant (PP) Purple heterozygous (Pp) Purple heterozygous (pP) White homozygous recessive (pp) P p p P p P P p + + + + F 1 Sperm F 1 Eggs F 2 Offspring

Using Punnett Squares in Genetic Crosses Named after geneticist Reginald Punnett Figured using Punnett squares Considers only genes of interest List sperm genotypes across top List egg genotypes down side Fill in boxes with zygote genotypes

Named after geneticist Reginald Punnett

Figured using Punnett squares

Considers only genes of interest

List sperm genotypes across top

List egg genotypes down side

Fill in boxes with zygote genotypes

Consider Flower Color Pretend flower color affected by only one gene ( monohybrid cross ) Assume all alleles are purple or white Purple (P) is dominant to white (p) Heterozygotes will have flowers as purple as homozygous dominants

Pretend flower color affected by only one gene ( monohybrid cross )

Assume all alleles are purple or white

Purple (P) is dominant to white (p)

Heterozygotes will have flowers as purple as homozygous dominants

Making a Punnett Square: Heterozygous X Heterozygous P p 1(25%) White 3 (75%) Purple Eggs of Heterozygous Plant Pollen of Heterozygous Plant 1 1 P p p P P p P P p p Frequencies Phenotypes Genotypes Frequencies 2 PP p p p P P p

Practical Application: The Test Cross A test cross is used to deduce the actual genotype of an organism with a dominant phenotype (i.e., is the organism PP or Pp ?) Cross the unknown dominant-phenotype organism ( P _) with a homozygous recessive organism ( pp )…

A test cross is used to deduce the actual genotype of an organism with a dominant phenotype (i.e., is the organism PP or Pp ?)

Cross the unknown dominant-phenotype organism ( P _) with a homozygous recessive organism ( pp )…

Practical Application: The Test Cross 2. If the dominant-phenotype organism is homozygous dominant ( PP ), only dominant-phenotype offspring will be produced ( Pp ) If the dominant-phenotype organism is heterozygous ( Pp ), approximately half of the offspring will be of recessive phenotype ( pp )

2. If the dominant-phenotype organism is homozygous dominant ( PP ), only dominant-phenotype offspring will be produced ( Pp )

If the dominant-phenotype organism is heterozygous ( Pp ), approximately half of the offspring will be of recessive phenotype ( pp )

Test Cross: Heterozygous X Homozygous Recessive p p (50%) White (50%) Purple Eggs of Homozygous Recessive Pollen of unknown plant with dominant phenotype (Heterozygous) P p p p P p P P p p Frequencies Phenotypes Genotypes Frequencies 2 Pp p p p P p p 2

Test Cross: Homozygous X Homozygous Recessive p p (100%) Purple Eggs of Homozygous Recessive Pollen of unknown plant with dominant phenotype (Homozygous) P P p P p P p P p P Frequencies Phenotypes Genotypes Frequencies Pp P p P p P p 4

Traits of Peas Studied by Mendel Plant size Flower location Flower color Pod color Pod shape Seed shape Seed color

Traits Are Inherited Independently Seed color (yellow vs. green peas) and seed shape (smooth vs. wrinkled peas) were the characteristics studied The allele symbols were assigned: Y = yellow (dominant), y = green (recessive) S = smooth (dominant), s = wrinkled (recessive) Two trait cross was between two true breeding varieties for each characteristic P: SSYY x ssyy

Seed color (yellow vs. green peas) and seed shape (smooth vs. wrinkled peas) were the characteristics studied

The allele symbols were assigned:

Y = yellow (dominant), y = green (recessive)

S = smooth (dominant), s = wrinkled (recessive)

Two trait cross was between two true breeding varieties for each characteristic

P: SSYY x ssyy

Traits Are Inherited Independently Genes of pea color and pea shape ( S , s and Y , y ) separate independently during meiosis ( Mendel’s Law of Independent Assortment ) Possible gametes of parent SSYY are SY , SY , SY , and SY (each S can combine with each Y ) Possible gametes of parent ssyy are sy , sy , sy , and sy (each s and combine with each y )

Genes of pea color and pea shape ( S , s and Y , y ) separate independently during meiosis ( Mendel’s Law of Independent Assortment )

Possible gametes of parent SSYY are SY , SY , SY , and SY (each S can combine with each Y )

Possible gametes of parent ssyy are sy , sy , sy , and sy (each s and combine with each y )

Dihybrid Cross: S s Y y X S s Y y SY S y s Y sy SsYy Parent Self-fertilizes 1 4 1 4 1 4 1 4 SY S y s Y sy 1 4 1 4 1 4 1 4 Eggs Sperm 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 1 16 SSYY SSY y S s YY S s Y y SS y Y SS yy S sy Y S syy s SYY s SY y ss YY ss Y y s S y Y s S yy ssy Y ssyy

Traits Are Inherited Independently Mendel then allowed the F1 offspring to self fertilize: SsYy x SsYy Gametes are ¼ S Y , ¼ Sy , ¼ sY , ¼ sy from each parent

Mendel then allowed the F1 offspring to self fertilize: SsYy x SsYy

Gametes are ¼ S Y , ¼ Sy , ¼ sY , ¼ sy from each parent

Traits Are Inherited Independently 4 x 4 Punnett square yields: 9/16 smooth yellow peas 3/16 smooth green peas 3/16 wrinkled yellow peas 1/16 wrinkled green peas

4 x 4 Punnett square yields:

9/16 smooth yellow peas

3/16 smooth green peas

3/16 wrinkled yellow peas

1/16 wrinkled green peas

Independent Assortment Meiosis II Meiosis I Randomly one or the other Chromosome Replication Y S S Y y s s y y S S y Y s Y s S y y S Y Y s s S s Y y S s Y y Y y S s Y Y S s y y S s S Y Y S s y y s

Genes on the Same Chromosome Mendel’s Law of Independent Assortment only works for genes whose loci are on different chromosomes Different gene loci located on the same chromosome tend to be inherited together Characteristics whose genes tend to assort together are said to be linked

Mendel’s Law of Independent Assortment only works for genes whose loci are on different chromosomes

Different gene loci located on the same chromosome tend to be inherited together

Characteristics whose genes tend to assort together are said to be linked

Linkage Red Allele, p Round Allele, l Purple Allele, P Long Allele, L Flower color gene Pollen shape gene

Recombination Genes on the same chromosome do not always sort together Crossing over in Prophase I of meiosis creates new gene combinations Crossing over involves the exchange of DNA between chromatids of paired homologous chromosomes in synapsis

Genes on the same chromosome do not always sort together

Crossing over in Prophase I of meiosis creates new gene combinations

Crossing over involves the exchange of DNA between chromatids of paired homologous chromosomes in synapsis

Crossing Over red red Purple Purple round round Long Long Sister Chromatids Sister Chromatids old combination new combination new combination old combination P P p p L L l l P p p L L l l P L p L l l P p P L p L l l P p L L l l P P p p P P p p L L l l P p p L L l l Duplicated Chromosome Duplicated Chromosome L L l l P P p p Homologous Chromosomes P P p p L L l l P p p L L l l p L P l L P l p Flower Color Pollen Shape

 

 

 

 

Sex Chromosomes and Autosomes Mammals and many insect species have a set of sex chromosomes that dictate gender Females have two X chromosomes Males have an X chromosome and a Y chromosome Sex chromosomes segregate during meiosis [The rest of the (non-sex) chromosomes are called autosomes]

Mammals and many insect species have a set of sex chromosomes that dictate gender

Females have two X chromosomes

Males have an X chromosome and a Y chromosome

Sex chromosomes segregate during meiosis

[The rest of the (non-sex) chromosomes are called autosomes]

 

Sex Determination in Mammals X 1 X 2 EGGS Male Parent Y X m S P E R M Female Offspring Male Offspring Y X m X m X 1 X 2 X m Y Y X 1 X 2 X 1 X 2 Female Parent

Sex-Linked Genes Are on the X or the Y Genes carried on one sex chromosome are sex-linked X chromosome is much larger than the Y and carries over 1000 genes Y chromosome is smaller and carries only 78 genes The X and the Y have very few genes in common Females (XX) can be homozygous or heterozygous for a characteristic Males (XY) have only one copy of the genes on the X or the Y

Genes carried on one sex chromosome are sex-linked

X chromosome is much larger than the Y and carries over 1000 genes

Y chromosome is smaller and carries only 78 genes

The X and the Y have very few genes in common

Females (XX) can be homozygous or heterozygous for a characteristic

Males (XY) have only one copy of the genes on the X or the Y

How Sex-Linkage Affects Inheritance Patterns of sex-linked inheritance were first discovered in fruit flies ( Drosophila ) in early 1900s Eye color genes were found to be carried by the X chromosome R = red eyes (dominant) r = white eyes (recessive)

Patterns of sex-linked inheritance were first discovered in fruit flies ( Drosophila ) in early 1900s

Eye color genes were found to be carried by the X chromosome

R = red eyes (dominant)

r = white eyes (recessive)

How Sex-Linkage Affects Inheritance Sex-linked (specifically X-linked ) recessive alleles displayed their phenotype more often in males Males showed recessive white-eyed phenotype more often than females in an X R X r x X r Y cross Males do not have a second X-linked gene (as do females) which can mask a recessive gene if dominant

Sex-linked (specifically X-linked ) recessive alleles displayed their phenotype more often in males

Males showed recessive white-eyed phenotype more often than females in an

X R X r x X r Y cross

Males do not have a second X-linked gene (as do females) which can mask a recessive gene if dominant

Sex Linkage: Eye Color in Fruit Flies 25% Normal f Carrier f Normal m 25% 25% 25% White-e m Eggs of X R X r Female Sperm of X R Y Male 1 1 Y X R X R X r X R X R Y X r Female Female Male Male 1 1 Frequencies Phenotypes Genotypes Frequencies X R X R X r Y X R X r X R Y R r R

Departure from Mendel’s Rules Assumptions drawn from Mendel’s Rules All genes are governed by alleles found at a single locus on a pair of homologous chromosomes There are two alleles (gene forms) for each characteristic or gene type One allele is dominant over the other , which is recessive

Assumptions drawn from Mendel’s Rules

All genes are governed by alleles found at a single locus on a pair of homologous chromosomes

There are two alleles (gene forms) for each characteristic or gene type

One allele is dominant over the other , which is recessive

Incomplete Dominance Dominance of one allele over another breaks down in incompletely dominant characteristics When the heterozygous phenotype is intermediate between the two homozygous phenotypes, the pattern of inheritance is called incomplete dominance

Dominance of one allele over another breaks down in incompletely dominant characteristics

When the heterozygous phenotype is intermediate between the two homozygous phenotypes, the pattern of inheritance is called incomplete dominance

Incomplete Dominance: Homozygous-X Homo Recessive R R (100%) Pink (intermediate) Eggs of Homozygous RR Red Parent Pollen of Homozygous R ' R ' White Parent R' R' R' R R' R R' R R' R Pink Pink Pink Pink 1 Frequencies Phenotypes Genotypes Frequencies R'R R'R R'R R'R

Incomplete Dominance: F 1 X F 1 (25%) (25%) Red White R R' (50%) Pink Eggs of Heterozygous RR ' Pink F 1 Parent Pollen of Heterozygous RR ' Pink F 1 Parent R R' R' R R R' R R R' R' 1 1 Red Pink Pink White Frequencies Phenotypes Genotypes Frequencies RR R'R' RR' R'R 2

Human Eye Color AB Ab aB ab AB Ab aB ab EGGS SPERM Mother AaBb Father AaBb AABB AABb AaBB AaBb black dark brown dark brown light brown AAbB dark brown AAbb light brown AabB light brown Aabb blue aABB aABb aaBB aaBb dark brown light brown light brown blue aABb aABb aaBb aabb light brown blue blue light blue

Multiple Alleles A species may have more than two alleles for a given characteristic Each individual still carries two alleles for this characteristic

A species may have more than two alleles for a given characteristic

Each individual still carries two alleles for this characteristic

Multiple Alleles Examples of multiple allelism Thousands of alleles for eye color in fruit flies, producing white, yellow, orange, pink, brown, or red eyes Human blood group genes producing blood types A, B, AB, and O Three alleles in this system: A , B , and O

Examples of multiple allelism

Thousands of alleles for eye color in fruit flies, producing white, yellow, orange, pink, brown, or red eyes

Human blood group genes producing blood types A, B, AB, and O

Three alleles in this system: A , B , and O

Codominance Some alleles are always expressed even in combination with other alleles Heterozygotes display phenotypes of both the homozygote phenotypes in codominance

Some alleles are always expressed even in combination with other alleles

Heterozygotes display phenotypes of both the homozygote phenotypes in codominance

Codominance Example: Human blood group alleles Alleles A and B are codominant Type AB blood is seen where individual has the genotype AB

Example: Human blood group alleles

Alleles A and B are codominant

Type AB blood is seen where individual has the genotype AB

Human ABO Blood Group 10% 40% 46% 4% B or AB A or AB O,AB, A,B (universal) AB (universal) B or O A or O O AB, A, B, O (universal) A B Both Neither BB or BO AA or AO OO AB O AB B A Freq Donates Re- ceives Anti- bodies RBCs Genotype Type

Polygenic Inheritance Some characteristics show a range of continuous phenotypes instead of discrete, defined phenotypes Examples include human height, skin color, and body build, and grain color in wheat

Some characteristics show a range of continuous phenotypes instead of discrete, defined phenotypes

Examples include human height, skin color, and body build, and grain color in wheat

Polygenic Inheritance Phenotypes produced by polygenic inheritance are governed by the interaction of more than two genes at multiple loci Human skin color is controlled by at least 3 genes, each with pairs of incompletely dominant alleles

Phenotypes produced by polygenic inheritance are governed by the interaction of more than two genes at multiple loci

Human skin color is controlled by at least 3 genes, each with pairs of incompletely dominant alleles

 

Pleiotropy Some alleles of a characteristic may create multiple phenotypic effects ( pleiotropy ) Mendel’s rules specify only one phenotype possible for any allele

Some alleles of a characteristic may create multiple phenotypic effects ( pleiotropy )

Mendel’s rules specify only one phenotype possible for any allele

Pleiotropy Example: The SRY gene in male humans SRY gene stimulates development of gonads into testes, which in turn stimulate development of the prostate, seminal vesicles, penis, and scrotum

Example: The SRY gene in male humans

SRY gene stimulates development of gonads into testes, which in turn stimulate development of the prostate, seminal vesicles, penis, and scrotum

Pedigree Analysis Records of gene expression over several generations of a family can be diagrammed Careful analysis of this diagram (a pedigree ) can reveal inheritance pattern of a trait Pedigree analysis is often combined with molecular genetics technology to elucidate gene action and expression

Records of gene expression over several generations of a family can be diagrammed

Careful analysis of this diagram (a pedigree ) can reveal inheritance pattern of a trait

Pedigree analysis is often combined with molecular genetics technology to elucidate gene action and expression

How to Read Pedigrees = male = female = parents or = individual who shows the trait or = heterozygous carrier of autosomal trait = offspring 1 2 3 I, II, III, IV, or V = generation

A Recessive Pedigree

Pedigrees: Legacy of Queen Victoria

Sickle-Cell Anemia Hemoglobin is an oxygen-transporting protein found in red blood cells A mutant hemoglobin gene causes hemoglobin molecules in blood cells to clump together Red blood cells take on a sickle (crescent) shape and easily break Blood clots can form, leading to oxygen starvation of tissues and paralysis Condition is known as sickle-cell anemia

Hemoglobin is an oxygen-transporting protein found in red blood cells

A mutant hemoglobin gene causes hemoglobin molecules in blood cells to clump together

Red blood cells take on a sickle (crescent) shape and easily break

Blood clots can form, leading to oxygen starvation of tissues and paralysis

Condition is known as sickle-cell anemia

Normal Red Blood Cells

Sickled Cells

Sex-Linked Genetic Disorders Several defective alleles for characteristics encoded on the X chromosome are known Sex-linked disorders appear more frequently in males and often skip generations Examples of sex-linked (X-linked) disorders Red-green color blindness

Several defective alleles for characteristics encoded on the X chromosome are known

Sex-linked disorders appear more frequently in males and often skip generations

Examples of sex-linked (X-linked) disorders

Red-green color blindness

 

 

Non-Disjunction Incorrect separation of chromosomes or chromatids in meiosis known as non-disjunction Most embryos arising from gametes with abnormal chromosome numbers abort spontaneously (are miscarried) Some combinations of abnormal chromosome number survive to birth or beyond

 

 

Incidence of Down Syndrome Age of Mother (years) Number per 1000 Births 10 20 30 40 50 0 100 200 300 400

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