Chromosomal InheritanceChromosomal Inheritance

Chromosomal Division for Chromosomal Division for Sperm and Egg ProductionSperm and Egg Production

Chromosomal AbnormalitiesChromosomal Abnormalities

Human Life CycleHuman Life Cycle

Nuclear division reducing the chromosome

number, leading to sperm or eggs

Diploid number of chromosomes,

two full sets

Haploid number of chromosomes,

one full set

Nuclear division retaining the original chromosome number

Cell Cycle With Meiosis Cell Cycle With Meiosis

G1cytoplasm doubles, including organelles

Schromosomesduplicate

G2synthesis of proteins and assembly of components for division

cytokinesis

Meiosis Interphase includes Interphase includes

G1 = growth phase 1G1 = growth phase 1 S = synthesis phaseS = synthesis phaseG2 = growth phase 2G2 = growth phase 2

Interphase

Meiosis IIcytok

inesis

Meios

is I

Meiosis includes two Meiosis includes two chromosomal divisionschromosomal divisions

Meiosis IMeiosis IMeiosis IIMeiosis II

Cytokinesis = division ofCytokinesis = division of cytoplasmic contents cytoplasmic contents

Homologous Chromosome PairsHomologous Chromosome Pairs

• Diploid cells have Diploid cells have pairs of pairs of chromosomeschromosomes

• Each homologous Each homologous chromosome pair is chromosome pair is genetically matched genetically matched so that the genes are so that the genes are arranged in the arranged in the same order same order

• Meiosis distributes Meiosis distributes members of each members of each pair to separate pair to separate nucleinuclei

Humans have 1 pair of sex chromosomes and 22 pairs of autosomes

Outcome of Meiotic DivisionsOutcome of Meiotic DivisionsDiploid Human Cell with 46 chromosomes (23 pairs)Diploid Human Cell with 46 chromosomes (23 pairs)

Duplication of Cell ContentsDuplication of Cell Contents

Meiosis I: Reduction DivisionMeiosis I: Reduction DivisionSeparation of Homologous Separation of Homologous Chromosomes into Different NucleiChromosomes into Different Nuclei

2 Genetically-Different Haploid Human Cells with 23 2 Genetically-Different Haploid Human Cells with 23 duplicated chromosomesduplicated chromosomes

Meiosis II: Equational DivisionMeiosis II: Equational DivisionSeparation of Duplicated Chromosomes Separation of Duplicated Chromosomes into Different Nucleiinto Different Nuclei

4 Genetically-Different Haploid Human Cells with 23 4 Genetically-Different Haploid Human Cells with 23 chromosomeschromosomes

Duplicated Duplicated ChromosomesChromosomes

in Early Meiosis in Early Meiosis

Homologous Homologous Chromosome Pair Chromosome Pair

Association of four chromatids of a

duplicated homologous

chromosome pair

Centromere = constricted region

Duplicated chromosomes joined at their centromeres

Nonsister Chromatids are joined to differentcentromeres

Prophase I of Meiosis IProphase I of Meiosis I

Chromosomes thickenChromosomes thickenGenetic exchange occurs between nonsister Genetic exchange occurs between nonsister chromatids through crossing-over chromatids through crossing-over

Metaphase I of Meiosis IMetaphase I of Meiosis I

Homologous pairs line up at the cell equatorHomologous pairs line up at the cell equatorSpindle fibers attached to centromeres cause Spindle fibers attached to centromeres cause chromosomal movement chromosomal movement

Spindle fiber

Anaphase I and Telophase I Anaphase I and Telophase I

of Meiosis Iof Meiosis I

Anaphase IAnaphase IMembers of homologous pair Members of homologous pair separate and are pulled to separate and are pulled to opposite poles of the cell opposite poles of the cell

Telophase ITelophase IChromosomes reach oppositeChromosomes reach opposite poles poles

+ cytokinesis

CytokinesisCytokinesisCytoplasm divides into two Cytoplasm divides into two separate cells separate cells

Daughter cells are haploid with duplicated chromosomes

Prophase II and Metaphase II Prophase II and Metaphase II of Meiosis IIof Meiosis II

Prophase IIProphase IIChromosomes thickenChromosomes thicken

Metaphase IIMetaphase IIChromosomes line up Chromosomes line up at cell equator at cell equator

Anaphase II and Telophase II Anaphase II and Telophase II of Meiosis IIof Meiosis II

Anaphase IIAnaphase IISister Chromatids Sister Chromatids separate and move to separate and move to opposite poles opposite poles

Telophase IITelophase IIChromosomes have Chromosomes have reached opposite poles reached opposite poles + cytokinesis

CytokinesisCytokinesisCytoplasm divides into Cytoplasm divides into

separate cells separate cells Daughter cells are haploid

and have genetic differences

Sperm formationSperm formation•Equal divisions of cytoplasmEqual divisions of cytoplasm•Four functional products per meiosisFour functional products per meiosis

Egg formationEgg formation•Unequal divisions of cytoplasmUnequal divisions of cytoplasm•Small polar bodies formedSmall polar bodies formed•One functional product per meiosisOne functional product per meiosis

Fertilization occurs after Meiosis I and

stimulates Meiosis II

Sex DeterminationSex Determination Sex ChromosomesSex Chromosomes: homologous : homologous

chromosomes that differ in size and chromosomes that differ in size and genetic composition between males and genetic composition between males and femalesfemales

Human Human ChromosomeChromosome

XX YY

SizeSize LargerLarger SmallerSmallerGenetic Genetic CompositionComposition

Multiple Multiple genesgenesunrelated unrelated to genderto gender

Very few genesVery few genes

TDF region TDF region determines determines maleness maleness

Chromosomal Number AbnormalitiesChromosomal Number Abnormalities

Arise by Nondisjunction = Failure of homologous Arise by Nondisjunction = Failure of homologous chromosomes or chromatids to separate during chromosomes or chromatids to separate during meiosismeiosis

Nondisjunction during Meiosis IINondisjunction during Meiosis IINondisjunction during Meiosis INondisjunction during Meiosis I

Human Autosomal AbnormalityHuman Autosomal Abnormality

How can Down Syndrome occur? How can Down Syndrome occur?

Eg. Egg with 2 copies of #21 Eg. Egg with 2 copies of #21 (24 chromosomes)(24 chromosomes) + Sperm with 1 copy of #21 + Sperm with 1 copy of #21 (23 chromosomes)(23 chromosomes) = Embryo with 3 copies of #21 = Embryo with 3 copies of #21 (47 chromosomes)(47 chromosomes)

Down SyndromeDown Syndrome Trisomy 21Trisomy 21

Three copies of Three copies of chromosome 21chromosome 21

Karyotype for Down SyndromeKaryotype for Down Syndrome

Eye foldEye fold Palm CreasePalm Crease

Physical FeaturesPhysical Features

Human Sex Chromosome AbnormalityHuman Sex Chromosome Abnormality Turner SyndromeTurner Syndrome XOXO

One copy of XOne copy of XNo second sex No second sex chromosomechromosome

How can Turner Syndrome occur?How can Turner Syndrome occur?Eg. Egg with 0 copies of XEg. Egg with 0 copies of X (22 chromosomes) (22 chromosomes) +Sperm with 1 copy of X+Sperm with 1 copy of X (23 chromosomes) (23 chromosomes) = Embryo with 1 copy of X= Embryo with 1 copy of X (45 chromosomes) (45 chromosomes)

Non-functional Ovaries From Adult Non-functional Ovaries From Adult Female with Turner’s SyndromeFemale with Turner’s Syndrome

Normal uterus, tubesNormal uterus, tubes and ovariesand ovaries

Karyotype for Karyotype for Turner’s SyndromeTurner’s Syndrome

Other Human Sex Chromosome Other Human Sex Chromosome Number AbnormalitiesNumber Abnormalities

Klinefelter Klinefelter SyndromeSyndrome

XXYXXY

Poly-X Poly-X FemalesFemales

XXXXXX

Jacobs Jacobs SyndromeSyndrome

XYYXYY

Sterile MaleSterile Male

Fertile FemaleFertile Female

Fertile MaleFertile Male

Chromosome Structure AbnormalitiesChromosome Structure Abnormalities

Williams syndrome is caused by a Williams syndrome is caused by a deletiondeletion = loss of a chromosomal segment. = loss of a chromosomal segment.

Chromosome Structure AbnormalitiesChromosome Structure Abnormalities

Alagille syndrome is caused by a Alagille syndrome is caused by a translocationtranslocation = = movement of a chromosomal segment to another movement of a chromosomal segment to another non-homologous chromosome.non-homologous chromosome.