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Chromosomal Basis of Inheritance. Chapter 3. Chromosomes and Cellular Reproduction. Eukaryote Chromosomes. Multiple linear chromosomes Many have two of each type Diploid zygote Fusion of two haploid gametes Called homologous chromosomes Autosomes Sex chromosomes. Eukaryote Chromosomes.

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Chromosomal Basis of Inheritance

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Chromosomal Basis of Inheritance

Chapter 3


Chromosomes and Cellular Reproduction


Eukaryote Chromosomes

  • Multiple linear chromosomes

  • Many have two of each type

    • Diploid zygote

    • Fusion of two haploid gametes

    • Called homologous chromosomes

  • Autosomes

  • Sex chromosomes


Eukaryote Chromosomes

  • Differ in size and morphology

  • Specific to each species

  • Centromere - constriction

    • Metacentric, submetacentric, acrocentric, telcentric

  • Karyotype – complete chromosome complement


Human Karyotype

  • Genes ID is chromosome # and loci band on that chromosome

    • Also p or q arm

    • BRCA1 is at 17q21


Mitosis

  • Cell reproduction includes growth, mitosis and cytokinesis

  • Cell cycle includes mitotic phase and interphase between division

  • Mitosis is a process for growth, repair, and asexual reproduction

  • Interphase: G1, S and G2


Interphase

  • G1- presynthesis

    • Cell prepares for DNA synthesis and chromosome replication

  • S – DNA synthesis and chromosome replication

  • G2- postsynthesis

    • Cell prepares for division


S Phase

  • During interphase chromosomes unwound

  • Chromosomes are replicated

    • Sister chromatids

    • Centromeres replicated but not separated

  • Become daughter chromosomes


Mitosis

  • Length of process varies

  • Continuous process

  • 4 Phases:

    • Prophase

    • Metaphase

    • Anaphase

    • Telophase


Prophase

  • Chromosomes coil

  • Spindle forms

    • Centriole in animals

  • Nuclear membrane breaks down

  • Nucleolus disappears

  • Kinetochore forms


Metaphase and Anaphase

  • Metaphase

    • Microtubules orient the chromosomes

    • Along plane of cell

    • Metaphase plate

  • Anaphase

    • Centromeres separate

    • Daughter chromosomes move toward poles


Telophase and Cytokinesis

  • Telophase

    • Chromosomes uncoil

    • Nuclear envelope forms

    • Spindle disappears

    • Nucleolus reforms

  • Cytokinesis

    • Separation of cytoplasm

    • Different in plants and animals


Meiosis

  • One replication, two divisions

    • Reduction in number of chromosomes

  • Occurs at certain points in a life cycle

  • Only in certain tissues

  • Makes gametes

    • Gametogenesis

  • Four haploid daughter cells


Meiosis I – Prophase I

  • Chromosomes have duplicated

  • 5 substages

    • Leptotene stage – chromosomes coil

    • Zygotene stage – homologous pairs align in synapsis

      • Synaptonemal complex - Aligns perfectly base pair to base pair

      • Telomeres move and align chromosomes

    • Pachytene stage – crossing-over takes place

      • Recombinant chromosome


Meiosis I – Prophase I

  • 5 substages

    • Diplotene stage – synaptonemal complex disassembles

      • Chiasma are formed

    • Diakinesis – nucleus and nuclear envelope disintegrate


Meiosis I – Metaphase I and Anaphase I

  • Metaphase I

    • Homologous pairs line up on plate

    • Spindle is completely formed

    • Kinetochores formed

  • Anaphase I

    • Homologous pairs separate

    • Move toward opposite poles

    • Chiasma separate

    • Sister chromosomes remain joined


Meiosis I – Telophase I

  • Nuclear envelope forms

  • Cytokinesis


Meiosis II

  • Similar to mitosis

  • Prophase II – chromosomes condense

  • Metaphase II – sister chromosomes line up

  • Anaphase II – sister chromatids toward poles

  • Telophase II – nuclear envelope reforms, chromosomes no longer visible


Gene Segregation in Meiosis

  • Results of meiosis

    • Haploid cells with half of the # of chromosomes

    • In independent assortment

      • Each pair of chromosomes sorts its maternal and paternal homologues into daughter cells independently of the other pairs

      • 2n-1 where n=# of chromosomes

    • Crossover increases variation


Meiosis vs Mitosis


Meiosis vs. Mitosis


Meiosis in Animals

  • Diploid for most of their life

    • Haploid gametes fuse to restore

  • Sexual reproduction

  • Gametes produced by spermatogenesis and oogenesis


Spermatogenesis

  • In the testes

    • 1° Spermatogonia

    • 2° Spermatogonia

    • 1° Spermatocytes

      • Go through Meiosis I

    • 2° Spermatocytes

      • Go through Meiosis II

    • Spermatids


Oogenesis

  • In the ovaries

    • 1° Oogonia

    • 2° Oogonia

    • 1° Oocytes

      • Go through Meiosis I and unequal cytokinesis

    • 2° Oocyte and first polar body

      • Go through Meiosis II

    • Ovum and 2nd polar body


Meiosis in Plants

  • Gametophyte and sporophyte stage

  • Alternation of generations

  • Flower is sexual structure

    • Can be bisexual or unisexual

    • Stamens and pistils

    • Pollen from anther

    • Ovule contains egg cells


Alternation of Generations

  • Multicellular gametophyte

  • Meiosis then mitosis BEFORE fertilization

  • Plants fungi and algae


Chromosome Theory of Inheritance


Chromosome Theory of Inheritance

  • Correlation between traits and separation of chromosomes in meiosis

  • First called inheritance factors genes

  • Chromosome # varies


Sex Chromosomes

  • Autosomes

  • Sex chromosomes – represented differently in the two sexes

  • When gametes are formed one sex chromosome goes to each

  • In humans male determines sex

  • Some animals have unpaired chromosomes


Sex Chromosomes

  • The X-O system

  • The Z-W system

  • Chromosome Number


Sex Chromosomes

  • Drosophila melanogaster

  • Heterogametic and homogametic sexes

  • Same size but different shape

  • Genes create characteristics of male and female


Sex Linkage

  • Sex chromosomes also carry genes, any gene located on the sex chromosome is called a sex-linked gene

  • Most are found on X chromosomes

  • Hemizygous

  • X-linked Allele Animation


Sex Linkage


Nondisjunction of Chromosomes

  • Homologous or sister chromosomes do not separate

  • Can involve either autosomes or sex

  • In sex chromosomes can lead to either 2 X chromosomes or no X chromosomes

    • X chromosome nondisjunction

    • Aneuploidy and polyploidy

    • Primary and secondary nondisjunction (XXY)


Nondisjunction of Chromosomes


Secondary Nondisjunction


Sex Chromosomes and Sex Determination


Genotypic Sex Determination

  • Sex chromosomes play a role in inheritance and sex determination

  • Placentals sex determined by Y

  • Y carries genes toward male sex determination

  • Testis-determining factor gene

  • Factor causes gonad tissue to become testes instead of ovaries


Sex Chromosome Nondisjunction

  • XO individuals –

    • Turner Syndrome

    • Genetically female

    • At puberty, develop poorly

  • XXY individuals

    • Klinefelter syndrome

    • Genetically male

    • Several variations XXY, XXXY, XXYY

    • Symptoms include underdeveloped testes, taller and some breast tissue


Turner Syndrome


Klinefelter Syndrome


Dosage Compensation with Sex Chromosomes

  • Cannot have an unequal dosage of genes from duplicate sex chromosomes

    • Can be lethal if they are not equal

  • Barr body

    • Condensed and inactive X chromosome

    • Has become lyonized

    • Only in females

    • X independently chosen from cell to cell

    • Epigenetic silencing of one chromosome


Barr Bodies


Genic Sex Determinations

  • Allelic differences determine sex

    • Mating types in yeast

    • a and α

    • Same morphologies, but mating only occurs between different type

    • Same in some basidiomycetes


Analysis of Sex-Linked Traits in Humans


X-Linked Recessive Inheritance

  • Trait resulting from recessive mutant allele

  • More than 100 traits

    • Hemophilia A

    • Blood lacks clotting factor

    • Queen Victoria

      • Carrier daughters son with hemophilia

  • Females must be homozygous to express


QueenVictoria

Albert

Alice

Louis

Alexandra

CzarNicholas IIof Russia

Alexis

X-Linked Recessive Inheritance


X-Linked Dominant Inheritance

  • Traits resulting from a dominant mutant allele carried on the X chromosome

  • Very few

  • Faulty tooth enamel

  • Heterozygous females express the trait

  • Milder in females than in males


Y-Linked Inheritance

  • Trait resulting from mutant gene that is carried on the Y chromosome

  • Easily recognizable

    • Every male in the family has it

    • No females express it

  • Hairy ears trait

    • Hehe!!!


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