Chromosomal Inheritance

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Chapter 17

• Chromosomal Inheritance

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Outline

• Human Life Cycle
• Mitosis
• Stages of Mitosis
• Meiosis
• Crossing-Over
• Stages of Meiosis
• Chromosomal Inheritance
• Autosomal Syndromes
• Sex Chromosomal Syndromes

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Human Life Cycle

• Mitosis ensures every body cell receives
  identical copies of all chromosomes
• Somatic cells are diploid (2n).
• Meiosis creates new combinations of genes on
  chromosomes and reduces the chromosome number by
  half in gametes
• Sperm and egg (gametes) are haploid (n).

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mitosis and meiosis in human lfe cycle
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Mitosis Overview

• forms cells for growth or repair
• daughter cells have the same number of
  chromosomes as the parental cells
• Identical sister chromatids separated into each
  daughter cell

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Cell Cycle
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Prophase

• Centrioles move to poles
• Spindle fibers appear
• Nuclear envelope breaks down

Prophase -----------------------?metaphase
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Metaphase

• Spindle fully-formed
• Chromosomes align at the equator.

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Anaphase

• Sister chromosomes separate and daughter
  chromosomes move to the poles

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Telophase

• Chromosomes arrive at the poles
• Chromosomes become indistinct chromatin

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Mitosis Summary
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Overview of Meiosis

• two nuclear divisions four genetically unique
  daughter cells, half the number of parental
  chromosomes

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Sources of Genetic Recombination in Meiosis

• Crossing-over recombines genes on sister
  chromosomes of homologous pairs
• Independent assortment of homologues and
  chromatids
• combinination of maternal and paternal
  chromosomes at fertilization

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Crossing Over during Synapsis of Prophase
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Spermatogenesis
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Oogenesis
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Stages of Meiosis

• First Division.
• Prophase I - Spindle appears, and nuclear
  envelope fragments.
• Metaphase I - Tetrads line up at equator.
• Anaphase I - Homologous chromosomes of each pair
  separate and move to opposite poles of the
  spindle.
• Telophase I - Spindle disappears and nuclear
  envelope reforms.
• Cytokinesis - Plasma membrane furrows.

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Stages of Meiosis

• Second Division.
• Prophase II - Spindle appears and nuclear
  envelope disassembles.
• Metaphase II - Dyads line up at equator.
• Anaphase II - Sister chromatids separate and move
  towards poles.
• Telophase II - Spindle disappears and nuclear
  envelope reforms.
• Cytokinesis - Plasma membrane furrows.
• Four haploid daughter cells produced.

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Chromosomal Inheritance

• Humans have 22 pairs of autosomes, and one pair
  of sex chromosomes.
• Abnormal chromosome number or structure often
  leads to a syndrome.
• Amniocentesis and Chorionic Villi Sampling can be
  used to obtain a genetic sample to produce a
  karyotype.
• Visual display of chromosomes arranged by size,
  shape, and banding pattern.

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Human Karyotype Preparation
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Autosomal Syndromes

• Nondisjunction occurs
• During Meiosis I when both members of a
  homologous pair go to the same daughter cell.
• During Meiosis II when sister chromosomes fail to
  separate and both daughter chromosomes go to the
  same gamete.

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Autosomal Syndromes

• Down Syndrome.
• Trisomy 21.
• Incidence increases with mothers age.
• Cri du Chat Syndrome.
• Chromosomal deletion.

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Sex Chromosomal Syndromes

• Fragile X Syndrome.
• Abnormal Sex Chromosome Number.
• Turner Syndrome.
• XO.
• Klinefelter Syndrome.
• Two or more X chromosomes with a Y.
• Poly-X Females.
• More than two X chromosomes.
• Jacobs Syndrome.
• XYY.

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Turner and Klinefelter Syndromes
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Review

• Human Life Cycle
• Mitosis
• Stages of Mitosis
• Meiosis
• Crossing-Over
• Stages of Meiosis
• Chromosomal Inheritance
• Autosomal Syndromes
• Sex Chromosomal Syndromes

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