Download CHROMOSOMAL BASIS OF INHERITANCE

Chromosomal Basis of
Inheritance
Chapter 15
• Most genetics work done on fruit
flies (little time to observe many
generations)
• Thomas Morgan - fruit fly eye
color.
• Wild type (normal) eye color - red.
• Mutant - white.
• Discovered mutant eye color
appeared more often in males some traits sex-linked (carried on
sex chromosomes).
• Chromosomes have hundreds or
thousands of genes.
• Genes located on same chromosome,
linked genes, inherited together chromosome passed as unit.
"A" and "B" are linked due to their occurrence in
the same chromosome.
Similarly, "a" and "b" are linked in the other
chromosome.
http://anthro.palomar.edu/biobasis/images/linked_genes.gif
• Production of offspring with new
combinations of traits inherited
from 2 parents - genetic
recombination.
• Can occur during crossing over sections of homologous
chromosomes exchanged during
meiosis I.
http://www.genomenewsnetwork.org/gnn_images/whats_a_genome/crossing_over.jpg
• Genetic map - list of the loci along
the chromosomes.
• Further apart genes are, higher
probability they will switch places.
Sex chromosomes
• 2 sex chromosomes - X and Y.
• Males – XY, females - XX.
• Other species - X-0 system, Z-W
system, haplo-diploid system.
• Humans - X-Y system like normal
chromosomes - 50/50 chance of
having male or female.
• Until embryo is 2 months old fetus female.
• If fetus XY - SRY gene turned on
making fetus male.
http://www.expectalipil.com/images/fetal_dev_2.jpg
• Sex chromosomes, have genes for
traits other than sex.
• Trait recessive - female will only
inherit it if both parents pass it on.
• Males - 50% chance of inheriting it
(only have 1 X chromosome)
• Males have higher rate of sexlinked diseases than females.
http://www.emc.maricopa.edu/faculty/farabee/biobk/hemophb.gif
• Muscular dystrophy - sex-linked
disease.
• Affects far more males than
females.
• Hemophilia (excessive bleeding) sex-linked.
http://upload.wikimedia.org/wikipedia/en/a/a3/XlinkRecessive.jpg
• Only 1 X in females turned on.
• Other - Barr body - reactivated in
ovaries during egg production (to
pass genes on).
• Females exhibit characteristics
from mother, some from father
(sex chromosomes only).
http://www.columbia.edu/cu/biology/courses/c2005/images/barr_body.19.gif
Barr body replicated,
not transcribed
• Pattern responsible for mosaic of
effects (tortoiseshell cats)
• Due to patches of cells expressing
orange allele, others have
nonorange allele.
http://www.cas.muohio.edu/~wilsonkg/gene2005/images/f3p27.jpg
Errors
• Errors can occur both in DNA and
in chromosomes.
• Nondisjunction - homologous
chromosomes fail to separate
during meiosis I, or chromatids during meiosis II.
• Some gametes receive 2 of same
type of chromosome; another
gamete receives no copy.
• Abnormal # of chromosomes aneuploidy.
• Trisomy - gamete receives 3 of
same chromosomes (2n + 1).
• Monosomy - gamete receives 1 of
same chromosome (2n – 1).
• Earlier in development - more
profound effect - those cells go
through mitosis.
http://www.musckids.com/health_library/genetics/images/chromosome_j.gif
• Organisms with more than 2
complete sets of chromosomes polyploidy.
• Happens more often in plants than
animals.
• Species with polyploidy usually more
normal than aneuploidy (no missing
chromosomes)
http://emedia.leeward.hawaii.edu/millen/bot130/learning_objectives/lo15/15b_p37b.gif
A rodent species that is the
result of polyploidy
• Deletion - piece of chromosome
broken off during cell division.
• Duplication - fragment becomes
attached as extra segment to
sister chromatid.
• Inversion - piece breaks off, turns
around, reattaches (backwards).
• Translocation - chromosomal
fragment joins nonhomologous
chromosome.
• Down syndrome - trisomy (Trisomy
21).
• Chromosome 21 - smallest
chromosome - individual can survive.
• Aneuploidy – can occur in sex
chromosomes.
• Klinefelter’s syndrome - male XXY
(nondisjunction)
• Trisomy X (XXX) can occur in
females.
• Monosomy X - Turner syndrome nondisjunction.
http://www.biology.iupui.edu/biocourses/N100/images/klinefelter.gif
http://www.tokyo-med.ac.jp/genet/kry/xok.jpg
• Deletion disease - cri-du-chat chromosome 5.
• Chronic myologenous leukemia example of translocation between
chromosome 9 and chromosome 22.
http://learn.genetics.utah.edu/units/disorders/karyotype/images/criduchat_karyotype.jpg
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Ph1Karyotype.gif
• Some traits dependent on who
passes alleles (mother or father)
• Prader-Willi syndrome caused by
deletion on chromosome 15 (father)
• Deletion from mother - Angelman
syndrome.
• Due to genomic imprinting - gene on
1 homologous chromosome silenced,
allele on homologous chromosome
expressed.
http://www.cytopix.com/ImageResizeCache/723578_t2001.5.25.11.38.0_q50_600x450.jpg
• Some eukaryotic genes located in
mitochondria.
• These genes all passed from
mother to offspring; none of
father’s mitochondrial genes passed
on.
Coloration due to mitochondrial genes