Two types of chromosomes are autosomes and sex chromosomes.
Autosomes (#s 1-22...44 total) are chromosomes not involved sex
determination. Sex chromosomes (23rd pair) either XX or XY directly
involved in sex determination
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Sex linked traits refers to traits that are carried on the sex
chromosomes. Typically sex linked traits are carried on the X
chromosome.
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H = no hemophilia h = hemophilia
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X-inactivation Female mammals inherit 2 X chromosomes one X
becomes inactivated during embryonic development condenses into
compact object = Barr body which X becomes Barr body is random
patchwork trait = mosaic XHXH XhXh XHXhXHXh patches of black
patches of orange tricolor cats can only be female
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Multiple allele traits Traits that are controlled by 3 or more
alleles of the same gene (blood grouping is controlled by A, B or O
alleles
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Polygenic traits Traits that are controlled by several genes
(skin, eye, hair color) AaAAaaAa = 4 genes but 2 alleles (A or a)
polygenic has several genes influencing a trait, multiple allele
has several alleles influencing a trait.
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Autosomal DOMINANT disorder Disorders carried on the autosomes,
controlled by a dominant allele (therefore you only need one
dominant allele to show the disorder)
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Autosomal recessive disorder Disorders carried on the
autosomes, controlled by a recessive allele (therefore you need two
recessive alleles to show the disorder)
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Chromosomal Abnormalities Nondisjunction chromosomes dont
separate properly during meiosis Chromosomal Mutations deletion
duplication inversion translocation
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Changes in chromosome structure deletion loss of a chromosomal
segment duplication repeat a segment inversion reverses a segment
translocation move segment from one chromosome to another error of
replication error of crossing over
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Autosomal Disorders Dominant Acondroplasia Dwarfism Lethal in
homozygous cond. Acromegaly Gigantism Overactive pituitary
Huntingtons Degeneration of nervous system Manifests around 40
years of age Recessive Albinism Melanin pathway mutated
photosensitivity Phenylketoneuria Cannot break down phenylalanine
Lead to mental retardation Cystic fibrosis Cl - channel problem
Mucus buildup Death around 40
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trisomy 2n+1 Nondisjunction Cause of aneuploidy (wrong
chromosome #) trisomy cells have 3 copies of a chromosome monosomy
cells have only 1 copy of a chromosome n+1 n monosomy 2n-1 n-1
n
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Down syndrome Trisomy 21 3 copies of chromosome 21 1 in 700
children born in U.S. Chromosome 21 is the smallest human
chromosome but still severe effects Frequency of Down syndrome
correlates with the age of the mother
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Down syndrome & age of mother Mothers age Incidence of Down
Syndrome Under 30
