Unit 4: Genetics

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Chapter 11Chromosomes and Human Inheritance

• Unit 4 Genetics

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Human Chromosomes

• Most animals have a _________number of
  chromosomes _____
• Humans have ____ pairs of chromosomes
• All (except one) of those pairs are called
  _______________
• Same length, shape, and centromere location
• Humans have ___
• ______ _______________ are the last pair

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Sex Chromosomes

• Sex chromosomes determine ________
• Males ___
• Females ____
• X and Y chromosomes differ in length, shape, and
  the genes they carry

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___ __________

• Each egg contains 22 autosomes an X chromosome
• Sperm will contain 22 autosomes either an X
  chromosome OR a Y chromosome
• Egg and sperm combine ? either XX (female) or XY
  (male)
• Reference figure 11.2, pg. 170

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Sex Determination Y Chromosome

• Fewer than two dozen genes identified
• The Y chromosomes carries the ____ ______
• Master gene for male sex determination
• Expression of SRY gene triggers formation of
  ________ , which are the primary male sex organs
  (or gonads)
• These secrete ________________, which is
  responsible for the male secondary sex traits

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Sex Determination

• Absence of the male-determining SRY gene in
  females results in the formation of ovaries
• Mutations in the SRY gene causes individuals who
  are XY to develop as females
• The X chromosome codes for sexual traits but ALSO
  carries many genes for nonsexual traits
• X chromosome carries over ______ genes
• Males only have one copy of these genes

Reference figure 11.2
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Karyotyping

• A _____________ is a diagnostic tool that is a
  preparation of an individuals metaphase
  chromosomes
• Mitosis is arrested in _________
• Chromosomes are photographed, and then cut out
  and arranged by pairs according to size, shape,
  and length
• Array can be compared to a normal standard and
  analyzed for extra or missing chromosomes

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Karyotyping
Figure 11.3, pg. 171
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Human genetic analysis

• Humans are difficult to study genetically due to
  long life spans (compared to a fruit fly or a
  garden pea) and small families
• Data on human inheritance is displayed in
  _________________
• A pedigree is a chart that shows genetic
  connections among individuals
• Analysis of family pedigrees provides data on
  inheritance patterns through several generations

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Pedigrees

• Knowledge of ______________ and
  ________________________________ is used in
  analysis of pedigrees to yield clues to a traits
  genetic basis
• Conclusions most accurate when drawn from large
  number of pedigrees
• Can be used to predict the risk of disease in
  future offspring in a family (genetic counseling)

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Pedigrees

• Uses standardized symbols
• Squares ________ , Circles ______
• Shaded squares/circles those who carry trait of
  interest
• Horizontal line between male/female
  __________________
• Number generations from oldest (top) to youngest
  (bottom) with Roman numerals
• Number individuals within a generation from
  oldest (left) to youngest (right) with Arabic
  numerals

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Example Pedigree
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A pedigree for polydactyly

• Polydactyly An unusual number of fingers of toes
• Figure 11.17, pg. 180

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Genetic deviations

• Genetic ________________ is a term applied to a
  genetic condition that is a deviation for the
  usual (or average) and is not life-threatening
• Rare or less common version of a trait
• Genetic ______________ is used to describe
  conditions that cause medical problems
• ______________ is a recognized set of symptoms
  that characterize an abnormality or disorder
• A disease is an illness caused by infection or
  environmental factors
• A genetic _____________ is a term used only when
  factors alter previously workable genes in a way
  that disrupts body functions

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Autosomal Inheritance Patterns

• Some alleles on autosomes are inherited in simple
  Mendelian patterns
• Certain mutated forms of alleles give rise to
  genetic abnormalities or genetic disorders

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______________________

• Figure 11.4a, pg. 172

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Autosomal Dominant Inheritance

• The dominant allele is nearly always expressed,
  even in heterozygotes
• If one parent is heterozygous and the other
  homozygous recessive, there is a 50 chance that
  their child will be heterozygous
• If the gene (and its resulting disorder) reduces
  the chance of surviving or reproducing, its
  frequency should decrease
• However, it may not due to

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Examples Autosomal Dominant

• Acondroplasia (dwarfism)
• A benign abnormality that does not affect
  persons ability to reproduce
• Adults have abnormally short arms and legs
• Huntington disease
• A serious degeneration of the nervous system with
  an onset from age 40 onwards
• At this point, the gene has typically been passed
  from parent to offspring unknowingly

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____________________

• Figure 11.4b, pg 172

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Autosomal recessive inheritance

• Either parent can carry the recessive allele on
  an autosome
• Heterozygotes are symptom-free homozygotes are
  affected
• Two heterozygous parents have a 50 chance of
  producing heterozygous children and a 25 percent
  chance of producing a homozygous-recessive child
• When both parents are homozygous, all children
  can be affected

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Example Autosomal Recessive

• Galactosemia the inability to metabolize lactose
• A single gene mutation prevents the manufacture
  of an enzyme needed in the conversion pathway
• Lactose ? galactose ? glucose-6-phosphate, which
  can be converted to glycogen or enter glycolysis

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Nuerobiological disorders

• Nuerobiological disoders (NBDs) include
• Changes in genes contribute to the abnormal
  biochemistry in NBDs
• Most NBDs involve multiple genes and environment
  factors not just a single allele
• Some mutated alleles are linked to these
  disorders and can predispose a person

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Hutchinson-Gilford Progeria syndrome

• Premature aging is caused by a mutated allele
• In one of 8 million newborn humans, a mutated
  gene will cause accelerated aging
• Observable symptoms arise by age two
• Their skin thins, skeletal muscles weaken, bone
  growth ceases, hair loss occurs, and they look
  old
• Most progeriacs expect to die in their teens

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______ Inheritance patterns

• Certain dominant and recessive alleles on the X
  chromosome are inherited in Mendelian patterns
• Approximately _________ of all genes are located
  on the X chromosome
• Mutated alleles on the X chromosome contribute to
  more than 300 known genetic disorders
• Males cant transmit X-linked alleles to sons

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X-linked inheritance

• In X-linked recessive inheritance, the mutated
  gene occurs only on the X chromosome
• Males are more often affected because a single
  recessive allele on the X chromosome cannot be
  masked by a dominant gene on another chromosome
• Heterozygous females are phenotypically normal

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X-linked inheritance

• Figure 11.7, pg. 174

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X-linked inheritance

• A normal male mated with a female heterozygote
  (or carrier)
• Homozygous recessive female and a normal male

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Hemophilia a

• Hemophilia is a serious X-linked recessive
  condition that prevents blood from clotting
  properly
• The blood cannot clot because the genes do not
  code for the necessary clotting agent or agents
• Today, hemophilia affects about 1 in 7,500 people
• This number may be increasing because hemophilia
  is now treatable

• Reference Figure 11.8 (pg 174)

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Red-Green Color Blindness

• Color blindness is the inability to distinguish
  colors
• Mutated genes change the light-absorbing capacity
  of sensory receptors in the eyes
• Normal people can distinguish among 150 colors
• People with red-green color blindness can only
  see 25 colors (or fewer)
• Males are 12 times more likely than women to be
  affected by color blindness

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Duchenne muscular dystrophy

• Duchenne Muscular Dystrophy (DMD) affects about 1
  in 3,500 boys
• Its characterized by a rapid degeneration of
  muscles
• A recessive allele encodes for dystrophin, a
  structural protein in muscle fibers
• Abnormal or absent dystrophin causes the muscle
  degeneration