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Unit 4: Genetics


CHAPTER 11: CHROMOSOMES AND HUMAN INHERITANCE In some animals, the male has two identical sex chromosomes, not the female Most animals, mammals -- this pattern ... – PowerPoint PPT presentation

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Title: Unit 4: Genetics

Chapter 11Chromosomes and Human Inheritance
  • Unit 4 Genetics

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

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

___ __________
  • 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
  • Reference figure 11.2, pg. 170

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

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
  • A _____________ is a diagnostic tool that is a
    preparation of an individuals metaphase
  • 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

Figure 11.3, pg. 171
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

  • 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)

  • Uses standardized symbols
  • Squares ________ , Circles ______
  • Shaded squares/circles those who carry trait of
  • 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

Example Pedigree
A pedigree for polydactyly
  • Polydactyly An unusual number of fingers of toes
  • Figure 11.17, pg. 180

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

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

  • Figure 11.4a, pg. 172

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

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

  • Figure 11.4b, pg 172

Autosomal recessive inheritance
  • Either parent can carry the recessive allele on
    an autosome
  • Heterozygotes are symptom-free homozygotes are
  • 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

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

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

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
  • Most progeriacs expect to die in their teens

______ 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

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

X-linked inheritance
  • Figure 11.7, pg. 174

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

Hemophilia a
  • Hemophilia is a serious X-linked recessive
    condition that prevents blood from clotting
  • 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)

Red-Green Color Blindness
  • Color blindness is the inability to distinguish
  • 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

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