Inheritance%20Patterns%20

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Inheritance Patterns Human Genetics

• Ch.12

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(12-1) Human Males Females

• Sex chromo.s (X Y)
• Male XY
• Female XX
• Gametes
• Egg carry only X
• Sperm carry X or Y

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Key Idea
50 chance female offspring 50 chance male
offspring
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Who Discovered Sex Chromosomes?

• Thomas Morgan
• Early 1900s
• Columbia University
• Worked w/ fruit flies

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Sex Linkage

• Gene on a sex chromo.
• X-linked genes
• Y-linked genes

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Sex Linked Traits

• Most sex linked genes found on the X chromo.
• Genes on the Y chromo. are for male reproductive
  organ development

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Sex Linked Genetic Problems

• In flies R red eyes, r white eyes
• Gene located on the X chromosome

X
X
X
Y
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Example 1

• White eye male mates w/ a red ho/go dominant
  female
• XrY x XRXR

Xr
Y
XRXr
XRY
100 red female 0 white female 100 red
male 0 white male
XR
XRXr
XRY
XR
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Example 2

• Red eye male mates w/ a red he/go female
• XRY x XRXr

XR
Y
XRXR
XRY
100 red female 0 white female 50 red
male 50 white male
XR
XRXr
XrY
Xr
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Example 3

• White eye male mates w/ a red he/go female
• XrY x XRXr

Xr
Y
XRYr
XRY
XR
50 red female 50 white female 50 red
male 50 white male
XrXr
XrY
Xr
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What would you expect from crossing 2 he/go flies?
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Morgans Results

• These characteristics are on the same chromo.,
  thus they are linked together during meiosis

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Linkage Groups

• Genes located on the same chromo.s therefore
  inherited together
• Goes against Law of
• Indep. Assortment

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How do linked genes get unlinked?

• Crossing over
• Frequency of crossing over b/w certain genes is
  used to make a chromosome map

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Chromosome Map

• Linear sequence of genes on a chromo.
• 1 map unit 1 chance of crossing over
• Farther apart greater chance of genes to be
  separated

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Which 2 genes have the highest probability of
crossing over? The lowest?
A
a
Highest A C Lowest A B
B
b
C
c
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Mutation

• Change in DNA
• Entire chromo. or a single nucleotide
• Can lead to genetic disorders or be beneficial

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Mutation Types

• Germ-cell mutation occurs in gametes
• Does not affect the organism, but can be passed
  on
• Somatic-cell mutation occurs in body cells
• Does affect organism is not passed on
• Lethal mutation causes death, often before birth

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Chromosome Mutations

• Change in the structure of a chromo.
• Deletion/addition
• Inversion segment breaks off reattaches in
  reverse
• Translocation segment breaks off reattaches to
  another chromo.
• Nondisjunction failure of chromo.s to separate
  during meiosis

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Nondisjunction
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Gene Mutations

• Point mutation substitution at 1 point in DNA
• Changes 1 codon
• Frame-shift mutation cause the misreading of all
  codons after the mutation

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Substitution
Deletion
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(12-2) Pedigree

• Diagram showing how a trait is inherited over
  several generations

Half-filled carrier
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Human Patterns of Inheritance

1. Single allele trait
2. Multiple allele trait
3. Polygenic trait
4. X-linked trait
5. Sex-influenced trait
6. Nondisjunction

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Single Allele Trait

• Trait controlled by a single allele of a gene
• Normal dom.-rec.
• Ex
• Huntingtons Disease (autosomal dom.)
• Cystic Fibrosis (autosomal rec.)

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Multiple Allele Trait

• 3 or more alleles of the same gene code for a
  single trait
• Ex ABO Blood Groups
• IA type A (dom.)
• IB type B (dom.)
• i type O (rec.)

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Blood Type Genotypes

• What are the genotypes for the following blood
  types?
• A
• IAIA or IAi
• B
• IBIB or IBi
• O
• ii
• AB
• IAIB

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Blood Type Problems

• A mother gives birth to a type O child. The
  mother is type A blood. The 2 potential fathers
  are type A (father 1) and type AB (father 2).
  Whos the daddy?

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Father 1 (Type A)
IA
i
IA
A
A
i
IA
i
A
O
IA
A
A
IB
AB
B
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Polygenic Trait

• Trait thats controlled by 2 or more genes
• Most human characteristics
• Range of phenotypes
• Influenced by environment too (complex characters
  environ. genes)
• Exs
• Skin color
• Eye color
• Human height

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X-Linked Trait

• Trait controlled by a gene on the X chromo.
• Exs
• Colorblindness (rec.)
• Muscular dystrophy (rec.)
• Hemophilia (rec.)

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Sex-Influenced Traits

• Presence of sex hormones influences expression of
  these traits
• Ex
• Pattern baldness

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Nondisjunction

• Failure of chromo.s to separate during meiosis
  resulting in 1 gamete w/ too many chromo.s 1
  w/ too few

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Nondisjunction (cont.)

• Trisomy cell w/ 3 copies of a chromo.
• Monosomy cell w/ 1 copy of a chromo.
• Ex
• Down Syndrome (Tri-21)
• Klinefelters syndrome (XXY)
• Turners Syndrome (XO)

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Detecting Disorders

• Before pregnancy
• Genetic screening
• Genetic counseling
• During pregnancy
• Amniocentesis
• Chorinonic villi sampling
• After birth
• Genetic screening