Inheritance Patterns

1
Chapter 12

• Inheritance Patterns Human Genetics

2
Bellwork Complete with your partner on the white
board

• The synthesis of polypeptides from the genetic
  information encoded in mRNA is
• A. Transcription
• B.Translation
• C. Transposon
• D. DNA Methylation
• At the end of DNA replication, each of the
  daughter molecules has one old strand and one new
  strand. This explains why DNA replication is
  described as _____________.

3
Chromosomes Inheritance

• Thomas Hunt Morgan- early 1900s
• -experiments with fruit flies
• -observed 4 pairs of chromosomes
• -noticed that 3 pairs were the same in males
  females but that 1 pair was different.
• - called these sex chromosomes.

4
Autosomes Sex Chromosomes

• Sex chromosomes- contain genes that determine the
  gender of an individual.
• Autosomes- the remaining pairs of chromosomes
  that do not directly determine sex.
• In mammals
• - 2 X chromosomes FEMALE (XX)
• - 1 X 1 Y is a MALE (XY)

5
In mammals, males determine the sex of the
offspring

• -each sperm has an equal chance of having an X or
  a Y
• -however- the only option for eggs is to receive
  an X chromosome.
• 11 male to female ratio

6
Karyotypes
7
Karyotype with an extra chromosome
8
Linked Sex-Linked Genes
9
A. Linked genes

• Genes which are close together on same
  chromosome.
• Inherited together
• Linked genes do not exhibit Mendels law of
  independent assortment

10
Chromosome Mapping

• The farther apart two genes are located on a
  chromosome, the more likely a cross-over will
  occur.
• Researchers use recombinant percentages to
  construct chromosome maps showing relative gene
  positions.

11
Sex-Linked traits

• are traits that are coded for by alleles on a sex
  chromosome.
• Genes found on the X chromosome are X-linked
  genes
• Since the X chromosome is larger- there are more
  X-linked than Y- linked traits.
• NOTE Since males have only 1 X- a male who
  carries the recessive allele will show the
  X-linked trait.

12
Sex Linked Traits
13
Mutations

• Mutation -a change in the nucleotide-base
  sequence of a gene or DNA
• - Germ cell- occurs in gametes
• - can affect offspring
• - Somatic Cell-occur in organisms body cells
• - may affect the organism (ex-cancer)
• - does NOT affect offspring

14
Mutations

• - Lethal Mutations-cause death, often before
  birth
• - Beneficial Mutations- result in phenotypes that
  are beneficial .

15
Types of Chromosome Mutations

• 1. Deletion- loss of a piece of chromosome due
  to breakage.
• 2. Inversion a chromosome piece breaks off,
  flips around backwards reattaches
• 3. Translocation a piece of chromosome breaks
  off attaches to a non-homologous chromosome
• Non-Disjunction a chromosomes fails to separate
  from its homologue during meiosis.

16
On your white board, with your partner, explain
why your assigned answer is either correct or
incorrect.
Your assigned answer is the letter on your
whiteboard!
17
Types of Chromosome Mutations
18
Types of Chromosome Mutations
19
An example of a human disorder with a deletion
error

• Cri du chat syndrome-
• missing part of chromosome 5-
• cry of infants is similar to that of a meowing
  kitten, due to problems with the larynx and
  nervous system.
• About 1/3 of children lose the cry by age 2.

20
Types of nondisjunction

• Trisomy- an extra chromosome leads to an
  individual with an extra chromosome in every cell
  of his/her body. 
• Monosomy- is a deficiency in number of
  chromosomes and is defined as only one copy of a
  chromosome that is normally present in two
  copies.    When fertilized, the outcome is 45
  chromosomes in total.  Monosomies are less likely
  to survive when compared to trisomies.

21
What causes non-disjunction?

• cause of non-disjunction is unknown. 
•  non-disjunction occurs more frequently in the
  eggs of women as they get older.

22
Non- Disjunction Disorders with an extra
chromosome(these folks have 47 instead of the
normal 46 chromosomes in people)

• Down syndrome- extra 21
• Edwards Syndrome- extra 18
• Patau syndrome extra 13

23
Examples Non disjunction

• Extra 21 Downs Syndrome
• Extra 18 (most dont live beyond 1st 7 months)
  This girl is
  now 6.)
• http//starbulletin.com/96/03/25/news/story2.html

24
Sex-chromosome abnormalities may also be caused
by non-disjunction.

• Klinefelters Syndrome- XXY ( extra X)
• Turners Syndrome only 1 X- missing a second X
  (XO)
• Super males XYY
• Any combination (up to XXXXY) produces maleness.
  Males with more than one X are usually
  underdeveloped and sterile.
• XXX and XO women are usually sterile

25
Gene Mutations

• changes in one or more of the nucleotides in a
  gene.

26
Types of Gene Mutation

• 1. Point Mutation- the substitution, addition
  or removal of a single nucleotide, occurs within
  a single gene or segment of DNA
• 2. Substitiution- one nucleotide replaces
  another
• 3. Frameshift Mutation- if some nucleotides are
  deleted- whole segment moves
• 4. Insertion Mutation one or more nucleotides
  added- also causes a frameshift

27
Gene Mutations
28

• Which type of gene mutation do you think would
  cause the most serious errors?
• Point mutation
• Substitution
• Frameshift

29
Example substitution error

• Just 1 Amino Acid is a Substitution ERROR in
  Sickle Cell Hemoglobin
• Causes Hb to be sickle shaped instead of round-
  cant fit into red blood cells changes their
  shape too.

30
On your white board, with your partner, explain
why your assigned answer is either correct or
incorrect.
31
Objective

• Check3210.4.3 Apply data to complete and
  interpret a genetic pedigree.
• SPI 3210.4.5 Apply pedigree data to interpret
  various modes of genetic inheritance.

32
Inheritance of Traits

• Pedigree - a diagram that shows how a trait is
  inherited over several generations
• Creating the foldable

33
Reading a pedigree
HE

• males are represented by squares
• females by circles.
• An individual who exhibits the trait ,
• (for example, someone who suffers from Marfan
  syndrome), is represented by a filled symbol.
• A horizontal line between two symbols is a mating
  

SHE
DAD MOM
34
Reading a Pedigree

• The offspring
• are connected to each other by a horizontal line
  above the symbols
• and to the parents by vertical lines.

35
Example pedigree

• Is the mom or dad in generation I affected by a
  trait?
• How many offspring are shown in generation II?
• How many daughters sons in generation II?
• How many have the trait?
• How many offspring does daughter 1 have? How
  many have the trait?

36

• Dominant traits
• are passed on to a son or daughter EVEN if only
  one parent has it.
• Every affected individual has at least one
  affected parent
• Affected individuals who mate with unaffected
  individuals have a 50 chance of transmitting
  trait to each child
• Two affected
• parents may have
• unaffected children.

37
Recessive Pedigree

• Where did the trait seen in generation III come
  from?
• Traits can be passed on to children if both
  parents, even if they may seem "normal, are
  carriers of the recessive trait.

38
Recessive pedigree
If individuals 2 3 in generation 3 have more
children- will they be affected? Can Individual
8 in gen. 3 have any unaffected children? Can
individual 9 in gen 3 have affected children?
39
Example pedigree of cystic fibrosis
www.cfscreening.com.au/.../CF/CFInherited.shtml
40
Objective

• 3210.4.4 Compare different modes of inheritance
  sex linkage, co-dominance, incomplete dominance,
  multiple alleles and polygenic traits
• 3210.1.6 Describe the connection between
  mutations and human genetic disorders
• 3210.4.7 Assess the scientific and ethical
  ramifications of emerging genetic technologies

41
Polygenic Inheritance

• - traits influenced by several genes
• (most human characteristics)
• example- skin color is additive effect of 6
  genes

42
Complex Characters

• traits influenced by both genes environment
• Example- height

43
3. Multiple Alleles-

• genes with 3 or more alleles.
• Example- human blood type. IA, IB, i
• 3 alleles- both IA IB are dominate over i,
  Codes for sugars that are on blood cell surface.
  
• four different blood types-
• A, B, AB, O

44

• What are the 2 genotypes for type B?
• Which blood type can donate to all the others?
  (universal donor?)
• Which blood type makes antibodies (will clot
  against) both A B blood types?

45
Incomplete Dominance

• there is an intermediate phenotype
• Human example- wavy hair is the intermediate
  between straight curly hair
• (remember chapter 9 plant example
• - pink 4 oclock flowers,
• In between red white flowers)

46
X-linked Traits

• Traits that are on the X chromosome.
• Since males only have one X chromosome- they are
  affected more than females
• Females have 2 chances to get a good copy of the
  gene but males only get 1 chance.

47
Examples of human X-linked traits

• Hemophilia- blood clotting disorder- boys may
  bleed to death
• Duchene muscular dystrophy -affects cardiac and
  skeletal muscle, as well as some mental
  functions.
• Fragile-X syndrome- part of X chromosome has
  errors- most common cause of mental retardation
  in males
• Red-green color blindness- males cannot see these
  2 colors.

48
Sex- Influenced Traits

• males females show different phenotypes with
  same genotype-
• example- male pattern baldness

49
7. Single Allele Traits

• trait controlled by 1 allele- Dominant or
  Recessive
• Dominant Examples
• Achondroplastic dwarfism- dwarf size
• Polydactly is the presence of a sixth digit.
• Huntington's disease (also called Woody Guthrie's
  disease)-progressive destruction of brain cells
  after age 30
• Marfans Syndrome- progressive connective tissue
  disorder. (some cases are new mutations with no
  family history)

50
Single allele recessive traits

• Albinism lack of pigmentation in skin, hair, and
  eyes, -Homozygous recessive (aa) people make no
  pigments
• PKU (Phenylketonuria) - lack enzyme to use the
  amino acid phenylalanine, buildups breakdown
  products leads to mental retardation. 1 in 15,000
  infants has- treat with DIET! (no phenylalanine)
• Tay-Sachs Disease- degeneration of the nervous
  system. Children rarely survive past five years
  of age.
• Maple Syrup Urine Disease (MSUD) like PKU amino
  acids leucine, isoleucine, and valine

51
More single allele recessive examples

• Sickel Cell Anemia- single amino acid
  substitution in hemoglobin causes lack of oxygen
  to body
• Cystic fibrosis- body creates sticky thick mucus
  chloride ions- detected in SWEAT TEST. - was
  once considered a fatal childhood disease- modern
  treatments can increase lifespan to 30 years
  plus.

52
Detecting Genetic Disease

• 1. Testing
• Amniocetesis- Dr removes some amniotic fluid,
  14th-18th week of pregnancy, analyze fluid for
  proteins look at chromosomes- some risk of
  pregnancy loss
• Chorionic Villi Sampling- clip cells from
  placental area- 8-14th week pregnancy
• 2. Treatments- vary with disease