Download Biology~Chapter 12

Inheritance Patterns &
Human Genetics
Chapter 12
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 _____________.
Chromosomes & Inheritance
A. Thomas Hunt Morgan- early 1900’s
-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”.
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)
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.
1:1 male to female ratio
Karyotypes
Karyotype with an extra
chromosome
Linked &
Sex-Linked Genes
A. Linked genes
 Genes which are close
together on same
chromosome.
 Inherited together
 Linked genes do not exhibit
Mendel’s law of independent
assortment
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.
Sex-Linked traits
 are traits that are coded for by
alleles on a sex chromosome.
 Genes found on the X chromosome are Xlinked 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 Xlinked trait.
Sex Linked
Traits
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 organism’s body cells
- may affect the organism (ex-cancer)
- does NOT affect offspring
Mutations
- Lethal Mutations-cause death, often
before birth
- Beneficial Mutations- result in
phenotypes that are beneficial .
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
4. Non-Disjunction – a chromosomes fails to
separate from its homologue during meiosis.
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!
Types of Chromosome
Mutations
Types of Chromosome
Mutations
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.
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.
What causes non-disjunction?
 cause of non-disjunction is
unknown.
 non-disjunction occurs
more frequently in the
eggs of women as they
get older.
Non- Disjunction Disorders
with an extra chromosome
(these folks have 47 instead
of the normal 46
chromosomes in people):
 Down syndrome- extra 21
 Edward’s Syndrome- extra 18
 Patau syndrome – extra 13
Examples Non
disjunction:
 Extra #21= Down’s Syndrome
 Extra #18= (most don’t live
beyond 1st 7 months)
This girl is now 6.)
http://starbulletin.com/96/03/25/news/story2.html
Sex-chromosome abnormalities
may also be caused by nondisjunction.
 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
Gene Mutations
 changes in one or more of the
nucleotides in a gene.
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
Gene Mutations
 Which type of gene mutation
do you think would cause the
most serious errors?
 Point mutation
 Substitution
 Frameshift
Example:
substitution error
 Just 1 Amino Acid
is a Substitution
ERROR in Sickle
Cell Hemoglobin
 Causes Hb to be
sickle shaped
instead of roundcan’t fit into red
blood cells &
changes their
shape too.
On your white board, with
your partner, explain why
your assigned answer is
either correct or incorrect.
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.
Inheritance of Traits

Pedigree - a diagram that
shows how a trait is inherited over
several generations
 Creating the foldable
Reading a pedigree
 males are represented by squares
 females by circles.
SHE
HE
 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
DAD
MOM
Reading a Pedigree
 The offspring:
 are connected to each other by a
horizontal line above the symbols
 and to the parents by vertical lines.
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?
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.
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.
Recessive pedigree:
If individuals 2 + 3 in generation 3 have more childrenwill they be affected?
Can Individual #8 in gen. 3 have any unaffected
children?
Can individual #9 in gen 3 have affected children?
Example pedigree of
cystic fibrosis
www.cfscreening.com.au/.../CF/CFInherited.shtml
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
Polygenic Inheritance
- traits influenced by several genes
(most human characteristics)
example- skin color is additive effect of
6 genes
Complex Characters
 traits influenced by both genes &
environment
 Example- height
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 typesA, B, AB, O
 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?
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 o’clock flowers,
In between red & white flowers)
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.
Examples of human Xlinked traits
 Hemophilia- blood clotting disorderboys 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.
Sex- Influenced Traits
 males & females show different
phenotypes with same genotype example- male pattern baldness
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)
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
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.
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