Transcript Biology 3201 Unit 3 – Genetic Continuity

Biology 3201
Unit 3 – Genetic Continuity
Chapters 16, 17, & 18
Ms. K. Morris 2010-2011
Chapter 16
Genetics & Heredity
p. 524-565
16.1
• Heredity- the passing of genetic traits such as the
colour of hair or eyes from one generation to the
next, resulting in similarities between one family or
strain.
• Traits- distinguishing characteristics that make an
individual unique. Traits that are passed on are
said to be inherited.
• Genetics- the branch of biology dealing with the
principles of variation and inheritance in
organisms; how traits are passed from generation
to generation.
• Variations- in genetics, the forms of the trait. Or,
also, significant deviations from the normal
biological form, function, or structure.
• Purebred- having descended from ancestors of a
distinct type, or breed. Purebred organisms in a
given species or variety all share similar traits.
• True Breeding- organisms that are homozygous
for a particular trait or set of traits and produce like
offspring.
• P generation (parent generation)- the
designation for the parent generation.
• Filial Generation- offspring of a cross of parent
generations; the F1 generation or subsequent
generations.
• F1 generation (first filial generation)- offspring from
the cross of the P (parent) generation.
• F2 generation (second filial generation)- offspring
from the cross of the F1 generation.
• Hybrid- an organism heterozygous for a trait.
• Monohybrid- a cross of two heterozygous individuals
that differ in one trait. For example, Aa x Aa.
• Dihybrid- a cross of two heterozygous individuals that
differ in two traits. For example, AaBb x AaBb.
• Dominant- type of trait, in which the characteristic is always
expressed, or appears, in the individual.
• Recessive- having an allele that is latent (present but
inactive) and is therefore not usually expressed unless there
is no dominant allele present.
• Principle of Dominance- when individuals of contrasting
traits are crossed, the offspring will express only the
dominant trait.
• Mendelian Ratio- ratio of dominant phenotype
(homozygous dominant genotype and heterozygous
genotypes) to recessive phenotype (homozygous recessive
phenotype); ratio of 3 : 1 (75% to 25%).
• Law of Segregation- Mendel’s first law of inheritance, in
which the hereditary traits are determined by pairs of alleles
from each parent. These alleles separate during gamete
formation, giving each offspring only one allele from each
parent.
• Gene- a specific sequence of DNA that governs the
expression of a particular trait and can be passed to an
offspring (part of the chromosome).
• Allele- alternate form of a gene.
• Homozygous- describes an individual with two alleles at
one locus that are identical.
• Heterozygous- describes an individual with two different
alleles at a locus.
• Mendel’s concept of ‘unit characters’ and
the ‘unit theory of inheritance’:
• Unit Characters- a term describing
Mendel’s “factors” of inheritance (genes),
which are inherited as independent units.
• Unit Theory- a term describing Mendel’s
laws of inheritance, from his discovery that
genes (which he called “factors”) are
inherited as independent units.
• Probability- the chance, or likelihood, of a particular
outcome; usually expressed as a ratio.
Probability = desired outcome ÷ total # of possible
outcomes
*Complete Questions 1-4 p. 531 (Probability Examples)
• Product Rule- a rule that states that the probability, or
chance, that two or more independent events will occur
together is the product of their individual probabilities of
occurring alone.
• Punnett Square- a simple grid used to illustrate all possible
combinations of gametes from a given set of parents.
*Complete Questions 1-3 p. 533 (Punnett Square
Practice)
• Genotype- Genetic make-up of an organism;
remains constant throughout an individuals life.
Usually indicated by the combination of letters in a
Punnett Square.
• Phenotype- the physical and physiological traits of
an organism.
• Complete Dominance- the type of inheritance in
which both heterozygotes and dominant
homozygotes have the same phenotype.
• Test Cross- cross of an individual of unknown
genotype with a homozygous recessive individual,
used as a method to determine the unknown
genotype.
• Explain the significance of a test cross. Use a test
cross to determine the unknown genotype of a
dominant organism. (p.533-534)
• It is impossible to determine the genotype of an
organism by simply looking at its appearance.
• “How would you determine the unknown genotype?”
• Note: the absence of the homozygous recessive
trait in the offspring does not confirm that the
unknown parent is homozygous dominant,
especially in small samples of offspring.
• Complete “Thinking Lab” p. 534
• The test cross is a way to set up a cross to figure
out an unknown genotype. The only unknown
genotype is if a phenotype is dominant.
• Basically, if someone expresses the dominant
phenotype, you often will not know whether that
person's genotype is homozygous dominant (DD) or
heterozygous (Dd).
• To do the test cross, you cross the individual with the
dominant phenotype (D?) (and unknown genotype)
with a homozygous recessive individual (dd).
• If any of the offspring appear with the recessive
phenotype (dd), you know that your parent with
the dominant phenotype that you crossed is
actually heterozygous (Dd).
– See ex. p. 534
___________________________________
• Complete 16.1 Review Questions
– P. 535 # 1-17
16.2
Recall:
• Monohybrid Cross- a cross of two heterozygous
individuals that differ in one trait.
– For example, Aa x Aa.
• Dihybrid Cross- a cross of two heterozygous
individuals that differ in two traits.
– For example, AaBb x AaBb.
• Law of Independent Assortment- (p. 537)
Mendel’s second law of inheritance, stating that
inheritance of alleles for one trait does not affect the
inheritance of alleles for another trait.
*Do Sample Problem page 540 (The Two-Trait Cross)
Incomplete Dominance (p. 541)
- Is inheritance in which an active allele does
not entirely compensate for an inactive allele.
- Examples include: snapdragon flowers
(heterozygous is pink) and Japanese 4
o’clock flowers (heterozygous is pink).
- Blending of the traits of two different alleles
at one locus that occurs when neither allele
is dominant.
*Locus- the location of a gene on a
chromosome.
• Predict the outcome of monohybrid and
dihybrid crosses for incomplete dominance:
Ex. For incomplete dominance for flower colour
in snapdragons the following can be used:
(i) R – red
(ii) FR – red
(iii) R – red
R’ – white (see figure 16.15 p. 541)
FW – white
W – white
*Be able to solve crosses involving one completely
dominant trait with one other trait that is not.
Co-dominance (p. 541)
- Is the condition in which both alleles of a
gene are expressed.
- Examples include: Roan horses (red and
white hair) and barred plumage chickens
(black and white feathers).
- In genetics, to be “co-dominant” describes a
situation in which two alleles may be
expressed equally.
- The situation occurs when two different
alleles for a trait are both dominant.
• Predict the outcome of monohybrid and
dihybrid crosses for co-dominance:
Ex. For co-dominance, blood type may be
represented as follows:
(i) IA – type A
(ii) A – type A
IB – type B
B – type B
*Be able to solve crosses involving one completely
dominant trait with one other trait that is not.
Multiple Alleles (p. 542)
- A pattern of inheritance when a gene may
have more than two alleles for any given trait.
- Examples include: the human ABO blood
type, eye colour in drosophila (fruit flies), and
colour patterns in ducks.
- Human Blood Types:
Phenotype (blood type)
Genotypes
A
IAIA or
IAi
B
IBIB or
IBi
AB
IAIB
O
ii
*Do Sample Problem page 542 (Human
Blood Types)
Outcome: Demonstrate the inheritance of
traits governed by multiple alleles by
predicting the genotypic and phenotypic
ratios in crosses involving human blood
types (ABO groups).
Carrier – an organism that is heterozygous for
the given trait but does not show the
recessive trait.
• Do Thinking Lab p. 543 (Inheritance of
Coat Colour in Rabbits)
• Do 6.2 Review Questions p. 544 # 1-8
16.3
The Chromosome Theory of InheritanceStates that genes are located on
chromosomes, and that chromosomes
provide the basis for the process of
segregation and independent assortment of
these genes.
Chromosome theory can also account for
patterns in inheritance that do not follow
Mendel’s laws.
Chromosome Theory of Inheritance…
(summarized):
- Mendel’s factors (genes) are carried on
chromosomes.
- It is the segregation and independent
assortment of chromosomes during
meiosis that accounts for the patterns of
inheritance.
Crossing-Over – (recall from 14.2) can occur among
chromosomes during cell division. In cellular
reproduction, the process in which non-sister
chromatids exchange genes (during prophase I of
meiosis) allowing for the recombination of genes.
Genes located very close together on a chromosome
will almost always be inherited together, while genes
located some distance apart are more likely to be
separated by a crossing-over event.
The emphasis on crossing-over is how it breaks
gene-linkages and creates variation.
Gene Linkage (linked genes) – genes are
carried on chromosomes. Gene linkage is a
way of expressing that genes are linked to
specific chromosomes.
Gene-Chromosome Theory of Inheritance–
A theory which states that genes exist at
specific sites arranged in a linear fashion
along chromosomes.
• Genes exist on specific sites on
chromosomes. When pairs of homologous
chromosomes separate during gamete
formation, they form two gametes. Each
gamete will contain a separate allele for
each trait. During fertilization,
chromosomes from one gamete will
combine with another gamete.
• When Mendel did his experiments with pea plants, he
did not know that chromosomes existed in cells. In the
early 1900s, chromosomes were discovered and
observed in cells.
• In 1902, two scientists Walter Sutton and Theodor
Boveri were studying meiosis (cell division) and found
that chromosomes behaved in a similar way to the
factors (genes) which Mendel described.
• Sutton observed behaviour of the chromosomes
during meiosis which accounts for Mendel’s
observations and conclusions concerning segregation
and independent assortment.
Sutton and Boveri made three observations:
• Chromosomes occur in pairs and these pairs
segregate during meiosis.
• Chromosomes align independently of each other along
the equator of the cell during meiosis.
• Each gamete (sex cell) receives only one chromosome
from each pair.
• From the above observations, they formed the
chromosome theory of inheritance (which we
defined in a previous note).
• The Law of Independent Assortment in modern
terms includes gene linkage and crossing over in its
explanation. (Mendel’s second law of inheritance,
stating that inheritance of alleles for one trait does not
affect the inheritance of alleles for another trait).
Morgan’s Discoveries
• In 1910, an American scientist called Thomas
Morgan made a very important discovery from his
work with fruit flies.
• Normal fruit flies have red eye color.
• Morgan crossed two red eyed parent flies and
obtained a white eyed male.
• In other crosses, he obtained red eyed females, red
eyed males and white eyed males.
• Since the white eye color was only present in the
male flies, Morgan concluded that eye color was
linked to an organisms sex.
• Thus, the gene for eye color in fruit flies was located
on the sex chromosome, in this case the X
chromosome.
• Such genes are called sex-linked genes.
• Morgan also stated that genes which are located on
the same chromosomes are linked to each other and
usually do not segregate (separate) when inherited.
• These are called linked genes.
• Morgan found that certain genes did not follow the
Law of Independent Assortment but instead tended
to be inherited together.
• However, Morgan found that some linked genes do
segregate.
• From his work, Morgan created the genechromosome theory which states that genes exist
at specific sites and are arranged in a linear fashion
along chromosomes.
• Morgan’s experiments restated Mendel’s Law of
Independent Assortment by including crossing
over.
Sex Chromosome – X or Y chromosome that
carries the genes involved in determining
the sex of an individual.
Sex-Linkage (sex-linked inheritance) –
The transfer of genes involved in
determining the sex of an individual. Sexlinked inheritance involves pairs of genes on
the X chromosome in the female, and a
single gene on the X chromosome in the
male. In this case, gender is important in
gene expression and gender must be
considered part of the phenotype.
Autosomal Inheritance- typically involves pairs of
genes, with gender being irrelevant to gene
expression.
Autosomes are chromosomes that are not directly
involved in determining the sex of an individual.
• Distinguish between genotypes and phenotypes
evident in autosomal and sex-linked inheritance.
Note: Genes which are located on the X chromosome
are called X-linked while those on the Y
chromosome are called Y-linked. Most sex-linked
genes are located on the X chromosome.
Females: XX
Males: XY
Chromosomes & Gene Expression
*Chromosome Inactivation p. 547-548
• Males and females produce the same amounts of
proteins. This is coded by genes which are located
on the X chromosome.
• Females have two X chromosomes in their cells
while males have only one X chromosome.
• From experiments, scientists have shown that one
of the two female X chromosomes is inactivated
and this inactivated chromosome is called a Barr
body.
• Ex. The tortoiseshell coat colour in cats is an ex. Of
the presence of an inactivated X chromosomes.
*Modifier Genes p. 549-550
• Certain genes, called modifier genes, work with
other genes to control the expression of a
particular trait.
• In humans, modifier genes help control the trait
of eye color. In this case, modifier genes
influence the level of melanin present in the
human eye to provide a range of eye colors from
blue to brown.
*Polygenic Inheritance (multiple gene inheritance) p.549
• Most traits are controlled by one gene, however, some
traits are controlled by more than one gene, this is
called polygenic inheritance; a pattern of inheritance
in which a trait is controlled by more than one gene
• Polygenic genes cause a range of variation in
individuals called continuous variation.
• In humans, traits such as height, skin color, etc. are
polygenic traits.
• traits are determined by a number of different
contributing genes present at different locations, and
expression depends on the sum of all the influences of
all of these.
Outcomes: Questions…
• Predict the outcome of monohybrid and dihybrid
crosses involving sex-linked traits.
• Predict the genotypes, phenotypes and ratios
among offspring and compare specific genotypes
and phenotypes for males and females.
• Solve dihybrid crosses involving one trait that is
completely dominant with one other trait that is
sex-linked.
• Explain why sex-linked defects are more common
in males than females.
• True or False? Males are biologically stronger
than females.
Changes In Chromosome Structure
Changes in the physical structure of chromosomes
can occur:
1. Spontaneously
2. As a result of irradiation
3. After exposure to certain chemicals
Different types of chromosome mutations (factors that may
lead to mutations in a cell’s genetic information) (p. 550-553)
(i) deletion
(ii) inversion
(iii) duplication
(iv) translocation
* nondisjunction (monosomy, trisomy)
• In a deletion, a piece of a chromosome gets lost.
• The lost piece contains genes and when they are
lost, genetic information is also lost.
• Viruses, irradiation, or certain chemicals can cause
pieces of a chromosome to be broken off.
• Example : Cri-du-chat (a piece of chromosome 5 is
lost and facial abnormalities and an abnormality in
the larynx cause the infants cries to sound like a cat
mewing)
• In an inversion, a piece of a chromosome
separates, flips over, and rejoins.
• A certain gene segment becomes free from its
chromosome momentarily before being reinserted in
reverse order.
• This completely changes the position and order of
the genes on a chromosome, and can alter gene
activity.
• Example : Certain forms of Autism.
• In a duplication, a sequence of genes is repeated
one or more times within one or several
chromosomes.
• The greater the repetition of genes, the greater the
chance of a problem occurring.
• Too many repeats affect the functioning of the gene
(even though some gene sequences can
be repeated thousands of times in normal
chromosomes).
• Example : Fragile X Syndrome
(1/1500 males, 1/2500 females).
A duplication occurs in chromosome X.
Normal people have 29 repeats, and
people with Fragile X Syndrome have
about 700 repeats of this sequence.
• In translocation, a piece of one chromosome
changes places with a piece of another
chromosome, or another part of that same
chromosome.
• Examples: Cancers- if a part of chromosome 14
exchanges places with a part of chromosome 8,
cancer can occur in the affected individual.
• Some occurrences of
Down Syndrome are
related to translocation
between chromosomes
14 and 21.
• One kind of leukemia
can be traced to
translocation between
chromosomes 22 and 9.
Nondisjunction
• Sometimes, chromosomes (chromatids) fail to separate from
each other during meiosis. This produces gametes (sex cells)
which have either too many or too few chromosomes.
• If a gamete which does not have the correct number of
chromosomes is involved in fertilization, an embryo will be
produced which has either too many or too few chromosomes
(other than 46).
• When an individual inherits an extra chromosome, the
condition is called trisomy.
• If an individual inherits one less chromosome, the condition is
called monosomy.
• There are relatively few syndromes in the human population
involving nondisjunction because most cases of
nondisjunction prove to be fatal.
• Human embryos with too many or too few autosomes rarely
survive.
• These embryos are usually aborted by the mother, but some
survive and have genetic disorders.
Complete Thinking Lab p. 552
Monosomy & Trisomy
Human genetic diseases caused by
chromosomal mutations (p. 553)
Chromosomal mutations are more serious than
gene mutations because they involve a larger
portion of genetic material.
1. Down syndrome (Trisomy 21)
2. Turner syndrome
3. Klinefelter syndrome (XXY syndrome)
4. Jacobs syndrome (XYY syndrome)
5. Triple X syndrome (XXX syndrome)
1. Down Syndrome
• This disorder is also called trisomy 21.
• This occurs when an individual receives three copies of
chromosome 21 instead of the normal two (it results from
nondisjunction).
• Individuals who have this syndrome have the following
symptoms:
– Mild to moderate mental impairment
– A large, thick tongue, resulting in speech defects
– A poorly developed skeleton; short, stocky body structure
– Thick neck
– Abnormalities in one or more vital organs
– About 40% have heart defects
– May survive into 30’s or 40’s and beyond
– Have a greater chance of becoming senile (similar to
Alzheimer’s)
– Almond-shaped eyes
– Prone to respiratory problems
– They have 47 chromosomes instead of 46.
Down Syndrome Karyotype
Down Syndrome
2. Turner Syndrome (XO)
• In this disorder, an individual inherits only a single X chromosome, as
well the Y chromosome is missing. Results from nondisjunction.
• This results in a female with the genotype XO, O represents a
missing chromosome. The female has 45 chromosomes.
• It occurs in about 1/2000 live female births
• These females will exhibit a number of symptoms including ;
– Infertile
– fail to develop secondary sex characteristics (external female
genitalia, but no ovaries)
– typically do not experience puberty without estrogen therapy,
– normal in childhood
– normal intelligence (learning difficulties in math)
– Webbed neck (sometimes)
– Skeletal abnormalities (very short stature, 4’8”)
– principal difficulty is acceptance by the peer group.
Most women with Turner Syndrome lead typical lives, including
normal family relationships.
Turners Karyotype (XO)
Turners Syndrome
3. Klinefelter Syndrome (XXY)
• This disorder results in a male who has an extra X
chromosome (results from nondisjunction).
• 47 chromosomes instead of 46.
• These individuals have the genotype XXY instead of
XY.
• Symptoms of this disorder include:
– usually normal in appearance
– normal intelligence
– tall
– underdeveloped testes, sterile
– may also cause female characteristics (breast
development, feminine body shape, lack of facial
hair).
Klinefelter XXY Karyotype
Klinefelter XXY
4. Jacobs Syndrome (XYY)
– results from nondisjunction
– extra Y in male
– low mental ability
– speech and reading problems
– normal appearance
– persistent acne
Jacob’s Karyotype (XYY)
5. Triple X Syndrome (XXX)
-
results from nondisjunction
47 chromosomes
female with an extra X chromosome
normal intelligence
normal in appearance
may be sterile
XXX Karyotype
Outcomes/Questions…
• Is it possible for a person born with a
chromosomal abnormality (such as Down
Syndrome) to have a ‘normal’ child?
• Given the high cost of health care, should
forced sterilization be mandatory for
individuals with genetic diseases?
• Complete 16.3 Review Questions p. 552
#1-11
16.4
The study of human genetics is a complicated field. This is due
to a number of reasons:
– Humans have long life spans.
– We produce very few offspring.
– Most people do not keep very accurate records of their
family history.
However, there are certain patterns of inheritance which
scientists have determined for particular human genetic
disorders.
These include (p.555-559):
1. Autosomal Recessive Inheritance (Tay Sachs, PKU)
2. Codominant Inheritance (Sickle Cell Anemia)
3. Autosomal Dominant Inheritance (Progeria, Huntington’s)
4. Incomplete Dominance (FH)
5. X-linked Recessive Inheritance (colour blindness,
hemophilia, muscular dystrophy)
1. Autosomal Recessive Inheritance
• An autosomal recessive disorder is carried
on the autosomes ( body chromosomes )
and are not specific to the sex of a person.
• Examples include ;
• Tay-Sachs disease
• Phenylketonuria ( PKU )
• Albinism
Tay-Sachs Disease
• This is a disease in which individuals lack an enzyme
in the lysosomes which are located in their brain cells.
Because of this, the lysosomes are unable to break
down specific lipids. Thus the lipids build up inside the
lysosomes and eventually destroy the brain cells.
• Children with Tay-Sachs disease appear normal at
birth, but experience brain and spinal cord
deterioration around 8 months old.
• By 1 year of age, the children become blind, mentally
handicapped, and have little muscular activity. Most
children with their disorder die before age 5.
• There is no treatment for this disorder.
Phenylketonuria ( PKU )
• In this disorder an enzyme which converts a substance
called phenylalanine to tyrosine is either absent or
defective.
• Phenylalanine is an amino acid which is needed for regular
growth and development and protein metabolism.
• Tyrosine is another amino acid which is used by the body
to make the pigment melanin and certain hormones.
• When phenylalanine is not broken down normally, harmful
products accumulate and cause damage to the individual’s
nervous system. This is called phenylketonuria ( PKU ).
• Babies who develop PKU appear normal at birth.
However, within a few months they can become mentally
handicapped.
• Today, testing and proper diet can prevent PKU from
occurring in children.
Albinism
• This is a genetic disorder in which the eyes, skin
and hair have no pigment.
• People with this disorder either lack the enzyme
necessary to produce the melanin pigment in their
cells or lack the ability to get the enzyme to enter
the pigmented cells.
•
Albinos face a high risk of sunburns and eye
damage from exposure to the Sun.
2. Codominant Inheritance
• An example of codominant inheritance is sickle cell anemia.
In this disorder, individuals have a defect in the hemoglobin of
their RBCs and therefore the shape of the RBC changes from a
normal round shape to an abnormal sickle shape. { See Fig.
16.33, P. 557 }
• Symptoms of this disorder include ;
• Blood clots
• Reduced blood flow to vital organs
• Lack of energy
• Suffering from various illnesses
• Constant pain
• Premature death
• In this trait, individuals can be either normal, have sickle cell
disease, or carry the sickle cell trait.
• Individuals who are heterozygous for the disorder have what is
called heterozygous advantage. These individuals will carry
one sickle cell allele as well as one normal allele for the trait,
but have a better chance of survival than those individuals who
carry two sickle cell alleles. { See Fig. 16.34, P. 557 }
3. Autosomal Dominant Inheritance
• Genetic disorders which are caused by
autosomal dominant alleles are very rare in
humans, but they do exist.
• Some of these disorders are caused by chance
mutations. Others arise only after individuals
have passed their child bearing age.
• Two examples of this type of disorder are ;
• Progeria
• Huntington’s disease
Progeria
• This is a rare disorder which causes a
person to age very rapidly.
• It affects only 1 / 8,000,000 newborns.
• This disorder results from a random,
spontaneous mutation of a gene.
• The mutated gene dominates the normal
gene and this accelerated the ageing of an
individual.
Huntington’s Disease
• This is a lethal disorder in which the brain progressively
deteriorates over a period of about 15 years.
• It begins to appear after the age of 35.
• Symptoms include ;
• Early symptoms include ;
– irritability,
– mild memory loss,
– involuntary arm and leg movements.
• Later symptoms include ;
–
–
–
–
Loss of muscular coordination
Loss of memory
Loss of speech
Death in the forties or fifties
4. Incomplete Dominance
• In this situation an individual which a disorder exhibits a
phenotype which is midway between the dominant and
recessive traits.
• An example of this type of disorder is Familial
Hypercholesterolemia ( FH ).
• Normal cells have surface receptors which absorb lowdensity lipoproteins ( LDLs ) from the blood.
• Individuals who have the FH disorder have cells which
only have half the normal number of LDL receptors on
their surface.
• Thus, the LDL molecules do not get absorbed from the
blood and the individual has a high level of cholesterol in
his / her blood.
• This increased cholesterol level can build up on the walls
of arteries and cause atherosclerosis which leads to heart
attacks and strokes.
5. X - Linked Recessive Inheritance
• These types of disorders occur from genes which are
located on the X chromosome.
• Disorders of this type are due to the recessive form of the
gene and only occurs if there is no dominant form of the
gene present.
• An example is a disorder called red-green colour
blindness. Here, an individual is unable to distinguish
between the colors red and green.
• About 8% of men and 0.04% of women suffer from this
disorder.
– Do colorblindness problems on the board.
• Inheritance of certain characteristics through sex
chromosomes:
– Red-green colour blindness
– Hemophilia
– Muscular dystrophy
• An example of such a disorder is
hemophilia. This is a disorder in which a
person’s blood lacks certain clotting
factors, thus the blood will not clot.
Because of this, a small cut or bruise may
kill an individual.
Human Genetic Analysis
• Geneticists are able to analyze the
patterns of human inheritance using two
methods;
– Examination of karyotypes
– Construction of pedigrees
Core Lab #6 – Karyotype Lab
(Appendix B)
• Analyze and interpret models of human
karyotypes. (p. 553-560)
The Human Karyotype
• Within our body cells, humans normally possess 46
chromosomes.
• 44 of these are autosomes (body chromosomes)
and 2 are sex chromosomes.
• A karyotype is a photograph of the chromosomes
which are located in the nucleus of a somatic cell
(body cell).
• Once a photograph has been taken of the
chromosomes in a cell’s nucleus, they are cut out
and arranged in pairs according to their size,
shape, and appearance.
• By observing the karyotype, disorders may become
apparent.
• See Fig. 16.37, P. 560
Constructing Pedigrees
• A pedigree is a chart which shows the genetic relationships
between individuals in a family.
• Using a pedigree chart and Mendelian genetics, scientists can
determine whether an allele (gene) which is responsible for a
given condition is dominant, recessive, autosomal, sex-linked,
etc.
• A pedigree can also be used to predict whether an individual
will inherit a particular genetic disorder.
• When studying human genetic inheritance it is not possible to
perform experimental crosses.
• Because of this, human geneticists use data such as medical,
historical, and family records which provide information on
different generations of humans.
• Using this information, they create a pedigree chart which
shows the genetic relationships among a group of related
individuals.
• See Fig. 16.17, P. 544 (& p. 558, 560-562)
Outcome…
• Draw and interpret pedigree charts from data on
single and multiple allele inheritance patterns.
• Be able to analyze inheritance data and infer the
method of inheritance (dominant, recessive, sexlinked).
• Compare pedigree charts for the inheritance of non
sex-linked and sex-linked conditions.
• Demonstrate the inheritance of autosomal traits
determined by single and multiple alleles, and sexlinked traits.
– Ex. Freckles, right or left handed.