Inheritance Principles and Human Genetics

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Transcript Inheritance Principles and Human Genetics

Inheritance Principles
and
Human Genetics
BioH - Chapter 11
Genetics Vocabulary Review
Genes – units of information about heritable traits
Homologous chromosomes – similar chromosomes received from
male and female that line up next to each during MetaphaseI in
meiosis
Alleles – different forms of a gene
Locus – location on a chromosome where specific genes are found
Linkage – when genes on a chromosome “stay together” even
during crossing-over
Genetic recombination – the “recombining” of genes as a result of
crossing-over
Chromosomes
 Thomas
Hunt Morgan
– Studied fruit flies
– Found X and Y chromosomes
Karyotypes
Karyotyping is a process that allows chromosomes to be presented
in an orderly, easily compared manner
 Sex
chromosomes (X, Y)
– Contain genes that
determine the sex (gender)
of an individual
 Autosomes
– Not directly involved in
determining the sex of an
individual
– Different organisms,
different number
X
Y
Sex determination
– Sperm has equal chance of receiving X or Y
– Egg only receives X
 XX
– female
 XY - male
– Totally RANDOM
process
 Sex-determination
Region Y (SRY)
– Found in mammalian Y chromosome
– Gene codes protein to cause
gonads to develop testes
Gene location

Sex-linked
– Traits coded for by an allele on a sex
chromosome
– Could be on X or Y chromosome
– More X-linked genes because X is much
larger
– If male carries a recessive allele on the
X chromosome, it will exhibit the trait
 Ex.
Hemophilia (blood disorder)
 Linked
genes
– Traits that are inherited together
– Makes a linkage group
– This happens because they are found
close to each other in the same
chromosome and not as easily
genetically recombined by “crossingover”
Chromosome Map
A
diagram that
shows the linear
order of genes on a
chromosome
 Map unit –
frequency of
crossing over of 1%.
Mutations
 Germ-cell
mutations
– Occur in gametes (may not be expressed
until offspring)
 Somatic-cell
mutations
– Occur in body cells
– May affect organs
 Skin
cancer and leukemia
– Lethal mutations
 Cause
death, often before birth
Inheritance of Traits
 Pedigrees
– A diagram showing how a trait is
inherited over several generations
Russian Royal Family &
hemophilia
Genetic abnormality – rare, uncommon trait version
Genetic disorder – inherited condition causing medical disorders
Syndrome – recognized set of disorders that characterize a disorder
Patterns of Inheritance
 If
a trait is
– Autosomal
 Appears
in both sexes equally
 Dominant
– Every individual with the trait will have parents
with the trait
 BB or Bb (dominant trait will show)
 bb (recessive trait will show)
 Recessive
– 1, 2, or no parent with the trait
– Bb X Bb will not show mutation but can produce
children for the recessive allele (bb)
– Bb (carrier)
Genetic Trait and Disorders
 Single-Allele
traits
– Controlled by a single allele of a gene
– More 200 human traits
– Huntington’s disease
 Forgetfulness
and irritability
Gene Inheritance & Disorders
 Polygenic
Inheritance
– Traits are influence by more than one
gene
 Skin
color
– 3 to 6 genes
– Genes control amount of melanin
 Eye
color, height, hair color
 Complex
characters
– Influenced both by environment and
genes
– Skin color, breast cancer, height
 Multiple
Alleles
– Genes with 3 or more alleles
– ABO blood groups
– IA, IB, and I
– IA and IB are codominant
 Codominance
– Both alleles are expressed
– IAIB is type AB
 Incomplete
dominance
– Trait that is displayed is intermediate
between the two parents.
– Hair type
 Curly
(CC) X Straight (cc)= Wavy hair (Cc)
 X-linked
– Genes are linked to x-chromosome
– Colorblindness
 Recessive
 Unable
to distinguish certain colors, eg.
green or red
 Sex-influence
traits
– Males and females can show different
phenotypes even with same genotypes
– Autosomal
– Type of Baldness
 Dominant
in males
 Recessive in females
Chromosomal disorders
Chromosome problems, not genes
Duplication – a repeat of
several gene sequences on
the same chromosome
Deletion – loss of a
chromosome
segment
Inversion – gene sequence
separated from
chromosome, reinserted into
same place, but in reverse
Translocation –
transfer of
one chromosome
part to a
non-homologous
chromosome
Chromosome number disorders
Nondisjunction – one or more pairs of
chromosomes fail to separate during mitosis
or meiosis (produces condition known as
aneuploidy – more or less chromosomes
than the parental number)
Down Syndrome
– one extra
chromosome at #21
Sex Chromosome number
changes
Turner syndrome – inheriting only one X
chromosome with no additional X or Y
chromosome
 Most X0 zygotes
spontaneously abort
 0.01–0.04% of
females
 Non-functional ovaries
(infertile)
 Short height
 Normal intelligence
Kleinfelter Syndrome – one extra X
chromosome with normal XY (XXY)
 0.05-0.2% of males
 Conditions develop after
puberty
 Smaller testes - usually
sterile (not always)
 Taller than normal
 Normal intelligence
 Very subtle phenotype
characteristics
XYY Condition – extra Y chromosome
as result of non-disjunction
 0.1% of males
 Taller than average
 Mild retardation
Detection
 Amnioncentesis
– Removal of amniotic
fluid from the
amnion, the sac
surrounding the
fetus
– Between 14 – 16
week of pregnancy
 Chorionic
sampling
villi
– Cells derived from
the zygote that
grow between
uterus and placenta
– Between 8th and
10th week
 Genetic
counseling
– Informing a person or couple about
their genetic makeup
– Form of medical guidance about
problems that might affect their
offspring
Treatment
 Usually
treat symptoms
 Gene therapy
– Replacement of defective genes with a
healthy one
– Somatic cell gene therapy (body cells)
– Germ cell gene therapy (eggs or
sperms)
 Poses
risks and ethical issues