Transcript bYTEBoss Doc

Genetics
Chapter 10 and Chapter 12
Vocabulary
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46 Chromosomes in your body cells.
23 Chromosomes in sperm and eggs.
Sex Chromosomes – X and Y.
Autosomes – all other chromosomes – the
other 22 pairs.
• Somatic cells – body cells.
• Gametes – sperm and egg.
Intro to the world of Genetics
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Genetics – study of heredity
In early 1800’s biologists believed the
blending hypothesis to explain how
offspring inherit traits from both parents.
a) Traits – is a characteristic passed
from parent to offspring.
b) Heredity – set of characteristics an
organism receives from its parents.
Gregor Mendel
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Used experimental approach
in science in the 1860’s.
Austrian monk who’s work
gave rise to genetics.
Father of Heredity
Came up with the theory that
parents pass units of
information to offspring
called factors (called genes
today).
Studied garden peas
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Grew fast and matured fast
Produced many offspring
Male/female on same flower
Mendel’s Big Experiments
•Mendel crossed two
plants that were “true
breeding” for a particular
trait and analyzed the
results.
•The P generation =
parents
•The F1 = 1st offspring
•The F2 = F1 X F1
•Comparing 1 trait at a
time is a monohybrid
cross
The Monohybrid Cross –
Plant Height
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When Mendel
crossed 1 tall plant
with 1 short plant he
found 100% of F1
was tall.
When Mendel
crossed F1 X F1 he
found the F2 to be
75% tall and 25%
short (3:1 ratio)
Probability
• Likelihood that a specific event will
occur.
Number of one kind of possible outcome
Total number of all possible outcomes
Mendel Develops Four
Theories
1) There are alternative forms of genes, for
example the gene for plant height in pea
plants can be tall or short – these are
called alleles
2) Each individual has two alleles for each
gene (one from each parent).
1) Homozygous – if each allele is the same
– HH or hh – also known as true breeding.
2) Heterozygous – if each allele is different
– Hh also known as a hybrid.
3) Presence of the alleles does not ensure
the trait will be expressed in the
individual.
1) Dominant – always expressed
2) Recessive – present but remains
unexpressed.
• Use letters to represent the alleles of
an organism.
• Capital letters mean dominant, lower
case letters mean recessive
• Always use the same letter for each
gene.
4) Two alleles for a
trait are segregated
during the formation
of gametes in
meiosis.
Theories become Law’s of
Heredity
• Law of Segregation – member of
each pair of alleles separates when
gametes are formed.
• Law of Independent Assortment
– pairs of alleles separate
independently of one another
during gamete formation.
Genotypes and
Phenotypes
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Phenotype – Physical
appearance or the
observable trait you
see in the mirror.
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Genotype – Genetic
makeup of an
organisms combination
of alleles or what’s
found in the DNA that
you don’t see.
Monohybrid Cross
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Cross that
provides data
about 1 pair of
traits.
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Can predict the
outcome by using
a Punnett Square
Dihybrid Cross
• Cross that involves 2 pairs of traits (16
boxes)
Patterns of Heredity Can be Complex
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Incomplete
Inheritance or
Incomplete
dominance – an
individual displays a trait
that is intermediate
between 2 parents
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Example: Cross
between a snapdragon
with red flowers and
white flowers produces
pink flowers)
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Codominance – the dominant alleles are
expressed at the same time (roan coat of a
horse has both red and white hairs)
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Multiple Alleles – some
traits have genes with
more than two alleles –
expands the possible
genotypes and
phenotypes of an
organism (ABO blood)
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A and B are both
dominant over O with is
recessive but neither A
or B are dominant over
the other
• Polygenic Inheritance – a trait
that is controlled by more than one
pair of genes – combinations of
genes (height, weight, body build,
hair and skin color)
• Environmental Influences – an
individual’s phenotype often
depends on conditions in the
environment – nutrition (affects
height), temperature (affects color
of coat), sunlight (affects skin)
• Genetic Linkage – tendency for
alleles on one chromosome to be
inherited together – the closer the
2 genes on the chromosome the
greater the linkage.
• Sex Linked Gene – involves genes
on the X chromosome or the Y
chromosome. Usually the X
because it is a bigger chromosome
Human Genome Project
• 2000 mapped all the genes in DNA
of humans.
1) Government funded project
2) Evolutionary benefit
3) Human Health benefit
Chromosomes Abnormalities
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Mutations can happen in any cells but
they are not always bad.
1) Source of variations helps species adapt to
its environment
2) Chance to improve the organism very slim.
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Types of mutations
1) Mutation in chromosomes – involve
segments of chromosomes, whole
chromosome and even set of chromosome.
2) Mutation in genes – occurs in individual
genes – may result from change in DNA itself
Genetic Disorders
Chromatin to Chromosomes
• DNA is found in the nucleus
of the cell.
•It is normally in the form of
chromatin which is long and
stringy.
•When the cell starts to divide
the DNA supercoils into
chromosomes.
Karyotype
• Display of the chromosomes of a cell.
• Usually displayed as an arrangement of
chromosome pairs in descending order of size.
• Homologous chromosomes are matched up.
• Identifies and evaluates the size, shape, and
number of chromosomes in a sample of body
cells.
• Extra, missing, or abnormal positions of
chromosome pieces can cause problems with a
person's growth, development, and body
functions.
• 46 chromosomes in body cells (somatic cells) –
known as diploid
• 23 chromosomes in gametes – known as haploid.
Normal Male Karyotype
Human disorders due to chromosome alterations in autosomes
(Chromosomes 1-22). There only 3 trisomies that result in a baby that can
survive for a time after birth; the others are too devastating and the baby
usually dies in utero.
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Patau syndrome (trisomy 13):
Symptoms Include: serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live
births. Children rarely live more than a few months.
Nondisjunction of the sex chromosomes (X or Y chromosome):
Can be fatal, but many people have these karyotypes and are just fine!
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Klinefelter syndrome: 47, XXY males. Male sex organs; unusually small
testes, sterile. Breast enlargement and other feminine body characteristics.
Normal intelligence.
Alterations in chromosome structure:
Sometimes, chromosomes break, leading to types of changes in
chromosome structure: Deletion, duplication or translocation (moved)
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Cri du Chat (Cry of the cat):
A specific deletion of a small portion of chromosome 5; these children have
severe mental retardation, a small head with unusual facial features, and a
cry that sounds like a distressed cat.
Determining if a genetic
disorder exists
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Genetic Counseling – pedigree/karyotype –
records inheritance patterns over generations.
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Ultrasonography – used to determine the
position, sex and if baby is developing
normally.
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Amniocentesis – sample fluid surrounding the
fetus is withdrawn through a long needle – fluid
analyzed.
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Fetoscopy – endoscope inserted through the
abdomen – allows direct observation of the
fetus – can remove excess fluid from brain of
fetus, give blood transfusion, sample skin and
blood.