Download Reproduction and Development

Cell division
When one cell divides into 2 identical
clones.
How then are we different?
Types of cell division
• Mitosis one mother cell into 2 daughter cells
– In growth, replacement, are identical to one another
• Meiosis one mother cell into 4 daughter cells
– Production of sperm (4) and egg (1+ 3 polar bodies)
– Will result in different individuals with differences.
Observable Patterns of
Inheritance
What you are is a result of genetic
expression
How Simple Traits Are Passed to the
Next Generation
Genetic Terms:
• Genes: carry encoded information about
specific traits
• Locus: the position of a gene on a
chromosome
• Homologous chromosome: two
chromosomes that contain the same genes
in diploid cells
More genetic terms
• Alleles: various molecular forms of a gene
for some trait. (same yet different)
• Homozygous: both alleles are the same
• Heterozygous: the alleles differ
• Dominant: (A) allele that shows the
phenotype
• Recessive: (a) allele that is masked
More gene words
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Homozygous dominant: AA
Heterozygous: Aa
Homozygous recessive: aa
Genotype: is the sum of all genes
Phenotype: genes that are expressed
Mendels three basic rules
• Inheritance is controlled by discrete units (genes)
• Each diploid organism has two units for each trait
(one from mom and one from dad)
• In parents different units assort independently into
gametes (law of segregtion)
– if dad is heterozygous you have 50% probability of
getting one or the other allele
The Pedigree
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Circles are females
Boxes are males
Empty boxes are normal (average)
Filled boxes have the trait of interest
A horizontal line indicates a mating or a
brother sister relationship
The Punnett Square
• Provides a simple way to view patters of
inheritance for a single pair of alleles
The Monohybrid cross
• Mating of two
individuals with
contrasting forms of
one trait
• one of these traits will
not show in the first
generation
Possible Male gametes
The testcross
Homozygous
recessive
• The old way to
determine if someone
is a heterozygote
Independent assortment
• When 2 different traits assort they do so
without any affect on one another
• 16 possible allele combinations exist
9:3:3:1 ratio in a dihybrid cross
Variations on Mendelian Genetics
• Codominance: both alleles are expressed in
heterozygotes like blood type
• Multiple effects: one gene may have many
phenotypes, cystic fibrosis, osteogenesis
imperfecta
• Penetrance: phenotype depends on other genes
• Polygenic traits: result from 2 or more genes skin
color, eye color, behavior, IQ
Height
controlled by
3
genes
Chromosome variations
The chromosomal basis of inheritance
• Gene: unit of a heritable trait
• genes are located on chromosomes (locus)
• genes of different chromosomes are
inherited independently
• genes on the same chromosome travel
together
Autosomes and sex chromosomes
• Autosomes
• Sex chromosomes:
consistently 44
determine gender
chromosomes of the
• females XX
same quantity and type • males XY
• all have 22 other
chromosomes that are
alike
Karyotype:
• Is a visualization of
the chromosomes
where the
chromosomes are
lined up by size.
• Is used to determine if
an abnormality
occurred.
The sex chromosomes
• One of the few genes on the Y chromosome
is the sry “make determining gene”
• Only one copy of the X chromosome is
required by the cells, the extra copy in
females is stored in a condensed form
• females are genetic mosaics because cell
may express different X chromosomes
Sex determination
• Gender is determined by the father’s sperm
• X bearing sperm fertilizes an egg, a female
results
• Y bearing sperm fertilizes an egg, a male
results
– Y has the male determining gene
X chromosome inactivation in
females
• Most or all of one X
chromosome is
switched off in early
development of the
female
• the female body is a
mosaic of cells in
which one or the other
X chromosome is
inactivated
Chromosome Linkage
• What chromosome a
gene is located on
• Chromosome #7 has
CF
• X is hemophilia
• Y is TV clicker gene
Mutations
• Are a change in the sequence of a gene
(DNA is altered)
• can be
– Neutral - no change in the information
– beneficial - makes and organism better
– harmful - can kill the organism
Genetic testing before birth
Human Genetic analysis
• The pedigree, be able to write one out
• abnormal: genetic condition that is a
deviation from the usual or average and is
not life threatening
• genetic disorder: conditions that cause
medical problems
• genetic counseling: determining the
probabilities and risks of having children
Patterns Autosomal Inheritance
Most of your genes have nothing to
do with sex
Autosomal Recessive
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Both parents must be a carrier
only homozygous children are affected
3:1 ratio of normal to affected children
Phenylketonuria: mental retardation
Cystic fibrosis: build up of mucus in lungs
Tay-Sachs disease: lipid buildup in brain
Autosomal dominant Inheritance
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Allele is expressed in each generation
Dwarfism: 4 feet in height
Progeria: rapid aging dies at age 10
Huntington’s disease: degeneration of
nervous system after age 40.
Patterns of X linked inheritance
• X linked recessive occurs more in males
than females
– Hemophilia A, Duchenne muscular dystrophy,
Color blindness
• Testicular feminizing syndrome
– mutation in the X chromosome on male results
in defective receptors for the male sex
hormones
– embryo develops into an apparent female
Chromosomes can be abnormal
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Deletion
Duplication
Insertion
Translocation
• A woman with cystic fibrosis comes into
your Genetic counseling clinic. She is
going to marry her first cousin. What she
wants to know that if they have children
what is the probability that they will have a
child with cystic fibrosis. Use your
knowledge of genetics to give her an idea of
the different probabilities.
• What does the filled figure mean? What
figure represents mails, which females. In
what generation are the woman’s
grandparents. Now that you know this
information , what is the woman’s
possibility of having a child with Cystic
fibrosis? Using this example, explain why
it is not a good idea for closely related
individuals to have children together?
• The widow’s peak is a feature where the hairline
dips down the forehead in a v like pattern. Look at
3 generations of your family Draw a pedigree and
give the names of all the members of your family.
Indicate weather they have a widows pear or if
they have a straight hairline. Indicate weather you
think the widows peak is dominant or recessive
give your reasoning. If your family is all straight
or widows peak describe what type of results you
would need in order to determine if a trait is
dominant or recessive.