Transcript Heredity - TeacherWeb

Heredity
• Genetic problems
– Apply rules of probability
• Multiplication rule
• Key terms
1. Gene the genetic material on a chromosome
that contains the instructions for creating a
particular trait (codes for a trait)
2. Allele  one of several varieties of a gene
3. Locus  location on a chromosome where a
gene is located
Heredity
• Key terms
4. Homologous pair  every cell contains two
copies of each chromosome, one inherited from
each parent.
5. Dominant/ Recessive
6. Homozygous dominant
7. Homozygous recessive
8. Heterozygous
9. Phenotype
10. Geneotype
Heredity
• Law of segregation
– Random segregation of alleles (and their
chromosomes) to separate gametes.
– Occurs during meiosis I.
• Law of independent assortment
– The migration of homologues within one pair
of homologous chromosomes to opposite poles
does not influence the migration of homologues
of another homologous pair.
Heredity
• Mendel
– Crossed (mated) two varieties of pea plants to form
offsprings, or hybrids.
– Monohybrid cross  involves a gene for only one
trait
•
•
•
•
Flower color (Purple and White)
P generation  parents
F1 generation  offspring from the parents
F2 generation  offspring produced from crosses among the
F1
Heredity
• Monohybrid Crosses
– Genotypic ratios
– Phenotypic ratios
• Test cross
• A test cross is a mating of an individual whose
genotype you are trying to determine with an
individual whose genotype is known.
• You will always know the genotype of the
individual that expresses the recessive trait.
Heredity
• Dihybrid Crosses
– Genes for two different traits are observed at the same
time.
• Incomplete Dominance
– The alleles for a gene do not exhibit the dominant and
recessive behaviors.
– Instead, the combined expression of two different
alleles in the heterozygous condition produces a
blending of the individual expressions of the two
alleles.
Heredity
• Codominance
– Both inherited alleles are completely expressed
• Multiple alleles
• Epistasis
– Occurs when one gene affects the phenotypic
expression of a second gene.
– Ex. mice hair color
• One gene codes for the presence or absence of pigmentation
• Second gene codes for the color of pigmentation (black or
brown)
• Phenotypic expressions: CCBB, CCBb, CcBB, CcBb
CCbb, Ccbb
ccBB, ccBb
Heredity
• Polygenic inheritance
– The interaction of many genes to shape a single
phenotype.
– Example: human height
• Linked genes
– Genes that reside on the same chromosome and
cannot segregate independently.
– Genes that are linked are usually inherited
together.
Heredity
• Sex-Linked Inheritance
– Sex chromosomes
– Sex-linked or X-linked
– Examples
• Hemophilia
– Inability to code for all factors required to form normal blood
clots.
• Color-blindness
– Inability to distinguish red from green
• Duschenne’s Muscular Dystrophy (MD)
– Absence of an essential muscle protein called dystrofin.
– Results in deteriorating muscles and loss of coordination.
Heredity
• X-inactivation
– During embryonic development in female
mammals, one of the two X chromosomes in
each cell does not uncoil into chromatin.
– Barr body- dark, compact body
– Example: female calico cat
• Yellow, black, and white hair.
– Yellow and black colors are coded by a gene on the X
chromosome.
– White color is coded by a different gene.
Heredity
• Nondisjunction
– Chromosomes do not properly separate
– Example
• Down syndrome (trisomy-21)
–
–
–
–
Mental retardation
Heart defects
Respiratory problems
Deformities in external features
• Turner syndrome
– Female  XO
– Physically abnormal and sterile
• Klinefelter syndrome
– Male  XXY
– Sterile and often mental retarded
Heredity
• Human Genetic Defects
– Caused by:
• inheritance of an allele
• Chromosomal abnormalities
– Results when the inherited genome is missing a
chromosome, or has an extra chromosome, or when one or
more chromosomes have portions:
» Deletion
» Duplication
» Translocation
» Inversion
Chromosomal Mutations
Common Genetic Defects
Phenylketonuria Autosomal
recessive
Inability to properly
breakdown phenylalanine.
Causes mental retardation
and death.
Tay-Sachs
disease
Autosomal
recessive
Inability to properly
breakdown certain lipids.
Causes progressive nervous
system dysfunction and is
usually fatal by age four.
Huntington’s
disease
Autosomal
dominant
Expression begins in
middle age with mild
mental illness and loss of
motor control progressing
to total physical and
mental incapability.
Cri du chat
Deletion in
chromosome 5
Physical and mental
retardation and catlike cry
PKU
Tay-Sachs Disease
Huntington’s Disease
Common Genetic Defects
Cystic Fibrosis
Autosomal
Recessive
Abnormal
chloride
transport
Sickle-cell Disease Codominant Abnormal
Hemoglobin
Achondroplasia
Autosomal
Dominant
Form of
dwarfism
Cystic Fibrosis
Sickle-cell Disease
Sickle-cell
Polydactyl- Right Hand
Polydactyl- Left Foot