Inheritance
Chapter 11 & 12
http://video.aol.com/video-detail/mendel-from-the-garden-to-the-genome/910839264?icid=acvsv2
Inheritance
• Gregor mendel- father of genetics
• “heritable factors” Genes
– Retain individuality generation after
generation
• Patterns of inheritence
– The study of how traits are passed from 1
generation to the next
Peas…who knew?
Terminology
• Genotype
• Gene vs allele
• Locus
Terminology
• Genotype
– An organism’s genetic makeup is the sequence of
nucleotide bases in DNA, the gene
– Always reveals phenotype
• Phenotype
– The phenotype is the organism’s specific traits- how
genes are expressed
– Physical manifestation of the characteristic
– May or may not reveal genotype
Genotype vs Phenotype
Terminology
• Dominant
– Always expressed if it is present
– Capitalized
• Recessive
– Only expressed if homozygous
– Lower case
• Homozygous- 2 alleles are the same
• Heterozygous- 2 alleles are different
Dominant & Recessive
BB or Bb Bb only
Homozygous vs Heterozygous
Terminology
• Self fertilization- aka asexual reproduction
• Cross fertilization- aka sexual reproduction
• True breeding-
– Produce offspring with same characteristic as parent
– Aka Homozygous dominant
• Hybrids aka cross
– heterozygous
True Breeding
Generation Terminology
• P generation- parental
• F1 generation- 1st generation of offspring
• F2 generation- offspring of 1st generation
Principle of Segregation
• Pairs of alleles segregate during gamete
formation;
• Fusion of gametes at fertilization creates
allele pairs again
Punnett Square
• Illustration used to study patterns of
inheritance
• Diagrams all possible results from random
fertilization
Punnet Square
Principle of Independent
Assortment
• Each pair of alleles segregates
independently of other pairs during
gamete formation
• Inheritance of one characteristic has no
effect on the inheritance of another
• ASSUMING characteristics are on
different chromosomes
Independent Assortment
Linked Genes
• Genes found on same
chromosome will be
inherited together
• do not exhibit
independent
assortment
Terminology
• Monohybrid cross
– One characteristic (gene)
• Dihybrid cross
– Two characteristics (genes)
Dihybrid Cross
Rules of Probability
• Alleles will segregate randomly during meiosis
• Flip a coin
– Probability of getting heads?
• ½ or 0.5
• Flip again
– Probability of getting heads?
– ½ or 0.5
• Each toss is an independent event
Rules of probability
Test Cross
• Ability to use a known genotype to
determine an unknown genotype
• Use recessive known
• Ex Brown eyed individual crossed with a
blue eyed individual
Test Cross
Pedigree
• Use Mendelian principles to assemble
information on family traits
• Study inheritance patterns when can’t
perform test cross
• Genetic counseling
• Track genetic disorders
• Carriers
– Carry allele for recessive disorder- do not
exhibit symptoms
Albinism Pedigree
Carrier
Single gene disorders
• One gene controls the disorder
• Exhibit simple inheritance patterns
• Can be dominant or recessive
Recessive Disorder
• Homozygous recessive
• Bulk of human genetic disorders
• Vary in effect
– Albinism
– Tay Sachs
• Inbreeding
– Mating of close relatives
– Increases frequency of homozygous
recessive genotypes??
Albinism
Inbreeding
Polydactyly
Dominant Disorders
• Disease expressed with only 1 allele
present
• Maintained in population because
– Not lethal
• Achondroplasia
• Webbing
• Extra digits
– Develop post- reproductive age
• Huntington disease
Dominant disorders
Syndactyly
Dominant disorders
Polydactyly
Achondroplasia
Other Patterns of Inheritance
• Incomplete dominance
• Codominance
• Pleiotrophy
• Polygenic inheritance
Incomplete dominance
• Pattern of inheritance in which the
heterozygous (Aa) phenotype is
intermediate between the phenotypes of
the homozygous parents (AA & aa)
Incomplete Dominance
Sickle Cell ANemia
codominance
• The expression of two different alleles of a
gene in a heterozygous condition
• Example Abo blood group
Co dominance
Pleiotropy
• The control of more than one phenotypic
characteristic by a single gene
• One gene many effects
Polygenic inheritance
• The additive effect of two or more gene
loci on a single phenotypic characteristic
• Majority of characteristics
• Example skin color
Polygenic inheritance
Sex-chromosomes
Sex linked genes
• Gene located on a sex chromosome
• X chromosome contains more genes than Y
chromosome
• Sex linked inheritance
– Males pass y linked only to sons
– Males pass x linked only to daughters
– Females can pass x linked to either sons or
daughters
Sex linked disorders
• Recessive sex linked
• Y linked recessive always exhibited in males
• X linked recessive exhibited in males and
homozygous females
• X linked dominant traits exhibited in both Males
& female carriers
• Color blindness (X)
• Hemophilia
– X linked recessive
Hemophilia
Y Linked disorders
• Androgen Insensitivity disorder
– XY genetics yield female phenotype as a result of an
inability to respond to testosterone
– Error in membrane protein receptors
• Congenital adrenal hyperplasia
– Xx genotype yield female with male genitalia
– Masculinization of genitals & defects in adrenal gland
function
Translocation
• Deletion
– Loss
• Duplication
– Added chromosome
Fragile X Syndrome
Duplication
Heredity & Environment