Heredity

• Genetic problems– Apply rules of probability

• Multiplication rule

• Key terms1. 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 gene3. Locus location on a chromosome where a

gene is located

Heredity

• Key terms4. Homologous pair every cell contains two

copies of each chromosome, one inherited from each parent.

5. Dominant/ Recessive6. Homozygous dominant7. Homozygous recessive8. Heterozygous9. Phenotype10. 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