The Molecular Basis of Mendelian Inheritance Patterns

Mutant Recessiveness: Recessiveness is observed in mutations in genes that are functionally WHAT (+/m, where m is a mutated allele). The mutated allele is the WHAT allele.

Mutant Recessiveness: Recessiveness is observed in mutations in genes that are functionally HAPLOSUFFICIENT (+/m, where m is a mutated allele). The mutated allele is the RECESSIVE allele.

• One wildtype allele (half the genotype) is sufficient for WT phenotype

Mutant Dominance: In genes that are WHAT, in a heterozygote (+/M), the single wild-type allele (+) WHAT provide enough product for normal function. The mutated allele (M) is the WHAT allele.

Mutant Dominance: In genes that are HAPLOINSUFFICIENT, in a heterozygote (+/M), the single wild-type allele (+) CANNOT provide enough product for normal function. The mutated allele (M) is the DOMINANT allele.

• One wildtype allele (half the genotype) is insufficient for WT phenotype

Single letter

Denotes MUTANT phenotypes (or recessive, if mutant in unknown)

Upper case letters

Denotes DOMINANT allele

Lower case letter

Denotes RECESSIVE allele

In nomenclature it should ideally be WHAT (or WHAT)

In nomenclature it should ideally be ITALICIZED (or UNDERLINED)

Slashes indicate WHAT

Slashes indicate alleles for genes on HOMOLOGOUS chromosomes

Semicolons indicate WHAT

Semicolons indicate genes on NON-HOMOLOGOUS chromosomes

Many traits are coded for by a WHAT gene

Many traits are coded for by a SINGLE gene

mutations in the WHAT result in an observable change in the WHAT

mutations in the GENE result in an observable change in the PHENOTYPES

Patterns of single gene inheritance first described by WHO

Patterns of single gene inheritance first described by GREGOR MENDEL

Gregor Mendel (1822-1884)

• WHAT, Pisum sativum

• Examined seven traits through WHAT and WHAT

• All WHAT traits (“either/or”)

Gregor Mendel (1822-1884)

• GARDEN PEA, Pisum sativum

• Examined seven traits through CROSSING and SELFING

• All DISCONTINUOUS traits (“either/or”) (either dominant or recessive)

Mendel’s Law Of Equal Segregation

• He started with WHAT of pea plants

Mendel’s Law Of Equal Segregation

• He started with PURE LINES of pea plants

Mendel’s Law Of Equal Segregation

• One trait: Flower colour - WHAT

Mendel’s Law Of Equal Segregation

• One trait: Flower colour - MONOHYBRID CROSS

Phenotype

What you see (e.g. yellow seeds)

Genotype - WHAT

Genotype - ALLELE combination (symbol indicates MUTANT OR RECESSIVE phenotype)

• use same letter for same GENE, different case for different ALLELES (basic)

What is a monohybrid cross

A cross between two heterozygotes for one trait

Test cross

Cross used to determine the genotype of an individual that is expressing a DOMINANT phenotype (the person is either heterozygous or homozygous) (cross with a homozygous recessive)

Test cross

• If dominant subject is Homozygous dominant then offspring will all be WHAT

• If dominant subject is Heteroygous dominant then offspring will be WHAT and the other WHAT

Test cross

• If dominant subject is Homozygous dominant then offspring will all be HETEROZYGOUS

• If dominant subject is Heteroygous dominant then offspring will be HALF HETEROZYGOUS and the other HALF HOMOZYGOUS RECESSIVE

Particulate inheritance through equal segregation

• Genes are in WHAT – gene may have different WHAT (WHAT)

Particulate inheritance through equal segregation

• Genes are in PAIRS – gene may have different FORMS (ALLELES)

Particulate inheritance through equal segregation

• Gametes contain only one WHAT of each WHAT

Particulate inheritance through equal segregation

• Gametes contain only one ALLELE of each GENE PAIR

Particulate inheritance through equal segregation

• Equal Segregation – WHAT

Particulate inheritance through equal segregation

• Equal Segregation – Half of gametes carry one allele of gene pair, half carry the other allele - MENDEL’S FIRST LAW

Particulate inheritance through equal segregation

• Random WHAT

Particulate inheritance through equal segregation

• Random FERTILIZATION

• Sister chromatids have the exact WHAT

• Non-sister chromatids can be WHAT (WHAT) or WHAT (WHAT)

• Sister chromatids have the exact SAME ALLELES

• Non-sister chromatids can be SAME (HOMOZYGOUS) or DIFFERENT (HETEROZYGOUS)

Chromosomal Theory of Inheritance (1902-03)

• Sutton and Boveri looked at the separation of WHAT during WHAT under a microscope

Chromosomal Theory of Inheritance (1902-03)

• Sutton and Boveri looked at the separation of CHROMOSOMES during MEIOSIS under a microscope

Chromosomal Theory of Inheritance (1902-03)

• Proposed that Mendel’s “particles” were associated with WHAT

Chromosomal Theory of Inheritance (1902-03)

• Proposed that Mendel’s “particles” were associated with CHROMOSOMES

Chromosomal Theory of Inheritance (1902-03)

• Morgan was a skeptic, but later proved them WHAT

Chromosomal Theory of Inheritance (1902-03)

• Morgan was a skeptic, but later proved them RIGHT

Testing for Mendelian Inheritance – Reciprocal Crosses

• mutant parent and wild- type parent are WHAT

• WHAT inheritance should give the same results

Testing for Mendelian Inheritance – Reciprocal Crosses

• mutant parent and wild- type parent are SWITCHED

• AUTOSOMAL inheritance should give the same results

Sex linkage

• Non-autosomes = WHAT

Sex linkage

• Non-autosomes = SEX CHROMOSOMES

Sex linkage

• If one sex does not have a pair of WHAT sex chromosomes, the other WHAT

Sex linkage

• If one sex does not have a pair of SIMILAR sex chromosomes, the other DOES

Sex linkage

• Homogametic: WHAT

Sex linkage

• Homogametic: matching pair of sex chromosomes (ex. XX)

Sex linkage

• Heterogametic: WHAT

Sex linkage

• Heterogametic: no matching pair (ex. XY)

Testing for sex linkage – Reciprocal Cross

• Mutant parent and wild- type parent are WHAT

• WHAT inheritance should give the same results

Testing for sex linkage – Reciprocal Cross

• Mutant parent and wild- type parent are SWITCHED

• AUTOSOMAL inheritance should give the same results

Autosomal

Sex-linked inheritance