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Mendel’s Laws & Chromosomal Inheritance - Coggle Diagram
Mendel’s Laws & Chromosomal Inheritance
CHROMOSOMAL INHERITANCE
Theory of chromosome inheritance
Genes reside on chromosomes
Supported by Morgan’s fruit fly experiments
Parallel behavior of alleles & chromosomes
Morgan’s findings
Drosophila melanogaster
Wild type vs. mutant
White-eye mutation on X chromosome
First evidence linking gene → chromosome
Sex Determination Systems
Human XY system
SRY gene → testes development
X and Y homologous regions pair during meiosis
Sex-Linked Genes
X-Linked
Color blindness
Duchenne muscular dystrophy
Hemophilia
males need one copy
females need two
Y-Linked
Mostly male-specific functions
lower genes
X inactivation
Random inactivation → Barr body
Females are mosaics
XIST gene involved in inactivation
Linked Genes
Genes on same chromosome inherited together
Do not assort independently
Parental phenotypes appear often
Genetic Recombination
Unlinked Genes
50% recombination frequency
Results from independent assortment
Linked Genes
Crossing over produces recombinants
Breaks physical connection
Explains why linked genes can still recombine
Chromosomal errors
Down syndrome (Trisomy 21)
Turner syndrome
Klinefelter
Mendel start of genetics
Mendel’s Experiments
True-breeding P generation
Cross → F₁ → F₂
Controlled fertilization
Quantitative approach
Characters vs. traits
Mendel's model
Alleles
Alternative versions of genes
Reside at specific locus
Inheritance
2 alleles per character
Dominance
Dominant allele determines phenotype
Recessive masked unless homozygous
Law of Segregation
Alleles separate during gamete formation
Law of Independent Assortment
Alleles of different genes assort independently
Applies to genes on different chromosomes or far apart
Dihybrid crosses
Mendelian genetics
Degrees of Dominance
Complete dominance
Incomplete dominance
Codominance
Pleiotropy
One gene → multiple effects
ex cystic fibrosis, sickle-cell
Epistasis
One gene masks another
Polygenic Inheritance
Many genes → one trait
Skin color, height
Mandelian patterns in humans
Pedigrees
Recessive disorders
Dominant disorders