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Inheritance - Coggle Diagram
Inheritance
Types of inheritance
Complete dominance
Recessive alleles only expresses itself in the absence of the dominant
Phenylketonuria
Recessive disorfer
Phenylketonuria (fen-ul-key-toe-NU-ree-uh), also called PKU, is a rare inherited disorder that causes an amino acid called phenylalanine to build up in the body. PKU is caused by a change in the phenylalanine hydroxylase (PAH) gene.
Behavioural difficulties such as frequent temper tantrums and episodes of self-harm.
Fairer skin, hair and eyes than siblings who do not have the condition (phenylalanine is involved in the body's production of melanin, the pigment responsible for skin and hair colour)
Eczema.
Repeatably being sick.
Genetic crosses in flowering plants
Incomplete dominance
Heterozygote has an intermediate phenotype
Codominance
Heterozygotes have dual phenotype
Blood type
Defined by a pair of three possibilities of alleles
X-linked
Gene for a specific trait is found on the X chromosome
Pedigree charts
Sexual reproduction
Source of variation
Higher chances of survival
HL
Crossing-over
Autosomal Gene Linkage
Linked genes: Located on the same chromosome, inherited together.
Linked genes shown on vertical lines representing homologous chromosomes.
Failure of independent assortment: Linked genes do not follow Mendel’s Second Law unless recombination occurs.
Recombinants in Linked & Unlinked Gene Crosses
Test cross: Heterozygous for both genes × Homozygous recessive for both.
Unlinked genes: Offspring show equal ratios of parental & recombinant phenotypes.
Linked genes: Recombinant phenotypes occur less frequently due to crossing over.
Sex determination
HL
Segregation & Independent Assortment of Unlinked Genes
Segregation: Each allele in a pair separates during meiosis.
Independent Assortment: Genes on different chromosomes assort randomly.
Relates to dihybrid crosses: Each trait is inherited independently if genes are unlinked.
Punnte Grids
Chi-Squared Test in Dihybrid Crosses
Purpose: Test if observed results match expected Mendelian ratios.
Null hypothesis (H₀): No significant difference between observed & expected.
Alternative hypothesis (H₁): There is a significant difference.
p = 0.05 level: If p < 0.05, reject H₀ (results not due to chance).
Application: Used to analyze F₂ ratios in dihybrid crosses.
Sampling importance: F₂ generation represents a population; larger samples increase accuracy.
9:3:3:1 ratio (heterozygous × heterozygous) in F2 generation.
1:1:1:1 ratio (heterozygous × homozygous recessive) in test crosses.
Mendel’s Second Law: Only applies if genes are unlinked (on separate chromosomes or far apart).
Exceptions: Linked genes deviate from expected ratios.
Loci of Human Genes
Gene locus: Physical location of a gene on a chromosome.
Databases show gene locations and their polypeptide products.
Unlinked genes: Found on different chromosomes.
Linked genes: Close together on the same chromosome.
Gene
Allele
Specific form of a gene
Section of the DNA that determines a certain trait
Traits are defined by a pair of alleles
Genotype
Combination of alleles inherited by an organism
Phenotype
Observable traits of an organism resulting from genotype and environment
