Download Lesson 4 and 5 Notes

Lesson 4 Heredity Notes
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Heredity- passing of genetic material from parents to offspring
o Gregor Mendel- hypothesized each parent has 2 heritable “factors” for each trait, one from each parent
o Characteristic- a feature with different forms (hair color, eye color, flower color, freckles)
o Trait- the options for the characteristics
 Blonde/brown/red/black hair
 Blue/green/brown eyes
 Freckles/no freckles
 Pink/white flowers
o Traits are passed from parents to offspring though genes
 Alleles- different versions of the gene (G- dominant, g- recessive)
 Heterozygous- trait is one dominant and 1 recessive allele (Gg)
 Homozygous- trait is two dominant or 2 recessive alleles (GG or gg)
o Genes influence traits
 Genotype- combination of alleles (genes) you inherit (GG, Gg, or gg)
 Phenotype- observable trait- what it looks like physically- (red hair, brown hair, etc.)
 Dominant allele contributes to phenotype if 1 or 2 alleles are present(GG, Gg)
 Recessive allele contributes to phenotype only when 2 alleles are present (gg)
Many genes can influence a single trait
o Eye color, skin color, hair color are all influenced by several genes
Single genes can affect multiple traits
o White tiger- white fur and blue eyes- same gene
o Sickle cell anemia
Environment can affect traits
o Can influence phenotype
 Artic fox- fur turns colors depending on amount of sunlight received
 Reaching your full height potential can depend on adequate nutrition
 Wrinkles on skin can increase due to sun exposure
Inherited vs. Acquired traits
o Inherited from parents from genes- eye color, dimples, freckles, hair color, etc.
o Acquired- learned traits- language, accent, ride a bike, play a sport
Dominance
o Complete dominance
 One or two alleles will cause dominant trait
 Recessive trait only shows with 2 recessive alleles
o Incomplete dominance
 A blend
 Snapdragons- red + white will result in pink offspring
 Hair- curly + straight will result in wavy
o Codominance
 Neither dominant
 AB blood type has both A and B antigens at work
Lesson 5- Punnett Squares and Pedigrees
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Punnett squares are used to predict patterns of heredity
o Graphic that predicts the possible genotypes from a given cross
Parent 1- genotype- Rr
Parent 2- genotype- rr
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R
r
r
r
Rr
rr
Rr
rr
To fill in the square place parent 1 genotypes on top of the square- 1 over each column
 Place parent 2 genotypes to the left of the square- 1 next to each row
 Bring each letter down
 Bring each letter over
Punnett squares can be used to make predictions
o In example above, possible genotypes are Rr, rr, Rr, and rr.
o Probability is the mathematical chance of each genotype occurring
 Ratio- compares 2 quantities- here # of a genotype to possible genotypes
 Ratio of Rr- 2 chances of 4, or 2:4 (read:2 to 4)
 Ratio of rr- 2 chances of 4, or 2:4
 Percentage compares the number to 100
 2:4 would be 50:100, or 50%
o Chance of Rr is 50%, chance of rr is 50%.
Pedigree is a chart that traces a trait through several generations of a family
Can be useful to trace sex-linked disorders (like colorblindness or hemophilia) and other genetic diseases (cystic fibrosis,
sickle cell anemia)
o Chart usually has a key to describe males/females, and whether individual has the trait (usually shaded in),
carries the trait (usually partially shaded in), or doesn’t carry or have the trait (not shaded at all)
Pedigree chart example: (or see p. 142)