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Lecture 18

BIOL 190 Lecture 18: Inheritance

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Towson University
BIOL 190
Angela Cox

● Gene- segment of DNA at at particular location on a particular chromosome- codes for a specific protein ● Allele- a unique version of a gene ○ Different alleles for the same gene differ by at least one nucleotide ○ We use different formats (upper and lower case) of the SAME letter for different alleles of the SAME gene- H,h ■ Ex: H= allele for functioning hexosaminidase ■ h= allele for non functioning or no enzyme ○ New alleles arise when mutations occur in existing alleles ● Alleles can be DOMINANT or RECESSIVE ○ Dominant alleles- (uppercase)- always show up in phenotype if present ■ Example- 2 unaffected parents- heterozygotes (carriers) for Tay Sachs disease- Hh ○ Recessive alleles (lowercase)- will be masked/ hidden by dominant allele if both are present ■ Only show up in phenotype if homozygous ● Example- children affected by Tay- Sachs, hh ● Phenotype- appearance or characteristic that results from the expression of the alleles in the genotype ○ Examples- tay sachs disease, brown hair, color blindness ● Genotype- combination of alleles present in a diploid cell/ organism ○ HH,hh, Hh if one gene is being considered ○ Can consider any number of genes, for example: ■ One gene- HH ■ Two genes- AaBb ■ Three genes- AAbbCc ● Gamete- haploid sperm or egg cell- H,h, if one gene is being considered Mendel’s Research Approach ● Pea plants (and not mice or humans) ○ Easy to maintain and breed ○ Quick generation time ○ Many offspring ● Easily categorized traits ○ Greens or yellow seeds ○ Round or wrinkled seeds ○ Purple or white flowers (nothing in between) ● Developed true breeding lines- offspring always carried the same phenotype as the parents ■ Mendel's monohybrid cross ● Parent differ in only one characteristic ○ Ex; flower color A dominant trait masks the effect of a recessive trait ● Cross breeding of organisms that differ in one or more traits Mendel’s Laws of Inheritance ● Law of gene segregation ○ In each (diploid) individual, there are 2 alleles for each trait ○ One on each on homologous chromosome ○ They are segregated = separated into 2 separate gametes during gamete formation (meiosis) ● Segregation: you got two copies of each gene but put only one copy in each sperm or egg ● Law of independent assortment ○ Pairs of alleles on different chromosomes assort independently of each other during gamete formation (meiosis) ○ That means that a particular gamete may end up containing the
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