Wolodkowicz

Biology 1H

Chapter 9Fundamentals of Genetics

  1. Genetics- The study of how traits are passed on from parents to offspring. Heredity is the actual transmission of these traits. Traits: distinguishing characteristics (hair color, eye color, ect.)
  2. Molecular genetics- the study of the structure of chromosomes 7 genes.
  3. Chromosome- cell parts with the information (DNA) that determines what traits a living thing will have. Remember, humans have 46 chromosomes or 23 pairs.
  4. Gene (allele)- small section of a chromosome that determines a specific trait of an organism. All genes or alleles are paired. You get one allele from your mom and one from your dad.
  5. Gregor Mendel- Austrian monk (1800’s) who is the father of genetics. Through the study of pea plants, he developed the following ideas.
  6. Law of segregation- states that when 2 gametes combine during fertilization, the offspring have 2 factors (alleles) controlling a specific trait. Each factor is separated during the formation of gametes.
  7. Law of independent assortment- factors for different characteristics are distributed to gametes independently. Ex. Seed color and flower color have no relation.
  8. Terms used in Genetic Crosses
  9. Genotype- actual alleles that you inherit from your parents. One allele from your mom and one from your dad. They are usually expressed as letters. Ex. Brown eyes is B, Tall is T.
  10. Phenotype- The expression of the gene or how this gene is seen on the outside. Ex. Bb is the Genotype; its phenotype is Brown eyes.
  11. Dominant trait- Expressed as a capital letter. This allele has dominance over another gene. For ex. B=brown, b=blue. Bb genotype, its phenotype is brown.
  12. Recessive trait- Written as a lower case letter. This allele’s trait is hidden or not expressed unless there are 2 recessive genes. Ex. bb=blue eyes.
  13. Homozygous- 2 of the same alleles for a given trait (purebred). Ex. Bb (homozygous recessive) or BB (homozygous dominant).
  14. Heterozygous- 2 different alleles for a given trait. (Hybrid). Ex. Bb.

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  1. Probability- the likelihood that a specific event will occur. It is written as a decimal, percentage, fraction, or ratio.

Probability= number of times an event is expected to happen

number of opportunities for an event to happen

Ex. In an experiment Brown hair is crossed with red hair. Brown hair appeared 10 times in offspring. Red hair appeared 5 times in offspring. What is the probability that Brown hair will appear? 10 = 2 or 2:3

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  1. Genetic Crosses via Punnett squares- Punnett squares can predict the probability of an organism being born with a certain trait. Each box represents an offspring. Outer left side = mom’s genotype, the outer top=dad’s genotypes.
  2. Terms- (used mostly with plant experiments for it involves crossing siblings).
  3. P1 generation- parental generation (original cross).
  4. F1 generation- the offspring of the P1 generation.
  5. F2 generation- the offspring of the P2 generation
  6. Height of pea plants (Mendel’s work): TT (tall) vs. TT (tall)

100% TT (genotype) or 100% Tall (phenotype)

  1. Height of pea plants: tt (short) vs. tt (short)

100% tt (genotype) or 100% short (phenotype)

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  1. Height of pea plants: Tt (tall) vs. Tt (tall)

25% TT (tall), 25% tt (short) and 50% Tt tall

  1. Eyes Ex.
  1. Incomplete Dominance (Codominance)- When 2 or more genes (alleles) influences the phenotype. Another words, neither allele is dominant. Not found in humans. Ex. Japanese Four O’clocks.
  1. Color of Four O’clocks. Red: RR, White: WW, and pink RW.

RW (pink) vs. RW (pink)

  1. Dihybrid Crosses- Cross between individuals that involve two pairs of contrasting traits Ex. RrYy vs. RrYy (R=round seed, r=wrinkled seed, Y=yellow seed, y=green seed).

RY / Ry / rY / ry
RY / RRYY / RRYy / RrYY / RrYy
Ry / RRYy / RRyy / RrYy / Rryy
rY / RrYY / RrYy / rrYY / rrYy
ry / RrYy / Rryy / rrYy / rryy

Results: Phenotypes:9/16 round/yellow Genotypes:RRYY,RRYy,RrYY,RrYy

Phenotypes:3/16 round/green Genotypes:RRyy & Rryy

Phenotypes:3/16 wrinkled/yellow Genotypes:rrYY & rrYy

Phenotypes:1/16 wrinkled/green Genotypes:rryy