Genetics: Mendel, Traits, and Punnett Squares

Gregor Mendel

• An Austrian monk who discovered dominant and recessive traits in pea plants.
• Known as "The Father of Modern Genetics" and kept very detailed notes.

Genetic Crosses and Traits

• Dominant trait for pea plants: Yellow (YY or Yy).
• Recessive trait for pea plants: Green (yy).
• Genotype of pure-breeding yellow line: YY.
• Genotype of pure-breeding green line: yy.

Inherited vs. Acquired Traits

• Inherited traits are passed on from parent to offspring via genes and DNA, examples including eye color and height.
• Acquired traits are learned or gained from the environment, like whistling or handwriting.

Chromosomes and Genes

• A chromosome example contains 5 genes: QQ, Rr, Ss, tt, uu.
• Heterozygous genes in the example: Rr, Ss (hetero means different).
• Homozygous genes in the example: QQ, tt, uu (homo means same).
• A human body cell contains 46 chromosomes.

Punnett Squares: Tongue Rolling

• R = tongue roller (dominant), r = non-tongue roller (recessive).
• Heterozygous = Rr; Homozygous = RR or rr.
• Probability of a child being a tongue roller from a Rr x rr cross: 50% (2/4).
• Probability of a child not rolling tongue: 50% (2/4).
• Probability of a child being homozygous dominant (RR): 0%.

Punnett Squares: Curly Hair in Dogs

• H = curly (dominant), h = straight (recessive).
• Heterozygous = Hh; Homozygous = HH or hh.
• Possible genotypes: HH, Hh, hh.
• Possible phenotypes: curly hair, straight hair.
• Probability of a puppy being heterozygous (Hh) from an Hh x Hh cross: 50% (2/4).
• Probability of a puppy having curly hair from an Hh x Hh cross: 75% (3/4).
• Genotype refers to the genetic code (letters), such as HH, Hh, or hh..
• Phenotype refers to physical appearance, such as curly or straight hair.

Pedigrees and Inheritance

• A pedigree traces an inherited disease through a family, using "B" for dominant and "b" for recessive alleles.
• If few individuals are shaded/affected, it's likely a recessive disease.
• Generations in the example pedigree: 4.
• Relationship between Person A and B: husband and wife.
• Relationship between Person A and C: father and daughter.
• Genotype of Person A (Bb): Bb.
• It is noted that if children have a recessive trait, the person must be "Bb".
• Genotype of Person B (Bb): Bb
• Children must have the recessive trait
• Genotype of Person C (bb) from the Punnett Square: bb (recessive trait).

DNA Structure and Function

• DNA Contains the instructions for living things and is found in the cell nucleus.
• DNA is shaped like a twisted ladder.
• DNA's four bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T)
• Base pairing: A=T, C=G
• Complimentary DNA strand example: if one strand is ATC CGT GTC AAT GGC CCG, the other is TAG GCA CAG TTA CCG GGC.
• The sides of a DNA molecule: backbone.
• The backbone consists: sugar and phosphate.
• DNA is found in the nucleus of animal cells.

Mutations

• Mutations can be deletion (shorter), addition (longer), or substitution (swapped).
• Mutations can be harmful (decrease chances of survival), beneficial (increase chances of survival), or neutral (no effect on organism's survival).
• Mutations increase variation in a population, therefore variation allows populations to adapt to changes in the environment.

Genes, Alleles and Inheritance

• Eye color is an inherited trait encoded in DNA, passed from parent to offspring.
• A gene is a segment or chunk of DNA that codes for a specific trait.
• A chromosome is a long, condensed strand of DNA with many genes, while a gene is only a small segment.
• DNA unzips inside the nucleus, mRNA transcribes the message and exits the nucleus, and takes the message to a ribosome for translation into a protein.
• Alleles are forms of a gene for a specific trait and you inherit one allele from mom and one from dad.
• Dominant alleles are represented with capital letters and recessive alleles with lowercase letters.
• Genotype is the genetic (letter) code, that can't be seen, phenotype is the physical trait which you can see.
• Examples of homozygous alleles (AA, EE, DD for dominant, aa, ee, dd for recessive), which are pure bred.
• Heterozygous alleles (Aa, Ee, Dd) can also be called hybrid.

Explore Gregor Mendel's work, genetic crosses, and the difference between inherited and acquired traits. Learn about chromosomes, genes, and how to use Punnett squares to predict inheritance. Discover dominant and recessive traits with key examples.