Genetics Pt. 2

What does P stand for?

• Parental

• Must be homozygous in the trait that is being studied in offspring

What does F1 stand for?

• First generation (first filial)

• Must be heterozygous

• Tells you which trait is dominant

What does F2 stand for?

• Second generation (second filial)

• Offspring produced from the F1 generation, showing both dominant and recessive traits.

What does monohybrid mean?

• A genetic cross between two individuals focusing on one trait, studying the inheritance of alleles.

• Hybrid: Heterozygous

• Mono: One characteristic

• Monohybrid: Viewing a heterozygous allele for one characteristic

Who was Gregor Mendel?

• 1822-1884

• Austrian Monk

• First person to describe the laws governing the Inheritance of Traits

What was the experiment that Mendel conducted?

• Between 1856 and 1863 Mendel grew and tested over 28, 000 pea plants for inherited characteristics

• Mendel looked at seven traits or characteristics of pea plants which were controlled by a single gene

• Each characteristic has only two possible alleles, no other options for these characteristics

What were the characteristics of the pea plants Mendel looked at?

• Round vs. Wrinkled

• Yellow vs. Green

• Purple vs. White Petals

• Inflated vs. Pinched ripe pods

• Green vs. Yellow unripe pods

• Axial vs. Terminal flowers

• Long vs. Short stems

What was the procedure of Mendel’s Experiments?

• First, Mendel created a “pure” generation or true-breeding generation for that characteristic

• Pure and homozygous means both genes for that characteristic are the same

• The first group was labelled as the Parental generation

• When Mendel crossed pure yellow peas with pure green peas, all the offspring were yellow

• The off springs of the pure yellow and pure green cross (called the f1 generation) each have one yellow and one green gene but they all looked yellow

Why were the resulting offspring of Mendel’s Experiments yellow?

• Due to dominant and recessive genes

What does Dominant gene mean?

• Dominant alleles turn off (mask) recessive alleles

• In Mendel’s peas, yellow was dominant, therefore being the colour seen in the off spring

• Dominant genes are represented by a capital letter

• Note: Dominant means chemically stronger, not more common

What does Recessive gene mean?

• The weaker gene

• Only seen if there is no dominant gene present

• Represented by a small letter version of the dominant gene

What are Mendel’s Conclusions?

• Characteristics are inherited

• Characteristics (genes) may have multiple different forms called alleles

• Some alleles are dominant and some are recessive

What is a Punnett Square?

• Calculates and predicts the probability of the offspring’s genes

• A useful tool to do genetic crosses

• For a monohybrid cross, a square divided by four is needed

• Looks like a window pane

• Used to predict the genotypes and phenotypes of the offspring

What are the steps to using a Punnet Sqauare?

• Determine the genotypes of the parent organisms

• Write down your “cross” (mating)

• Draw a p square

• Split the letters of the genotype for each parent and put them outside the p square

• Summarize results (genotype and phenotype of offspring)

What happened during Mendel’s second cross (Monohybrid cross)

• Allowed the F1 generation to self pollinate and produce the F2 generation

• This revealed the segregation of alleles, showing a 3:1 ratio in phenotypes for dominant to recessive traits.

What are some key questions to ask during Mendel’s second cross?

• Did the recessive allele completely disappear?

• What happened when he crossed two tall pea hybrid plants?

What are some key facts about Dominant alleles?

• Dominant alleles are not necessarily better or more common than a recessive allele

• Some dominant alleles are less desirable

What are some Dominant Allele Disorders?

• Achondroplasia

  • One form of dwarfism

  • Person grows no taller than 4’ 4

  • Not more common and not an advantage

• Polydactyly

  • The presence of more than the normal number of fingers or toes

  • Can usually be corrected by surgery

What are some Recessive Allele Disorders?

• Albinism

  • Lack of pigment in skin, hair, and eyes

  • Mutation in one of several genes which provide the instructions for producing one of several proteins in charge of making melanin

• Cystic Fibrosis

  • Caused by recessive allele on chromosome 7

  • Carried by 2.5% of Europeans,

  • Small genetic change (removes one amino acid) that changes the protein

  • If two parents carry the recessive gene of Cystic Fibrosis, if they are heterozygous, one in four of their children is expected to be homozygous for cf and have the disease

Punnett Square only gives us the…

• Probability

• The likelihood of a particular event occurring

• Chance

• Can be expressed as a fraction or a percent