Introduction to Genetics Chapter 11

What is genetics?  Genetics is the scientific study of heredity

Mendel’s Work  In the mid-1800s, an Austrian monk named Gregor Mendel studied how traits were passed from one generation to the next using pea plants  His ideas form the foundation of the principles of heredity, known as Mendelian genetics

Mendel’s Work  Pea plants can produce purebreds (genetically identical offspring to the parent plant through self- pollination)  Mendel did cross- pollination to interbreed the pea plants

Mendel’s Work  Mendel studied 7 traits (specific characteristics), such as seed color or plant height  The parent generation is called the P generation  The offspring from those parents are called the F 1 generation (first filial)

Mendel’s F 1 crosses

Mendel’s Conclusions 1.Biological inheritance is determined by factors (genes) that are passed from one generation to the next Each trait is controlled by one gene occurring in two contrasting forms – the different forms of each gene are called alleles for example, the gene for plant height has alleles for both tall and short plants

Mendel’s Conclusions 2. Some alleles are dominant and others are recessive if the dominant allele is present, that form of the trait will always be present the recessive trait will only show if there is no dominant allele

Mendel’s F 2 Cross  Mendel allowed the F 1 generation to self- pollinate

Mendel’s F 2 Cross  Alleles are segregated from each other so that each gamete (egg, sperm) carries only a single copy of each gene

Probability  The likelihood that an event will occur is called probability  For example, coin flipping: - the probability of flipping heads is ½ (50%) - the probability of flipping three heads in a row is ½ x ½ x ½ = 1/8 (1 in 8 chance)  Past outcomes do not affect future ones!

Punnett Squares  A Punnett square is a diagram to identify possible combinations of alleles in offspring when two parents are “crossed”

Two types of alleles  DOMINANT alleles are represented by CAPITAL letters ex: T is for tall  recessive alleles are represented by lowercase letters ex: t is for short

 Which of the following alleles are DOMINANT? AtqRsAtqRs  Which of the following alleles are recessive ? AtqRsAtqRs  Which of the following alleles are DOMINANT? A tq R s Dominant or recessive?  Which of the following alleles are recessive ? A tq R s

Two types of alleles  Each person has 2 alleles – one from mom, one from dad  homozygous means you have 2 of the same allele (either both dominant, TT, or both recessive, tt) also known as purebred  heterozygous means you have 2 different alleles (one dominant, one recessive: Tt) also known as hybrid

Homozygous or heterozygous?  Label the following as homozygous (homoz) or heterozygous (heteroz): Hh BB rr Ss Tt qq HH  Label the following as homozygous (homoz) or heterozygous (heteroz): Hh heteroz BB homoz rr homoz Ss heteroz Tt heteroz qq homoz HH homoz

Genotype and phenotype  A phenotype is the physical characteristic (what it looks like) ex: tall plants  A genotype is the genetic make-up (the actual alleles) ex: TT or Tt

Monohybrid Crosses  single gene cross (each parent has one gene, each with two alleles)

Monohybrid Crosses  parents go along the top and side  offspring shown in the middle 4 squares

Monohybrid Crosses  cross a homozygous tall plant with a homozygous short plant