CH 9 FUNDAMENTALS OF GENETICS

Genetics  What is it? Define it in your notebook with a partner.  Field of biology devoted to understanding how characteristics are transmitted from parent to offspring

Gregor Mendel  “Father of genetics”  Studied science and mathematics  Austrian monk mid 1800s  Researched heredity: transmission of characteristics from parent to offspring  Worked with pea plants

Mendel and pea plants  Observed 7 heritable characteristics of pea plants  Trait: genetically determined variant such as color  The pea plant characters existed in two variants Height Flower position Flower color Pod color Pod appearance Seed texture Seed color

Methods  Pollination: combination of male and female gametes  Self-pollination: same plant  Cross-pollination: different plants

Methods  Needed true breeding plants (pure; offspring always had same variant of trait as parent)  Then crossed two true breeding plants for a single trait (one of each variant; one purple flowered and one white)  This is the P generation: true-breeding parents  Resulting generation called F1 generation  F1 self crossed to get F2 generation

3 steps in Mendel’s experiment

Results  Observed similar frequencies of traits  Traits came out in consistent ratios of 3:1

Dominance  Dominant traits: always observed; can mask a recessive trait  Recessive traits: only observed when dominant trait is not present; can be masked by dominant trait

Mendel’s conclusions  Open books to page 177. read paragraphs for the following and rewrite the definition in your own words. 1. Law of segregation 2. Law of independent assortment

Mendel’s factors  Remember, Mendel didn’t know about genes.  We call mendel’s factors: Alleles  Alleles: alternative forms of a gene  Example: brown hair vs blond hair  Example: purple flowers vs white flowers

 Alleles represented by letters  Capital letter of dominant trait  Alleles for flower color in pea plants:  P = purple and p = white

9-2: Genetic crosses  Genotype: genetic makeup  Consists of alleles inherited from parents  for flower color in peas there are three possible combinations of the two alleles (P & p)  PP = purple genotype  Pp = purple genotype  pp= white genotype

phenotype  Phenotype: organism’s appearance (physical characteristic)  PP and Pp = purple flowers  pp= white flowers

 Homozygous: when both alleles are the same  Homozygous dominant = PP (purple)  Homozygous recessive = pp (white)  Heterozygous: when both alleles are different = Pp (purple)

Probablity  Likelihood a specific event will occur  Genetic crosses deal with probability  Punnett squares used to predict the possible distribution of inherited traits in offspring  Tells potential genotypes and phenotypes of offspring  Monohybrid cross: cross in which only ONE trait os tracked

Punnett squares 1. Need genotypes of parents (PP x pp) 2. Draw a punnett square 3. Place parents alleles on either side of square 1. Each parent can give only one of their two alleles to the offspring 4. Combine columns and rows 5. Count genotypes and determine probabilities

Lets do some crosses!  Pea color: Yellow dominant to green  Cross a homozygous dominant plant with a heterozygous plant  What is the probability of each genotype?  What is the probability of each phenotype?

Lets do some crosses!  Cross a plant with green peas with one that is heterozygous.  What is the probability of each genotype?  What is the probability of each phenotype?

More crosses!!!!!  Cross two heterozygous plants for pea shape where Round is dominant to wrinkled.  What is the probability of each genotype?  What is the probability of each phenotype?

Bikini Bottom Genetics time  Work with a partner to complete the worksheet.  Ask questions when needed.

Test cross  Test cross: cross between an unknown genotype and a homozygous recessive individual  bb x B?  Second individual could be BB or Bb  Offspring will show what original genotype was.

Incomplete dominance  Phenotype of heterozygous individual is an intermediate trait  flower color in four o’clocks  RR – red  rr – white  Rr – pink

Codominance  Two dominant alleles  Both are expressed in heterozygote  Blood type: A, AB, B, O  I A and I B are both dominant to i  I A I A, I A i = type A  I B I B, I B i = type B  I A I B = type AB  ii = type O

Dihybrid cross  Cross in which two characteristics are tracked  Round dominant to wrinkled. Yellow dominant to green  Cross two individuals who are heterozygous for both traits