Chapter 8 Genetics

Father of Genetics Austrian monk named Gregor Mendel Did experiments on pea plants Heredity-the passing of characters from parent to offspring Genetics- the branch of biology that focuses on heredity Character- inherited characteristic (example: flower color) Trait- single form of character (example: purple flowers)

Pea reproduction True- breeding- always produce the same trait when self-pollinating Cross-pollinate- removing the male part of the flower and dusting with pollen from a flower. Hybrids- offspring of crosses between parents with different traits

Mendal’s 1st cross Crossed white flowered plants with purple flowered plants All the offspring were purple- why??

Principal of Dominance For most simple traits there are 2 possible versions of the gene (alleles) Each organism gets 2 alleles for a simple trait (one from the Mom and one from its Dad) Dominant alleles mask the other allele and are UPPERCASE Recessive alleles are masked by the dominant allele and are LOWERCASE

Purple is dominant over White The offspring of Mendel’s first cross were all purple but they had a purple allele (P) from one parent and a white allele (p) from the other parent Genotype- which alleles are present (letters) The genotype of the offspring was Pp

Phenotype Which trait is actually seen The phenotype of the 1st cross offspring was purple

Other Traits Mendal Tested

Example Problem 1 A pea plant has round seeds and has an allele for round and an allele for wrinkled. Genotype-? Phenotype-?

Example Problem 2 A pea plant has white flowers. Genotype-? Phenotype-?

Mendal’s 2nd Cross Crossed the offspring of the first cross with each other. Why had the white flowers reappeared?

Segregation Segregation- alleles for the same gene separate from each other during gamete formation so that each gamete cell gets only 1 type Homologous chromosomes separate during Prophase I!

Biological Inheritance Genes- chemical factors that determine traits Pieces of DNA that code for proteins Different alleles produce different shaped proteins

Homozygous and Heterozygous Homozygous- individual with 2 dominant alleles or 2 recessive alleles. Example: TT or tt Heterozygous- individual with one dominant allele and one recessive allele Example: Tt

Review Questions Who is the father of genetics? What type of plant was used in the first genetics experiments? What does true-breeding mean? What is meant by the term F1? Hybrid? Define the terms “gene” and “allele”. Explain the principle of segregation.

Probability Likelihood that an event will occur Probability can be used to predict outcomes of genetic crosses

Punnett Squares Used to predict and compare the genetic variations that will result from a cross

Independent assortment -Genes assort independently during gamete formation Having one trait doesn’t increase the chance of having the other

Incomplete dominance Heterozygous organisms have intermediate trait (combination of dominate and recessive trait)

Codominance Heterozygous organisms have both dominant and recessive trait Example- animals with speckled fur

Multiple alleles More than 2 alleles exist for a certain trait, but each organism can still only have 2 -- Example: Blood type has 3 alleles (A, B, and O)

Sex Linked Traits Gene occurs on the X or Y chromosome Males cannot be heterozygous because they only have 1 X!!! Example: genes for baldness and colorblindness occur on the X chromosome so men are more likely to be affected Heterozygous female X normal male

Polygenetic traits Produced by interaction of several genes