Daily Agenda • • • • • • Daily Trivia Agenda Check Homework Notes on Genetic Crosses Groupwork on HW worksheets Homework RR / BIO 137 What is genetics? • Genetics is the study of HOW traits are passed from parents to offspring. – Offspring show some traits of each parent – These traits from parents are passed onto the offspring by sex cells Body Cell vs. Sex Cell Body Cell Sex Cell make up most of the tissues and organs in body Has 23 pairs of chromosomes (total=46 chromosomes) The chromosomes are paired up sperm or egg cell only Has 23 chromosomes Only 1 of each chromosome Chromosomes BODY CELL SEX CELL • A gene is a small section of chromosome that determines a specific trait • Genes are arranged on a chromosome • Each chromosome carries specific genes Chromosome Genes gene Genes • The genes on chromosomes in body cells are paired Same Trait Gene 1 Gene 2 –2 genes represent a trait in each body cell Pair of chromosomes Fertilization • FERTILIZATION: we get genes from each of our parents • The only way traits are passed onto offspring MOM DAD Offspring Dominant Genes • Genes that keep other genes from showing their traits • EX: plant size • “T” is for the tall gene for a tree • Uppercase letters only Recessive Genes • The genes that do not show their traits when dominant genes are present • Lowercase letters only EX: plant size “t” is the gene for a short tree Dominant vs. Recessive • Pure Dominant – an organism with 2 dominant genes for a trait • Pure Recessive – an organism with 2 recessive genes for a trait • Heterozygous – an organism with 1 dominant and 1 recessive gene for a trait – The dominant gene will overpower the recessive gene. – The dominant gene will be expressed Example: Palm Tree Height Dominant Recessive Gene is depicted by a lower case letter Ex: t TT = pure tt = pure dominant recessive Tt = heterozygous TALL SHORT Gene is depicted with a capital letter Ex: T TT or Tt tt Punnett Square Mother’s Genes Father’s Genes • A way to show which genes can combine when and egg and sperm join • Letters are used in place of genes • Large letter = dominant gene (F) • Small letter = recessive gene (f) Homework • p. 11-12 • 211s Daily Trivia • Elephants can “hear” through their feet. Agenda • • • • • • DT Agenda HW Check Finish Notes Punnett Squares Homework Punnett Square • Large letter goes first in heterozygous organisms (Ff) • Let’s do a cross between a pure dominant male (sperm) for free earlobes (FF) and a female (egg) who is heterozygous for free earlobes (Ff) F f F FF Ff F FF Ff F is dominant over f What are the expected results? F f F FF Free Earlobes Ff Free Earlobes f Ff Free Earlobes ff Attached Earlobes Expected vs. Observed Results Expected Observed Can be calculated Actually seen Predicted Not Predicted Genotype: The combination of genes one has What you expect to observe Phenotype: the physical trait that you can see What you actually observed Dominant/Recessive • One allele is dominant over the other (capable of masking the recessive allele) PP = purple pp = white Pp = purple Problem: Dominant/Recessive • In pea plants, purple flowers (P) are dominant over white flowers (p) show the cross between two heterozygous plants. P p GENOTYPES: - PP (1); Pp (2); pp (1) P PP Pp - ratio 1:2:1 PHENOTYPES: - purple (3); white (1) - ratio 3:1 p Pp pp Punnett Square • 5 Steps – Type of cross – Key – Cross – Square – Answer the question • Practice Problems on the board • Pages 13-16 Homework • 2 Worksheets