DNA in a Normal Cell (one chromosome from each parent) Allele Allele  A version of a gene Dominant Dominant  Allele that may mask the presence of another Recessive Recessive  Allele that may be masked by another Heterozygous Heterozygous  The 2 alleles are different Homozygous Homozygous  The 2 alleles are identical Earlobe Gene Toe Gene Polydactyly Gene FFreefAttached tLong big toe tLong PExtraFingersPExtraFingers ♂♀

DNA in a Normal Cell (one chromosome from each parent) Genotype Genotype  The set of alleles an organism possesses Phenotype Phenotype  The outcome resulting from the genotype Earlobe Gene Toe Gene Polydactyly Gene FFreefAttached tLong big toe tLong PExtraFingersPExtraFingers ♂♀

Meiosis F f F f f f F F f f F F Maternal/Paternal alleles segregate

Genetic Crosses Geneticists perform crosses to predict what offspring will result from two parents. Geneticists perform crosses to predict what offspring will result from two parents. 1. Determine parent genotypes. 2. Determine possible gametes. 3. Use a Punnett square to show possible gamete combinations. 4. List possible offspring genotypes. 5. List possible offspring phenotypes. A woman with attached earlobes has a child with a man who is heterozygous. A woman with attached earlobes has a child with a man who is heterozygous. f f ♀ x F f ♂ f or fF or f

Practice Problems Y = yellow pea seedsy = green pea seeds Y = yellow pea seedsy = green pea seeds Perform this cross:Y y x Y y 1.What is the probability of the first offspring having green seeds? 2.What about the 5 th ? 3.What are the chances of the first 5 plants having green seeds? 4.Out of 1000 offspring, how many would you expect to have green seeds?

Practice Problems 1.Cystic fibrosis is a recessive genetic disease caused by buildup of mucus in the lungs, liver, and pancreas. If two healthy people have a child with cystic fibrosis, what are the chances of their next child having CF? 2.People with the nervous system disorder Huntington’s disease (caused by a dominant allele) usually don’t show symptoms until their 30’s. A 27-yr-old man’s family has no history of the disease. His 26-yr-old wife’s grandmothers both had the disease though her parents do not. What are the chances of their 1 st kid having HD?

P Y p y P Y p y P Y p y P Y p y Pp Yy p Y P y Gametes PY py PpYy Pp Yy ORPypY Law of Independent Assortment

Practice Problem P:FfTt ♂ x Fftt ♀ F = Free earlobes f = attached earlobes T = 2 nd toe longest t = great toe longest F 1 Genotypes F 1 Phenotypes