Standard Biology Chapter 26 Inheritance of Traits Section 1 Genetics, How and Why

Genetics Genetics: the study of how traits are passed from parent to offspring Mystery for a long time Now know traits are passed in sex cells

Chromosomes Nucleus found in center of cell which directs the cell’s activities Chromosomes are found in nucleus Chromosomes are thickened and easy to see Remember, chromosomes are duplicated before cell reproduction

Chromosomes Two kinds of cells Body cells- chromosomes in pairs (diploid) Sex cells- single chromosomes (so ½ the number of chromosomes as body cells) (haploid)

Genes on Chromosomes Gene Small section of chromosome that determines a specific trait; examples Eye color Wing shape Chemical process Humans have about 23,000 genes

Genes on Chromosomes Genes are arranged on a chromosome like beads on a necklace Chromosomes are paired, so genes are paired (except sex cells)

Passing Traits to Offspring Female egg Traits are passes from parent to offspring in sex cells Example: Ear Lobe Shape p. 548 A A AF F Child will have free ear lobes F Male sperm A= attached ear lobes F= free ear lobes

Dominant and Recessive Genes One trait dominates another like free dominates attached Free=dominate and Attached=recessive Mother is pure attached (AA) or homozygous recessive (homo means same) Father is pure dominate (FF) or homozygous dominate Child is one Free and one Attached (FA) or heterozygous (hetero means different)

Traits of Plants and Animals Trait found in Dominant Trait Recessive Trait Flies Long wings Short wings Pea plants Purple flowers White flowers Humans Can roll tongue Can’t roll tongue Corn plants Normal height Dwarf Dogs Short hair Long hair

When Both Parents are Heterozygous If mother is heterozygous (FA), she can make F eggs and A eggs If father is Heterozygous (FA), he can make F sperm and A sperm How many combinations of traits in children as possible? Table 26-2 p. 551

When Both Parents are Heterozygous Mother’s eggs: F and A Father’s sperm: F and A Child: FF, FA, AF or AA So four combinations of genes possible (although FA and AF are the same) Child will have free ear lobes if FF, FA or AF Child will have attached ear lobes if AA

Standard Biology Chapter 26 Inheritance of Traits Section 2 Expected and Observed Results

Punnett Square Easy way to look at combinations of traits is with a Punnett Square Letters used represent genes Capital letters dominant Lower case letters recessive Trait’s letter based on dominant

Punnett Square Example: Mother’s genes Free ear lobes dominant F Attached ear lobes recessive f Homozygous recessive mother ff Homozygous dominant father FF f f F Ff Ff Ff F Ff Father’s genes

Punnett Square Example when parents are heterozygous: Mother’s genes F FF Ff Father’s genes ff f Ff

Directions for Punnett Square Draw a Punnett Square (4 boxes). Each box shows possible combination of genes in offspring. Decide what genes will be in the sex cells of each parent. Write mother’s genes on top; write father’s genes on side. Copy the letters that appear at the top of the square into the boxes below each letter. Copy the letters that appear at the side into the boxes next to each letter. Look at the 4 small boxes in the Punnett Square, these are possible combinations in the offspring.

Expected Results Get from Punnett Square What you expect to happen Probability Expected Results

Observed Results The numbers you actually get Expected Results The numbers you actually get They don’t match up exactly with what you expect The greater the number of offspring, the closer you should get to the expected results. Table 26-3 p. 557 Observed results when you count the pods of this one cross: 71 yellow pods and 24 green pods

Mendel’s Work Gregor Mendel Father of Genetics 1865 Austrian monk/teacher in Czech Grew garden peas, came up with ideas about how traits are inherited Counted 1000’s of traits in pea plants and conducted scientific investigations (applied math to science)

Mendel’s Work Traits he studied: Plant height Pod color Pod shape Seed color Seed shape Flower color Flower position Always found 3 dominate to 1 recessive when heterozygous parents were crossed