 Introduction to Genetics How are traits passed on?

Gregor Mendel  Austrian monk who studied pea plants  He chose these plants to study because they were:  Easy to grow  Mature quickly  Have sharply contrasting traits

Traits of Pea Plants

Pea Plants  Naturally, pea plants self -pollinate.  Mendel observed that some plants, when they were allowed to self-pollinate, always “bred” true.  This means that these plants were “ true-breeding ” (Ex. Tall plants always produced tall plants.)  Mendel cross -pollinated some plants to observe the results.

 When he crossed true-breeding tall plants and true breeding short plants, he found that he always got tall plants  Then, he crossed the resulting tall plants, and found that the short plant reappeared.  P = Parental Generation  F1 = first filial generation  F2 = Second filial generation

Why did Mendel get these results?  All living things have genes, or sections of chromosomes that have instructions for making different characteristics  There are always two versions of these genes, one from each parent  Called Alleles  Represented by letters

Alleles  Alleles, or the two forms of each gene, can be  Dominant –  this trait will always show up if the dominant gene is present  Represented by capital letters (B)  Recessive –  this trait will only show up in the absence of the dominant gene  Represented by lowercase letters (b)  Examples of  Dominant traits – tongue rollers, brown eyes, dark hair, left thumb hand clasping  Recessive traits – non-tongue rollers, light eyes, light hair, right thumb hand clasping

Allele Combinations (Genotype)  Depending on the two alleles present, an organism can be considered homozygous or heterozygous for a trait  Homozygous – two alleles are the same, either both dominant or both recessive  Homozygous Dominant (HD) – two dominant alleles (TT)  Homozygous Recessive (HR) – two recessive alleles (tt)  Heterozygous – two alleles are different, one dominant and one recessive (Tt)  The different arrangements of alleles is called an organism’s genotype

Phenotype  An organism’s genotype will determine its phenotype, or physical characteristic  For example:  A plant with the alleles TT is homozygous dominant & one with the alleles Tt is heterozygous  Both plants have the dominant gene for tallness (T) and will therefore have a tall phenotype

Back to Mendel’s Plants  Why did the trait for short plants disappear in the F1 generation?  Why did it reappear in the F2 generation?  Punnett squares can be used to demonstrate the different possible combinations of alleles…..

 Brown eyes are dominant over blue eyes. A man with brown eyes, whose entire family has only ever had brown eyes, marries a woman with blue eyes. Give the genotype and phenotype ratios possible for their future children.

 A brown-eyed man, whose mother had blue eyes, marries a blue-eyed woman. Give the genotype and phenotype ratios possible for their future children.

 Right-handedness is dominant over left-handedness. Give the genotype and phenotype ratios possible for the future children of a heterozygous couple.

 In certain goats, there is a fainting gene that is recessive if the goats are startled. Give the genotype and phenotype ratios possible for the offspring of two heterozygous goats. Can they have offspring that will faint?

 In fruit flies, normal wings are dominant over vestigial wings. A purebred normal-winged male is mated with a vestigial- winged female. Show the results for the F1 and F2 generations. Include all work and ratios.

 Punnett Square Competition

 A left-handed woman, whose mother was right-handed, marries a right-handed man, whose father was left-handed. What are the genotypes and phenotypes possible for their future children? Show all work and ratios.

 In seals, long whiskers are dominant over short whiskers. Show the genotype and phenotypes possible for the offspring of two heterozygous seals. Include all work and ratios.

 In pea plants, tall stems are dominant over short stems. A short plant is crossed with a pure tall plant. Show the results for the F1 and F2 generations. Include all work and ratios.

 Normal skin pigment is dominant over the albino allele, which causes a lack of pigment in the skin. An albino man marries a normally-pigmented woman, whose mother was albino. What are the possible genotype and phenotypes for their future children. Include all work and ratios.

 In dogs, wire hair is dominant to smooth hair. A purebred wire-haired female is mated with a smooth-haired male. Show the results for the F1 and F2 generations. Include all work and ratios.

 Tongue rolling in humans is a dominant trait. A man, who cannot roll his tongue marries a woman who can roll her tongue. Their first child is not able to roll her tongue. What are the chances for the other possible future children as to whether or not they can roll their tongue? Show all work and genotype and phenotype ratios.