Genes, traits, and this guy named Mendel

Genes, traits, and this guy named Mendel Biology Mr. D

Meiosis • Before meiosis begins, the cell has __ chromosomes or two sets of __ • 46 chromosomes • 2 sets of 23 • So, let us take for example, chromosome 5 codes for hair color • How many copies of chromosome 5 do we have? • 2

Meiosis • Where did we get each chromosome? • One from our mom • One from our dad • Let’s pretend Chromosome 5 has the gene for hair color • Let’s say that your mom blonde hair and your dad has brown hair • If I tell you that allele means different form of a gene, how many forms of hair color could you have? • 2

Genes • Let’s say your dad’s side of the family all have brown hair. • Also, let’s say that all your mom’s side has blonde hair. • Therefore, your parent’s hair color is purebred (only one color ever appears in their family) • What will the hair color be when they have a child? • The child ends up with brown hair. So, which allele (different form of a gene) is dominant? • Which is recessive?

Genes • Now we know which allele for hair color is dominant (brown) and which is recessive (blonde). • Dominantalleles are capital letters like “H” • Recessivealleles are small letters like “h” • How many forms of a gene do we have for each trait (ex. hair color)? • What are some possible combinations?

Different combinations • Homozygous • genotype of identical alleles, ex. HH or hh • Heterozygous • genotype of different alleles, ex. Hh • So, how can we figure out the traits passed on to each generation (heredity)? • Now we can talk about Punnett squares

Gregor Mendel • Monastery of St. Thomas, Brno, Czech Republic. • Taught physics and natural science. • Performed experiments 1856-1868, published in 1866. • Used pea plants

How Mendel performed his crosses with pea plants

Fig. 8.5

Gregor Mendel • “I like to pea…I mean I like pea plants” • Why peas? • Easy to grow • Self-fertilize or can hybridize artificially • Matures quickly • Contrasting traits are easy to see

Mendel’s Laws • Law of dominance • Some alleles (variation) are dominant over other alleles • Law of segregation • Each gamete gets one copy of the gene • Law of independent assortment • Each trait separates independently during formation of gametes

Mendel’s 7 traits 1. 2. 3. 4. 5. 6. 7.

Probability • Sometimes we want to know how often something will occur • What is the chance of getting tails when you flip a coin? • How about 2 tails in a row? • For example

Probability and punnett squares • Punnett squares can help us determine genetic crosses

Punnett square • Predicts possible offsprings • Capital letter = dominant allele (ex. “H”) • Lower case letter = recessive allele (ex. “h”) • Same letter used for dominant/recessive • HH, not HM, HL and so on • Expressed traits called phenotype • What you see/observe • Genetic makeup =genotype • The type of alleles

O.J. Simpson capital murder case,1/95-9/95 • Odds of blood in Ford Bronco not being R. Goldman’s: • 6.5 billion to 1 • Odds of blood on socks in bedroom not being N. Brown-Simpson’s: • 8.5 billion to 1 • Odds of blood on glove not being from R. Goldman, N. Brown-Simpson, and O.J. Simpson: • 21.5 billion to 1 • Number of people on planet earth: • 6.1 billion • Odds of being struck by lightning in the U.S.: • 2.8 million to 1 • Odds of winning the Illinois Big Game lottery: • 76 million to 1 • Odds of getting killed driving to the gas station to buy a lottery ticket • 4.5 million to 1 • Odds of seeing 3 albino deer at the same time: • 85 million to 1 • Odds of having quintuplets: • 85 million to 1 • Odds of being struck by a meteorite: • 10 trillion to 1

This is a simple Punnett square. It looks like a window pane You put the alleles on the outside P1 and F1 generations It helps us figure out what offspring we get H H h h Punnett Square

Cross the following • Count the number of genotypes and phenotypes • HH x hh • HH x Hh • Hh x Hh • Rr x Rr • Cross a heterozygous brown haired male with a homozygous recessive blonde female

Genes, traits, and this guy named Mendel