B IOLOGY C HAPTER 8 Heredity

8.1 O BJECTIVES Discuss Mendel’s experiments and his results. Explain the three principles of genetics Mendel obtained through his experiments. Solve genetics problems using Punnett Squares.

8.1 P RINCIPLES OF G ENETICS Discuss Mendel’s experiments and results. Explain the three principles of genetics Mendel obtained through his experiments. Solve genetics problems using Punnett squares.

P RINCIPLES OF G ENETICS The passing of traits from parents to offspring is termed heredity. Can we predict certain traits? Can we determine what types of genetic information parents have by looking at certain traits of the offspring? We can answer these questions through genetics – the science of heredity.

O RIGIN OF G ENETICS Father of genetics: Gregor Mendel ( ) Tended to a garden of pea plants in a monastery. Published results from 8 years of research, only to be ignored until 1900.

M ENDEL ’ S E XPERIMENTS Peas are grown easily and produce large numbers of offspring in a short time. Chose 7 traits to study: Seed Shape Seed Colo r Flowe r Color Flower Position Pod Color Pod Shape Plant Heigh t Dominant Trait RoundYello w PurpleAxial (side)GreenInflatedLong Recessive Trait WrinkledGreenWhiteTerminal (tips) YellowConstrictedShort

M ENDEL ’ S P ROCESS Mendel crossed pea plants w/ different traits. Offspring of parental cross were called F 1 Offspring of F 1 crosses called F 2. He noted for each trait, there was a dominant and recessive form. In his crosses, recessive trait disappeared in F 1 generation and then reappeared in F 2.

M ENDEL ’ S H YPOTHESIS He reasoned that for every trait, there must be a pair of factors. He called them characters, but we now know them as genes. One gene came from each parent.

P UNNETT S QUARES

T HE T EST OF S EGREGATION He predicted if the F1 purple flowered plants were crossed with white flowered plants, he would get ratios different from any of his previously obtained ratios.

T ERMINOLOGY Each alternative form of a gene for a certain trait are called alleles. Combination of genes for a given trait referred to as genotype. Example: WW and Ww The physical appearance of a trait is the phenotype. Example: Blue and brown eyes. Homozygous = two of same alleles: WW or ww (homozygous dominant and homozygous recessive) Heterozygous = two different alleles: Ww

T WO T RAITS (D IHYBRID C ROSSES )

8.2 S OLVING G ENETICS P ROBLEMS Objectives: Apply the rules of probability to solve genetics problems. Demonstrate the inheritance of traits resulting from incomplete dominance, codominance, and multiple alleles.

P ROBABILITY What is the probability of getting heads or tails when you toss a coin? There is a list of steps to follow on page 208 in text, but we have already been doing this. Remember, we can find either genotypic or phenotypic ratios.

I NCOMPLETE D OMINANCE : 4 O ’ CLOCK PLANTS AS AN EXAMPLE

M ULTIPLE A LLELES : H UMAN B LOOD T YPES

8.3 T HE C HROMOSOME T HEORY OF H EREDITY Walter Sutton’s work showed good evidence that genes reside on chromosomes. Some genes appear only on sex chromosomes. XX = female and XY = male in humans. Different combinations for different species. Example: Grasshoppers X = male and YY = female. Sex-linked traits are traits that result from genes on the sex chromosomes.

S EX -L INKED T RAITS IN H UMANS Hemophilia – gene is a recessive gene found on the X chromosome. Mostly, males get the disease. Color-blindness is the same way.

M ANY G ENES – O NE E FFECT Height, hair, eye, and skin color all controlled by multiple alleles. Sample genotypes: AABBCCDD AaBbCcDd Aabbccdd Modifier genes can also impact things like eye color. Brown, blue, hazel, green, mixed etc.