Genetics

Biology I Factoids

Factoid 124

• Section 9

• Gregor Mendel was an Austrian monk who is known as the father of genetics due to his work with garden peas. Since he was into math, he wanted to know if there was a way to calculate the offspring’s traits.

Factoid 125

• Mendel proved that if you cross a tall plant with a short plant, all of the offspring would be tall. Then if you crossed those tall plants, 75% of them would be tall and 25% would be short.

Factoid 126

• A gene carries encoded information about specific traits. Each gene has a location on a chromosome called a “locus.”

Factoid 127

• Alleles are various molecular forms of a gene for the same trait. An allele usually refers to a single letter, “T” for example.

Factoid 128

• Homozygous = Same letters; AA or aa for example.

• Heterozygous – Different capitalization; Aa for example

Factoid 129

• Homozygous dominant = AA

• Homozygous recessive = aa

• Heterozygous = Aa

Factoid 130

• Genotype is the sum of the genes (letters)

• Phenotype is how the genes are expressed (words/descriptions)

Factoid 131

• Mendel’s Law of Dominance

• Some traits are dominant and others are recessive.

Factoid 132

• A Punnett Square is a diagram used to predict the outcome of a cross between individuals.

Factoid 133

• Mendel’s Law of Segregation

• Half of your traits come from one parent and the other half come from the other parent.

Factoid 134

• In rabbits brown fur is dominant to white fur. Predict the outcome between a homozygous dominant brown rabbit and a white one.

• In flowers, red is dominant to white. Predict the outcome between a heterozygous flower and a homozygous dominant flower.

Factoid 135• In bears, long fur is dominant to short fur.

Predict the outcome between a short furred bear and one that is heterozygous.

• In some plants, tall is dominant to short. Predict the outcome between two heterozygous tall plants.

Factoid 136

• An organism is heterozygous or homozygous dominant they look identical. To determine which is which, you perform a test cross.

Factoid 137

• If you cross your unknown (either heterozygous or homozygous dominant) with homozygous recessive and ANY ONE of the offspring is recessive, then your unknown organism is heterozygous.

Factoid 138

• A monohybrid cross involved only 1 trait at a time. A dihybrid cross involves 2 traits.

Factiod 139

• Mendel’s Law of Independent Assortment

• Traits are not linked to one another and you have and equal chance of getting each gene independently of the others.

Factoid 140

• A dihybrid cross between two heterozygous organisms for two contrasting traits results in a 9:3:3:1 ratio.

Factoid 141

• In some species of plants, red flowers are dominant to white flowers and tall plants are dominant to short plants. Predict the outcome between 2 heterozygous organisms.

Factoid 142

• In incomplete dominance, the heterozygous results in a blending of the traits.

• RR = Red

• WW = White

• RW = Pink

Factoid 143

• In codominance the traits don’t blend but both show up. The heterozygous results in spotted or speckled off spring.

• FBFB = Black feathers

• FWFW = White feathers

• FBFW = Speckled feathers

Factoid 144

• Where there are more than 2 alternative forms of a trait, it is said to have multiple alleles.

Factoid 145

• Blood type is a common example of multiple alleles.

• Type A = IAIA or IAi

• Type B = IBIB or IBi

• Type AB = IAIB

• Type O = ii

Factoid 146

• Some traits actually ARE linked by sex. These include baldness, color blindness, and hemophilia.

Factoid 147

• Males are represented by XY. The X from the mother and the Y from the father. Sperm can carry either an X OR a Y chromosome.

• Females are represented by XX. They inherit and X from both parents. All eggs carry an X chromosome.

Factoid 148

• XAXA – Normal female

• XAXa – Normal female (but a carrier)

• XaXa – Affected female

• XAY – Normal male

• XaY = Affected male

Factoid 149

• A pedigree shows the history of a trait in a family.

Factoid 150• Circles represent females.

• Squares represent males

• Horizontal lines represents a mating

• Vertical lines represent an offspring

• A triangle represents an abortion of miscarriage.

• A diamond indicates unknown sex.

• Shaded in means affected

• A diagonal lines means dead.

Factoid 151

• All pedigrees must have a title, each generation must be numbered with a roman numeral, and each member must be numbered.