Honors Biology Chapter 13 - Genetics

heredity

the passing on of characteristics from parents to their offspring

traits

consist of two genes: one from one parent, and one from the other parent

examples of traits

hair color, eye color, height

allele

refers to a single gene; either uppercase letters or lowercase letters

how many alleles are in one trait

2

dominant gene

represented by a capital letter

dominant trait

if a dominant gene is present, the dominant trait will be visible

examples of dominant traits

AA or Aa

recessive gene

represented by a lowercase letter

recessive trait

can only appear if both genes are recessive

example of a recessive trait

aa

homozygous trait (purebred)

a trait that contains two genes that are the same

examples of homozygous traits

AA or aa

heterozygous trait (hybrid)

a trait that contains two genes that are different

example of a heterozygous trait

Aa

phenotype

the visible characteristics the genotype produces

examples of phenotypes

brown hair, yellow flower, blue eyes

genotype

the actual allele combination

example of a genotype

BBHhggTTddFf

answer questions on the genotype to demonstrate understanding

Gregor Mendel

father of genetics; used pea plants

5 reasons why Gregor Mendel used pea plants for his experiments

they reproduce quickly, so you can study several generations in a short period of time; they are easy to grow and they mature fast; they have many contrasting traits; they are able to either self-pollinate or cross-pollinate; he was a gardener

7 traits that Mendel studied in pea plants

height - tall or short; flower color - purple or white; seed texture - wrinkled or smooth; seed color - green or yellow; flower position - axial or terminal; pod appearance - inflated or constricted; pod color - green or yellow

Mendel’s first experiment (the example here is the height of pea plants)

He grew plants that were pure for each trait; He crossed a pure tall plant with a pure short plant from the P1 generation; all of the offspring were tall; he called this his F1 generation

P1 Generation

the parent generation

F1 generation

the offspring of the P1 generation

Mendel’s second experiment (example: on height of pea plants)

He crossed two plants from the F1 generation; 3/4 of the offspring were tall and 1/4 of the offspring were short, which he called the F2 generation

F2 generation

the offspring of the F1 generation

what did Mendel call genes

factors or units

Mendel’s Laws

Law of Dominance; Law of Segregation; Law of Independent Assortment

Law of Dominance

if a dominant gene is present, the dominant trait will show; example: Aa

Law of Segregation

during gamete formation, gene pairs for every trait will separate; example: offspring will either get A or a

Law of Independent Assortment

during gamete formation, gene pairs separate independently from one another; example: Aa and Bb pairs separate separately to form AB, Ab, Ba, or ab

probability

the chance that something will or will not happen; a percent, a ratio, or a fraction

example of probability

probability of landing tails after flipping a coin is 50%, or 1/2 or 1:1

product rule

probability of more than one thing happening at the same time

example of product rule

probability that a gamete will receive both dominant traits is 25%, or 1/4, or 1:3

punnett squares

a way to determine the probability of the genotype and phenotype of the offspring

monohybrid cross

a cross that involves one trait; example: cross a heterozygous brown eyes with a homozygous blue eyes

draw a monohybrid cross (punnett squares) and determine the phenotype and genotype ratios

phenotype ratio

the number of offspring that have the same phenotype

genotype ratio

the number of offspring that have the same genotype

dihybrid cross

a cross that involves two different traits

two steps before creating a dihybrid cross

come up with the genotype of the parents; find all the possible combinations

practice using dihybrid crosses (punnett squares) and fine the genotype and phenotype ratios

incomplete dominance

a cross in which neither gene is dominant; monohybrid

practice using punnett squares with incomplete dominance