GENETICS!

GREGORY MENDEL

Born 1822; Died 1884 Monk and a teacher Work not recognized

until 1900 Studied heredity by

studying pea plants What is heredity?

MENDEL’S PEA PLANTS Observed seven

characteristics of pea plants with two different traits

Controlled how each plant was pollinated Self-pollination or

cross-pollination What’s the

difference?

MENDEL’S EXPERIMENTS

Grew true-breeding plants What does it mean to be true breeding?

Starting strain called parent generation or P generation

Cross-pollinated P generation to produce offspring called the first filial generation or F1 generation

F1 generation self-pollinated and produce the second filial generation or F2 generation

xP generation

xP generation

F1

generation

All of the F1 showed one color

x

F2 produced plants about ¾ one trait and ¼ the other trait

P generation

F1

generation

F2

generation

RESULTS Factor was controlling the traits since there were two

traits there were two factors Alleles: represent the factors - dominant CAPITAL

LETTERS; recessive lower case letters; They are alternate forms of genes.

Dominant trait: Able to repress the other trait Recessive trait: repressed by the dominant Homozygous: same alleles; RR or rr – also called

purebred or true breeding Heterozygous: one of each allele forming a hybrid Rr Genotype: allele pairs/actual DNA: RR, Rr, or rr Phenotype: physical appearance; red, yellow, green,

tall, short, etc. *You only see the recessive phenotype when there are two of the recessive alleles. Whenever you see the dominant phenotype, you cannot tell the genotype.*

Lead to the modern study of molecular genetics, the study of chromosomes and genes.

Y

y

LAWS OF GENETICS Law of Segregation: a

pair of factors is segregated or separated during the formation of gametes (i.e. the homologous chromosomes are separated during anaphase I of meiosis I into different gametes.)

Law of Independent Assortment: factors for different characteristics are distributed to gametes independently – factor for different traits do not follow each other into the same gamete

PROBABILITY

Probability that a specific event will occur; expressed as a decimal, fraction, or percent

Probability = Number of times an event happened

Number of possible opportunities The predicted results are more likely to occur the

more trials that are performed

MONOHYBRID CROSSES

Monohybrid cross: between individuals with one pair of contrasting traits ( mono = one)

Punnett squares are used to help predict the probability of a trait

HOMOZYGOUS X HOMOZYGOUS

Crossing two plants homozygous for color (P)

One dominant one recessive

PP x pp Genotype

4 Pp Phenotype

4 purple

HOMOZYGOUS X HETEROZYGOUS

Crossing a homozygous dominant with a heterozygous plant for color (P)

PP x Pp Genotype

2 PP 2 Pp

Phenotype 4 purple

HOMOZYGOUS X HETEROZYGOUS

Crossing a heterozygous plant with a homozygous recessive for color (P)

Pp x pp Genotype

2 Pp 2 pp

Phenotype 2 purple 2 white

HETEROZYGOUS X HETEROZYGOUS

Both heterozygous for color (P)

Pp x Pp Genotype

1 PP 2 Pp 1 pp

Phenotype 3 purple 1 white

TESTCROSS

Used to determine the genotype of a individual with an unknown genotype

Must use an organism of an known genotype hence use a homozygous recessive