Genetics

Terminology Allele – contrasting form of a gene –Ex: T = tall; t = short –Ex: G = green; g = yellow –CAPITAL LETTERS – DOMINANT TRAIT –lowercase letters – recessive trait

More Terms Genotype –Genetic makeup of an organism Phenotype –Physical appearance

More Terms Homozygous Alleles – when the alleles of a pair are the same –Ex: GG, TT, rr, nn Heterozygous Alleles –when the alleles are not the same –Ex: Gg, Tt, Rr, Nn

Probability The likelihood that a specific event will occur Probability = # of one kind of event # of all events

Coin Toss Probability of a coin landing heads up? The more times you flip the coin, the closer to 50% the probability will get

Punnett Squares Device used in predicting possible offspring

Monohybrid Cross A cross that involves only one trait with two phenotypes Ex: Seed color – GG x gg; – G = green, g = yellow

Making a Punnett Square Draw a box Put one set of traits on top –Male parent Put the other on the side –Female parent

Parent Generation: P 1 GG x gg G G g g Gg

Cross F 1 Generation Gg x Gg Genotype? Phenotype?

Parent Generation: F 1 Gg x Gg G g g G GG Gg gg

Results Genotypes – 25% GG – 25% gg – 50% Gg Phenotypes – 75% green – 25% yellow GG Gg gg G G g g

You Try TT x Tt (T = tall; t = short)

T T t T TT Tt TT Genotypes – 50% TT – 50% Tt – 1:1 Phenotypes – 100% tall

Bb x bb (B = black; b = white) You Try

Bb x bb (B = black; b = white) Genotypes – 50% Bb – 50% bb – 1:1 Phenotypes – 50% black – 50% white –1:1 B Bb b b b bb Bb

A cross between a homozygous recessive individual and an unknown Used to determine whether an individual is homozygous dominant or heterozygous Testcross

Mendel developed what is known as a test cross. He took a homozygous recessive individual and mated it with a pea plant showing the dominant trait. bb xBb or BB

Testcross If in the F1 generation all the offspring showed the dominant trait, then the dominant parent was probably BB. b b B B ? Bb

Testcross If there were any recessives in the F1, then the dominant parent had to be Bb. b b B b ? Bb bb

What if we are looking at two traits at a time?

What if we are looking at Tall plants with Axial flowers (TTAA) and cross it with a short plant with terminal flowers (ttaa)?

T If we look at meiosis what does that tell us? T A AT T A A Parent TTAA

Parent TTAA can only pass on the alleles TA to the offspring What about Parent ttaa? Can only pass on the alleles ta to the offspring

TA taTtAa Parents: TTAA x ttaa Parent TTAA produces only one kind of gamete. Parent ttaa produces only one kind of gamete. Thus our punnett square is very simple.

What about the F 1 generation? T t a t A t T T a A A aParent TtAa

TA ta tA Ta TA Ta tA ta TTAA ttaa TTAa Ttaa TtAA TtAa ttAa TtAaTTaa ttAa TtAA TtAa Ttaa ttAA F 1 generation: TtAa x TtAa TA

A cross with two traits Ex: seed color & seed shape –R = round, r = wrinkled; Y = yellow, y = green –RRYY x rryy –YYRr x yyRR Dihybrid Cross

You try RRYY x rryy R = round, r = wrinkled; Y = yellow, y = green Dihybrid Cross

Parents: RRYY x rryy RrYy RY ry All offspring will be heterozygous

You try F 1 generation: RrYy x RrYy R = round, r = wrinkled; Y = yellow, y = green Dihybrid Cross

F1 generation RrYy x RrYy

Phenotypes –Round: Yellow –Round: Green –Wrinkled: Yellow –Wrinkled: Green – 9:3:3:1 ratio F1 generation: RrYy x RrYy

Sex-linked Genes Genes carried on the X and Y chromosomes are called sex-linked genes. Traits that are controlled by these genes occur more often in one sex than the other. Can you explain why?

Colorblindness is one example of a trait controlled by sex-linked genes. Sex-linked Genes

Color blindness The normal human retina's color receptors are tuned to green, blue, and red. Working together, the three give us our colorful view of the world. When one or more of those color receptors is missing the result is color-blindness. The genes for our red and green color receptors are located on the X-chromosome, giving women a redundant set of receptor genes. This is why men are far more prone to color- blindness than women.

X C Y x XX Sex-linked Genes Recessive gene for color blindness

Sex-linked Genes XCXC Y X X XCXXCX XCXXCX XY