Genetics

Gregor Mendel: Father of Genetics Genetics: study of heredity Heredity: passing traits from parent to offspring Used peas to study heredity

Why Peas? 1. Several Traits 2. Control mating 3. Small, grow easily, and matures quickly

Alleles: Different versions of a gene Ex: White and Purple Flowers

Mendel’s Experiment Monohybrid Cross: One pair of contrasting traits.  Ex: Mating a plant with purple flowers with white flowers True-breeding: All offspring would have only one form of the trait  Ex: Purple-flowering plant only has purple- flowered offspring

Mendel’s Experiments

Vocabulary Dominant: Expressed in appearance (A) Recessive: Not noticeable in appearance (a) Homozygous: AA or aa Heterozygous: Aa

More Vocabulary Genotype: Genetic make up (ex: Pp) Phenotype: Appearance (ex: Purple flowers)

Laws of Heredity Law of Segregation  The two alleles for a trait separate when gametes are formed Law of Independent Assortment  Alleles of different genes separate independently of each other during meiosis

Law of Segregation Separation of alleles into separate gametes 50% chance that one allele will go into a gamete

Law of Independent Assortment

Punnett Square

Ratios

Test Cross

Dihybrid Cross: Cross that involve two traits

Incomplete Dominance and Codominance 17

Incomplete Dominance F1 hybrids in betweenphenotypes F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. Example:snapdragons (flower) Example: snapdragons (flower) red (RR) x white (rr) RR = red flower rr = white flower 18 R R rr

Incomplete Dominance 19RrRrRrRr R Rr All Rr = pink (heterozygous pink) produces the F 1 generation r

Incomplete Dominance 20

Codominance Two alleles are expressed (multiple alleles) in heterozygous individuals. Two alleles are expressed (multiple alleles) in heterozygous individuals. Example: blood type Example: blood type 1.type A= I A I A or I A i 1.type A= I A I A or I A i 2.type B= I B I B or I B i 2.type B= I B I B or I B i 3.type AB= I A I B 3.type AB= I A I B 4.type O= ii 4.type O= ii 21

Codominance Problem Example:homozygous male Type B (I B I B ) x heterozygous female Type A (I A i) 22 IAIBIAIB IBiIBi IAIBIAIB IBiIBi 1/2 = I A I B 1/2 = I B i IBIB IAIA i IBIB

Another Codominance Problem 23 Example:Example: male Type O (ii) x female type AB (I A I B ) IAiIAiIBiIBi IAiIAiIBiIBi 1/2 = I A i 1/2 = I B i i IAIA IBIB i

Sex-linked Traits Traits (genes) located on the sex chromosomes Traits (genes) located on the sex chromosomes Sex chromosomes are X and Y Sex chromosomes are X and Y XX genotype for females XX genotype for females XY genotype for males XY genotype for males Many sex-linked traits carried on X chromosome Many sex-linked traits carried on X chromosome 24

Sex-linked Traits 25 Sex Chromosomes XX chromosome - femaleXy chromosome - male fruit fly eye color Example: Eye color in fruit flies

Sex-linked Trait Problem Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) X R Y x X r X r Remember: the Y chromosome in males does not carry traits. RR = red eyed Rr = red eyed rr = white eyed XY = male XX = female 26 XRXR XrXr XrXr Y

Sex-linked Trait Solution: 27 X R X r X r Y X R X r X r Y 50% red eyed female 50% white eyed male XRXR XrXr XrXr Y

Female Carriers 28