WHAT IS GENETICS? • GENETICS is the study of how traits are passed from parent to offspring in the form of Genes.
HISTORY!Gregor Mendel • Born 1822 • Austrian Monk • Examined reproduction of pea plants
Plants reproductive organs are called FLOWERS • A flower has both male and female parts. • The pea plants Mendel was working with were typically TRUE-BREEDING, meaning they self-pollinated • EX, TALL pea plants would always be pollinated by tall pea plants and produce tall offspring!
WHAT WE KNOW (MENDEL DIDN’T) Genes– control a heritable feature (characteristic); Example: Hair color, seed shape, height; Allele – controls the variation of a feature (trait). Example: brown, blonde, black hair
Homologous chromosomes may…… • Both have the same alleles HOMOZYGOUS (aka: pure or true-breeding) • Both have different alleles HETEROZYGOUS (aka: hybrid)
Mendel’s Idea • Cross two pea plants with different contrasting traits! • Ex: • First cross : Crossed true breeding purple with true-breeding white plants. • Called offspring F1 Generation • Results were that offspring were_100% PURPLE_ • Had the white allele disappeared????
Mendel’s Law of Dominance • some alleles over power others. So even if both alleles are present, we only “see” the dominant one. • the “hidden” allele is called recessive • This only applies to SOME genes, not all
Second cross two of the purple F1 Offspring Called offspring the F2 Generation Results • 75 % purple • 25 % were white • White trait had reappeared!
Mendel’s Law of Segregation • during meiosis, the pair of alleles in a parent will separate. • Only ONE allele for EACH TRAIT will pass from each parent to the offspring
Ex. sugar beet preference. • dominant allele (A) prefers sugar beets • recessive allele (a) does not. • Heterozygote produces gametes • 50% chance • Get A • Get a Question: If a heterozygous sugar beet eater marries a non-sugar beet eater, what possible offspring could they have?
Mendel’s Law of Independent Assortment • Alleles for different genes are passed to offspring independently of each other. • The result is that new combinations of genes present in neither parent is possible. • How many allele combinations could the following genotype produce? • RRYY • RRYy • RrYy
Genetic Terms • Diploid (2n)- Two sets of chromosomes. • Somatic Cells • Haploid (n)- One set of homologous Chromosomes • (gametes) • Egg- Female haploid gamete • Sperm- male haploid gamete
Parent – Seriously, you should know this Meiosis – Cell division that produces haploid gametes Testes – Site of male meiosis Gamete – Haploid sex cell (sperm, egg, pollen)
Zygote- Single cell (result of sperm and egg) Progeny - Offspring Offspring – see above Fertilization – gametes fuse into zygote Ovary- site of female meiosis - eggs
Genotype: the alleles that an organism has. • alleles are abbreviated using the first letter of the dominant trait. • capital letter represents the dominant • ex: P for purple flower allele • lower case represents the recessive. • ex: p for white flower allele
All diploid organisms have two alleles for each trait: • Can be two of the same allelesEx: PP or pp called Pure or Homozygous. OR • Can be two different alleles • Ex: Ppdescribed as Hybrid or Heterozygous
Phenotype: physical appearance • Examples: brown hair, widows peak, purple flowers • the trait that “wins” in the case of complete dominance; • depends on the combination of alleles GENOTYPE
MENDEL’S CROSSES • P Generation: “parents;” • F1 Generation offspring of P generation • F2 Generation offspring of F1 generation Punnet Squares How we show allele combinations in crosses
Allele in Egg 2 Allele in Egg 1 Zygote formed if sperm 1 fertilizes egg 1 Zygote formed if sperm 1 fertilizes egg 2 Allele in sperm 1 Allele in sperm 2 Zygote formed if sperm 2 fertilizes egg 1 Zygote formed if sperm 2 fertilizes egg 2
Monohybrid CrossTall vs. Short Example • Tall allele T Short allele t • P Cross TT x tt • F1 Generation • Genotypes • Phenotypes T T t t
F2 Generation F1 Generations 100% Tt Tt x Tt F2 Generation Genotypes- Ratio = Phenotypes- Ratio = T t T t
Sample Problems • Homozygous Tall x Heterozygous Tall • Heterozygous Tall x Homozygous Short
Probability • Probability is only the LIKELIHOOD of an event happening. • It does not mean it is what HAS to happen • Ex. Coin Toss. Two tosses, always one heads and one tails? • What happens when we look at very large samples? • Ex. Male/female ratio of a family vs. the world!
INHERITENCE PATTERNS • Every gene demonstrates a distinct phenotype when both alleles are combined (the heterozygote) • Complete dominance is when both alleles are present, only the dominant trait is seen. • Incomplete dominance - when both alleles are present, the two traits blend together and create an intermediate trait
Inheritance Patterns: Co-dominance - when both alleles are present, both traits are visible Different notation: Use first letter of the feature with a superscript for the trait. Example: CW or CR for white petals or red petals;
Women have two X’s but men only have one. How do we deal with the genes on the X chromosome?
Probabilities • Question 1: What is the probability of having a female offspring? • Question 2: After having 4 sons in a row, what is the probability the next kid will be male? • Question 3: What is the probability of having three daughters in a row?
Sex-Linked Traits • Refers to traits coded by genes found on the X chromosome • Females will have 2 copies of these genes • Males will have 1 copy of these genes • Significance??? • If males get a bad (recessive) allele for a sex-linked trait, THEY WILL EXPRESS THE RECESSIVE TRAIT!
Example – Color Blindness • Seeing color (XC) is dominant to being color blind (Xc) • Identify the sex and trait of the following: • XCY XCXc XCXC • XcXc XcY
XC XC XC Xc Xc Y XC Y Cross Number 1: What % chance of having color blind daughter? Son? XC Xc XC Y
SEX-LINKED TRAITS COLOR BLINDNESS AFFLICTS 8% MALES AND 0.04% FEMALES.
Test cross: a cross that determines genotype of dominant parent - Cross unknown dominant parent (possibilities BB or BB) with a recessive parent then analyze the offspring. Ex. B- Black Hair b- white hair You are given a black-haired guinea pig and need to determine whether homozygous dominant or heterozygous.
Multiple Alleles • Genes may have more than two alleles.
Multiple alleles: Some genes have more than two variations that exist, although we still only inherit 2 Example: Human blood types Three alleles: IA IB i
Polygenic – • Multiple genes code for a trait each with 2 alleles • Examples in humans: • Skin Color • Eye Color • Height • Why so many possibilities??? SKIN PIGMENTATION
Dihybrid cross: A cross that focuses on possibilities of inheriting two traits - two genes, 4 alleles Black fur is dominant to brown fur Short fur is dominant to long fur What is the genotype of a guinea pig that is heterozygous for both black and short fur?
Dihybrid cross: Parent phenotypes: BbSs x BbSs Figure out the possible gametes: Then set up punnett square