Unit 6 Inheritance Part 1 Simple Mendelian Inheritance

Unit 6: Inheritance Part 1: Simple (Mendelian) Inheritance

Vocab review • • Homologous chromosome pair Sister chromatid Diploid, haploid Independent assortment Gamete Gene Allele

Gregor Mendel

Mendel's experiments • • Characters and traits Self-fertilization True-breeding Cross-fertilization (monohybrid cross)

Mendel's results: flower color P generation F 1 generation, hybrid F 2 generation genotype phenotype

Mendel's Results

What did Mendel’s findings mean? • Some traits mask others – purple & white flower colors are separate traits that do not blend • purple x white ≠ light purple • purple masked white – dominant allele • masks other alleles – recessive allele • no noticeable effect when inherited with the dominant allele I’ll speak for both of us! homologous chromosomes

Punnett squares male 1 st Pp x Pp female phenotype & genotype can have different ratios generation (hybrids) % genotype male / sperm female / eggs P p PP Pp P PP Pp pp % phenotype 25% 75% 50% Pp pp 25% 1: 2: 1 3: 1

Mendel's hypotheses • There alternate versions of genes (alleles) that result in variation in heritable characteristics. • For each character, an organism inherits two alleles (one from each parent). – Homozygous – Heterozygous • If the two alleles differ, one is dominant over the other (determines the organism's appearance). The other has no effect and is called recessive. – Complete dominance • A sperm or egg carries only one allele because alleles segregate (separate) from each other during gamete production – Law of Segregation – What phase of meiosis does this occur during?

PRACTICE! Monohybrid crosses Allele key Genotype key Packet p. 2 -3

Vocab Check • • P, F 1, F 2 generations dominant allele recessive allele genotype phenotype homozygous heterozygous complete dominance

Genotype mystery • Sir Snowy Penguini Shackleton is a three-time “Best in Show” winner at the Annual Antarctic International Penguin Show • His owner would like to capitalize on this success and breed Sir Snowy to make more orange-footed penguins. • The problem is that he doesn’t know Sir Snowy’s genotype. In show penguins, the dominant allele for foot color, O, results in orange feet, but the recessive allele, o, codes for green feet, which disqualifies a penguin from shows. • Sir Snowy will earn lots more money if his owner can prove that Sir Snowy’s offspring will have only orange feet. • Questions: – What genotype does Sir Snowy have to be to guarantee all orange-footed offspring? – How can his owner prove that Sir Snowy is that genotype?

Testcross example Sir Snowy's genotype could be OO or Oo. To know for sure, Sir Snowy will be bred with a female that has green extremities. O? oo X If the offspring all have orange feet, what genotype is Sir Snowy? o o O Oo Oo Gametes will include only a little o allele since the female is homozygous recessive. What if some offspring have o o green feet? 100% orange O o Oo Oo oo oo 50% orange 50% green

Testcross: genotype detective tool • Crossing an individual of unknown genotype with a homozygous recessive individual to determine the genotype.

Organisms have more than 1 trait! • After monohybrid crosses, Mendel looked at seed shape and color together. • Found that they were inherited separately (not dependent on each other). • This led to the Law of Independent Assortment.

Law of Independent Assortment RRYY x rryy Possible gametes: RY and ry Rr. Yy x Rr. Yy Possible gametes: RY r. Y Ry ry

PRACTICE! Dihybrid crosses

Using probability to solve genetic problems • Rule of multiplication: probability of 2 or more events both happening. – Each heterozygous parent will have half her/his gametes with B and half with b. – The probability of B from the mother combining with B from the father is ½ x ½ = ¼ – Multiply individual probabilities – What is the probability that the couple will have a girl with the genotype bb? – ½ x ¼ = 1/8

Using probability to solve genetic problems • Rule of addition: probability of an event happening via two different ways. – What is the probability that an offspring will be heterozygous if both of the parents are heterozygous? – Two combos of gametes will yield a heterozygote. – ¼+¼=½ • You will probably use this less frequently than the Rule of Multiplication (mostly for working with two heterozygous parents as in the above example).

Practice! Complete the problems on page 6 in your packet.

Practice On scrap paper In dragons, the allele for fire breathing (F) is dominant to the allele for non-fire breathing (f) and the allele for wings (W) is dominant to the allele for a wingless body (w). 1. If a homozygous dominant dragon mates with a homozygous recessive dragon, what will the genotype(s) and the phenotype(s) of the offspring be? Ff. Ww 2. If two of the offspring from the F 1 generation are crossed, what are the potential combinations of alleles in the gametes? FW, Fw, f. W, fw 3. Make a Punnett square to show the potential genotypes of the F 2 generation. 4. How many potential genotypes are there for the F 2 generation? 9 5. What is the ratio of possible phenotypes for the F 2 generation? 9: 3: 3: 1 (fire & wings: no fire & wings: fire & no wings: no fire & no wings)