What is the point of meiosis and sexual reproduction?

Agenda for Jan 22nd 1.Go over test2.Punnett Squares

Heredity

• What is heredity? – The passing on of characteristics from parents to

offspring

• Genetics is the branch of biology that studies heredity – characteristics that are inherited are traits

• Mendel was the first to succeed in predicting how traits would be transferred from one generation to the next

Mendel• Father of genetics• Loved nature• Austrian monk

– taught natural science – worked on plant breeding experiments using pea

plants

• Developed basic understanding of genetics and inheritance

Mendel’s Work• Used pea plant• He collected data for 10 years• Large sample sizes;

– Results from 28,000 pea plants

• Published work but was dismissed– Found later

Mendel’s Experiment

• P Generation – parent generation• F1 generation – first filial generation, offspring

of parents• F2 generation – second filial generation,

offspring of F1 generation

Grandparents Parents You

Collected 6022 yellow and 2001 green3:1 ratio

Mendel’s ResultsP1 F1 F2 F2 ratio

smooth X wrinkled seeds

all smooth 5474 smooth1850 wrinkled

2.96:1

yellow X green seeds

all yellow 6022 yellow2001 green

3.01:1

axial X terminal flowers

all axial 651 axial207 terminal

3.14:1

red X white flowers

all red 705 red224 white

3.15:1

inflated X constricted pods

all inflated 882 inflated299 constricted

2.95:1

green X yellow pods

all green 428 green152 yellow

2.82:1

tall X dwarf plants

all tall 787 tall277 dwarf

2.84:1

3:1 ratio

Conclusions1. Inheritance of traits are determined by "units" or

"factors" that are passed on to offspring– called genes– Different forms of a gene are alleles

2. For each trait, an individual inherits one gene from each parent

3. A trait may not show up in an individual but can still be passed on

Allele for purple flowers

Locus for flower-color geneHomologouspair ofchromosomes

Allele for white flowers

Rule of Dominance

• The trait that is observed in the F1 offspring is the dominant trait (uppercase)

• The trait that disappears in the offspring is the recessive trait (lowercase)

Law of Segregation

• The two alleles for a trait must separate when gametes are formed – A parent randomly passes

only one allele for each trait to each offspring

Law of Independent Assortment• Random distribution of alleles during meiosis

Dominant and Recessive Genes•Gene that prevents the other gene from “showing” – dominant

•Gene that does NOT “show” even though it is present – recessive

•Symbol – Dominant gene – upper case letter – T Recessive gene – lower case letter – t

Dominant color

Recessive color

Dominant and Recessive

• Capital letters= dominant alleles • Lower case letters = recessive alleles

• Two alleles for each trait

Which is better, dominant or recessive?

Homozygous (pure bred)

Organism with two of the same allele

HH hhHomozygous dominant Homozygous recessive

Heterozygous (hybrid)

Organism with two different alleles

Hh Rr

Dominant trait observed (notice the dominant allele)

Genotype

Allele makeup of an individual

Tt T T tt

RR Rr rr

PhenotypeObservable characteristics of an individual

Flashcards

• Phenotype• Genotype• Heterozygous• Homozygous• Allele• Diploid• Haploid

Predicting traits• Monohybrid Crosses Provide information about one pair of

contrasting traits.

Parent’s Genotype

Parent’s Genotype

Law of Segregation

• Mechanism of gene transmissionFertilization:alleles unite

Gametogenesis:alleles segregate

Parent’s 1 Genotype = Aa Gametes =

Parent’s 2 Genotype = AAGametes =

Ratios:Genotypes: Homozygous dominant:Hetergozygous:Homozygous recessive

AA:Aa:aa

Phenotypes:Dominant:recessiveTall:short

Define the following:Dominant, recessive, homozygous,

heterozygous.

Agenda for Friday Jan 23rd 1.Review2.Punnett Square practice

PracticeA Tt (tall) plant is crossed with a Tt (tall plant).1. What are the gametes formed by each parent?2. What is the genotypic ratio?

A green pea sead (gg) is crossed with a hybrid yellow seed (Gg). What will be the genotypic and phenotypic ratios of the offspring?

A heterozygous plant (Tt) is crossed with short (tt) plant.

What percentage of the offspring will be tall?What percentage of the offspring will be short?

In guinea pigs, rough coats are dominant over smooth coats. An Rr guinea pig is crossed with an Rr guinea pig. What are the chances of each genotype and phenotype? Agenda for Tuesday April 15th 1.Punnett Square practice

The punnett square shows the offspring of two parents. What are the genotypes of the parents?

Agenda for Thursday April 17th 1. Compare ratio labQUIZ WEDNESDAY

Rr Rr

rr rr

In pea plants, round (R) is dominant to wrinkled (r). A heterozygous female is crossed with a wrinkled male. What is the probability (percent) of having an offspring that is round?

Agenda for Tuesday April 22nd 1.Dihybrid crossesQuiz tomorrow

Polyploidy• Most cells are Diploid (2n)• Some are polyploid

– One or more extra sets of chromosomes

– Triploid – 3n• Rarely occurs in animals • Mostly plants– Roughly 1 in 3 plants are polyploidy

• Increased vigor and size

Types of genetic crosses• Monohybrid

– Mono = 1– Cross looking at 1 trait

• Dihybrid– Di = 2– Cross looking at 2 traits– Traits are not linked (do not affect each other)– For example: round vs. wrinkled seeds and yellow vs.

green seeds

Dihybrid CrossMaking gametes• Independent assortment – each allele distributes

randomly with the other **more combinations than with a monohybrid

RrYy

Round (R) is dominant to wrinkledYellow (Y) is dominant to greenCross a RRYy with a Rryy

What would the gametes look like for a RrYy genotype?

Agenda for Wednesday April 23rd 1. TEST

Genetic Recombination

• New combination of genes produced by crossing over and independent assortment

Why is genetic recombination important?

Gene Linkage

• Genes on same chromosomes are said to be linked– Travel together during Meiosis

• Not always true – crossing over occurs

• Genes further apart cross over more frequently– Make chromosome maps based on that info.

Chromosome Map

• Map genes A, B, C, D– AB=3 AC=1– AD=4 BC=2– BD=7 CD=5

• Map genes A, B, C, D– AD = 25 AB = 30– CD = 15 BD = 5– BC = 20