Genetics Objective: There is a genetic basis for the transfer of biological characteristics from one generation to the next through reproductive processes.

Genetics

Objective: There is a genetic basis for the transfer of biological characteristics from one generation to the next through reproductive

processes.

1/13 Genetics and Chromosomal Mutations

• O. All living organisms have genetic material that carries hereditary information.

• J. I can explain how DNA codes for proteins which are expressed as the heritable characteristics of an organism (explain transcription and translation, at least 5 sentences.)

TermsCharacteristic: heritable feature (plant height)Trait: variant of a characteristic (tall and short)

Gene: section of DNA that codes for a trait, they make up the chromosomeAllele: different forms of a gene ex. tall, short

Dominant allele: if it is present it will be expressed

Recessive allele: will not be expressed in the presence of the dominant alleleHomozygous: carrying two of the same alleles (TT, tt)

Heterozygous: carrying two different alleles (Tt)

Terms continuedGenotype: the actual genes an individual carries ex. Tt

Phenotype: the expression of those genes, tall

Parent generation (P) – the first cross

Filial (F1)– first son or offspring from the parent cross (F2) – offspring from the F1 generation

One-factor cross(monohybrid cross) – cross involving 1 character

Two-factor cross(dihybrid cross) – cross involving two characters

Gregor Mendel• Father of Genetics• Monitored 7 characteristics in pea plants for

many generations and picked up on patterns in the inheritance of these characteristics.

• Developed three laws that still hold true today

1. Law of Dominance2. Law of Segregation3. Law of Independent Assortment

Pea plants naturally self-pollinate. This means there were alltrue-breeding plants.

Mendel caused the plants to cross-pollinate in his experiments.He created hybrids.

Punnett Square

The method used to predict the outcome of the offspring from two organisms.

Basic steps in using the Punnett Square:1. Pick the letters for the alleles

dominant allele – capital letterrecessive allele - lowercase letter

2. Determine the Parents (P generation) genotypenote: each individual has two alleles/trait

3. Complete the Punnett Square4. Determine the genotypic ratio and phenotypic ratio

Practice: Cross a homozygous dominant tall plant with a homozygous recessive short plant. Determine the genotypic and phenotypic ratios in the offspring.

Tall - ______ Short - _____ Parent cross: ______ x _______

F1 cross:Cross the offspring of the last cross together and predict the genotypic and phenotypic ratios for the F2 generation.

ApplicationYou are using the Law of Dominance when you predict the

phenotype of an individual with a genotype of Tt.

You are representing the Law of Segregation when you separate the alleles in the formation of gametes in the Punnett square.

You are moving through the same steps that Mendel took in his discoveries. (a shortened version)

The Punnett square also represents what is going on in meiosis.

Let’s tie it all together….

Meiosis review…• One cell makes _______ daughter cells• Daughter cells are identical or nonidentical • Meiosis forms gametes which are ____ and

________ • There are ____ divisions in meiosis• If a diploid cell with 24 chromosomes divides

four haploid cells with ____ chromosomes are made

• Tetrads form in ____________ • Crossing-over occurs in ____________

Meiosis, segregation, gamete formation, fertilization – What elsecould you ask for in a Punnett square?

1/8 Genetics

• O. All living organisms have genetic material that carries hereditary information.

• J. If it is known that brown is dominant to gray coat color in mice, what do you know about the genotype of a mouse with gray coat color? Why?

Law of Independent Assortment

Mendel proved that chromosomes sort independently of one another. We can show this using the Punnett square and a two-factor cross. I can also show you using chromosomes.

• What happens if there is more than one gene?

• Does inheriting a certain gene for seed color affect the inheritance of another trait like plant height?

2 Factor Crosses

• Mendel performed experiment to follow two different genes as they passed from one generation to the next.

• These experiments are known as two factor (Dihybrid) crosses.

• Mendel crossed plants that were true-breeding for two different traits.– Round, yellow peas

• Genotype RRYY

– Wrinkled green peas• Genotype rryy

Which traits are dominant? Which traits are recessive?

RRYY X rryy

Why are there so many boxes?•Each parent can produce 4 different kinds of sex cells (gametes)

•Each gamete has an equal chance of combining with each of the other parents 4 types of gametes.

F2: Dihybrid Cross

• Each of the offspring in the example are hybrids for BOTH traits - Dihybrids

• Mendel crossed these offspring to produce another generation of plants (F2)

• If the genotype of each parent is RrYy, What kinds of gametes will each parent produce?

Gametes

• Parent 1: RrYy– _____ _____ _____ _____

• Parent 2: RrYy– ______ ______ _____ _____

RrYy x RrYy

Results

• The results of the F2 cross showed that the alleles for the two different traits segregated independently into the gametes.

• The offspring from this cross showed a 9:3:3:1 ratio of the different phenotypes.

Summary of Mendel’s Principles• Inherited traits are determined by genes.

Genes are passed from parents to offspring• Some forms of the gene may be dominant

and others may be recessive• The genes segregate during meiosis so only

one copy of a gene goes into the gamete• Alleles for different genes usually segregate

independently of one another.