Genetics UnitGenetics Unit

Genetics = the field of biology Genetics = the field of biology devoted to understanding devoted to understanding how characteristics are how characteristics are transmitted from parents to transmitted from parents to offspringoffspring

Heredity = the transmission Heredity = the transmission of characteristics from of characteristics from parents to offspringparents to offspring

MendelMendel- “father” of modern genetics - “father” of modern genetics

= laid the groundwork= laid the groundwork

- experimented with garden - experimented with garden peaspeas

- looked for traits = - looked for traits = specific specific characteristicscharacteristics

MendelMendel (cont) (cont)- P- P11 generation = parental generation = parental

generationgeneration

- F- F11 generation = offspring of generation = offspring of the parental generationthe parental generation

- F- F22 generation = offspring of generation = offspring of the Fthe F11 generation generation

MendelMendel (cont) (cont)Mendel’s 1st Law = Law of Mendel’s 1st Law = Law of

SegregationSegregation

1) Organisms inherit two copies 1) Organisms inherit two copies of each gene, one from each of each gene, one from each parentparent

2) Organisms donate one copy of 2) Organisms donate one copy of each gene in their gametes.each gene in their gametes.

MendelMendel (cont) (cont)Mendel’s 2nd Law = Law of Mendel’s 2nd Law = Law of

Independent AssortmentIndependent Assortment

1) The presence of one trait does 1) The presence of one trait does not affect the appearance of not affect the appearance of another trait another trait

Basics of GeneticsBasics of Genetics- Gene = a segment of DNA on a - Gene = a segment of DNA on a

chromosome that controls a chromosome that controls a specific traitspecific trait

- because chromosomes come - because chromosomes come in pairs, genes come in pairsin pairs, genes come in pairs

Basics of GeneticsBasics of Genetics (cont) (cont)- Allele = each of several forms - Allele = each of several forms

of a gene of a gene - aka: letters- aka: letters

- each allele has a specific - each allele has a specific location on a chromosome (= location on a chromosome (= locus)locus)- capital letters = dominant - capital letters = dominant alleles - lowercase letters = alleles - lowercase letters = recessive allelesrecessive alleles

Basics of GeneticsBasics of Genetics (cont) (cont)- Homozygous = both alleles are - Homozygous = both alleles are

alikealike

- homozygous dominant = both - homozygous dominant = both capital letters = BBcapital letters = BB

- homozygous recessive = both - homozygous recessive = both lowercase letters = bblowercase letters = bb

- Heterozygous = alleles are - Heterozygous = alleles are different = Bbdifferent = Bb

PolydactylPolydactylyy

Polydactyly is Polydactyly is the condition of the condition of having more having more than the typical than the typical number of number of fingers or toes. fingers or toes. The allele for The allele for polydactyly is polydactyly is dominant.dominant.

Basics of GeneticsBasics of Genetics (cont) (cont)

- Genotype = genetic makeup of - Genotype = genetic makeup of an organisman organism

- consists of alleles (letters)- consists of alleles (letters)

- Phenotype = the appearance of - Phenotype = the appearance of an organism as a result of its an organism as a result of its genotypegenotype

- aka: what does it look like- aka: what does it look like

- human phenotype can be - human phenotype can be altered by behavioraltered by behavior

Monohybrid Crosses

= a cross between individuals that involves one pair of traits

- Example: Black hair (B) in guinea pigs is dominant to brown hair (b)

Example 1:Homozygous Dominant X Homozygous Dominant

Genotypic Ratio

Phenotypic Ratio

Example 2:Homozygous Recessive X Homozygous Recessive

Genotypic Ratio

Phenotypic Ratio

Example 3:Homozygous Dominant X Heterozygous

Genotypic Ratio

Phenotypic Ratio

Example 4:Homozygous Recessive X Heterozygous

Genotypic Ratio

Phenotypic Ratio

Example 5:Heterozygous X Heterozygous

Genotypic Ratio

Phenotypic Ratio

Testcross

= an individual of unknown genotype is crossed with a homozygous recessive individual

- can be used to determine the genotype of any phenotype that is dominant

Example 6: Testcross

Genotypic Ratio

Phenotypic Ratio

Example 6: Testcross

Genotypic Ratio

Phenotypic Ratio

Example 6: Testcross

Genotypic Ratio

Phenotypic Ratio

Incomplete Dominance

= the F1 Generation will have a phenotype in between that of the parents

- Example: Red flowers (R) and White flowers (r) can make Pink flowers (Rr)

Example 7: Incomplete Dominance Pink Flower X Pink Flower

Genotypic Ratio

Phenotypic Ratio

Example 7: Incomplete Dominance Pink Flower X Red Flower

Genotypic Ratio

Phenotypic Ratio

Example 7: Incomplete Dominance White Flower X Red Flower

Genotypic Ratio

Phenotypic Ratio

Example 7: Incomplete Dominance Pink Flower X White Flower

Genotypic Ratio

Phenotypic Ratio

Codominance

= when both alleles for a gene are expressed in a heterozygous offspring

- Example: Red coat color (R) in horses is codominant with white coat color (R’) to make a horse with a mix of red and white coat color (RR’)

Example 8: Codominance Red Coat X White Coat

Genotypic Ratio

Phenotypic Ratio

Example 8: Codominance Red/White Coat X White Coat

Genotypic Ratio

Phenotypic Ratio

Example 8: Codominance Red/White Coat X Red Coat

Genotypic Ratio

Phenotypic Ratio

Dihybrid Cross

= a cross between individuals that involves two pairs of traits

- Example: Black hair (B) in guinea pigs is dominant to brown hair (b) and rough coat (R) is dominant to smooth coat (r)

Example 1:

Homozygous Dominant X

Homozygous Recessive

Example 1: Homozygous Dominant X Homozygous Recessive

Example 2:

Heterozygous X

Heterozygous

Example 2: Heterozygous X Heterozygous