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Intro to Genetics

Mrs. MacWilliamsBiology

+Objectives1. Describe how homologous chromosomes

carry the same genes, but may be different alleles.

2. Define the terms dominant, recessive, genotype, phetotype homozygous, and heterozygous.

3. Compare Mendel’s three laws of heredity.

+Key TermsGenetics

The study of heredity

Heredity

The study of HOW parents pass certain traits to offspring.

Chromosome

Rod shaped structures within the nucleus of the cell that contain genes

+Key Terms continuedGenesUnits of heredity information located on chromosomes

GametesReproductive cellHuman: sperm & eggs; Flowers: pollen (sperm) & pistil (eggs)

AllelesEither member of a pair of GENES that determines a single traitEx: gene pair Yy

+Two factors involved in Two factors involved in developmentdevelopment

1. Heredity1. Heredity2. Environment2. Environment

+Relationship of Genes to Each Relationship of Genes to Each OtherOther1. 1. DOMINANTDOMINANT- trait that hides the recessivetrait that hides the recessive

2. 2. RECESSIVERECESSIVE- trait that is hidden by the - trait that is hidden by the dominantdominant

+ Homozygous vs. Heterozygous

Homozygous (PUREBRED) (homo=same)Two genes in a pair are identical

Homozygous Dominant – both genes in the pair are the dominant traitExample: AA

Homozygous Recessive – both genes in the pair are the recessive traitExample: aa

Heterozygous (HYBRID) (hetero=different)There is one dominant gene and one recessive

geneExample: Aa

**ZYGOUS = ZYGOTE

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Ha Ha Just kidding… this is not what they would look like!!!!

+ Two Ways to Designate OrganismsTwo Ways to Designate Organisms1. 1. GENGENotypeotype ( (GENGENes)es)

a. Actual genetic info on the a. Actual genetic info on the chromosomechromosomeb. Uses b. Uses DOUBLE LETTERSDOUBLE LETTERS to signify to signify

double letters because double letters because eacheach parent parent ““sendssends”” a trait a trait

double letters due to HOMOLOGUS double letters due to HOMOLOGUS nature of chromosomesnature of chromosomes

HOMO = SAMEHOMO = SAME LOGOUS = LOCATIONLOGOUS = LOCATIONc. Use only one letter per TRAITc. Use only one letter per TRAIT

uppercaseuppercase letters for letters for dominantdominant traits traits lowerlower case letters for case letters for recessiverecessive traits traits i.e. AA, Aa, aa (NOT AB)i.e. AA, Aa, aa (NOT AB)

+2. 2. PHPHenotypeenotype ( (PHPHoto)oto)a. Outward appearance of a. Outward appearance of organismorganismExample: brown eyes, Example: brown eyes, blonde hairblonde hair

+ GREGOR MENDEL“The Father of Genetics”

Mendel was a pioneer in genetics, born 1822, lived in a monastery, plant breeding experiments.

Used pea plants. WHY? 1. Easy to grow2. short gestation time3. produced many offspring at a time.

Studied traits that had 2 contrasting forms:Ex. Tall vs. short; yellow vs. green

Kept meticulous records and calculated ratios.

Did this through many generations several times for each trait.

+ Mendel’s 1st Law of HeredityDEALS WITH ONE GENE

1. Law of Segregation

-In a pair of alleles (e.g. blue and brown eye color) only ONE of the two are represented in a gamete.

**Alleles SEGREGATE into different gametes during meiosis

+ Mendel’s 2nd Law of HeredityDEALS WITH 2 OR MORE GENES

2. Law of Independent Assortment Alleles of different genes separate independently

of one another during gamete formation (ex. Alleles for eye color separate independently from hair type)

The combination of alleles in any one gamete is totally random Mother donates blue eyes allele and straight hair allele Father donates brown eyes allele an curly hair allele Offspring can get any combo

Blue eyes straight hair Blue eyes curly hair Brown eyes straight hair Brown eyes curly hair

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3. Law of Dominance

One gene in a pair may prevent the other gene in the pair from being expressed.

ALWAYS REPRESENTED BY A CAPITAL LETTER

Recessive- the gene that is hidden by the dominant gene

ALWAYS REPRESENTED BY lower case letters

Example

Yellow (A) Dominant

Green (a) recessive

MendelMendel’’s 3rd Law of s 3rd Law of HeredityHeredity