Chap. 11/14 Genetics or Why do you look Like that!?!

Chap. 11/14 Genetics

orWhy do you look Like

that!?!

Trait Inventory ActivityPart 1

• Complete H.O. on traits of peers

• Write “yes” or “no” based on what you see!

• How are we all alike? (trait)• How do some of us differ?

(characteristic)• Part II later!!

I. Meiosis - Reduction Division

•Produces gametes… •Gametes are 1n/haploid…

• In males – 4 sperm cells produced

• In females – 1 egg cell and 3 polar bodies (“duds”) produced.

Recall…•Mitosis …•Somatic cells/body cells…

•2n/diploid…

Terms-•Homologous pairs – original chromosome pair and their copies.

•Tetrad – chromosome pair &

corresponding homologous pair

•A tetrad contains 4 chromatids

II. Gregor Mendel – •“Father of genetics”

•Pea plants… •Characteristics and traits

•Some characteristics were visible,some were not

•Ex. Plant height – tall or short…

3 Principles of Genetics•They are based on alleles – contrasting genes that determine a trait.

•Ex. BLUE vs BROWN EYES

*A. Principle of Segregation – •Alleles segregate/separate

•Occurs during meiosis…

*B. Prin. of Independent Assortment –

•Alleles are randomly arranged

•Ex. Trait “a” is not dependant

on trait “b”

*C. Prin. Of Genes and Dominance –

•One allele “hides“ another.

•Dominant… •Recessive…

• Fig. 11-3

III. Crash course in crossing

•P1 – original parents with

pure traits – called true

•F1 – first generation with a mix of parent traits – hybrids

•F2 – second generation with a mix of their parents traits

A. Punnett squares -•Predicts…•Tells the – –Genotype …–Phenotype …

•Capitals represent dominant characteristics

•AA, BB•Lower case represent recessive characteristics

•aa bb

•Purebred means two identical alleles

•GG, mm, •Can be dominant or recessive

•This is homozygous •“same trait/allele”

•Hybrid means two different alleles

•Nn,Oo•Will always be dominant --- why???)

•This is heterozygous •“different trait/allele”

B. Types: •Monohybrid cross - “One trait; one letter”

•Dihybrid cross - “Two traits; two letters”

V. Gene expression is…

•Based on the environment, and the effect of other

genes. –Toxins, disease, drugs…

•“Nature vs nurture”–Over/under nutrition–Soil acidity & flower color

A.Dominant Alleles • Conditions that are expressed provided one

dominant allele is present

• Ex. PP or Pp – Tall plants• HH or Hh – Huntington’s

disease

B. Recessive Alleles• Trait is expressed provided two recessive alleles are present.

• Ex. tt – short plants• In humans …• tt – Tay-sachs• aa - albinism

 C. Incomplete Dominance - • There is no dominance.

• The heterozygous genotype shows a mix of both phenotypes.

• Ex. White and red roses make pink roses.

D. Codominance – •A type of incomplete dominance.

•Both alleles share dominance & are expressed in the

organism.•Ex. Roan cattle have both red and white fur.\

• In humans – sickle-cell anemia

Codominance in humans …• Expressed in varying degrees

• Sickle-cell anemia–Person is either unaffected, a carrier, or affected

E. Multiple Alleles – •Genes that have more than 2 possible alleles -

C, cch, ch, c •Each allele being expressed, not contrasting like in

peas!•Ex. Rabbit fur – p. 273

Multiple Alleles in humans…• Blood types• A• B • AB (universal receiver)• O (universal donor)• Could be + or -

F. Polygenic traits – •“Many genes” – traits due to the interaction of more than 3 genes.

•These traits tend to “blend” from one extreme to the other.

•Ex. Skin/fur color, eye color….

Very dark to very light

Polygenic traits in humans• Height• Healthy weight• All vary from one to the other extreme

G. Determing Sex•Only one X is required for survival.

•XX – female•XY - male

H. Sex-linked Conditions – •Traits that are linked or found on the X or Y chromosomes

•Ex. Colorblindness,

hemophilia, muscular dystrophy

•Y – says “just make me a boy!”

P.350

VI. Determining Genetics•A. Karyotype - picture of an individual’s

chromosomes–Homologous chromosomes

are paired & analyzed

B. Pedigree•Family record that shows how a trait is inherited over

several generations.

• Identifies the carriers, those that are normal, & the affected individuals.

VII. MUTATIONS & HUMAN GENETICS

A. CHROMOSOMAL MUTATIONS affect the entire chromosome–May be deletion, duplication, inversion, or translocation

B. NUCLEOTIDE MUTATION–Affects the nucleotide of DNA which makes the chromosome

C. NONDISJUNCTION•Homologous chromosomes do not

separate during meiosis.

•Some effects may or may not be lethal.

•Autosomal chromosome:

•Ex. Down syndrome - due to trisomy 21 - having 3 of #21 chromosomes

•Can affect sex chromosomes–Turner’s Syndrome – XO – affects females

–Klienfelter’s Syndrome – XXY- affects males

•Chromosomes carry the alleles that produce the trait that makes you look the way you do!!!