Genetics Basics

http://www.youtube.com/watch?v=Y1PCwx

http://www.youtube.com/watch?v=y4Ne9DXk_JcUDTl8

http://anthro.palomar.edu/mendel/mendel_2.htm

http://www.khanacademy.org/science/biology/heredity-and-genetics/v/punnett-square-fun

http://www.mhhe.com/biosci/genbio/virtual_labs/BL_05/BL_05.html

Gregor Mendel:Father of Genetics

studied inheritance in pea plants – 1 trait at a time

– self vs. cross pollination

– true breeding vs. hybrid

Mendel’s Principles

genes determine biological characteristics

Organisms receive one allele for each gene from each parent

http://www.phschool.com/science/biology_place/biocoach/inheritance/laws.html

Monohybrid Cross

(heterozygous 3:1 ratio)

Dihybrid Cross – looks at 2 traits at one 9:3:3:1 ratio

Alleles separate during sex cell formation

One allele may be dominant over the other (recessive)

genes segregate independently (independent assortment)

Gene: short section of a chromosome that contains the code for a trait

Allele: different versions of the same gene hair color – brown or blonde

WHY 2 copies of each gene ?

23 pairs - 1 from each parent

23x2 = 46 chromosomes for humans

Dominant: expressed trait, 1st letter in genotype, capital letter

Recessive: hidden trait, 2nd letter

in genotype, lower case letter

Phenotype: physical expression of a

trait Ex. My hair is brown

Genotype: alleles present ex. BB TT Bb Tt bb tt

BB: homozygous dominant

same alleles

Bb: heterozygous

different alleles

bb: homozygous recessive

same alleles

Punnett Square – method to visualize and determine possible offspring in a cross

Segregation - 2 alleles separate

Independent Assortment - genes for different traits segregate independently

MEIOSIS: process by which haploid

sex cells (gametes) are made

http://www.tokresource.org/tok_classes/biobiobio/biomenu/meiosis/

Males = 4 sperm

Females= 1 egg

& 3 polar bodies

http://wps.aw.com/

bc_martini_eap_4/

40/10469/2680298.

cw/

Genetic Diversity

Humans have 23 pairs of chromosomes (223 = 8,388,608 possibilities)

Genes on the same chromosome tend to be inherited together

Crossing Over – pieces of homologous

chromosomes change places in meiosisI

Incomplete Dominance Ex – snapdragons heterozygote is in between the 2 homozygous phenotypes (a mixture)

RR = red

Rr = pink

rr = white

Exceptions to Mendels Rules

Codominance

heterozygote both alleles are expressed

Chicken: black & white feathers

Roan cattle

Multiple Alleles (blood type)

type A (AA, AO) type B ( BB, BO)

type AB (AB) type O (OO)

Polygenic Traits - traits controlled by more than one gene, create a wide range

of phenotypes

ex. Parakeet color

Human ex: height, eye color, skin color

http://www.geocities.ws/nkourani2002/Inheritance.htm

Human Inheritance

(23 pairs)= 46

chromosomes

first 22 pairs

are autosomes

23rd pair are

the sex

chromosomes

XY = male

XX = female

Sex determination

X Y

X XX XY

X XX XY

Karyotype

picture of all

chromosome

pairs, lined up

largest to

smallest, sex

chromosomes

are last

Pedigree: diagram to show how a

recessive trait is inherited within a family

?

?

Susan

Lisa Mary

Jack

Sex Linked Inheritance

genes on X chromosome males are more affected than females

WHY? ……

only one X chromosome

ex: Hemophilia, colorblindness, DMD

http://colorvisiontesting.com/ishihara.htm

Hemophilia – blood clotting

protein (royal family pedigree)

XH

Y

XH

XHXH

XHY

Xh

XHXh

XhY

different in men & women

gene carried on autosome not

on the X chromosome

ex. male pattern baldness

Sex Influenced Traits

Autosomal Disorders

Autosomal Recessive: 2 copies

Albinism, Cystic Fibrosis,

Tay-Sachs, Sickle Cell, PKU

Autosomal Dominant 1 copy

Huntingtons Disorder

Chromosome Number Disorders

Downs Syndrome – 3 of # 21

Turner Syndrome –XO

Klinefelters Syndrome –XXY

Metafemale – XXX

Male - XYY

Chromosome Deletions

pieces of chromosomes

break off & get lost

Chromosome Translocations

broken pieces get reattached

to other chromosomes

Prenatal Diagnosis

Amniocentesis:

amniotic fluid sample

Chorionic Villus Sampling:

tissue sample