Genetics

I. Foundations

A. Principles1. Developed by Mendel w/o knowledge of

genes or chromosomes (“heredity factors”)

2. Developed principles of dominance, segregation and independent assortment by analyzing pea plants

I. Foundations

B. Gene – Chromosome Theory1. Using Drosophila (fruit flies), scientists

linked chromosomes and their migration during meiosis to traits, called genes

2. Genes are found at specific locations on chromosome

3. Allele – the gene for a trait4. Homologous Chromosomes – pair of chrom

that control the same traits (may not have the same genes)

II. Genetic Concepts

A. Dominance1. Dominant Allele

a. The ONE gene of a pair that expresses it’s trait, (T)

2. Recessive Allelea. The OTHER gene that doesn’t show trait (t)

3. Homozygousa. Both genes of the pair are the same (TT or tt)

4. Heterozygous (hybrid)a. Both genes are different (Tt)

II. Genetic Concepts

5. Phenotypea. Physical appearance of individual

6. Genotypea. Genes of individual

II. Genetic Concepts

7. Mendel’s Pea Plant

F1 (First Generation)

Cross TT x tt

T T

t

t

T

t

T tF2 (Second Generation)

Cross Tt x Tt

T t

T t

T t

T t

t t

T T

T t

T t

G: 100% Tt

P: 100% Tall

G: 25% TT, 50% Tt, 25% tt

P: 75% Tall, 25% Short

II. Genetic Concepts

B. Segregation and Recombination1. When gametes are formed (meiosis)

chromosomes separate RANDOMLY

2. After fert, alleles (chrom) recombine, generally forming NEW combinations

II. Genetic Concepts

3. After large # of crossesa. Phenotype = 3:1 (75% tall, 25% short)

b. Genotype = 1:2:1 (25% TT, 50% Tt, 25% tt)

4. Genotype of Dominant Individual (T?)a. Cross with recessive ind

b. If offspring show trait, parent was Tt

T

?

t t

? t

T t

? t

T t

II. Genetic Concepts

C. Intermediate Inheritance1. Traits are NOT clearly dom/rec (mixture

of traits)

2. Codominancea. BOTH dominant traits are expressed in hetero

individual

b. Coat color in Roan cattle1) RR = Red coat

2) WW = White coat

3) RW = Roan (mixture of red

and white hairs)

II. Genetic Concepts

F1 = RR x WWG: 100% RW

P: 100% Roan

F2 = RW x RW

G: 25% RR, 50% RW, 25% WW

P: 25% Red, 50% Roan, 25% White

R R

W

W

RW

RW

RW

RW

R W

R

W

RR

WW

RW

RW

II. Genetic Concepts

3. Incomplete Dominancea. Heterozygous ind is a mixture (half way)

between both homozygous parentsb. RR = Red snapdragon

WW = White

RW = Pink

II. Genetic Concepts

D. Independent Assortment1. If genes for TWO different traits are on

DIFFERENT chromosomes, they are inherited INDEPENDENTLY of each other

E. Gene Linkage1. If genes for TWO different traits are on

the same chrom pair, they are linked (inherited together)

II. Genetic Concepts

F. Crossing Over1. During meiosis, pairs of chroms can twist

around each other, break, exchange segments and rejoin (swap parts)

2. Gives a rearrangement of linked genes, increases variability of offspring

II. Genetic Concepts

G. Multiple Alleles1. Human Blood type is determined by 3

alleles (IA, IB or ii)2. IA and IB are codominant and “i” is rec to

both IA and IB 3. Blood Type

a. A = IAIA or IAib. B = IBIB or IBic. AB = IAIB

d. O = ii

II. Genetic Concepts

IAi x IBiG: 25% IAIB

25% IAi

25% IBi

25% ii

G: 50% IAIB, 50% IBi

P: 50% AB, 50% B

IA i

IB

i

IAIB

ii

IBi

IAi

IA i

IB

IB

IAIB

IBi

IBi

IAIB

P: 25% AB

25% A

25% B

25% O

IAi x IBIB

II. Genetic Concepts

H. Sex Determination1. Two types of chromosomes in humans

a. Autosomes = 22 pairs (44 chroms)

b. Sex Chrom = 1 pair (2 chrom)

2. Sex Chromosomesa. X and Y

b. XX = female, XY = male

c. Sex of offspring is determined by the gene in the sperm (either X or Y)

II. Genetic Concepts

I. Sex Linked Genes1. Genes for some traits are on X

chromosome

2. Most SL are recessive and appear more often in males

3. Hemophilia and Color BlindnessX Y

X

X’

XX

X’Y

XY

XX’

III. Mutations

A. Random changes in genetic material

B. MUST be in sex cells to get passed on to offspring

C. Body cell mutations ONLY effect ind, cannot be passed on

D. Some are obvious (albino), others not easily noticed

E. MOST are harmful (depends on mutation and type of environment

III. Mutations

F. Types1. Change in Number

a. Sometimes in meiosis, a pair of chromosomes do NOT separate (non-disjunction), making gametes with > or < normal #.

b. If these gametes are fert, zygote can have > or < 2n number

c. Downs Syndrome – extra 21st chromd. Plants CAN be polyploid (3n or 4n), makes larger

or more vigorous, some are sterile (seedless)

2. Change in Structurea. Breaking or recombining parts

III. Mutations

G. Mutation rate can increase with:1. Radiation (X-rays, UV rays)

2. Chemicals (formaldehyde, asbestos)

IV. Human Heredity

A. Difficult to study humans because:1. Generation time is too long (40 weeks)2. Small # of offspring3. Unethical to perform exp on humans

B. Pedigree Charts1. Trace a trait through family for generations2. Shows presence / absence of trait3. Can identify carriers of rec genes

V. Heredity and Environment

A. Phenotype can be influenced by env (nutrients, sunlight, temperature)

B. Himalayan Rabbit1. Temp affects fur color

C.Plants need sunlight to make chlorophyll.

VI. Plant and Animal Breeding

A. Artificial Selection1. Desirable Traits (sheep w/ thick, soft

wool) are crossed hoping the offspring will have the traits

B. Inbreeding1. Mating closely related organisms to make

more w/ desirable traits2. Increases chances of harmful rec genes

to be inherited and cause disorders

VI. Plant and Animal Breeding

C. Hybridization1. Crossing 2 individuals w/ diff traits in

hope offspring will have both traits

2. Rose w/ large petal X Rose w/ nice smell hopefully = Rose w/ large petal and nice smell

VII. Genetic Disorders

A. Detected before / after birth

B. Techniques1. Screening – analysis of blood, urine

2. Amniocentesis – analysis of fluid around baby

3. Karyotyping – picture of paired chroms

VII. Genetic Disorders

C. Sickle – Cell Anemia1. Rec blood disorder

2. Mutated gene causing abnormal hemoglobin and RBC

3. RBCs don’t carry O2 well b/c of different shape

VII. Genetic Disorders

D. Tay–Sachs1. Rec disorder (fatal)2. Nerve tissue in brain

breaks down b/c of build up of fatty material

3. Body cannot make enzyme to break down the fat

VII. Genetic Disorders

E. Phenylketonuria (PKU)1. Rec disorder

2. Body cannot make enzyme to break down aa phenylalanine

3. Causes mental retardation

4. Detected by urine analysis or amniocentesis

5. Can be prevented by diet