UNIT 8: GENETICS

1. What is the molecule responsible for passing on hereditary traits?2. What is it’s structure?

•Deoxyribonucleic Acid (DNA) is a nucleic acid that contains genetic instructions used in the development and functioning of all known living organisms and some viruses•The main role is the long-term storage of information.•DNA is often compared to a set of blueprints

DNA consists of ________ complementary chains of nucleotides

The DNA ladder consists of: U______________: alternating phosphates and deoxyribose R_________: Pairs of nitrogen bases held together by weak Hydrogen bonds

ADENINE always pairs with THYMINE CYTOSINE always pairs with GUANINE

Twisted in to a

double helix

Functional unit: _____________________

ab

c

Nucleotide

PhosphateDeoxyribose

Nitrogen Base Pairs (A, T, C, G)(Sticks and curves)

2

RailingSteps

----

T

A

C

G

3. How does DNA replicate (make more copies of itself)

1. The ladder __________________

It breaks apart at the weak Hydrogen Bonds between the bases.

2. Newly synthesized nucleotides line up by

_________ ________________

Result: ___________________________________ Identical to the first strand and to each other.

Splits

Base Pairing

Two new strands of DNA

•exist at different loci (permanent locations) in a linear fashion on chromosomes.•Two genes associated with a specific characteristic are known as _____________ and are located on homologous chromosomes

Pair of allelesIndividual genes

DOMINANT ALLELE: Always exerts full effect, will mask the other gene characteristics

RECESSIVE ALLELE: The gene is present, but not always expressed

Different combinations of alleles result in different patterns of inheritance:

GENOTYPE: Describes the genetic combination

HOMOZYGOUS: two of the same alleles HETEROZYGOUS: two different alleles

PHENOTYPE: Describes the physical appearance

5. What is gene chromosome theory?

Genotype Phenotype

Homozygous

Heterozygous

4. What is a gene?

6. Can offspring have traits that are different than their parents

Gene: __________________________

Gene pool: __________________________

DNA Coding for 1 protein

All available genes in a population

Genes

alleles

Loci for a single alleleLocation

How many genes are on a single chromosome?

• A Lot!• Chromosome 1– Contains over 3000 genes– Contains over 240 million base

pairs, of which ~90% have been determined

• These things are mapped out on chromosome maps

•exist at different loci (permanent locations) in a linear fashion on chromosomes.•Two genes associated with a specific characteristic are known as _____________ and are located on homologous chromosomes

Pair of allelesIndividual genes

DOMINANT ALLELE: Always exerts full effect, will mask the other gene characteristics

RECESSIVE ALLELE: The gene is present, but not always expressed

Different combinations of alleles result in different patterns of inheritance:

GENOTYPE: Describes the genetic combination

HOMOZYGOUS: two of the same alleles HETEROZYGOUS: two different alleles

PHENOTYPE: Describes the physical appearance

5. What is gene chromosome theory?

Genotype Phenotype

Homozygous

Heterozygous

4. What is a gene?

6. Can offspring have traits that are different than their parents

Gene: __________________________

Gene pool: __________________________

Codes for 1 protein

All available genes

Genes

alleles

TT Can Roll Tongue tt Cant roll tongue

Tt Can Roll Tongue

__ __

____ _______ _____

__ __What you can see

T tTongue Roller

T

t

Tongue Roller

T

T

t

t

T T

t t

NOT a tongue Roller!

Law of ____________________: When an individual pure for the dominant trait is crossed with an individual pure for the recessive trait, the physical appearance of the offspring is like that of the dominant parent.

TRAIT DOMINANT FORM RECESSIVE FORM

Stem Length Tall (T) Short (t)

Seed Color Yellow (Y) Green (y)

Pod Shape Inflated (I) Constricted (i)

Seed Shape Round (R) Wrinkled (r)

7. What insights did Mendel give us into patterns of inheritance?

Law of ____________________:When gametes are produced, the genes separate so that each gamete receives only one copy.A gamete will receive one allele or the other.The direct proof of this was later found when the process of meiosis came to be known.

PUNNETT SQUARE SOLUTIONS:

Stem Length: Seed Color: Seed Shape:Pure Tall X Pure Short Hybrid yellow X pure green Monohybrid cross

In the 18th century, an Austrian monk and teacher Gregor Mendel developed some basic principles of heredity without any knowledge of genes or chromosomes.

He experimented with pea plants.

As a result of mathematical analysis of ratios associated with characteristics in the offspring, Mendel proposed that characteristics were inherited as a result of the transmission of hereditary factors.

Dominance

Segregation

T Ttt

Tt TtTt Tt

Y yyy

Y yY y

yyyy

R rRr

RRRr

Rrrr

Hybrid = 2 together

Dominance

• Dominant allele represented by a Capital Letter

• Always masks over any recessive alleles– For example:

Tongue Rolling (T)Not tongue rolling (t)Tt = what phenotype?

(remember phenotype and physical appearance)

Segregation• Every person has two alleles for any

given trait (one from the mom, one from the dad)

• Offspring will get either one of those• Ex:– Of a mom is Tt for tongue rolling she

can give either the T or the t, and this is determined by chance.

– Same for the father with Tt. He can give T or t

• This is demonstrated by a punnett square

Warm up

• Complete this punnett square:

C c

C

c

C C

C c

C c

c c

What if “c” was a recessive disease?

What are the chances of an offspring getting the disease in this example?

8. What are some genetic diseases caused by recessive alleles

CYSTIC FIBROSIS•Affects about 1 in 1600 people in the USA•It is caused by a recessive defective gene inherited from both of the parents.•The result is that the body produces thick sticky mucus in the lungs which has to be removed•Excessive mucous occurs in the pancreas causing digestive problems•The most serious problem is the blockage of air passages in the lungs, results in many infections•Both parents must carry the gene, and there is a 1 in 4 chance of their child being born with CF

SICKLE CELL ANEMIA•Causes red blood cells to be shaped like sickles, they get stuck in the capillaries and deprive body cells of oxygen.•Rare in the USA, but common in some African countries. This is because carriers of the disease are more immune to malaria. Hence, being a carrier increased chance of survival.

9. Are there other patterns of inheritance? Are the relationship between genes and traits more complex than Mendel’s Laws illustrate with peas?

MULTIPLE ALLELESMORE THAN TWO ALLELES ARE INVOLVED

BLOOD TYPES in humans. Three possible alleles: ____ ____ ____

EACH INDIVIDUAL INHERITS SOME COMBINATION OF 2 ALLELES Gene Combination Blood

Type

ABABO

Sample Crosses: Mom: Type ABMom: Type O Dad: Type BDad: Type B His mom type o

each person only inherits 2

C cCc

CC CcCc cc

50% carriers

25% withDisease

S sSs

SS SsSs ss

IA IB i

IA IA IAiIBIB IB i

IA IB

ii

i iIB

iB BO O

IA IB

IB

iAB B A B

More complex!

CONTINUOUS VARIATION

Results when several genes influence a trait•Height: TTTTTTT --------- tttttttt•Skin ToneMany different variations of the trait are expressed

10. Can patterns of heredity can be more complex?

1. Plants require sun to “turn on the gene” produce green chlorophyll. In the absence of sun, the gene will not be expressed, and the plants will be white.

2. Pigment producing genes of the arctic fox do not function in the winter due to the cold temperature. In the warmer summer, the genes function As a result, the fur is white in the winter and to produce a reddish-brown pigment. the animals blend in to the background. Now the fox resembles the tundra of summer

3. When an icepack is placed on the shaved skin of a Himalayan hare, the fur grows in dark.

4. TWIN Studies (upbringing means the same thing as environment) Twin’s genes are identical, so any difference between them must be caused by

slight differences in their environment throughout their lives.

Ex: Height differences due to differences in nutrition Muscular development in an athlete.

CROSSING OVER during MEIOSIS & GAMETE FORMATION increases variety

11. Can environment influence heredity? Can certain environmental conditions alter phenotypes?

NOTE: only changes in DNA of the sex cells can be passed on to the next generation