genetics

GENETICSChapters 11 and 14

GENETICS The scientific study of heredity- how

traits are passed down to offspring

TRAIT---Specific characteristic ( blonde hair, blue eyes)

GENE A hereditary unit consisting of a

sequence of DNA that occupies a specific location (LOCUS) on a chromosome and determines a particular characteristic in an organism.

(Genes undergo mutation when their DNA sequence changes)

LOCUS (LOCI PLURAL) Is a location on a

chromosome where a gene occurs

Loci will be written as-----6p21.2

6- chromosome number

P- arm 21.2- distance from

centromere

CHROMOSOME MAP / IDIOGRAM

Detailed diagram of all the genes on a chromosome

CHROMOSOME NUMBER DIPLOID- cell that contains all the

chromosomes of an organism (Humans= 46)

HAPLOID- cell that contains only HALF the chromosomes of an organism (ex- egg or sperm cell) (Humans=23)

CHROMOSOMESSEX CHROMOSOMES- chromosomes that

are responsible for determining sex of an organism (ex- X and Y in humans)

AUTOSOMES- chromosomes that determine traits other than sex in an organism (ex- humans- chromosome 1-22)

HOMOLOGOUS (PAIR) CHROMOSOMES pair of chromosomes that carry the same

genes

You will have one from each parent, they will both code for the same types of characteristics

KARYOTYPE a photograph that shows the complete

DIPLOID set of chromosomes arranged in homologous pairs and arranged in order of decreasing size.

ALLELE Alternate forms of a gene/factor. Examples:

--brown eyes vs blue eyes --blonde hair vs brown hair

--dimples vs no dimples

FATHER OF GENETICS

Gregor Mendel

GREGOR MENDEL An Austrian Monk (1822-1884) Developed these principles without

ANY scientific equipment - only his mind.

Tested over 29,000 pea plants by crossing various strains and observing the characteristics of their offspring.

GREGOR MENDEL Studied the following

characteristics:1. Pea color (Green,

yellow)

2. Pea shape (round, wrinkled)

3. Flower color (purple, white)

4. Pod shape ( inflated,

constricted)

5. Pod color (green, yellow)

6. Plant height (tall, short)

7. Flower position(axial, terminal)

MENDEL’S EXPERIMENTSMendel noticed that some plants always produced offspring that had a form of a trait exactly like the parent plant. He called these plants “purebred” plants. For instance, purebred short plants always produced short offspring and purebred tall plants always produced tall offspring.

Mendel called these the P 1 generation. (pure bred, parental)

X

Purebred Short Parents

Purebred Tall Parents

X

Short Offspring

Tall Offspring

MENDEL’S FIRST EXPERIMENT

Mendel crossed purebred plants with opposite forms of a trait. He called these plants the parental generation , or P generation. For instance, purebred tall plants were crossed with purebred short plants.

Parent TallP generation

Parent ShortP generation

X

Offspring TallF1 generation

Mendel observed that all of the offspring grew to be tall plants. None resembled the short short parent. He called this generation of offspring the first filial , or F1 generation, (The word filial means “son” in Latin.)

MENDEL’S SECOND EXPERIMENT

Mendel then crossed two of the offspring tall plants produced from his first experiment.

TallF1 generation

X

3⁄4 Tall & 1⁄4 ShortF2 generation

Mendel called this second generation of plants the second filial, F2, generation. To his surprise, Mendel observed that this generation had a mix of tall and short plants. This occurred even though none of the F1 parents were short.

Parent Plants Offspring

TERMS TO KNOW

MONOHYBRID CROSS- cross using only one trait

SELF CROSS- (SELF FERTILIZATION)- produce offspring asexually

P1 GENERATION-- parents- usually pure bred

F1 GENERATION- 1st set of offspring (1st family)

F 2 GENERATION- 2nd set of offspring (2nd family)

TYPES OF ALLELES Dominant: An allele which is expressed

(masks the other). Recessive: An allele which is present

but remains unexpressed (masked)

PHENOTYPE VS GENOTYPE Genotype: combination of alleles an

organism has. (Ex- BB, Bb, or bb )

Phenotype: How an organism appears.(Ex- brown hair, blonde hair )

GENOTYPES Homozygous: Both alleles for a trait

are the same. (BB- homozygous dominant, bb homozygous recessive)

Heterozygous: The organism's alleles for a trait are different. (Carrier of the recessive allele) Bb

DEVELOPED 3 LAWSLAW OF DOMINANCE- one allele always

shows of the other

LAW OF INDEPENDENT ASSORTMENT- states that each pair of genes (chromosomes) separate independently of each other in the production of sex cells. (example– you could have brown hair and blue eyes)

LAW OF SEGREGATION-

MENDEL’S LAW OF SEGREGATION

Mendel’s first law, the Law of Segregation, has three parts. From his experiments, Mendel concluded that:

1. Plant traits are handed down through “hereditary factors” in the sperm and egg.

2. Because offspring obtain hereditary factors from both parents, each plant must contain two factors for every trait.

3. The factors in a pair segregate (separate) during the formation of sex cells, and each sperm or egg receives only one member of the pair.

PREDICTING OFFSPRING Punnett square

INCOMPLETE DOMINANCE A third (new) phenotype appears in the

heterozygous condition. Flower Color in 4 O’clocks

RR = red rr = white Rr = pink

PROBLEM: INCOMPLETE DOMINANCE

Show the cross between a Red and a White flower.

-RR (0), Rr (4); rr (0)

- pink (4); white ()

R R

r

r

GENOTYPES:

PHENOTYPES:

PROBLEM: INCOMPLETE DOMINANCE

Show the cross between a Pink and a Pink flower.

- RR (1); Rr (2), rr (1)

-Red (1) pink (2); white (1)

R

r

GENOTYPES:

PHENOTYPES:

R r

CODOMINANCE The heterozygous condition, in which both

alleles are expressed equally Sickle Cell Anemia in Humans

NN = normal cells

SS = sickle cells NS = some of each

PROBLEM: CODOMINANCE Show the cross between an individual with

sickle-cell anemia and another who is a carrier but not sick.

N S

S

S

NS

NS

SS

SS

- NS (2) SS (2)- ratio 1:1

- carrier (2); sick (2)- ratio 1:1

GENOTYPES:

PHENOTYPES:

MULTIPLE ALLELES

There are more than two alleles for a trait

Blood type in humans Blood Types?

Type A, Type B, Type AB, Type O Blood Alleles?

A, B, O (in book – IA, IB, I)

PROBLEM: MULTIPLE ALLELES

Show the cross between a mother who has type O blood and a father who has type AB blood.

- AO (2) BO (2)- ratio 1:1

- type A (2); type B (2)- ratio 1:1

GENOTYPES:

PHENOTYPES:

O O

A

B

AO

BO

AO

BO

PROBLEM: MULTIPLE ALLELES

Show the cross between a mother who is heterozygous for type B blood and a father who is heterozygous for type A blood.

-AB (1); BO (1); AO (1); OO (1)- ratio 1:1:1:1

-type AB (1); type B (1) type A (1); type O (1)- ratio 1:1:1:1

GENOTYPES:

PHENOTYPES:

A O

B

O

AB

OO

BO

AO

Dihybrid Cross:a cross that shows the possible

offspring for two traitsFur Color:

B: Black b: White

Coat Texture:R: Roughr:

SmoothIn this example, we will cross a heterozygous individual with

another heterozygous individual. Their genotypes will be:

BbRr x BbRr

DIHYBRID CROSSBbRr x BbRr

First, you must find ALL possible gametes that can be made from each parent.

Remember, each gamete must have one B and one R.

DIHYBRID CROSSBbRr x BbRr

Possible gametes:BRBrbRbr

Next, arrange all possible gametes for one parent along the top of your Punnett Square, and all possible gametes for the other parent down the side of your Punnett Square…

DIHYBRID CROSS

Fur Color:B: Black b: White

Coat Texture:R: Roughr:

Smooth

BbRr x BbRr B

RbR

br

bR

Br

BR

br

Br

Then, find the possible genotypes of the offspring

DIHYBRID CROSS

Fur Color:B: Black b: White

Coat Texture:R: Roughr:

Smooth

BbRr x BbRr

BR

bR

br

bR

Br

BR

br

BrBBRR

BbRR BbRr

BBRr BBrr BbRr Bbrr

BbRR BbRr bbRR bbRr

BbRr Bbrr bbRr bbrr

BBRr

BR bR

br

bR

Br

BR

br

Br

BBRR

BbRR

BbRr

BBRr BBrr BbRr Bbrr

BbRR

BbRr bbRR

bbRr

BbRr Bbrr bbRr bbrr

BBRr

How many of the offspring would have a black, rough coat?How many of the offspring would have a black, smooth coat?How many of the offspring would have a white, rough coat?How many of the offspring would have a white, smooth coat?

Fur Color:B: Black b: White

Coat Texture:R: Roughr:

Smooth

BR bR

br

bR

Br

BR

br

Br

BBRR

BbRR

BbRr

BBRr BBrr BbRr Bbrr

BbRR

BbRr bbRR

bbRr

BbRr Bbrr bbRr bbrr

BBRr

How many of the offspring would have black, rough coat?How many of the offspring would have a black, smooth coat?How many of the offspring would have a white, rough coat?How many of the offspring would have a white, smooth coat?

Fur Color:B: Black b: White

Coat Texture:R: Roughr:

Smooth

Phenotypic Ratio

9:3:3:1

CHAPTER 12--SEX LINKAGE All chromosomes are homologous

except on sex chromosomes. Sex chromosomes are either X or Y. If an organism is XX, it is a female, if

XY it is male. If a recessive allele exists on the X

chromosome. It will not have a corresponding allele on the Y chromosome, and will therefore always be expressed

is an important tool for studying inherited diseases

uses family trees and information about affected individuals to:figure out the genetic basis of a

disease or trait from its inheritance pattern

predict the risk of disease in future offspring in a family (genetic counseling)

PEDIGREE ANALYSIS

How to read pedigreesBasic patterns of inheritance

1. autosomal, recessive2. autosomal, dominant3. X-linked, recessive4. X-linked, dominant (very rare)

HOW TO READ A PEDIGREE

Sample pedigree - cystic fibrosis

femalemale

affected individuals

Autosomal dominant pedigrees

1. The child of an affected parent has a 50% chance of inheriting the parent's mutated allele and thus being affected with the disorder.

2. A mutation can be transmitted by either the mother or the father.

3. All children, regardless of gender, have an equal chance of inheriting the mutation.

4. Trait does not skip generations

Autosomal dominant traitsThere are few

autosomal dominant human diseases (why?), but some rare traits have this inheritance pattern

ex. achondroplasia (a sketelal disorder causing dwarfism)

AUTOSOMAL RECESSIVE

1. An individual will be a "carrier" if they posses one mutated allele and one normal gene copy. 2. All children of an affected individual will be carriers of the disorder. 3. A mutation can be transmitted by either the mother or the father. 4. All children, regardless of gender, have an equal chance of inheriting mutations. 5. Tends to skip generations

Autosomal recessive diseases in humansMost common ones

• Cystic fibrosis • Sickle cell anemia• Phenylketonuria (PKU)• Tay-Sachs disease

AUTOSOMAL RECESSIVE