GENETICS

The Study of HeredityHeredity The passing of traits from parents to their offspring

Causes children to resemble their parents.

Genetics - The study of heredity

The Study of HeredityGregor Mendel - the father of modern genetics Austrian monk - trained in mathematics and natural

sciences. Work conducted over period of 8 years with

common garden peas -1856 to 1865. Kept careful records. Applied mathematical studies to his work. Worked with different kinds of plants. Selected peas

The Study of Heredity

The Study of HereditySelected peas because they: Grew rapidly. Produced many seed (offspring). Flower structure made it easy to control Pollination

Transfer of pollen from stamen to pistil of a flower. Pistil - female reproductive structure - egg at base. Stamen - male reproductive structure - produces

pollen contains sperm.

Self –pollination - process where pollen from stamen falls on pistil of the same flower.

Cross-pollination - process where pollen from stamen of 1 flower falls on pistil of another

flower on another plant.

The Study of Heredity

The Study of HeredityIdentified 7 different characteristics in pea plants

Each had two contrasting forms. Seed Shape - Round Vs. Wrinkled Seed Color - Yellow Vs. Green Flower Color - Purple Vs. White Pod Shape - Inflated Vs. Constricted Pod Color - Green Vs. Yellow Flower Position - Axial Vs. Terminal Plant Height - Tall Vs. Short

The Study of Heredity

The Study of HeredityHis experiments were different from earlier workers Studied only 1 trait at a time, rather than everything about the

offspring at once. Studied results of many matings and pooled the results - earlier

workers had looked at only a few offspring from a single mating Counted 7324 peas for seed shape (F2 generation) Counted 8023 peas for seed color (F2 generation)

Used the large number of offspring to discover definite ratios of characteristics among the offspring.

5474 Round Seed: 1850 Wrinkled Seed 2.96:1 6022 Yellow Seed: 2001 Green Seed 3.01:1

The Study of HeredityMendel's Experiments and Observations

When the plants were allowed to self-pollinate, the trait always stayed the same - called them "Truebreeding " or "Pure "plants;

Tall plants x Tall plants produced Tall plants. Removed stamens from the pure plants that produced wrinkled seeds. Dusted pistil with

pollen from plants that produced only round seeds Called these the Parental or P1 generation

All of the offspring of this cross resulted in plants that had round seed Called this the First Filial or F1 generation; Also called HybridsHybrid - offspring from a cross between parents differing in 1 or more traits.Found that 1 trait of the parents always disappeared in the F1 generation.

The F1 generation plants were allowed to self-pollinate Called the next generation the Second Filial or F2 generation. Found that some F2 plants had round seed; some had wrinkled seeds. Similar results were obtained with the other traits

always 75% of 1 trait; 25% of other trait - a 3:1 ratio.

The Study of HeredityMendel’s Cross

P1 Round Seed x Wrinkled Seed

F1 All Hybrid Round SeedHybrid Round Seed x Hybrid Round

Seed

F2 ¾ Round Seed; ¼ Wrinkled Seed

The Study of HeredityMendel's Conclusions Did not know anything about cell reproduction

Work based on hypothesis that Factors or units carried the traits he was studying - called Genes today.

Observed that offspring of true breeding plants with contrasting traits showed the trait of only 1 parent plant

Called trait Dominant – disappearing trait called Recessive

Observation lead to his Law of Dominance - one form of a hereditary trait, the dominant trait, Dominates or prevents the expression of the recessive trait.

Mendel hypothesized that factors exist in pairs since the plants which had 1 trait could produce seeds with the opposite trait.

The Study of HeredityMendel’s Conclusions

Mendel hypothesized that paired factors separate or segregate during gamete formation - lead to Law of Segregation - During gamete formation the pairs of genes responsible for each trait separate so that each gamete contains only 1 gene for each trait.

During fertilization the zygote gets 1 gene for the trait from mom and 1 from dad.

The different forms of a gene for a trait are known as Alleles Combination of alleles or genetic makeup is the organism’s

Genotype The appearance of the organism regardless of its genetic makeup is

its - physical appearance - Round, yellow, etc.

The Study of Heredity

The Study of Heredity Dominance is expressed by a capital letter - usually the first

letter of the dominant trait; Recessive trait is expressed by a small letter (same as the dominant trait)

For round Vs. wrinkled seed - R - dominant; r - recessive

Hybrid would be Rr During gamete formation the pairs of genes responsible for

each trait separate so that each gamete contains only 1 gene for each trait.

Rr / \ R r

Mendel’s Cross

P1 Round Seed x Wrinkled SeedRR x rr

F1 All Hybrid Round Seed (Rr)Hybrid Round Seed x Hybrid Round

SeedRr x Rr

F2 ¾ Round Seed; ¼ Wrinkled Seed RR, Rr rr

The Study of Heredity

The Study of Heredity

The Study of HeredityGenetic Terminology Dominant - trait which stays visible Recessive - trait which disappeared Alleles - alternate forms of a gene for a trait   Genotype - genetic makeup of a trait   Phenotype - physical appearance of a trait   Homozygous - both alleles are the same   Heterozygous - two alleles are different Homozygous Dominant - pure dominant  Homozygous Recessive - pure recessive   Heterozygous Dominant - Hybrid with 1 dominant -

The Study of HeredityMendel’s Laws

LAW OF DOMINANCE - one form of a hereditary trait, the dominant trait, dominates or prevents the expression of the recessive trait.

LAW OF SEGREGATION - During gamete formation the pairs of genes responsible for each trait separate so that each gamete contains only 1 gene for each trait.

LAW OF INDEPENDENT ASSORTMENT - Alleles segregate independently of each other during gamete formation.

ProbabilityThe likelihood of an event occurring as expressed as a

ratio or a percentage.

Flipping a coin – ½ heads; ½ tails

Cards - Chance of drawing an ace –4/52 or 1/13 Chance of drawing a spade - 13/52 or 1/4 Chance of drawing the Ace of Spades

1/13 x 1/4 = 1/52

ProbabilityProduct Rule  

To find the probability of 2 events occurring you multiply the individual probabilities.  

Chance of a head – ½ ; Chance of another head – ½  Chance of 2 heads in a row – ½ x ½ = ¼  Chance of 4 heads in a row – ½ x ½ x ½ x ½ =

1/16  

Each gamete has ½ chance of getting a particular allele  Homozygous Dominant - RR: Alleles - R or R = 1/1  Homozygous Recessive - rr: Alleles - r or r = 1/1  Heterozygous Dominant - Rr: Alleles - R or r; ½ R; ½

r  

ProbabilityPUNNETT SQUARE

Special chart used to show possible combinations resulting from a cross of 2 organisms.

Put female gametes along top; male gametes along left side

Squares show possible genotypes of offspring -used to determine phenotype and ratio of offspring.

Used to predict; it doesn’t mean it will happen

Types of CrossesMONOHYBRID CROSS - involves only one set of contrasting factors for a trait

Cross a homozygous yellow with a homozygous green Yellow – dominant (Y); green - recessive (y) Y YP1 YY x yy

y

F1 all Yy heterozygous yellow y

Cross two of the F1 generation Y yYy x Yy Y

F2 – ¼ YY; ½ Yy; ¼ yy ¾ Yellow; ¼ green y

Yy Yy

Yy Yy

YY Yy

Yy yy

Types of CrossesDIHYBRID CROSS - involves two sets of contrasting

traits at one time; genes are on separate chromosomes

Each gamete contains 1 allele for each trait

LAW OF INDEPENDENT ASSORTMENT - Alleles segregate independently of each other during gamete formation.

Types of CrossesHet Round, Het Yellow RrYyx Het Round, Het YellowRrYy

Gametes:RYRyrYry

Types of CrossesINCOMPLETE DOMINANCE/NONDOMINANCE

Phenotype between dominant and recessive trait Heterozygous condition Example - Four-O-Clocks

RR - red flowers rr - white flowers Rr - Pink flowers

Cross of 2 pink flower plants - Rr x Rr Results – ¼ red (RR); 2/4 (½) Pink (Rr); ¼ white

Types of Crosses

Types of CrossesDetermination of Sex By the Sex Chromosomes - x or y

Other chromosomes are called Autosomes Male - xy; Female - xx Get ½ males and ½ females on Punnett square

x x x y

 

xx xx

xy xy

Types of Crosses

Types of CrossesSEX LINKED CHARACTERISTICS Recessive trait linked with a certain sex - usually males Carried on the x-chromosome;

Male has only 1 x, the trait is visible Females with 2 x's - not visible if 1 of the x has a

dominant gene for the trait. Female only shows trait in homozygous recessive. Woman is called a "Carrier" in heterozygous condition. Examples:

Red-Green color blindness Hemophilia

Types of Crosses

Male Female

Types of Crosses

Types of CrossesMULTIPLE ALLELES More than 2 alleles exist for a particular trait In humans - blood types is an example of multiple

alleles 3 different alleles - A, B, O Alleles A and B are codominant O is recessive

Types of CrossesBlood Type

Due to presence of antigens on the red blood cells - produces antibodies in blood

Type A - Antigen A on cells Plasma contains anti B

Type B - Antigen B on cells Plasma contains anti A

Type O - No Antigens on cellsPlasma has anti A and anti B

Type AB - Antigens A and B on cellsPlasma lacks anti A and anti B

Types of Crosses

Types of CrossesPhenotypes and genotype combinations  

Type A - AA or AO   Type B - BB or BO   Type AB - AB   Type O - OO

Types of CrossesBlood Donor ReceivesGroup to from

O O, A, B, AB O Universal Donor

A A, AB O, A

B B, AB O, B

AB AB O, A, B, AB Universal Recipient

Other Related TopicsGENE LINKAGE

Concerned with the presence of 2 different genes on the same chromosome

Does not follow usual dihybrid results - follows monohybrid.

Variation can occur due to crossing over - pieces of chromatids exchange places during synapsis of tetrads in meiosis.

Other Related TopicsLETHAL GENES Genes which can cause death or harm in the

homozygous condition. Examples:

Sickle-cell anemia PKU Tay Sachs - Jews of middle eastern European origin. Diabetes mellitus

Other Related Topics

Other Related TopicsNONDISJUNCTION

Failure of chromosomes to segregate properly during gamete formation.

Can involve sex chromosomes as well as the autosomes - zygote gets an improper number of chromosomes

Examples: Down's Syndrome - three #21 chromosomes -

autosomal Turner's Syndrome - has only 1 x, no y chromosome -

female Klinefelter's Syndrome - xxy - male Jacob’s Syndrome- xyy - male –thought to show criminal behavior at one time; not any higher.

Other Related Topics

Normal Male

Male – Down’s

Other Related Topics

Klinefelter’s Syndrome Turner’s Syndrome

Jacob’s Syndrome

Other Related TopicsMUTATIONS

Change in the genetic code or genes of an organism. Can occur naturally or by exposure to agents that produce

mutations. Breaks during crossing over which do not reattach. Increased chance of breakage by exposures to

mutagens Mutagens - agents that cause mutations.

Radiation - x-rays, UV, gamma Chemicals