PATTERNS OF INHERITANCEChapter 11

Pre-Mendel’s Theories

Blending Hypothesis: when parents with different traits have offspring, they will always show a blending of the traits

Spontaneous generation: Non-living matter giving rise to living matter

Homunculus: The little man inside the sperm

Particulate hypothesis: Parents pass on to their offspring separate and distinct factors (genes) that are responsible for inherited traits

Gene: factors pass on from parents to offspring. Sequence of DNA that determines a trait

Trait: a specific characteristic of an individual

Genetics: the study of heredity

Mendel’s experiments with pea plants

https://www.youtube.com/watch?v=hf9XlqXcal0 3:00https://www.youtube.com/watch?v=ExaQ8shhkw8 10:00

Mendel’s experiments started with

True-breeding plants: when self-fertilized, a true-breeding plant produces offspring identical in appearance to itself generation after generation

Cross-fertilization, sperm from the pollen of one flower fertilizes the eggs in the flower of a different plant

the offspring of two different true-breeding varieties are called hybrids.

Monohybrid cross: pairing in which the parent

plants differ in only one (mono) character.

HUMAN KARYOTYPE

A display of all the 46chromosomes of an Individual.

9.5 page 2

Genus species (organism) NUMBER OF CHROMOSOMES Homo sapiens (human)______________________________46

Mus musculus (house mouse)_________________________40

Drosophila melanogaster (fruit fly)_____________________8

Caenorhabditis elegans (microscopic roundworm)_________12

Saccharomyces cerevisiae (budding yeast) ______________32

Arabidopsis thaliana (plant in the mustard family) ________10

Xenopus laevis (South African clawed frog)______________36

Canis familiaris (domestic dog)________________________78

Gallus gallus (chicken) ______________________________28

Zea mays (corn or maize)____________________________20

Muntiacus reevesi (the Chinese muntjac, a deer) _________23

Muntiacus muntjac (its native american cousin) __________6

Myrmecia pilosula (an ant) ___________________________2

Parascaris equorum var. univalens (parasitic roundworm)___2

Cambarus clarkii (crayfish)___________________________200

Equisetum arvense (field horsetail, a plant)______________216

Horsetail

Mendel’s principle of segregation

There are alternative forms of factors (genes) called alleles.

For each character, an organism has two alleles for the gene controlling that character, one from each parent. Homozygous = same alleles Heterozygous = different alleles

Principle of segregation (cont.)

When only one of the two different alleles in an heterozygous individual appears to affect the trait, that allele is called the dominant allele. The allele that does not appear to affect the trait is called the recessive allele

The two alleles for a character segregate (separate) during the formation of gametes (sex cells). Each gamete carries only one allele of each character (Principle of segregation)

Phenotype refers to the observable trait (purple flowers)

Genotype refers to the combination of alleles (PP)

Phenotypic ratio: ratio of plants with purple flowers to those with white flowers (3 purple : 1 white)

Genotypic ratio: ratio of possible combinations of alleles (1 PP : 2 Pp : 1 pp)

Phenotype refers to the observable trait (purple flowers)

Genotype refers to the combination of alleles (Pp)

• Phenotypic ratio: ratio of plants with purple flowers to those with white flowers (3 purple : 1 white)

• Genotypic ratio: ratio of possible combinations of alleles (1 PP : 2 Pp : 1 pp)

Probability and Punnett Squares

Probability: Chance of Something happening

Punnett Square: Diagramused to show the probabilityof a genetic cross

How can you find out the genotype of an individual showing the dominant trait?

TESTCROSS

In a testcross, an individual of unknown genotype, but dominant phenotype is crossed with a homozygous recessive individual

DIHYBRID CROSS

crossing of organisms differing in two characters

Possible allele combinations from a heterozygous dihybrid for round an yellow seed

R r Y y

DHYBRID CROSS

Principle of Independent Assortment

During gamete formation in an F2 cross, a particular allele for one character can be paired with either allele of another character

Not all traits are inherited following the patterns found by Mendel in pea plants

Intermediate or incomplete inheritance

CodominanceMultiple allelesPolygenic inheritanceEnvironment - Epigenetics http://www.biologycorner.com/bio2/genetics/

notes_incomplete_dominance.html

Intermediate or Incomplete Inheritance

The heterozygotes have a phenotype that is intermediate between the phenotypes of the two homozygotes

Codominance

condition in which both alleles for a gene are expressed when present (cattle: red, white, roan coat = codominant)

Multiple Alleles -

Genetic Determination of Blood Type

Phenotype(Blood type)

Genotypes

O

A

AB

B

IA IB

IB IB or IB i

IA IA or IA i

ii

For many genes several alleles exist in the population.

Multiple alleles control the character of blood type in humans.

There are six possible genotypes.

The alleles IA and IB exhibit codominance, meaning that a heterozygote expresses both traits.

http://www.youtube.com/watch?v=L06TJTMVkBo

Polygenic inheritance

When two or more genes affect a single character

In humans, height, eye and skin color have polygenic inheritance

The Environment - Epigenetics

Phenotype depends on environment as well as genes

Temperature affects fur color in Siamese cats

In humansNutrition affects built

Exposure to sun affects skin tone

Sex-Linked Genes (any gene located on sex chromosomes)

http://www.youtube.com/watch?v=EGzFsme22s8

Bill Nye – Greatest Scientific Discoveries (genetics 3:40-8:00)

HUMAN KARYOTYPE

A display of all the 46chromosomes of an Individual.

http://www.youtube.com/watch?v=CWyrp3hu4KE

Morgan's monohybrid cross for fly eye color produced a 3 : 1 phenotypic ratio of red to white eyes in the F2 generation. However, none of the flies with white eyes were female.

Chromosome Theory of Inheritance

Genes are located on chromosomes

Behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns – chromosomes undergo segregation and independent assortment during meiosis

INDEPENDENT ASSORTMENT OF CHROMOSOMESDURING GAMETEFORMATION

Gene locus: location at which alleles of a gene reside on homologous chromosomes

Linked genes: genes that are located in the same region of a chromosome

Genetic linkage: tendency for the alleles on one chromosome to be inherited together. The closer two genes are on a chromosome, the greater the genetic linkage

Meiosis

• Organisms that reproduce sexually have specialized cells called gametes (sex cells)

• Gametes are the result of a type of cell division called meiosis

Diploid and haploid

• Almost all human cells are diploid or containing two homologous sets of chromosomes

2n = 46• Eggs and sperm cells (gametes) are haploid or

containing a single set of chromosomes n = 23

MITOSIS

Meiosis

In the human life cycle a haploid egg and sperm fuse and form a diploid zygote. Mitosis produces an embryo with numerous cells that continue to multiply and develop.

haploid egg and sperm

diploid zygote

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio17.swf::Comparison%20of%20Meiosis%20and%20Mitosis

2n

2n 2n

MITOSISMEIOSIS

Original diploid cell

2 diploid daughter cells

Genetic variation is a result of two processes that occurs during meiosis:

• Independent assortment of chromosomes, and • Crossing over

• During metaphase I, the independent assortment of chromosomes that end up in the resulting cells occurs randomly

• Crossing over: exchange of genetic material between homologous chromosomes during prophase I of meiosis

• Genetic recombination: new combination of genetic information in a gamete as a result of crossing over during prophase I of meiosis

(pages 195, 200, & 201) MITOSIS MEIOSIS

TYPE OF CELL (that undergoes this division)

# OF CELL DIVISIONS

Starts/ends as diploid or haploid cell

# OF DAUGHTER CELLS

# OF CHROMOSOMES AFTER DIVISION

EXCHANGE OF DNA (Y/N)

UNIQUE OR IDENTICAL CELL AFTER DIVISION

Development of egg and sperm