PATTERNS OF INHERITANCE Chapter 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

Mendel’s experiments with pea plants 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

https://www.youtube.com/watch?v=hf9XlqXcal0 3:00 https://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 46 chromosomes of an Individual.

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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 Punnett Square: Diagram used to show the probability of a genetic cross Probability: Chance of Something happening

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

crossing of organisms differing in two characters 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

Intermediate or incomplete inheritance Codominance Multiple alleles Not all traits are inherited following the patterns found by Mendel in pea plants Intermediate or incomplete inheritance Codominance Multiple alleles Polygenic inheritance Environment - 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

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

Genetic Determination of Blood Type Multiple Alleles - Genetic Determination of Blood Type 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. Phenotype (Blood type) Genotypes O ii A IA IA or IA i B IB IB or IB i AB IA IB

http://ww w.youtube .com/watc h?v=L06T JTMVkBo

Polygenic inheritance When two or more genes affect a single character In humans, height, eye and skin color have polygenic inheritance Polygenic inheritance

The Environment - Epigenetics Phenotype depends on environment as well as genes Temperature affects fur color in Siamese cats In humans Nutrition 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 46 chromosomes 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 CHROMOSOMES DURING GAMETE FORMATION

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

haploid egg and sperm diploid zygote 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.

2 diploid daughter cells 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 MEIOSIS MITOSIS Original diploid cell 2n 2n 2n 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

MITOSIS MEIOSIS TYPE OF CELL (that undergoes this division) (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