Chapter 14: Mendel And The Gene Idea

Front 1

Character

Back 1

heritable feature that varies among individuals

Example: in flower, color.

Front 2

Trait

Back 2

variant for a character

Ex: flower color, white, or purple.

Front 3

True-Breeding

Back 3

Referring to plants that produce off-spring of the same variety when they self-pollinate.

Ex: plant with purple flowers is true-breeding if the seeds produced by self-pollination in succesive generations all give rise to plants with purple flowers too.

Front 4

Hybridization

Back 4

mating, or crossing of 2 true-breeding varities.

True-breeding parents: P-generation (parent gen.)

Hybrid offspring: F1-generation (first filial gen.)

F1 reproduces = F2 generation ( second filial gen.)

Front 5

Laws of Segregation

Back 5

Dominant Trait: a.k.a domiant allele, an allele that is fully expressed in the phenotype of a heterozygote.

Recessive Allele: an allele whose phenotypic effect is not observed in a heterozygote.

Front 6

Mendel's Model

Back 6

4-Related Concepts of 3:1 Inheritance Patterns

Front 7

1. Alternative versions of genes account for variations in inherited characters

Back 7

These alternative versions of a gene are alleles.

Ex: eye color is a single trait with many color variations; blue, green, hazelm brown.

Front 8

2. For each character, an organism inherits 2-alleles, one from each parent.

Back 8

each somatic cell in a diploid organism has 2-sets of chromosomes. Genetic locus usually represented twice in a diploid cell; once on eachi homolog of a specific pair of chromosomes.

Front 9

4. Law of Segregation: the 2 alleles for a heritable character seperate during gamete formation (after telophase 1) and end up in diff. gametes (variability).

Back 9

segregation like the distribution of the 2 members of a homologous pair of chromosomes to diff. gametes in meiosis.

Front 10

3. If the 2-alleles at a locus differ, then...

Back 10

1. the dominant allele determines the organisms appearance.

2. the recessive allele has no noticeable effect on the appearance.

Front 11

Punnentt Square

Back 11

diagrammatic devce for predicting the allele composition of off-spring from a cross between individuals of a know genetic make-up.

Front 12

Homozygous

Back 12

organism that has a pair of indentical alleles for a character; reside at same locus (location).

Ex: dominant = PP
recessive = pp

Front 13

Heterozygous

Back 13

organism that has 2 diff. alleles for a gene.

Ex: Pp

Front 14

Phenotype

Back 14

organism's appearance or observable traits.

Front 15

Genotype

Back 15

the genetic make-up of the phenotype; not observable.

Front 16

The Law of Independent Assortment

Back 16

Monohybrids: heterozygous for one-character (dealing w/ one trait)

Ex:hair or eye color

-all the offspring from a cross between parents homozygous for diff. alleles are monohybrids.

Ex: parents of genotypes AA and aa produce a monohybrid of genotype Aa.

Front 17

The Law of Independent Assortment (continued)

Back 17

Dihybrids: Individuals heterozygous for 2-characters (dealing with 2 traits at one time).

Ex: hair AND eye color

-all off-spring from cross between parents doubly homozygous for diff. alleles are dihybrids.

Ex: parents of genotype AABB and aabb produce a dihybrid of genotype AaBb.

Front 18

Law of Independent Assortment states that...

Back 18

each pair of alleles segregates independently of each other pair of alleles during gamete formation.

-law applies ONLY to genes (allele pairs) located on different chromosomes (chromosomes that are not homologous)

if F1 all RrYy = 4 possible gametes (RY, Ry, rY, ry). 16 possible gamete formations

If F2 shows 9:3:3:1 pheno ratio, sum of pheno ratio (16) = # of possible gamete combos

Front 19

Multiplication Rule

Back 19

to determine this probability we multiply the probability of one event by the other.

Ex: toss 2 coins at the same time, probability that both land tails: 1/2 x 1/2 = 1/4

Front 20

Addition Rule

Back 20

the probability that any one of 2 or more mutually exclusive events will occur is calculated by adding their individual probabilties.

Ex: Hetero (Rr) off-spring in a monohybrid cross: R from male and r from girl; probability = 1/4 or r from male and R from girl; probability = 1/4...1/4 + 1/4 = 1/2 genotypic ratio.

Front 21

Solving Complex Genetics Problems with the Rules of Probability

Back 21

Dihybrids, or other multi-character crosses is equivalent to 2 or more independent monhybrid crosses occuring simultaneously.

-calculating chance of offspring genotypes from such crosses, each character first considered seperately then the individual probabilties are multiplied.

Front 22

Degrees of Dominance

Back 22

1. Complete Dominance: the situation in which the phenotypes of the heterozygotes and dominant homozygote are indistinguishable.

Front 23

Patterns of Inheritance

Back 23

Greeks believed in Pangenesis: inheritance "particles" for every characteristic collected in eggs & sperm, passed to the next generation.

Front 24

19th Century "Blending Hypothesis"

Back 24

Characteristics of parents blend in offspring

Front 25

Gregor Mendel

Back 25

worked with peas b/c
1. short life span
2. numerous & distinctive characteristics
3.mating can be controlled

Intentionally self-fertilized flowers by covering with bag; generations of this = true-breeding plants

Cross-fertilized flowers by dusting carpels of one w/ pollen from another.

Published in obscure journal in 1866: argued there are discrete, heritable factors (genes) that retain individuality from generation to generation.

Front 26

Hemizygous

Back 26

indicates a gene is present & active w/ only one copy.

Front 27

Incomplete Dominance

Back 27

the situation in which the phenotype of heterozygous is intermediate between the phenotypes of individuals homozygous for either allele.

*F1 offspring may attain a phenotype that wasnt present in either parent.

*one allele not completely dominant in heterozygote.

Ex: red-snap dragons are crossed with white: All the F1 hybrids have pink flowers.

Front 28

Co-dominance

Back 28

2 alleles both affect the phenotype in seperate, distinguishable ways.

Ex: Human blood group MN (not A,B, or O) determinded by codominant alleles for 2 specific molecules located on the surface of red blood cells.

Front 29

Relationship Between Dominance and Phenotype

Back 29

For any character, the observed dominant (recessive relationship of all alleles depends on the level at which we examine phenotype).

Ex: Tay Sach's; only kids who inherit 2 copies of the disease alleles (homozygotes) have it.

Front 30

Tay Sachs at Multiple Levels

Back 30

Organismal = recessive

Biochemical = incomplete dominance

Molecular = TS allele is co-dominant

Front 31

Determining Unknown Genotypes

Back 31

Test Cross: crossing unknown genos (shows dominant pheno) with recessive pheno (homo).

-2 possible genotypes for unknown give diff pheno ratios in F1...
a. unknown homo- all offspring dominant pheno
b. unknown hetero- 1/2 offspring dominant, 1/2 recessive

Front 32

During Independent Assortment...

Back 32

1.Chromosomes randomly line up during Metaphase 1

2. Diff. alleles segregate independently of one another

3. Alleles of non-homologous chromosome assort independently during gamete formation

Front 33

2n Rule

Back 33

AaBBbbDdEeff

Q. How many Gametes?

A. 3 Heterozygous...2 ^3 = 8 Gametes

Front 34

Segregation Example

Back 34

P-gen: start w/ 2 true-breeding plants. The 2 genes specify seed color (Y- yellow, y- green) and seed shape (R- round, r- wrinkled). These 2 genes are on diff. chromosomes.

F1- R and r alleles seg. at Anaphase 1 = 2 types of daughter cells for this locus; each gamete gets 1 chromosome ( R or r) allele.

F2- fertilization recombines the R and r alleles at random.

Front 35

Independent Assortment Example

Back 35

F1- follow long and short chromosomes.Alleles at both locs seg. in Anaphase 1; 4 types of daughter cells depending on chrom. arrangement at Metaphase 1. Each gamete gets long and short chrom. in 1 of 4 allele combos.

F2- fertilization results in 9:3:3:1 pheno ratio

Front 36

Non-Mendelian Inheritance

Back 36

Inheritance that doesn't follow strict patterns of dominant vs. recessive (relationship between geno and pheno not simple).

Incomplete Dominance: one allele not completely dominant in heterozygote.

- in F1 offspring: may attain a pheno that wasnt present in either parent.

Front 37

Multiple Alleles

Back 37

Most genes exist in more than 2-allele forms.

Ex: ABO blood groups in humans. A, B, AB, O.

Front 38

Pleiotrophy

Back 38

ability of a single gene to have multiple effects.

Ex: responsible for the multiple symptoms associated with certain herditary disease (Sickle Cell, Anemia, Marfan's Syn).

Front 39

Epistasis

Back 39

gene at one locus alters the phenotypic expression of a gene at a second locus.

Ex: coat color in mice

Front 40

Quanitative Character

Back 40

heritalbe feature that varies continuously over a range rather than in either-or-fashion.

- usually indicates Polygen Inheritance: additive effect of 2 or more genes on a single phenotypic character (height).

Front 41

Autosomal Recessive Disorders

Back 41

Tay Sacs, Sickle Cell, Hungington's Achondroplasia, Neurofibromatosis.

Front 42

Norm of Reaction

Back 42

phenotypic range of particular genotype

Front 43

Multifactorial Characteristics

Back 43

Polygenic characters that are also influenced by the enviroment.

Front 44

Family Pedigree

Back 44

diagram of a family tree showing the occurance of heritable characters in parents and offspring over multiple generations.

- used to deduce possible genotypes of individuals and make predicitons.

Front 45

Behavior of Recessive Alleles

Back 45

genes code for proteins of specific function, so an allele thatt causes a genetic disorder codes for either a malfunctioning protein or no protein at all.

Front 46

Carriers

Back 46

individual who is hetero at a given locus w/ one normal allele and one recessive allele. The hetero is phenotypically dominant for the character determinded by the gene but can pass on the recessive allele to offspring.

Front 47

Consanguineous

Back 47

same blood matings.

- Indicated in pedigrees by double lines.

Front 48

Dominantly Inherited Disorders

Back 48

dominant alleles that cause a lethal disease are much less common than recessive alleles that do so.

- all lethal alleles arise by mutations in cells that produce sperm/eggs.

-occurs equally often wether mutant allele is dom. or rec.

-lethal dom. alleles eliminated from population if affected ppl die before reproducing.

-non-lethal dom. alleles and lethal ones that strike later in life inherited Mendelian way.

Ex: Achondroplasia, Huningtons.

Front 49

Multifactorial Disease

Back 49

Many human diseases have both genetic and enviromental components and do not follow simple Mendelian Inheritance patterns.

Front 50

Mapping Concept

Back 50

crossing over procedures new combos of genes.

- distance between genes on same chrom is proportional to the rate of recombination between genes.

Front 51

Sex and Inheritance

Back 51

sex determinded by chromosome.

Humans: non-identical homologous pair.

Female = XX
Male = XY (hemizygous)

Front 52

Sex-Linked Genes

Back 52

don't follow simple Mendelian Inheritance.

-Humans: most sex-linked characteristics are due to genes on X-chromosome.

Ex: color-blindness, muscular dystrophy, hemophilia.

Front 53

X-Inactivation in Female Mammals

Back 53

All normal females have only one functional x chromosome.

- the inactive x condenses inside the nuclear envelope, producing a Barr Body.

Front 54

Barr Body

Back 54

appears as dark spot in nucleus (so does nucleolous).

Front 55

Chromosomal Basis of Inheritance

Back 55

-genes on same chromosome tend to be inherited together

- genes located close together on same chromosome ("linked") dont follow principle of independ assortment

Front 56

SRY (Sex Determining Region of Y)

Back 56

gene on Y chromosome that hold male characteristics (testes)

Front 57

XIST ( X- Inactive Specific Transcript)

Back 57

active only on the Barr-Body chromosome.

-multiple copies of RNA product of this gene attatch to X-chromosome and cover it.

- cause cytosine residues to be methylated in such a way that the DNA may never be read or used to make proteins.

Front 58

Hereditary Factors During Sexual Life Cycles (Walter S. Sutton, Theodor Boveri)

Back 58

1. Chromosomes and genes are both present in pairs in diploid cells.

2. Homologous chromosomes seperate and alleles segregate during the process of meosis.

3. Fertilization restores the paired condition for both chromosomes and genes.

Front 59

Chromosome Theory of Inheritance

Back 59

genes are located on chromosomes and the behavior of them during meosis accounts for inheritance patterns.

-behavior of homologous during meosis account for seg. of the alleles at each locus to diff. gametes.

-behavior of non-homologous chroms account for independent assortment of alleles for 2 or more genes on diff. chroms.

Front 60

Morgan's Experiment

Back 60

-species of flies= drosophilia Melanogaster: 4 pairs of chroms.
-1907 in fly room
-discovered single fly w. white eyes instead of usual red.

Wild Type: phenotype for a character most commonly observed in natural populations.

Front 61

Genetic Recombination & Linkage (Unlinked)

Back 61

UnIinked Genes: 50% frequency of recombination for anyy 2 genes that are located on diff chromosomes.

-physical basis of recombination between unlinked genes is random orientation of homologous chromosomes at Metaphase 1 which leads to independent assortment of the 2 unlinked genes.

Front 62

Recombination of Linked Genes: Crossing Over

Back 62

Crossing Over: some process had to occasionally break the physical connection between specific alleles of genes on some chromosome.