BIOL 3301 Daane/Lin Exam 1 Notes

Pangenesis Theory

Early concept of heredity proposing that particles ("seeds") carry genetic information from different parts of the body to the reproductive organs.

Blending Hypothesis

the idea that genetic material from the two parents blends together.

Mendel's experiments with garden peas refute this idea.

Gregor Mendel

Augustinian monk and botanist whose experiments in breeding garden peas led to his eventual recognition as founder of the science of genetics (1822-1884)

* Ignored for 34 years, the title of work did not capture the importance of the work

* Lack of understanding of chromosome transmission

Pea Plant 7 Types

1. Seed form

2. Seed color

3. Pod form

4. Pod color

5. Flower color

6. Flower position

7. Stem length

Why the garden pea (Pisum sativum)?

* traits are true-breeding -invariant generation

* 4 of 7 traits studied fall on separate chromosomes

Characters

observable characteristics of an organism (ex. eye color)

Trait/Variant

specific properties of a character (ex. blue eyes)

Parent generation (P or P1)

the two plant selected to cross for a breeding experiment.

First generation (F1)

self pollinate each line

Second generation (F2)

assess traits in 2nd generation

genes

DNA segments that serve as the key functional units in hereditary transmission.

law of segregation

Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

homozygous

having two identical alleles for a trait AA

heterozygous

having two different alleles for a trait Aa

genotype

An organism's genetic makeup, or allele combinations.

phenotype

physical characteristics of an organism

law of independent assortment

each allele is separately and randomly passed to the next generation

- plant with genotype Tt can pass either T or t (but not both) to the next generation

RrYy x RrYy

9:3:3:1

probability

probability = number of times an event occurs / total number of events

probability that 2 independent events will occur

equal to the sum of their probabilites

ex. probability of getting tails 3 times?

1/5 1/5 1/5

degrees of freedom

n-1

a ____ is a variation of a gene

allele

chromosomes

structures that carry the genetic information

- composed of: DNA, proteins

chromatin

DNA-protein complex

haploid

(genetics) an organism or cell having only one complete set of chromosomes

diploid

containing two complete sets of chromosomes, one from each parent.

locus

Location of a gene on a chromosome

mitosis

cell division in which the nucleus divides into nuclei containing the same number of chromosomes

s phase

prior to mitosos

- chromosomes replicated

- duplicated chromosomes form a pair called sister chromatids, joined at a centromere

Interphase

Cell grows, performs its normal functions, and prepares for division; consists of G1, S, and G2 phases

G0

resting phase

Prophase

nuclear envelope dissociates into small vesicles

- chromosomes begin to separate

chromatids condense

prometaphase

centrosomes move to opposite ends of the cell emitting microtubules

- spindle fibers interact w/ sister chromatids; spindle apparatus forms

- two kinetochores on a pair of sister chromatids are attached to kinetochore MT on opposite poles

aster microtubules

important for positioning of the spindle apparatus

polar microtubules

help tp push the poles away from each other

kinetochore microtubules

attach to the kinetochore, which is bound to the centromere of each individual chromosome

metaphase

Chromosomes line up in the middle of the cell, called metaphase plate

each pair of chromatids (dyad) attached to both poles by kinetochore microtubules

anaphase

sister chromatids separate to a separate pole

kinetochore MTs shorten, polar MTs lengthen

telophase

chromosomes reach their poles and decondence

- nuclear membrane reforms to form two separate nuclei

cytokinesis

Division of the cytoplasm during cell division, cleavage furrow

meiosis

produces germ cells w/ only one set of chromosomes (haploid)

Meiosis I - Prophase I key events

The nuclear membrane dissolves.

Chromatin tightly coils up.

Homologous chromosomes, each composed of two sister chromatids, come together in pairs in a process called synapsis.

During synapsis, chromatids of homologous chromosomes exchange segments in a process called crossing over.

The chromosome tetrads move toward the center of the cell.

synapsis

the fusion of chromosome pairs at the start of meiosis.

crossing over, recombination

meiosis II: cell division

each daughter cell from meiosis divides again but without DNA replication, results in cells that are haploid

germ cells

haploid cells that fuse together to form a new diploid organism during fertilization

heterogamous

gametes are morphologically different

spermatogenesis

Formation of sperm

Oognesis

the production or development of an ovum.

- only one cell per meiosis becomes an egg

- division in meiosis I is asymmetric producing two haploid cells of unequal size

Which of the following does not occur during prophase of meiosis I?

separation of homologous chromosomes (anaphase)

the separation of homologs during meiosis explains the law of

segregation

the random alignment of homologs during meiosis explains the law of

independent assortment

monad

1 chromatid

dyad

paired sister chromatids

bivalent

paired homologous chromosomes

synapsis

pairing of homologous chromosomes during meiosis I

chiasma

site where crossing over occurs (point of physical contact between non-sister chromatids)

synaptonemal

complex that holds a DNA-protein mixture binding the chromosomes

kinetochore

attaches at centromere, a gene-poor region of a chromosome loaded w/ special nucleosomes

telomeres

ends of chromosomes, added on after DNA replication

- shrink slightly after every DNA replication

ploidy

counted by number of centromeres

Which of the following accurately reflects the relative chromosome composition at the beginning and end of meiosis II in humans?

1 N -> 1 N

Arrange the following events in the proper order in which they occur during meiosis I.

a = separation of homologous chromosomes

b = synapsis

c = crossing-over

b, c, a

simple mendellian inheritance involves

- a single gene with two different alleles

- alleles display a simple dominant/recessive relationship

wild-type alleles

prevalent alleles in a population

wild-type alleles encode proteins that

function normally and are made in proper amounts

mutant alleles

altered by mutation

mutant alleles are often defective in their ability to express a functional protein

- often inherited in a recessive fashion

- loss of function

knockout alleles

loss of function generated in the lab

Why are recessive alleles not observed in heterozygous individuals?

- 50% of normal protein is enough to accomplish protein's cellular function

- heterozygote may produce more than 50%

- normal gene "up-regulated t compensate for lack of function of defective allele

gain-of-function

protein encoded by the mutant gene is changed so it gains a new or abnormal function

dominant-negative

protein encoded by the mutant gene acts antagonistically to the normal protein

haplosufficiency

mutant is loss-of-function, but heterozygote does not make enough product to five the wild-type phenotype

incomplete penetrance

the genotype does not always produce the expected phenotype

expressivity

the degree to which a trait is expressed

ex. polydactyly influenced by environment, modifier genes

environmental effects on expressivity

- many traits vary in accordance w/ environment

- traits have a "reaction norm" of potential phenotypes

incomplete dominance

heterozygote exhibits a phenotype that is intermediate between corresponding homozygotes

ex. red x white = pink flowers

The arctic fox is primarily white in winter months, but brown in summer when it is warmer. What accounts for this phenomemon?

environmental effect

overdominance

a heterozygote has greater reproductive success compared with either of the corresponding homozygotes

"heterozygote advantage"

ex. sickle cell unaffected, malaria-resistant

explanations for overdominance

1. Disease resistance

2. Homodimer formation

3. Variation in functional activity

overdominance 1. disease resistance

microorganism will infect a cell if certain cellular proteins function optimally

- heterozygotes can have one altered copy of a gene

- not enough to cause serious side effects, but enough to prevent infections

overdominance 2. homodimer formation

many proteins function as homodimers, composed of two subunits encoded by the same type of gene

overdominance 3. functional activity

a gene, E, encodes a metabolic enzyme

Allele E1 encodes an enzyme that functions better at lower temp.

Allele E2 encodes an enzyme that functions better at higher temp.

Heterozygotes E1E2 encodes an enzyme that functions better at range of both temps.

multiple alleles

most populations have multiple allele variants at any given locus

in diploids, any individual has at most two of these alleles, but many variants present in the broader population

ex. blood type

co-dominance

both alleles are expressed and affect phenotype

blood type i

encodes a defective enzyme

blood type IA

encodes a form of the enzyme that can add the sugar N-acetylgalactosamine to the carbohydrate tree

blood type IB

encodes a form of the enzyme that can add sugar galactose to the carbohydrate tree

A male with blood type B and a woman with blood type A have a child with blood type AB. The blood type of the child is possible due to what type of inheritance pattern?

codominance

pseudoautosomal inheritance

refers to the very few genes found on both X and Y chromosomes

behave like autosomes (non sex chromosomes)

little recombination on

y chromosome

x-linked

hemizygous in males

- only one copy

- males are more likely to be affected

y-linked

relatively few genes in humans

- referred to as holandric genes

- transmitted only from father to son

lethal alleles

have the potential to cause death

- result of mutations in essential genes

- often recessive

- onle 1/3 of genes are essential

Pleiotropy

most genes affect > 1 trait

single genes causes multiple phenotypes

ex. cystic fibrosis

complementation

two affected parents have unaffected offspring due to having mutations in separate genes

epistasis

one gene masks phenotype of an allele of another gene

modifier

one gene modifies phenotype of an allele of another gene

redundancy

mutation in >= 2 genes necessary for phenotype

gene redundancy

one gene compensates for the function of another

- common w/ loss-of-function alleles (mutations that eliminate the activity of gene products)

gene knockout

loss-of-function in the lab mutation