Genetics Exam 1 (Ch 2-4)

Meiosis produces

Sex cells, gametes, or spores

When cells are not undergoing division, genetic material is in what form?

Chromatin

Central Dogma

DNA --transcription-> RNA --translation-> Protein

Genetics

The branch of biology associated with the study of heredity and variation; the study of genes

Examples of humans and selective breeding

Animal domestication (horses, camels, oxen, dogs) and plant cultivation (maize, wheat, rice)

Homunculus

17th C idea that sex cells contain a complete, but miniature, adult

Gregor Mendel

His 1860s work led to understanding of variation and inheritance; basis for the modern field of genetics

What is critical to understanding genetics

The structure of DNA packaging

Chromosome theory of inheritance

inherited traits are controlled by genes on chromosomes that are transmitted through gametes

Diploid number (2n)

characteristic number of chromosomes in most eukaryotic cells; 2 complete sets

Haploid number (n)

the number of chromosomes in one complete set

Karyotype

a visual representation of ones chromosomes/genotype

p-arm

short arm of a chromosome (petite)

q arm

longer arm of a chromosome

Homologous chromosomes

Have the same centromere placement

Genome

the haploid set of chromosomes of a species

locus

identical gene sites along the lengths of homologous chromosomes

Sister chromatids

Replicated forms of a chromosome joined together by the centromere

If two chromosomes of a species are the same length and have similar centromere placements, yet are not homologous, what is different about them?

The genes they code for

Progeria

Rare, fatal genetic condition of accelerated aging resulting from defects in nuclear lamin; affects cell division and causes a lack of nuclear support

In G1, there is how much DNA content? Ploidy?

2x; 2n

In G2, there is how much DNA content? Ploidy?

4x; 2n

In pro I, there is how much DNA content? Ploidy?

4x; 2n

In telo I, there is how much DNA content? Ploidy?

2x; n

In pro II, there is how much DNA content? Ploidy?

2x; n

In telo II, there is how much DNA content? Ploidy?

1x; n

Cell cycle

repeating pattern of growth (interphase) and division (mitosis); G1->S->G2->Mitosis

Where are cell checkpoints in the cell cycle?

G1/S; G2/M; M

Interphase- Mitosis

DNA is replicated; growth; chromosomes are extended and uncoiled, forming chromatin

Prophase- Mitosis

Chromosomes condense; centrioles divide and move apart; nuclear envelope begins to break down

Sister chromatids are held together by

Cohesin

Prometaphase- Mitosis

Chromosomes are clearly double structures; centrioles reach the opposite poles; spindle fibers form; Chromosome movement! Nuclear envelope fully breaks down

Metaphase- Mitosis

Centromeres align on metaphase plate; cohesin is degraded by separase

kinetochore

A specialized region on the centromere that links each sister chromatid to the mitotic spindle.

What enzyme degrades Cohesin

Separase

What protein protects cohesin from being degraded at the centromere?

shugoshin

Anaphase- Mitosis

Centromeres split and sister chromosomes migrate to opposite poles

Disjunction

occurs during anaphase; it is the name for the process of the sister chromatids splitting

Telophase- Mitosis

The two cells re-enter interphase; 2 daughter cells are identical to each other and parent; cytokinesis results at the end of telophase (splitting of cytoplasm)

Heritability

ensures genetic continuity, each gamete recieves exactly one member of each homologous chromosome pair

Variation

Unique combinations of maternal and paternal homologous chromosomes

Crossing over

genetic exchange between members of each homologous pair of chromosomes producing mosaics (occurs in Prophase 1)

What is the major source of genetic recombination within a species

Meiosis

Synapsis

homologous chromosomes form pairs

Bivalent

Pair of synapsed homologous chromosomes

Tetrad

refers to the four chromatids within that group

Meiosis 1

reductional division; number of centromeres is reduced by half (produces 2 dyads)

Meiosis 2

equational division; number of centromeres remains equal (produces 4 monads)

Prophase 1- Meiosis

chromatin thickens and coils into visible chromosomes; synapsis and crossing over occurs

Metaplase 1- Meiosis

Homologous chromosomes align randomly

Anaphase 1- Meiosis

Homologous chromosomes separate

Telophase 1- Meiosis

Reductional division (2 haploid cells produced)

Meiosis 2

4 monads produced from equational division (haploid n)

In what ways does meiosis contribute to genetic variation

crossing over & independent assortment

How do homologous chromosomes find eachother

they look for similar loci in telomere convergence

Spermatogenesis

production of male gametes; occurs in testes

Oogenesis

production of female gametes; occurs in ovary

Meiosis achieves haploid number in order to prepare for

fertilization

diploid organisms store genetic info in

homologous chromosomes

true breeding strains

each trait that appears unchanged for multiple organisms

monohybrid crosses

reveals how a single trait is inherited

mendels traits were

reciprocal- not dependent on sex

What are mendels first 3 postulates

1). Unit factors- genetic characters are controlled by unit factors existing in pairs in individual organisms

2). Dominance/Recessiveness

3). Segregation- paired unit factors separate randomly so that each gamete receives one or the other with equal likelihood.

genotype

two unit factors in an individual

phenotype

physical expression

genes

unit factors

alleles

alternate forms

Punnet square convention

for letter selection, use the recessive trait as the letters

testcross

cross between an organism with an unknown genotype and an organism with a recessive phenotype

random fertilization

any sperm can fertilize any egg

Dihybrid cross

reveals how two traits are inherited

Product law

when two independent events occur simultaneously, the probability of the two outcomes occurring in combination is equal to the product of their individual probabilities of occurrence.

Mendels 4th postulate

independent assortment

independent assortment

during gamete formation, segregating pairs of unit factors assort independently of each other; means many possible gametes

trihybrid crosses can only be done when

each trait is on different chromosomes and they assort independently of one another

How to calculate gamete possibilities

2^n where n is haploid number

Sum law

the probability of obtaining any single outcome, where that outcome can be achieved by 2 or more events

chance deviation

just by chance the expected ratios will deviate

as sample size increases,

chance of deviation decreases

null hypothesis

there is no difference between the measured values and predicted values

Chi squared

(observed-expected)^2/expected

degrees of freedom

n-1 where n= number of possible outcomes

dont say accept null hypothesis, rather say

fail to reject

4 Categories of exceptions to Mendel's postulates

1). Dominance/recessive

2). 1 gene - 1 trait

3). 1 gene in pairs (2 alleles)

4). genotype-> phenotype

Examples of exceptions to dominance recessive postulate

incomplete dominance, codominance, multiple alleles, lethal alleles

Examples of exceptions to 1 gene- 1 trait postulate

pleiotropy

wildtype (WT)

allele that occurs most often in a population

Loss of function mutation

function of the WT allele is diminished; if entirely lost, it is called a null mutation

Gain of function mutation

function of WT allele is enhanced

Neutral mutation

function of the WT allele is unchanged

Incomplete (partial) dominance

offspring of parents with contrasting traits have an intermediate phenotype

Codominance

heteroygotes express both alleles as distinct gene products

Multiple alleles

when 3+ alleles of a gene exist; can only be studied in populations

Pleiotropy

when 1 gene affects multiple phenotypes

Recessive lethal allele

alleles that cause death in homozygous recessive individuals (Death depends on when gene product is required)

Dominant lethal allele

alleles that cause death with just one copy of an allele