Genetics Exam 1

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Dolly sheep experiment procedure & significance

used cytoplasmic and nuclear donor of nucleus and mammary cells to create the first instance of successful mammal cloning

idea of preformation/humunculus

17th and 18th century idea that humans develop from miniature versions of themselves that are either in the egg (ovist), or sperm (spermist) - now discredited (obviously)

blending hypothesis

outdated theory that traits from each parent were blended onto offspring

why did Mendel use peas

cross-breed them easily, multiple characters, short lifespan, big sample size (high reproductive rate & self fertilization)

how did Mendel cross fertilize pea plants?

cut off anthers of one flower, transfer anthers from another flower into the original flower’s stigma, plants seeds in peas

7 characters studied by Mendel

height, flower color & position, seed color & shape, pod color & shape

true breeding

when individuals with a particular trait are bred together and offspring have the same trait as parents (trait is homozygous)

monohybrid cross

A monohybrid cross is a genetic cross between two individuals that differ in only one trait. Single gene/allele from each parent.

how did Mendel discover recessive, and heterozygous traits?

bred two true breeding parents of different parents, found all offspring had one trait, and amongst the offspring self fertilizing, the more common trait was present 3:1

Particulate theory of inheritance

Mendel - hereditary traits are determined by discrete units called genes, which are passed from parents to offspring. Genes are individual and do not blend in reproduction

genotype vs phenotype

Genotype refers to the genetic makeup of an organism (allele combination), phenotype are physical characteristics.

gene vs allele

A gene is a segment of DNA with specific instructions for building a protein. An allele is a variant form of a gene.

homozygous vs heterozygous

homozygous two identical alleles. heterozygous two different alleles

dominant vs recessive

dominant masks recessive. dominant is expressed if one allele is present, recessive is only expressed if both alleles are recessive.

somatic cell vs gamete

A somatic cell is any cell in the body except for reproductive cells (diploid & mitosis). Gametes are reproductive cells (gamete and egg, haploid & meiosis).

diploid vs haploid

diploid cells have two sets of chromosomes, one from each parent. haploid cells have one set of chromosomes.

law of segregation and what it tells you

two alleles for a given gene segregate away from each other during the production of gametes (think of diploid to haploid) - tells you that the segregation is random

what are Punnett squares and why is it important that we understand how to set them up?

we can predict offspring traits and better understand genetic inheritance

Test Cross

Dominant phenotype individual, cross with a recessive phenotypic individual to know if the dominant phenotypic individual is homozygous or heterozygous

goal of mitosis

diploid parent cell forms two diploid daughter cells (daughter cells look genetically identical)

Which cell cycle phase is the shortest?

Mitosis

Interphase includes…

G1, S, G2

S phase

DNA replication

G1 & G2 Phase

cell growth, protein synthesis, checkpoints (G1 checks mitotic issues, G2 checks replication errors)

how long does a normal cell go through the cell cycle typically?

approx. 24 hours

linked assortment hypothesis

certain genes located close to each other on the same chromosome tend to be inherited together (wrong)

independent assortment hypothesis

different PAIRS of genes (alleles) separate independently into gametes during meiosis. (correct)

Dihybrid cross

breeding including two different traits (genes) that are located on separate pairs of homologous chromosomes

dihybrid cross heterozygous ratio

9:3:3:1

genetic polymorphism

refers to the presence of multiple variations (alleles) of particular genes within a population

wild type allele criteria (4)

most prevalent alleles, promotes reproductive fitness, DOES NOT MEAN DOMINANT, there can be more than one wild type allele

Mutant alleles

non wild type alleles, commonly recessive, can be dominant (gain of function allele, dominant-negative allele)

when are most mutations for alleles usually produced?

during DNA replication (common but many are inconsequential)

what are some reasons to why do mutations cause a lack of function?

blocks activity (screws up as a protein), blocks folding, blocks transcription of a particular enzyme,

gain of function allele

type of mutant allele that results in a gene having a new or enhanced function when compared to the wild type allele

dominant negative allele

mutant allele that can negatively effect the ability of the wild type allele to function

polydactyly is an example of

a dominant allele mutation that exhibits incomplete penetrance

incomplete penetrance

individuals carrying a specific genetic mutation do not always express the expected phenotype

expressivity

the range of a allele (gene’s) phenotypic expression in an individual

interphase

growth, DNA replication, cell functions (cells spend most of their time here)

chromosomes

condensed DNA and proteins

centromere

part of a chromosome where sister chromatids are held together

chromatids

strands of replicated chromosomes

Prophase

(before) nucleus is present, chromosomes are condensing, nuclear membrane/envelope is beginning to break down, spindle fibers/microtubules begin to form and extend from opposite ends of the cell, centrioles present

Metaphase

(middle) chromosomes align at the middle of the cell, spindle fibers attach to chromosome’s (two sister chromatids) centromeres (kinetochore region). Metaphase plate forms, bivalent attachment occurs

Anaphase

sister chromatids separate and are pulled to centrioles by spindles

Telophase

spindles break down, nuclei reforms

sister chromatid vs homologous chromosome

sister chromatids are like identical twins of a single chromosome (same color and shape) while homo chromosomes are not identical, but work together (similar shapes, usually different colors unless it’s after replication)

centriole

organelles commonly found on opposite ends of the cell that contain microtubules

centrosome

contains a pair of centrioles, organizes microtubules

kinetochore

protein structure that forms on centromere region of a chromosome

metaphase plate

tells where cytokinesis will occur later

bivalent attachment

proper and stable attachment of homologous chromosomes to the microtubules of the spindle

Cytokinesis

cleavage furrow forms and cytoplasm is eventually divided into two and two daughter cells are formed that are genetically identical to parent

actin’s role in mitosis

animal cell protein that is responsible for forming a contractile ring (cleavage furrow process) in cytokinesis

how is cytokinesis different in plant cells?

due to a rigid cell wall, a cell plate is formed instead of a cleavage furrow to separate two daughter cells

After replication, a homologous pair of chromosomes (different colors but similar shape), turn into

two sets of homologous chromosomes that are each similar in color, and each contain two sister chromatids

s phase

DNA replication & metabolic activity

prophase 1

chromosomes condense, thicken, align with homologous pairs - CROSSING OVER occurs

metaphase 1

chromosome pairs align at middle of cell

anaphase 1

spindle fibers pull away chromosome pairs to opposite sides of the cell

telophase 1

nuclear envelope reforms, revealing two distinct nuclei

prophase 2

spindles begin to form in each distinct nuclei

metaphase 2

chromosomes align in the middle of each distinct nuclei

anaphase 2

sister chromatids are pulled to opposite ends the cell by spindle fibers (each chromatid is now a referred to as a chromosome)

telophase 2

nuclei reforming, two cells divide into four cells

karyokinesis vs cytokinesis

karyokinesis is the division of the cell nucleus and separation of chromosomes while cytokinesis is the division of the cytoplasm and separation of other cellular components

Mendel's work with two-factor (dihybrid) crosses led directly to which law?

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law of independent assortment

Mendel’s work with one factor monohybrid crosses led directly to what law?

law of segregation

complete dominance

for a given gene, the dominant allele completely masks the other allele

incomplete dominance

neither allele is completely dominant over the other, in which heterozygotes display a phenotypic blend

tay Sachs disease incomplete dominance example

homozygous recessive disease, but individuals who are heterozygous only have about half of normal enzyme function that of a normal individual (on a genotypic-molecular level)

over dominance (heterozygous advantage)

heterozygous genotype when viewing two different genes, has higher selective advantage/reproductive fitness

sickle cell disease overdominance example

Ss heterozygous individuals have an advantage against both non sickle cell, and being malaria resistant. While homozygous dominant are at a disadvantage having no malaria resistance, and homozygous recessive being full sickle cell disease

hybrid vigor (heterosis)

highly unrelated individuals mate, offspring will be heterozygous at most loci, often healthy and vigorous. ex: hybrid corn and mutts

inbreeding depression

two closely related individuals mate, many of same alleles, offspring are homozygous at many loci, often less vigorous, high incidence of recessive genetic disease

Co-Dominance

two dominant alleles, in which phenotypes are both expressed, neither of which are compromised.

Mechanisms to explain overdominance (3)

disease resistance, versatility in dimer formation (enzyme functional diversity), variation in functional activity

codominance example (ABO blood type)

blood types with a mix of genotype (ex: IA & IB), express both type A antigens and type B antigens, and neither are compromised

ABO blood types and antibody composition

depending on blood type, your body produces anti antigens for the blood type you do not have (note: type O can give their blood to anybody b/c they have no A or B antigens)

sex-linked inheritance

genes responsible for certain traits are located on sex chromosomes

hemizygous

in males, sex chromosomes are XY, and these chromosomes are very different from each other

ichthyosis sex linked inheritance example

impacts male skin, making it scaly, on X chromosome

reciprocal cross

in two crosses, first take a affected male and breed with a unaffected female, then, in the reciprocal cross, take a unaffected male and breed with a affected female. if ratios are different between crosses, it tells you the gene is X linked

X linked traits

can impact both males and females

Y linked traits

exclusively impact males

holandric genes

genes only found on Y chromosomes

SRY genes

found on Y chromosome in mammals, gene activation causes testosterone boost to signal male sex development

pseudoautosomal

fake autosomal inheritance so it looks autosomal, but truly is not

mic 2 gene example

of pseudoautosomal gene

sex influenced traits

trait influenced by what sex you are, commonly found in heterozygotes

example of sex influenced trait

scurs in cattle, Sc Sc = scurs in both sexes, but Sc sc = scuts in males only.

Sex limited trait

only seen in one sex & never in another (ex: physical appearance differences)

pleiotropy

one gene that is responsible/contributes to multiple different phenotypes

CFTR mutations are an example of

pleiotropy

epistasis

one gene can modify the effects of a completely different gene (multiple genes contributing to a common pathway)

epistasis example

phenotype of purple pigment is only expressed when complementation occurs in white pea plants

maternal effect genes

non mandelian inheritance pattern, only thing that influences phenotype of offspring is the genotype of the mother

null hypothesis

data observed are the result of random chance alone

chi squared formula

x^2 = (o-e)^2/e