Genetics Final

Monohybrid Cross

A cross between two true-breeding (Homozygous dominant and homozygous recessive) parents with different variants for a given character to follow one character from generation to generation.

Monohybrid Cross Generations

P: Tall x Dwarf

F1: All tall

F2: 3 Tall: 1 dwarf

Dihybrid Cross

Track two traits that are inherited independently

F2 ratio of a dihybrid cross

9:3:3:1

Gene

unit of heredity that may influence outcome of a trait in an organism

Trait

characteristics of an organism

Dominant allele

allele that determines the phenotype in the heterozygous condition

recessive allele

allele masked by the presence of a dominant allele

True breeding

organism is homozygous for selected trait(s)

Homozygous

diploid individual with two identical alleles of a gene

Heterozygous

two different alleles for a particular trait

genotype

The genetic makeup of an organism

phenotype

The observable characteristics of an organism

Law of segregation

During gamete formation, the alleles for a trait separate from each other, so each gamete carries only one allele for that trait.

When does the law of segregation occur in cell divison?

Anaphase of Meiosis I

What experiment led to the creation of the law of segregation?

Mendel’s monohybrid cross with a 3:1 ratio.

Law of Independent Assortment

Two different genes will randomly assort their alleles during the process that gives rise to gametes.

When does the law of assortment occur?

Metaphase of meiosis I

What experiment led to the law of independent assortment?

Mendel’s dihybrid cross with 9:3:3:1 ratio.

Prophase of mitosis

Chromosomes condense and become visible. Nuclear membrane dissolves. Spindle fibers form and attach to chromosomes.

Metaphase of mitosis

Sister chromatids align in the middle and are attached to both poles by microtubules

Anaphase of mitosis

sister chromatids separate and move towards opposite poles of the cell, pulled by spindle fibers.

Telophase of mitosis

Chromosomes reach opposite poles and nuclear envelope reforms around each set of chromosomes.

Prophase of meiosis I

chromosomes condense and pair up, forming tetrads. Nuclear envelope breaks down, spindle fibers form, and homologous chromosomes cross over.

metaphase of meiosis I

Pairs of sister chromatids align at the metaphase plate.

Anaphase of meiosis I

The two pairs of sister chromatids separate and migrate to a pole

Telophase of meiosis I

the nuclear envelope reforms around the separated chromosomes.

Cytokinesis of mitosis

resulting in two daughter cells

Cytokinesis of meiosis I

results in two daughter cells containing half the number of chromosomes as the parent cell

prophase of meiosis II

Same as prophase of mitosis

metaphase of meiosis II

Same as metaphase of mitosis

Anaphase of meiosis II

Same as anaphase of mitosis

Telophase of meiosis II

Chromosomes reach respective poles and decondense while the nuclear membrane reforms.

Cytokinesis of meiosis II

results in 4 haploid cells

testcross

used to determine the genotype of an individual displaying a dominant trait by crossing the individual with a homozygous recessive individual

wild-type allele

the most common or naturally occurring form of a gene in a population

mutant allele

altered version of a gene that can cause changes in an organism's phenotype

Why can heterozygotes display the same phenotype as a homozygous dominant individual when they only have a single copy of the dominant allele?

half of the enzymes is sufficient or the dominant copy is upregulated

Complete dominance

dominant allele is fully expressed, while the recessive allele remains hidden

codominance

both alleles in a gene pair are fully expressed, resulting in a phenotype that shows traits from both alleles

X-linked inheritance

Genetic inheritance pattern where the gene responsible for a trait or disorder is located on the X chromosome.

Y-linked

Y-linked refers to genes located on the Y chromosome. These genes are passed down exclusively from fathers to their sons.

Sex-influenced inheritance

expression of traits that varies between sexes due to hormonal difference

reciprocal cross

helps determine if the inheritance pattern is influenced by parental sex

incomplete penetrance

a situation in which an allele that is expected to cause a particular phenotype does not

expressivity

degree to which a gene or trait is expressed in an individual

incomplete dominance

intermediate phenotype is expressed when both alleles are present

overdominance

a heterozygote has greater reproductive success than either of the corresponding homozygotes

Codominance

When both alleles of a gene are fully expressed in the phenotype, resulting in a heterozygous individual displaying traits of both alleles

pleiotropy

a single gene influences multiple traits or characteristics in an organism

epistasis

one gene masks or modifies the expression of another gene

Chi-Square formula

Σ((O - E)^2 / E)

gene mapping steps

1. determine parentals

2. determine double crossovers

3. determine middle gene

4. find short map distances

5. find long map distance

Formula used for map distance

recombinants/ total number of offspring

Three ways scientists can organize and classify chromosomes

size, location of centromere, and g-banding

deletion

region of a gene is lost

insertion

genetic mutation where a nucleotide is added to a DNA sequence, altering the genetic code.

duplications

a region of a gene is repeated

inversions

a region of a gene is reversed

simple translocations

part of one chromosome is attached to another chromosome

reciprocal translocations

swapping regions in two different chromosomes

When will deletions result in phenotypic effects?

when they remove or alter necessary genes

When will duplications result in phenotypic effects?

when they involve a large piece of a chromosome or occur in multiple generations

When will inversions result in phenotypic effects?

when the location of a gene changes and causes a change in expression

When will translocations result in phenotypic effects?

when they have position effect, break up an essential gene, or are imbalanced

Which type of chromosomal abnormality results in the formation of gene families?

Duplications

Why are gene families evolutionarily important for a species?

allow for the evolution of new gene functions while preserving essential ones to increase diversity

Balanced translocations

when segments from two different chromosomes swap places without any loss or gain of genetic material

Unbalanced translocations

when exchange of genetic material between chromosomes is unequal, resulting in an abnormality

Between balanced translocation and unbalanced translocation, which is more like to have a phenotypic effect?

unbalanced translocation

Non-homologous crossing over

DNA segments from non-homologous chromosomes exchange places due to the two chromosomes having the same repetitive sequences

Homologous crossing over

when two homologous chromosomes exchange piece

Euploid

when chromosomes are divided into equal sets

Diploid

two sets of chromosomes (2n)

triploid

three sets of chromosomes (3n)

tetraploid

four sets of chromosomes (4n)

Aneuploidy

total number of chromosomes cannot divide into equal sets

Trisomy

an additional chromosome (2n + 1)

monosomy

lacking a chromosome (2n - 1)

Experiment performed by Griffith

Showed that genetic material can be transferred between bacteria. Live harmless bacteria transformed into deadly bacteria when exposed to heat-killed bacteria.

Experiment from Avery, McCarty, and McCloud

Determined DNA as the genetic material. They used enzymes to destroy proteins, RNA, and lipids in a bacteria sample. Transformation only occurs when DNA is intact, proving it carries genetic information.

Experiment from Hershey and Chase

Demonstrated that DNA, not protein, is the genetic material. Bacteriophages were labeled with radioactive isotopes (sulfur for proteins and phosphate for bacteria), infecting bacteria. Only DNA was found inside the bacteria, supporting the conclusion that DNA carries genetic information.

Chemical structure of a nucleotide and the parts that make it up

At least one phosphate group, a pentose sugar, and a nitrogenous base

position of a phosphodiester bond

Attachment of a phosphate to the 3’ carbon in one nucleotide and to the 5’ carbon in another

function of a phosphodiester bond

Essential for the formation of the DNA double helix and the stability of the RNA molecule.

Four nitrogenous bases

Adenine (A), Thymine (T) Guanine (G) and Cytosine (C)

Purines

adenine (A) and guanine (G)

Pyrimidines

thymine, uracil (RNA), and cytosine

importance of hydrogen bonding to the structure of DNA

Stabilizing the double-stranded structure of the DNA

RNA polymerase II

reads DNA from 3’ to 5’ and produces it from 5’ to 3’

DNA helicase

an enzyme that separates the two strands of DNA by breaking hydrogen bonds

Topisomerase

travels in front of the helicase to relieve tension by cutting. untwisting, and ligating DNA back together

Primase

synthesizes short RNA primers during DNA reproduction.

DNA Ligase

catalyzes the formation of a covalent bond within the backbones of two DNA strands

End-replication problem

the ends of our chromosomes get a little bit shorter because a primer cannot be made upstream from the 3’ end

Telomerase

Maintains the length of telomeres by acting as a protective cap to help prevent DNA degradation

What cells express telomerase?

Stem cells

Euchromatin

Less condensed form of chromatin that is actively transcribed and accessible for gene expression

Heterochromatin

highly compacted regions of chromosomes in which DNA is transcriptionally inactive

Constitutive heterochromatin

always heterochromatin and permanently transcriptionally inactive