Cell Biology and Genetics Exam 3

cell cycle

interphase → mitosis or meiosis → cytokinesis

sister chromatids

half of a chromosome

homologous chromosomes

same trait, different allele

non-homologous chromosomes

different traits

locus

a gene’s location on a chromosome

haploid

half of a set of chromosomes

diploid

one set of chromosomes

human chromosomes

humans contain 23 pairs of chromosomes

• 22 pairs of autosomes

• 1 pair of sex chromosomes

sex chromosome

• X = female, 1,100 genes

• Y = male, 450 genes

• female is better for survival

heredity

transmission of traits from one generation to the next

trait

a variant of a character

character

a heritable feature that varies among individuals

genetics

study of heredity

karyotype

chromosomal make-up

mitosis vs meiosis

• mitosis produces diploid cells (one division, somatic cells)

• meiosis produces haploid cells (two divisions, gametes)

sperm and oocyte anatomy

• zona pellucida egg membrane provides protection

• only head of sperm penetrates membrane to form zygote

sexual reproducing organism

• in animals, only gametes are haploid

• plants and some algae have haploid multicellular stage

• fungi and some protist primarily have haploid unicellular stage

prophase I

• mitotic spindle forms, chromosomes condense, and nuclear envelope disappears

• crossing over occurs at chiasmata (location where non-sister chromatids intersect)

• microtubules (centrosome) attach to kinetochores at centromere

metaphase I

chromosomes line up on metaphase plate

• chromatids of one homologous pair is attached to microtubules on one pole, chromatids of other homolog is attached to microtubules at opposite pole

anaphase I

proteins that hold homologous chromosomes together are degraded and homologous chromosomes are pulled to opposite poles

telophase I

nucleus divides, nuclear envelope reappears, spindles disappear

cytokinesis I

cytoplasm divides

prophase II

(meiosis)

• mitotic spindle forms, chromosomes condense, and nuclear envelope disappears

• microtubules (centrosome) attach to kinetochores at the centromere

• no crossing over occurs at this point

metaphase II

(meiosis)

chromosomes line up on metaphase plate

• due to crossing over, sister chromatids aren’t identical

anaphase II

breakdown of proteins that hold sister chromatids together

• sister chromatids separate and are pulled to opposite poles

telophase II and cytokinesis II

(meiosis)

nuclear envelope reappears, chromosomes become less condense and microtubules disassemble

egg meiosis

1. egg arrests in prophase I after birth

2. after puberty, egg completes meiosis and arrests in metaphase II

3. after fertilization, egg completes meiosis II

non-disjunction

causes aneuploidy

• chromosomes fail to properly separate

• Ex: Trisomy 21 - chromosome 21 fails to properly separate = Down Syndrome

• in sex-chromosomes: Turner syndrome (X), Klinefelter’s syndrome (XXY), Jacob syndrome (XYY)

aneuploidy

the occurrence of one or more extra or missing chromosomes in a cell or organism

factors that create genetic variation

• crossing over- creates recombinant chromosomes

• independent assortment- creates different combinations of genetic material in gametes

• random fertilization- creates different combinations of zygotes

crossing over and synapsis process

1. homologous chromosomes align precisely (corresponding genes match up). DNA of non-sister chromatids is broken by specific proteins

2. synaptonemal complex holds homologous chromosomes (sister chromatids) tightly together, chromosomes now in synapsis

3. broken ends are fixed by joining segment of sister chromatid from homologous chromosome

4. synaptonemal complex dissembles and chromatids begin moving toward metaphase plate

independent assortment

chromosomes (and by extension alleles) are sorted into gametes independently of other genes

genotype

genetic makeup

phenotype

physical makeup

allele

different versions of gene

heredity

transmission of traits from one generation to the next

trait

a variant of a character

character

a heritable feature that varies among individuals

genetics

study of heredity

Lamarck inheritance

acquired traits can be inherited

• Jean Baptiste Lamarck (1744-1829)

• long neck giraffe

Mendelian inheritance

Gregor Mendel (1822-1884) conducted pea plant experiments to gather evidence to show how traits are inherited

• determined dominant traits are expressed over recessive traits

• determined organisms only inherit two copies of a gene

• P generation (parental generation), F1 generation (parental generation offspring), F2 generation (F1 generation offspring)

• true-breeding (homozygous for specific alleles)

law of segregation

alleles are present for each trait and segregate during division

law of independent assortment

the inheritance of one character has no impact on the inheritance of another character

common complete-dominance recessive disorders

• sickle cell

• cystic fibrosis

• Tay-Sachs

common complete-dominance dominant disorders

• Huntington’s disease

• autosomal dominant polycystic kidney disease

• osteopetrosis

exceptions to Mendelian inheritance

Mendel stated dominant alleles mask recessive alleles for a given trait. Except:

• incomplete dominance

• codominance

• epistasis

• polygenic inheritance

• epigenetic inheritance

incomplete (partial) dominance

• Carl Correns (1864-1933)

• snap dragon experiment

• the intermediate phenotype of two traits

incomplete dominance in humans

humans have a straight hair allele and a curly hair allele, people who inherit both alleles have wavy hair

• straight hair - homozygous; incomplete dominant

• curly hair - homozygous; incomplete dominant

• wavy hair - heterozygous; a mix (straight and curly)

codominance

two traits are equally dominant, therefore both are present

• ex: calico cats - multiple colors are expressed

• ex: AB blood type (O is recessive)

epistasis

one gene influences the phenotype produced by another gene

• ex: Labradors - black is dominant to brown; pigment is only deposited if pigment localization protein is present (if not = yellow)

polygenic inheritance

traits are controlled by two or more genes

• skin color

epigenetic inheritance

traits are influenced by environment

• challenges ideal genetic makeup is 100% a mixture of parent’s DNA

• ex: variations in identical twins

sex-linked traits

• X chromosome = female chromosome (1,100 genes)

• Y chromosome = male chromosome (450 genes)

sex-linked conditions

men primarily inherit sex-linked traits because they lack extra X to mask recessive traits

• ex: Duchenne Muscular Dystrophy; Hemophilia; Color Blindness

Duchenne Muscular Dystrophy

muscles deteriorate as a result of essential muscle proteins

Hemophilia

blood unable to form clots, due to defects in platelets

multiplication rule in determining probability

multiply probability of two independent events occurring at the same time (or from the same sample group at different times)

addition rule in determining probability

add probability of two mutually exclusive events

chromosomal theory of inheritance

genes have specific locations (loci) on chromosomes, that undergo segregation and independent assortment

genes in the human body

each chromosome contains hundreds/thousands of genes

model organism

an organism extensively studied to understand different biological processes and how these biological processes work across a wide range of species

• cost, reproducibility, manipulability

• ex: rat, mouse, fruit fly

Thomas Morgan

provided the first piece of evidence that suggested specific genes correspond with specific chromosomes

• Drosophila melanogaster (fruit fly) - crossed red eyes until found white eyed fly; crossed white eyed and red eyed, all F1 progeny had red eyes; crossed F1 and found 3:1 red to white eye ratio in F2

family pedigree

helps to determine genetic family lineage; used in genetic tracing studies

Barr bodies

female mammals have one X-chromosome inactivate (becomes heterochromatin)

• random in each individual cell (either X)

law of independent assortment

suggests alleles for one trait do not influence the inheritance for an allele of another trait

• Mendel

• Thomas Morgan exceptions

linked genes

sit close together on a chromosome, making them likely to be inherited together

• genes on separate chromosomes are never linked

• not all genes on a chromosome are linked

deletion

(chromosome alteration)

loss of chromosome fragment

• ex: Prader-Willi and Angelman Syndromes

duplication

(chromosome alteration)

portions of chromosome are copied

• ex: Charcot Marie Tooth Disease

inversion

(chromosome alteration)

portions of chromosome locations are switched

• ex: Walker-Warburg Syndrome

translocation

(chromosome alteration)

portions of one chromosome move to another chromosome

• ex: Emmanuel Syndrome

Prader-WIlli Syndrome

chromosomal deletion on the paternal copy of chromosome 15

• symptoms: hypogonadism, hyperphagia, obesity, intellectual disabilities, etc.

Angelman Syndrome

chromosomal deletion on the maternal copy of chromosome 15

• symptoms: ataxia, uncontrolled laughing and smiling, seizures, minimal speech, etc.

Charcot Marie Tooth Disease

chromosomal duplication on chromosome 17

• symptoms: defects in motor and sensory neurons; arched foot

Walker-Warburg Syndrome

a condition caused by an inversion on chromosome 9

• most severe of the muscular dystrophies - impacts brain, eye, and muscle development

• life expectancy = 3 years

Emmanuel Syndrome

a condition caused by chromosome translocation

• symptoms: hypotonia, delayed growth, small jaw, microcephaly

mitochondrial DNA (mtDNA) defects

primarily affect muscle and nervous tissue

• mitochondrial myopathy

• Leber’s heredity optic neuropathy

anaphase

chromosomes pulled apart

gametes

egg and sperm

HeLa Cells

human cells used for research

zygote

sperm fertilized egg

cytokinesis

cytoplasm divides

binary fission

how bacteria are produced

heredity

transmission of traits from one generation to the next

hemophilia

one of the sex-linked traits

telomere

end of chromosome

mitosis

process needed to replace somatic cells

Turner Syndrome

a single X syndrome

locus

the location of a gene on a chromosome

pea plant

focal species of Mendel’s research

phenotype

physical makeup

centrosome

organize microtubules

epistasis

one gene directly impacts another

codominant

AB blood type

haploid

half of a chromosome set

interphase

G1 - S - G2

diploid

one set of chromosomes

genetics

the study of heredity

partial

intermediate phenotype

gene

a coding region of DNA

Duchenne Muscular Dystrophy, Hemophilia, Color Blindness

name 3 X-linked traits discussed in class