biology

what is genetics

study of heredity and variation

what is phenotype

observable trait

what is genotype

allele combination

DNA

molecule storing genetic info

gene

sequence encoding a trait/product

allele

alternative version of a gene

locus

position of a gene on a chromosome

chromosome

DNA + protein structure carrying genes

genome

all of an organism's DNA

genomics

study of whole genomes

mutation

heritable change in DNA (source of new alleles)

evolution

change in allele frequencies/genetic makeup of populations over generations.

Model organism traits

short generation time, easy/cheap to cultivate, genetically tractable, many offspring, small size

Model organism examples

E. coli, yeast, C. elegans, flies

Artificial selection

humans choose which individuals mate to shape the next generation's traits, with no guarantee of results

Pangenesis

info travels from body parts to gametes, incorrect

Inheritance of acquired characteristics

traits acquired in life are inherited by offspring, false

Preformationism

mini organism begins inside as homunculus, incorrect

Blending inheritance

incorrect

Germ-plasm theory

germ-line tissue holds the complete genetic info and passes it to gametes, correct

Cell theory

correct

Mendelian inheritance

correct

Prokaryote

circular chromosome, no nucleus, no histones

eukaryote

linear chromosomes, a nucleus, and DNA wrapped on histones

Somatic

body cells, diploid

gametes

sperm/egg, haploid

Chromosome structure: G1

each chromosome is one chromatid (1 DNA molecule)

Chromosome structure: after S phase

two identical sister chromatids joined at the centromere (cohesin), still counted as one chromosome but 2 DNA molecules. A chromatid becomes its own chromosome when sisters separate in anaphase.

Cell cycle: G1

growth

Cell cycle: S

DNA replication

Cell cycle: G2

prep

Cell cycle: M

mitosis and cytokinesis

Cell cycle: G0

non dividing

Mitosis Prophase

chromosomes condense, nuclear envelope breaks down, spindle fibers begin forming

Mitosis Metaphase

chromosomes line up at the plate

mitosis anaphase

sister chromatids are pulled apart

mitosis telophase

chromosomes decondense, cytokinesis occurs, nuclear envelope begins reforming, spindle fibers breaking down

chromosome / dna molecules per cell in G1

46/46

chromosome / dna molecules per cell in G2

46/92

chromosome / dna molecules per cell in prophase

46/92

chromosome / dna molecules per cell in metaphase

46/92

chromosome / dna molecules per cell in anaphase

92/92

chromosome / dna molecules per cell after cytokinesis

46/46

asexual reproduction pros and cons

one parent, genetically identical offspring, fast, no mate needed, preserves a successful genotype

secual reproduction pros and cons

random combination of genetic material from two parents, genetic variation (adaptation, resisting pathogens, purging harmful alleles).

monohybrid cross

heterozygous for one gene

dihybrid cross

for two genes

reciprocal cross

sex of parental phenotypes swapped

test cross

unknown dominant-phenotype individual x homozygous recessive

dominant/recessive

which allele shows in a heterozygote

heterozygous

two different alleles

homozygous

two identical alleles

Why Mendel's experiments worked

pea plant is easy to grow, short cycle, many seeds, controlled matings, either-or traits; true-breeding lines; reciprocal crosses; controlled environment; large samples and statistical analysis.

Segregation

two alleles of a gene separate equally into gametes. Basis: homologs separate in anaphase I.

Independent assortment

alleles of different genes assort independently (genes on different chromosomes). Basis: random orientation of homolog pairs at metaphase I.

Probability “and”

independent events multiply

Probability “or”

mutually exclusive outcomes add.

Autosome

non-sex chromosome

sex chromosome

determines sex

Androgen insensitivity

X-linked recessive androgen receptor mutation; XY with feminized external genitalia, infertile.

5-alpha-reductase deficiency

autosomal recessive; XY cannot convert testosterone to DHT; ranges from male to ambiguous to mostly female external genitalia

Turner

45,X; female, short stature, webbed neck, gonadal dysgenesis.

Klinefelter

47,XXY; male with testicular failure

Poly-X (47,XXX) and poly-Y (47,XYY):

typically no major anatomical differences; cognitive risk rises with extra X's.

Nondisjunction

failure of chromosomes to separate in meiosis I (homologs) or II (sisters), producing aneuploid gametes.

what causes male calico cats

the orange and black coat alleles are X-linked, so heterozygous females show patches of both. Male calicos are XXY (Klinefelter).