Heredity

haploid vs. diploid

haploid (n): organism with only one copy of each type of chromosome - for humans, one copy of each homologous chromosome

diploid (2n): organism with two copies of each chromosome - for humans, pairs of homologous chromosomes

n

number of sets of chromosomes

meiosis differences from mitosis

After G_2, will have two cell divsions

second division for gametes to be haploid. They will join with haploid gamete to produce diploid zygote

homologous chromsomes

chromosomes that resemble each other in shape, size, function, and genetic information

Meiosis I

prophase I, metaphase I, anaphase I, telophase I, cytokinesis

similar to mitosis

prophase I is where crossover happens

daughter cells become haploid after cytokinesis

Meiosis II

Prophase II, metaphase II, anaphase II, telophase II, cytokinesis

no replication because cells already haploid

crossing over makes nothing genetically identical

each daughter cell is haploid, only have 1 non-replicated chromsomes

spermatogenesis and oogenesis

spermatogenesis: the process of sperm cell development in males

oogenesis: the process of egg cell development in females - however the secondary oocyte will pause during metaphase II and only develop until fertilized by sperm

polar bodies

the other cell resulting from oogenesis after Meiosis I

split again, so the two polar bodies only hold half genetic information and are cast away

fertilization

haploid egg and haploid sperm join in fertilization to make diploid zygote

zygote undergoes mitosis from embryonic development

mitosis vs meiosis important

prophase I, homologous pairs join together. In mitosis, they simply align at metaphase plate

no crossover in mitosis

mitosis is for all cells except gonads (reproductive cells) while meiosis is just for gonads

mitosis results in two diploid daughter cells, meiosis results in four haploid daughter cells

allele

variant of gene for a particular character

F_#

Generation and its number, starts at F₁

Genotype and phenotype

genotype: organism’s genetic makeup for a given trait (ex: BB or Bb)

phenotype: physical expression of trait based on genotype (ex: black fur or brown fur)

homozygous dominant, recessive, and heterozygous

homozygous dominant: two dominant alleles

homozygous recessive: two recessive alleles

heterozygous: one dominant and one recessive allele

karyotype

chart that organizes chromosomes in relation to number, size, and type

Nondisjunction

improper separation of chromosomes during meiosis, leading to improper number of chromosomes in offspring - aneuploidy

Monohybrid cross

Both parents are heterozygous, crossing with one trait

homo dom 25%, homo rec 25%, het 50%

dihybrid cross

crossing two different traits from heterozygous parents

9:3:3:1 raito

test cross

unsure if phenotype displayed is homozygous dominant or heterozygous

law of segregation

alleles segregate during formation of gametes, so each cell would receive one of the alleles

law of independent assortment

alleles for different traits segregate independently during the formation of gametes

BbRr - Bb assort independent from Rr

law of dominance

the dominant allele masks the effect of the recessive allele in a heterozygous genotype

intermediate inheritance

incomplete dominance/”blending inheritance” and codominance

linked vs unlinked genes

linked: close on a chromosome, move together during meiosis - less crossover

unlinked: far apart on a chromosome, assort independently during meiosis - more crossover

linkage maps: genetic map using crossover frequencies to geographically relate the genes

incomplete dominance

phenotype thats a blend of both

ex: hypercholesterolemia - recessive disorder that makes cholesterol abnormally high, dominant are normal and heterozygous are intermediate

codominance

both alleles are expressed so the phenotype is neither dominant or recessive - sort of a third category independent of dominant or recessive traits

ex: AB blood type, where both A and B antigens are present.

polygenic traits

traits controlled by multiple genes, resulting in a range of phenotypes

ex: eye color (tone, amount, position)

multiple alleles

exists when a gene has more than two allele forms, allowing for multiple phenotypes. An example is the ABO blood group system.

epistasis

expression of one gene affects the other genes

example: albinism is a separate allele that controls pigment deposition regardless of what the pigment color actually is

pleiotropy

single gene has multiple affects on organism

ex: sickle cell anemia - affecting hemoglobin production and causing various health issues such as pain crises and increased susceptibility to infections

sex-linked traits

autosomal chromosome: chromosome not involved in determining sex

fathers do not give any X chromosomes to their sons, only their daughters

three common sex-linked disorders

duchenne’s muscular dystrophy: absence of essential muscle protein

hemophilia: a disorder that impairs the body's ability to make clots, leading to excessive bleeding

red-green colorblindness: primarily in males

X inactivation

X inactivation is a process in female mammals where one of the two X chromosomes is randomly silenced to ensure dosage compensation of X-linked genes.

law of multiplication

multiply probability one by probability two

pedigrees

autosomal dominant will never skip a generation. autosomal recessive will sometimes skip a generation because of heterozygotes

common autosomal disorders

tay-sachs: inability to break down lipids - recessive disease

cystic fibrosis: recessive, excessive secretion of mucus into lungs

sickle cell: recessive disorder of red blood cells due to abnormal hemoglobin

Phenylketonuria (PKU): recessive disease - children cannot digest amino acid, can lead to mental impairment

huntington disease: dominant, breakdown of nervous system

trisomy disorders

down syndrome - mostly sterile, metal impairment, 21

patau - brain defects, 13

edwards - affects all organs, 18

aneuploidy of sex chromosomes

klinefelter syndrome: male receiving extra X

turner: female with a missing X chromosome

deletion

piece of chromosome lost

cri-du-chat: portion of chromosome 5, leading to developmental delays and a distinct cry

chromosomal translocations

piece of chromosome attached to another

chronic myelogenous leukemia: translocation of chromosomes 9 and 22

chromosome inversion and chromosome duplication

inversion: portion of chromosome separates and reattaches in opposite location

duplication: section of a chromosome is replicated, resulting in extra genetic material.