BSC2086L Lesson 11

day 0 of embryonic development: zygote

formed from sperm and egg nuclei fusion (fertilization); divides without growth to form small cells called blastomeres

day 3 of embryonic development: morula

when zygotic division reaches 32 cell

day 4-6 of embryonic development: blastocyte

hollowed out morula; has inner cell mass (forms the embryonic body) and outer trophoblast layer (forms the chorion and fetal part of placenta)

implantation

blastocyst attaches to uterine wall

day 7 of embryonic development

blastocyst implants with inner cell mass facing uterine wall; trophoblast secrete enzyme to erode uterine mucosa to expose vascular network in submucosa; chorionic villi from trophoblast & uterine tissue will form placenta; as implanted blastocyte grows, 3 embryonic layers form

amnion

encases embryo in fluid-filled chamber; protects against trauma, temperature, and adhesion from rapid embryonic growth

yolk sac

forms embryo's first blood cells and primordial germ cells here migrate to embryo body to form become germ cells in gonadal tissue

allantois

helps form umbilical cord

day 14 of embryonic development

uterine mucosa envelops embryo (decidua capsularis); uterine wall beneath inner cell mass(decidua basalis) will form part of placenta; embryo in gastrula stage - three primary germ layers present and begin to differentiate (for the next 6 weeks)

endoderm

forms mucosa of digestive and respiratory system and their associated glands

ectoderm

forms skin and nervous system

mesoderm

forms everything in between (skeleton, skeletal muscles, walls of digestive organs, urinary and circulatory system, etc)

week 9 of embryonic development

embryo is referred to as a fetus, major focus of development at this point is for fetal growth and tissue/organ specialization/growth

genetics

all somatic (body) cells contain 46 chromosomes (diploid, 2n); egg and sperm contain 23 chromosomes (haploid, n) - their fusion yields 23 pairs of homologous chromosomes (46 chromosomes)

gene

unit/area on DNA (or sometimes RNA) that contains hereditary information

alleles

genetic information coding for the same traits found on each pair of homologous chromosomes

homozygous trait

both alleles express the same information

heterozygous trait

one allele is dominant, while is the other allele is recessive (is masked by the expression of the dominant allele)

dominant gene

requires only 1 copy of the gene for expression

recessive gene

requires both alleles to contain the gene for expression

genotype

an individual's genetic makeup (whether he/she is homozygous/heterozygous for various alleles)

phenotype

the physical appearance of the genes

4 main types of inheritance

- dominant-recessive inheritance

- incomplete dominance

- sex-linked inheritance

- co-dominance

dominant-recessive inheritance

Mendelian genetics:

- dominant alleles are expressed

- recessive alleles are expressed only when they are homozygous

- genotype & phenotype determined by using Punnett square

melanin vs. albinism

melanin is dominant and albinism is recessive

achondroplasia vs. average height and limb proportions

achondroplasia is dominant and average height and limb proportions is recessive

heterochromia vs. same colored eyes

heterochromia is dominant and same colored eyes is recessive

incomplete dominance

heterozygous alleles yield phenotype different than from homozygous dominant

sickle cell trait vs. sickle cell anemia

sickle cell trait is heterozygous and sickle cell anemia is recessive homozygous

sex-linked inheritance

inheritance of genes from the X (23rd) chromosome (the sex chromosome contains genes that determine color vision, blood clotting, baldness, etc)

females vs. males

females are XX and males are XY

extra copies of X in females and extra Ys in males

does not appear to cause any physiological problems for people

turners syndrome

X-

klinefelters syndrome

XXY

alteration in female's genes vs. male's genes

females are usually carriers while males are affected

hemophiliac male vs. carrier vs. hemophiliac female

Xh-Y vs. Xh-X vs. Xh-Xh

co-dominance

all alleles are expressed in the phenotype

A allele, B allele, O allele

A and B alleles are dominant to O allele, but A and B can be expressed together

Rh factor dominance

+ is dominant to -

genotype % and phenotype % for melanin (M) and albinism (m): Mm vs. mm

Mm: 50%

mm: 50%

melanin: 50%

albinism: 50%

genotype % and phenotype % for two people with sickle cell trait

AA: 25%

Aa: 50%

aa: 25%

normal: 25%

sickle cell anemia: 25%

sickle cell trait: 50%

genotype % and phenotype % for AB and AO genotypes for blood

AA: 25%

AB: 25%

AO: 25%

BO: 25%

Type A: 50%

Type AB: 25%

Type B: 25%

Type O: 0%

genotype % and phenotype % for a couple having a girl

XX: 50%

XY: 50%

female: 50%

male: 50%

genotype % and phenotype % for color blind father and a mother who isn't colorblind but her father is colorblind

XcXc: 25%

XXc: 25%

XcY: 25%

XY: 25%

colorblindness: 50%

carrier: 25%

normal: 25%

female colorblindness: 50%

female carrier: 50%

male colorblindness: 50%

male normal: 50%

genotype % and phenotype % for two people with achondroplasia have a child

AA: 25%

Aa: 50%

aa: 25%

dwarfism: 2/3 (66.7%)

normal: 1/3 (33.3%)