Meiosis + Chromosomal Disorders

Genes, loci, alleles

Homologous Chromosomes

• Chromosomes carrying the same __ at same__

• May carry different __

Spermatogenesis

Sperm produced in testes from germ cells migrated to gonad during early puberty

Puberty, mitosis, diploid, meiosis I, haploid, meiosis II, haploid, spermatozoa

Spermatogenesis

• Occurs during __

• DNA replication and __ produce primary spermatocytes (_loid)

• Primary spermatocytes undergo __ _ - produce 2 secondary spermatocytes (_loid)

• Each secondary spermatocyte undergoes __ _ - produce 2 spermatids (immature _loid)

  • Immature Spermatids → haploid mature __

Oogenesis

Production of oocytes from germ cells migrated to gonad during early embryogenesis

4 months, mitosis, diploid, prophase, meiosis I, haploid, meiosis II, haploid

Oogenesis

• Oogonia produced during first _ __ of embryonic development

• DNA replication and __ produce primary oocytes (_loid)

• Primary oocytes begin __ I before birth

• Primary oocyte continues __ _ - produce secondary oocytes (_loid)

• Remaining secondary oocyte begins __ _ and arrests at metaphase II

• If fertilized, will complete meiosis II → produce ovum (_loid)

Longer, stronger, stop, start

Sources of Chromosomal Abnormalities from Oogenesis

• Due to __ time frame of oogenesis, there are __ environmental influences

• Presence of “__ and __” stages

Synapsis, prophase I

__ is when homologous chromosomes become closely associated, form complexes between the 2 chromosomes

• Occurs in early __ _

Crossing Over

Genetic recombination between non-sister chromatids via the chiasmata

NO, identical, replication

If sister chromatids “crossed over”, there would be __ (yes/no) genetic diversity

• Sister chromatids are __ in nature coming from DNA __ stage (of interphase)

Meiosis I

Goes diploid (n =46) to haploid (n=23) via separation of homologous chromosomes

Prophase I

Chromosomes coil tighter and become visible, nuclear envelope disappears, spindle forms; synapsis event

(Meiosis I)

Metaphase I

Terminal chiasmata hold 23 pairs of homologues together (on top of each other) following crossing over

(Meiosis I)

Anaphase I

Microtubules of spindle shorten → chiasmata break → homologues separated from each other to opposite poles

(Meiosis I)

Telophase I

Nuclear envelope re-forms around each daughter nucleus, may involve cytokinesis, outcome is haploid

(Meiosis I)

Meiosis II

Goes haploid (n =23) to haploid via separation of homologous chromatids

End result of 4 haploid cells

Haploid, replicated, haploid, unreplicated

Meiosis I is __ and __

Whereas Meiosis II is __ and __

(Diploid vs haploid AND replicated vs unreplicated)

Karyotype

Number and type of chromosomes found in individual

Y, X, autosomes, p, q

Karyogram Features

• Sex - _ chromosome is much smaller than _ chromosome

• __ are Chromosomes 1-22

• Each arm of chromosome is separated by centromere (point of indentation)

  • Short arm “petite” = _ long arm = _

Metacentric, submetacentric, acrocentric

• __: Centromere at/near center of chromosome

• __: Centromere between middle and tip of chromosome

• __: Centromere located at tip of chromosome

13, 14, 15, 21, 22

Key acrocentric genetic disorders by chromosome… (5)

Euploid cells

Cells containing multiple of 23 chromosomes (normal)

Polyploidy, fertilization

__ploidy is when cells contain extra sets of 23 chromosomes

• Results from __ from more than 1 sperm → Not viable for life

Aneuploidy, nondisjunction, anaphase, 13, 18, 21

__ploidy is when cell is containing 1 extra chromosome or missing 1 chromosome

• Result of __ during meiosis (specifically in __ I or II)

• Trisomy __/__/__ are viable with life as these contain X and Y chromosomes

Meiosis I Nondisjunction

Homologous chromosomes fail to separate

Meiosis II Nondisjunction

Sister chromatids fail to separate

Down Syndrome

Intellectual disability, delayed speech/motor skills, postnatal growth slow down, hearing loss, GI/cardio defects, hypotonia at birth, short stature, flat head

Trisomy 21

47, XX/XY, +21

Down Syndrome Karyotype

Edward’s Syndrome

Intrauterine growth retardation, low birth weight, brain malformations, prominent occiput, cardiac defects, intellectual disability, microcephaly

• Poor prognosis for neonates → Survival up to 1 year

• Trisomy 18

47, XX/XY, +18

Edward’s Syndrome Karyotype

Patau Syndrome

Failure of brain development, cleft lip/palate, cardiac defects, renal issues

• Worst prognosis or viable trisomies → Pass following birth

• Trisomy 13

47, XX/XY, +13

Patau Syndrome Karyotype

Turner’s Syndrome

Short stature, gonadal dysgenesis (infertility), webbed neck, broad chest, renal/cardiac issues, short 4th metacarpal

• Monosomy X

45, X

Turner’s Syndrome Karyotype

Klinefelter’s Syndrome

Tall and thin stature, hypogonadism at puberty, low testosterone, underdeveloped secondary sexual characteristics, gynecomastia, infertility

• No symptoms prior to puberty

• Trisomy XXY

47, XXY

Klinefelter’s Syndrome Karyotype

Reciprocal, little

__ Translocations denote breakage of 2 non-homologous chromosomes

• Observe __ (little/major) pathology to parent/offspring

Robertsonian, no, visible

__ Translocations denote 2 acrocentric chromosomes fusing at centromere (13/14/15/21/22)

• Observe __ (visible/no) pathology to parent and __ (visible/no) pathology to offspring

45, XY, der(2 acrocentric)

Robertsonian Translocation Karyotype

22, 9, dimerization, uncontrolled

Chronic Myelogenous Leukemia

• Result of balanced translocation between chromosomes __ + __

• Translocation effect of tyrosine kinase on chromosomes

  • Forcing __ of RTKs → __ cell growth from hyperactive cell responses

46, XX, t(9;22)

Leukemia Karyotype

Cri-du-Chat Syndrome

Laryngeal defects, infants with high-pitched cry, microcephaly

• Partial deletion of chromosome 5 on short arm

46, XY, Del(5)

Cri-du-chat Syndrome Karyotype

DiGeorge Syndrome

Developmental delay, cardiac issues, abnormal face, thymic hypoplasia, cleft palate, hypocalcemia

• Microdeletion of transcription band of chromosome 22

Charcot-Marie-Tooth Disease I

Slow progressive weakness, leg muscle atrophy, sensory impairment, decreased reflexes, ataxia, tremor

• Duplication of PMP22 gene → Demyelating peripheral polynephropathy