oogenesis STUDY MEISOSIS AND GENETICS

what happens to one cell in meiosis one in oogenesis

one cell receives half genetic info and majority of the cytoplasm of the parent cell

polar body

receives half of the genetic info and cast away (they die)

during meiosis 2 what does the remaining cell do

divides a second time and forms a polar body that is cast away

a single haploid ovum that contains half the genetic info and nearly all the cytoplasm of the original parent cell

what does the process of oogenesis produce?

2 polar bodies and a single haploid ovum

test cross —

crossing of an organism of unknown dominant genotype with an organism that is homozygous recessive, resulting in offspring with observable phenotypes. Test crosses used to determine the unknown genotype

hypercholesterolemia

recessive disorder (hh) causing cholesterol levels to be many times higher than normal → leads to heart attacks in kids as young as 2yrs.

polygenic traits

traits affected by 1+ gene (eg eye color)

multiple alleles

some traits involving more than 2 alleles

epistasis

expression of 1 gene affects the expression of another gene

eg The wild-type coat color, agouti (AA), is dominant to solid-colored fur (aa). However, a separate gene (C) is necessary for pigment production. A mouse with a recessive c allele at this locus is unable to produce pigment and is albino regardless of the allele present at locus A (Figure 1). Therefore, the genotypes AAcc, Aacc, and aacc all produce the same albino phenotype. A cross between heterozygotes for both genes (AaCc x AaCc) would generate offspring with a phenotypic ratio of 9 agouti:3 solid color:4 albino (Figure 1). In this case, the C gene is epistatic to the A gene.

gene locus

A locus is the specific physical location of a gene or other DNA sequence on a chromosome, like a genetic street address

epistasis ratio

9 : 4 : 3

pleitropy

a single gene has multiple effects on an organism

eg. sickle cell anemia → the gene mutation “sickles” the blood cells, leading to systemic symptoms like heart, lung, and kidney damage

Duchenne’s muscular dystrophy

sex-linked disorder caused by the absence of an essential muscle protein

symptoms: progressive loss of muscle strength & coordination

hemophilia

caused by an absence of a protein vital to the clotting process

symptoms: difficulty clotting blood after even the smallest wounds

red-green color blindness

condition primarily found in males

symptoms: cant tell between red & green

Barr body

inactivated genes on X chromosomes that’s coiled (one of them)

why are all cells in a female not identical?

cell expresses the alleles only of the X chromosome (not Barr body). Occurs separately in each cell & involved random activation of one of a female’s X chromosomes

holandric traits

traits inherited from Y chromosome. eg ear hair distribution

linked genes

lie on the same chromosome → don’t follow Mendel’s law of independent assortment

the less often crossing over happens, how far/close are the genes

closer the genes must be on the chromosome

linkage map

genetic map put together using crossover frequencies, does not provide exact location of genes, only relative location

map unit

aka centigram → used to geographically relate the genes on the basis of these frequencies

how can pedigrees be used?

determine risk of parents passing certain conditions to offspring

tay-sachs

AUTOSOMAL RECESSIVE — renders the body unable to break down a particular type of lipid that accumulates the brain and eventually causes blindness and brain damage.

Carriers of this disease don’t show any of the effects of the disease. Usually eastern European Jewish descent

cystic fibrosis (CF)

AUTOSOMAL RECESSSIVE — located on chromosome 7. Deletion mutation, so incorrect shape. Excessive secretion of a thick mucus that accumulates in the lungs & digestive tract. 1 in 25 Caucasians is a carrier for this disease

sickle cell anemia

AUTOSOMAL RECESSIVE — improper amino acid substitution during translation of hemoglobin. Results in hemoglobin that’s less efficient in carrying oxygen → leads to pain, muscle weakness, and fatigue

common among African Americans (1 in 10) heterozygous condition protects against malaria

phenylketonuria (PKU)

AUTOSOMAL RECESSIVE — cause by single gene defect. Unable to digest phenylalanine (amino acid) → accumulation of a by-product in blood that can cause mental retardation. Avoid that amino acid early on

Huntington disease

AUTOSOMAL DOMINANT — repeat expansion in HTT gene. Breakdown of nervous system. Doesn’t show itself until in the 30s-40s. 50% of passing to offspring.

Patau syndrome

trisomy 13. Causes brain & circulatory defects

Edwards syndrome

trisomy 18. Can affect all organs

Klinefelter syndrome

male receives extra X (XXY). Infertile, has male sex organs but show feminine body characetristics

turner syndrome

sterile females that have sex organs that don’t mature at puberty (XO)

deletion —

a piece of the chromosome is lost in the developmental process

cri-du-chat syndrome

result of deletion in chromosome 5. Mental retardation, abnormal facial features, and small head

chromosomal translocation

piece of 1 chromosome is attached to another, nonhomologous chromosome

chronic myelogenous leukemia

cancer affecting white blood cell precursor cells. A portion of chromosome 22 has been swapped with a piece of chromosome 9

chromosome inversion

portion of a chromosome separates and reattached in the opposite direction

can have no effect or have a gene nonfunctional if it occurs in the middle of a sequence

chromosome duplication

repetition of a genetic segment.

often have serious effects on an organism

phenotype plasticity

• environmental factors influence gene expression

• individuals with the same genotype exhibit different phenotypes in different environments