我没见过的外婆

 

 我从来没见过外婆. 外婆长的什么样全靠自己的想象， 或从母亲和舅舅的回忆及描述中稍微了解一点她的身世和模样. 在我想象中她身高一米六上下, 圆脸, 双眼皮，一头乌黑的长头发, 性情温和, 眼神有点扰郁。 

 外婆年轻时长得很漂亮，是附近几个村的佳丽，但她出身贫苦，虽有自己的意中人，还是嫁给外公做了填房。当时（大至在1930年代）家境逐渐衰落, 虽有十来亩地, 外加四十多亩竹林地, 生活也将将过得去, 不算贫困, 但也不富裕.  外婆婚后育有两女一丁, 我姨妈是长女, 舅舅老二, 我母亲末小. 我母亲和姨妈在农忙时都要下地干活, 放牛割草都是份内活. 外公比较重男轻女, 舍得化钱供舅舅念书 (解放后考上医科大学成为外科医生). 舅舅不用干农活. 姨妈是老大, 干活最多, 所以没念多少书. 我母亲一直念到初中, 毕业后失去经济来源选择报考农校(中专), 农校毕业后参加工作, 以农技员/农技师职务长年工作在基层(县, 区, 社都干过). 母亲一直敬佩她的大姐, 到至今还时不时地给她寄钱. 可谓是姐妹情深。 听舅舅说, 外公不太顾家, 家里全靠外婆操劳. 也许是劳累过度, 或是心情扰郁, 嫁入殷实人家并没有给她带来很多快乐，年纪轻轻四十岁不到就病逝了。以前的农家女子真可怜，不会生儿育女会被公婆/老公休了；生的多了又要自己尽力抚养， 耗尽力气。

 外婆生的两女一儿，他们又育有九个儿女。重外孙(女)辈又有十几号，  在北美重外孙就 有六个。如果不是外婆生养了我母亲，我不知道今生今世在哪儿。明年回国时定要回外婆老家祖坟上给她烧上几枝香，再烧好多金元宝 (乡村习俗, 金元宝是阴间流动货币)。

 在这感恩节里，草写小文，以表示我对早逝的外婆感恩之心。

 

科普附文：线粒体DNA是以母系遗传 (Human mitochondriaare normally inherited exclusively from the mother) . 线粒体合成 ATP, 给身体提供能量. 所以从生物化学的角度, 父亲只是给予资助,母亲是能源的最终提供者.

Mitochondrial DNA

From Wikipedia, the free encyclopedia

MitochondrialDNA (mtDNA) is the DNA located in organelles called mitochondria,structures within eukaryotic cells that convert the chemical energy fromfood into a form that cells can use, ATP. Most other DNA present in eukaryoticorganisms is found in the cell nucleus.

Mitochondrialinheritance

In most multicellularorganisms, mtDNA is inherited from the mother (maternally inherited).Mechanisms for this include simple dilution (an egg contains 100,000 to1,000,000 mtDNA molecules, whereas a sperm contains only100 to 1000), degradation of sperm mtDNA in the fertilized egg, and, at leastin a few organisms, failure of sperm mtDNA to enter the egg. Whatever themechanism, this single parent (uniparental) pattern of mtDNA inheritance isfound in most animals, most plants and in fungi as well.

Female inheritance

In sexual reproduction, mitochondria are normallyinherited exclusively from the mother. The mitochondria in mammalian sperm areusually destroyed by the egg cell after fertilization. Also, most mitochondriaare present at the base of the sperm's tail, which is used for propelling thesperm cells. Sometimes the tail is lost during fertilization. In 1999 it wasreported that paternal sperm mitochondria (containing mtDNA) are marked with ubiquitin toselect them for later destruction inside the embryo.^[4]Some invitro fertilization techniques, particularly injecting a sperm into an oocyte, mayinterfere with this.

The fact that mitochondrial DNA ismaternally inherited enables researchers to trace maternallineage far back in time. (Ychromosomal DNA, paternally inherited, is used in an analogous way to tracethe agnatelineage.) This is accomplished in humans by sequencing one or more of the hypervariable control regions (HVR1 orHVR2) of the mitochondrial DNA, as with a genealogical DNA test. HVR1 consists of about440 base pairs. These 440 base pairs are then compared to the control regionsof other individuals (either specific people or subjects in a database) todetermine maternal lineage. Most often, the comparison is made to the revised Cambridge Reference Sequence. Vilà etal. have published studies tracing the matrilineal descent of domestic dogsto wolves.^[5]The concept of the Mitochondrial Eve is based on the same type ofanalysis, attempting to discover the origin of humanity by trackingthe lineage back in time.

Because mtDNA is not highlyconserved and has a rapid mutation rate, it is useful for studying theevolutionary relationships - phylogeny - of organisms. Biologists can determine and thencompare mtDNA sequences among different species and use the comparisons tobuild an evolutionary tree for the species examined.

Because mtDNA is transmitted frommother to child (both male and female), it can be a useful tool in genealogicalresearch into a person's maternal line.