你和你的兄弟姐妹有相同的父母，相同的祖先，但是怎么可能会有不同的祖先基因？本文讨论同家族成员为什么有不同的 DNA 和造成基因测试不准确的因素。

词汇：ancestry 祖先

Have you ever wondered why your brother or sister doesn’t look exactly like you despite having the same family tree? If you think that’s odd, even stranger is the idea that you and your sibling may have very different ancestry genes. You have the same parents, and therefore the exact same ancestors, but somehow your DNA tests come back with very different results. How is this even possible?

Children inherit half of their DNA from each parent, via the sperm from the father and the egg from the mother. Our bodies contain 46 chromosomes, or 23 pairs. However, each reproductive cell has only 23 individual chromosomes. When the bodies of our forbearers created their sex cells, the cells engaged in genetic reshuffling, meaning each of the 23 chromosomes is a unique combination of an original pair. This process is also called genetic recombination.  

This is why Dr. Prosanta Chakrabarty, a scientist who studies fish to help explain the evolution of human beings and our planet, says that your sister could be 10% more 'French' than you, despite having the same primogenitors. And the further you go back in your lineage, the more confusing it can be.

You inherit 25% of each grandparent's DNA. However, this process of recombination means that inevitably some of their genetic make-up will be lost along the way. This could mean that the genes you inherited from your grandparent, could be completely different to those your cousin received.  

Those studying genealogy should also be aware that modern DNA testing might not give you an accurate idea of your ancestry as it is tested against a current, but incomplete database. Many of the genetic samples come from North America and Western Europe. The genes passed down from your ancestors is sampled and matched with people who originated from a certain area. However, without enough samples from the Middle East or Africa, the results may be inaccurate.

Dr. Prosanta Chakrabarty says that only 1% of our genetic make-up is unique to us, and that it is an incomplete mash-up of our ancestors'. So, the next time someone says you look a bit like you're from a certain country, you may well be. But it might not show up in your tests.

词汇表

genes 基因
ancestors 祖先，祖宗
inherit 经遗传而得
sperm 精子
egg 卵子
chromosome 染色体
reproductive cell 生殖细胞
forbearers 祖先
genetic reshuffling 基因重组
genetic recombination 基因重组
primogenitor 祖先，始祖
lineage 血统，家系
genetic makeup 基因组成
genealogy 家谱学
originate 起源于，来自

测验与练习

1.  阅读课文并回答问题。

1. Why does Dr. Prosanta Chakrabarty say that your sister could be 10% more 'French' than you?

2. How many chromosomes are in each sex cell?

3. Why is the database potentially incomplete?

4. How much of our genetic code is unique to us?

5. What is another term for 'genetic reshuffling'?

2. 选择意思恰当的单词或词组来完成下列句子。

1. I reckon I ­­­­_______ my looks from my father.

 inherit                       inheriting                   inherits                   inherited

2. Where did you grandfather _______ from?

origin                         originated                   originate                originates

3. The male's sex cell is known as a _______.

sperm                        egg                            chromosome          genetic

4. _______ is the study of your family genetic structure. 

Genealogy                 Chromosome             Reshuffling             Lineage

5. _______ is not a synonym of ancestor.

Precursor                   Primogenitor              Lineage                  Forebearer

答案

1.  阅读课文并回答问题。  

1. Why does Dr. Prosanta Chakrabarty, say that your sister could be 10% more 'French' than you?
This is due to genetic recombination.

2. How many chromosomes are in each sex cell?
In each sex cell there are 23 chromosomes.

3. Why is the database potentially incomplete?
Because there are not as many samples coming from certain regions.

4. How much of our genetic code is unique to us?
According to Dr Chakrabarty, around 1%.

5. What is another term for 'genetic reshuffling'?
Genetic recombination.

2. 选择意思恰当的单词或词组来完成下列句子。

1. I reckon I inherited my looks from my father.

2. Where did you grandfather originate from?

3. The male's sex cell is known as a sperm.

4. Genealogy is the study of your family genetic structure.

5. Lineage is not a synonym of ancestor.