基础生物实验 23 - 实验八实验手册：孟德尔遗传学
本期内容是 实验八：孟德尔遗传学 的实验手册，实验模拟请看下一期。本部分内容来自 University of California, Berkeley - UC Berkeley Extension, 虚拟实验的内容来自 Labster. 本部分内容均不会标记为为原创，但由于是UP主购买的课程，因此不接受非授权的转载，谢谢您的理解。
每一个生物基础实验均会分为三部分：第一部分为实验的生物理论；第二部分为实验的指导手册；第三部分为 Labster 的虚拟实验模拟。第一部分的基本信息由 Ying Liu, Ph.D. 提供，第二部分的实验手册来自 Labster, 第三部分的实验模拟过程由UP主操作。
Virtual Lab Manual 8 - Mendelian Inheritance
Synopsis
Did you know that more than 99% of your genes are identical to those found in any other human being on the planet? In this simulation, you will learn how Mendel's postulates can be applied to determine how characteristics are inherited by being passed from one generation to the next.
Cross purebred mice and observe their phenotypes
To understand the fundamental laws of inheritance, you will cross purebred mice and see how their genes can influence their fur color. Can you figure out which fur color is dominant?
Experience inheritance at the cellular level
Dive deeper into the laws of inheritance as you watch how cells divide to become gametes inside the reproductive system. By unraveling the laws of X-linked inheritance, discover why color blindness affects more men than women.
Predict the genotypes in the patient’s family
Explore Punnett squares and Pedigree trees to predict the genetic makeup of a family. What is valid for the fur color in mice, can also be applied to human color blindness! Will you be able to determine if the patient’s children will inherit his color blindness?
Learning Objectives
At the end of this simulation, you will be able to…
● Explain how traits are passed on from parents to their offspring and what causes variation between siblings
● Describe Mendel’s Laws of Inheritance in color deficiency
● Compare and predict the phenotypes of offspring with given genotypes using Punnett squares
● Analyze dominant and recessive alleles, and how they play a part in an individual’s biological make-up
Techniques in Lab
● Pedigree trees
● Punnett squares
Theory
Color blindness
Color blindness is a reduced or inexistent ability to see certain colors. In the most common type of color blindness the individual is unable to differentiate between red and green.
Genotype
The genotype consists of an organism's DNA segments or genes, which make up its phenotype.
Phenotype
The phenotype is an organism's set of observable traits. The phenotype results from the expression of an organism's genotype, inherited epigenetic factors and environmental conditions.
Traits can be observable (e.g. eye color), or physiological (e.g. lactose intolerance).
Allele
An allele is one of a number of alternative forms of the same gene or same genetic locus. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation. However, most genetic variations result in little or no observable variation.
Most multicellular organisms are diploid. This means that they possess two alleles for each gene, one inherited from each parent. If the two alleles are the same, the organism is said to be homozygous with respect to that gene. If they are different we call the organism heterozygous with respect to that gene.
Hybridization
Hybridization refers to the process of mating two individuals from different breeds which are genetically distinct.
Mating of two purebred parents that express different traits for only one characteristic is called a monohybrid cross. The example below shows a cross between two pea plants with yellow and green seeds respectively:
All seeds of the first (F1) generation have yellow phenotypes, because the yellow seed color is dominant over the green seed color. In the second generation (F2) the ratio between yellow and green seeds becomes 3:1 as depicted in the Punnett square.
Punnett square
A Punnett square is a visual representation of a cross. The genotypes of the parents are denoted along the top and the side of the grid. The possible genotypes of the offspring are obtained by combining the different alleles in the grid.
The Punnett square below shows an example of a cross between a heterozygous father and a homozygous dominant mother.
Pedigree
A pedigree tree is a diagram depicting members of a family, their inter-relations, and their disease/phenotypic status. It provides an overview of the inheritance pattern and frequency of a specific trait.
Each family member is represented by a symbol: circles for females and squares for males. Filled symbols represent affected individuals, and empty ones represent normal individuals. Matings are illustrated by connecting horizontal lines, while their offspring is depicted beneath. Each generation is assigned a Roman number (e.g. I, II, III) while individuals of a generation are assigned Arabic numbers (e.g. 1, 2, 3).
Law of segregation
The law of segregation states that genes are distributed into gametes, so that each offspring inherits one allele from each parent.
Law of independent assortment
The law of independent assortment states that genes do not influence each other with regard to the sorting of alleles into gametes; every possible combination of alleles is equally likely to occur.
X-linked mode of inheritance
The X-linked mode of inheritance refers to the inheritance of genes that are present on X-, but not on Y-chromosomes.
Some examples of X-linked, recessive inheritance include:
- Red-green color blindness
- Hemophilia A and B
- Duchenne muscular dystrophy
X-linked dominant inheritance is less common. Some examples include:
- X-linked hypophosphatemia
- Fragile X syndrome
本期内容到此结束，感谢阅读！下一期将进行 Labster 实验！
