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Heredity

Heredity (유전);

Transmission of traits from one generation to the next.

Genetics (유전학);

The scientific study of heredity, began in the 1860s, when Gregor Mendel deduced its fundamental principles by breeding garden peas.

Gregor Mendel(20 July 1822 – 6 January 1884)

Gregor Johann Mendel (20 July 1822 – 6 January 1884) was a German-speaking Moravian scientist who gained posthumous fame as the founder of the modern science of genetics. Though farmers had known for centuries that crossbreeding of animals and plants could favor certain desirable traits, Mendel's pea plant experiments conducted between 1856 and 1863 established many of the rules of heredity, now referred to as the laws of Mendelian inheritance.

Mendel worked with seven characteristics of pea plants: plant height, pod shape and color, seed shape and color, and flower position and color. With seed color, he showed that when a yellow pea and a green pea were bred together their offspring plant was always yellow. However, in the next generation of plants, the green peas reappeared at a ratio of 1:3. To explain this phenomenon, Mendel coined the terms “recessive” and “dominant” in reference to certain traits. (In the preceding example, green peas are recessive and yellow peas are dominant.) He published his work in 1866, demonstrating the actions of invisible “factors”—now called genes—in providing for visible traits in predictable ways.

Gene (유전자);

Represents the genetic material on a chromosome that contains the instructions for creating a particular trait.

Ex) In pea plants, there is a gene for flower color

Allele (대립 유전자);

One of several varieties of a gene.

Ex) In pea plants, there are two alleles of the gene for flower color – the purple allele and the white allele

Locus (유전자자리);

Refers to the location on a chromosome where a gene is located.

Homologous chromosome (상동염색체);

Refer to a pair of chromosomes that contains the same genetic information, gene for gene.

Dominant and Recessive (우성, 열성);

An individual with one dominant and one recessive allele for a gene will have the dominant phenotype.

Ex) In pea plants, purple flower color is a dominant phenotype.

Homozygous Dominant (동형접합성 우성);

Refers to the inheritance of two dominant alleles (PP).

Homozygous Recessive (동형 접합성 열성);

Refers to the inheritance of two recessive alleles (pp).

Heterozygous (이형 접합성);

Refers to the condition where the two inherited alleles are different; only the dominant allele is expressed.

Phenotype vs. Genotype (표현형 vs. 유전형);

Phenotype: An actual expression of a gene.Genotype: Represents the actual alleles.

Seven characters of pea plants

Law of SegregationThe principle, originated by Gregor Mendel, stating that during the production of gametes the two copies of each hereditary factor segregate so that offspring acquire one factor from each parent.

Law of Segregation_Monohybrid Cross

A monohybrid cross is a mating between two individuals with different alleles at one genetic locus of interest.

Law of Independent AssortmentThe principle, originated by Gregor Mendel, stating that when two or more characteristics are inherited, individual hereditary factors assort independently during gamete production, giving different traits an equal opportunity of occurring together.

Law of Independent Assortment_Dihybrid CrossDihybrid cross is a cross between two pure lines (varieties, strains) that differ in two observed traits.

Family Pedigrees (혈통; 계통)

A pedigree is a drawing of a family tree.The pedigree is used by genetic counselors and other medical professionals to assess families and try to spot patterns or indications which may be helpful in diagnosing or managing an individual’s health.

Disease

PKU___ Autosomal recessive___ Inability to break down the phenylalanine amino acid

Cystic fibrosis___ Autosomal recessive___ the most common lethal genetics disease, characterized by build up of extracellular fluid in the lungs

Tay-sachs disease___ Autosomal recessive___ lack of the enzyme needed to break down lipids

Huntington’s disease___ Autosomal dominant___ A degenerate disease of the nervous system resulting in certain and early death

Hemophilia___ sex-linked recessive___ Caused by the absence of normal blood clotting

Color blindness___ sex-linked recessive

Down syndrome ___ 47 chromosome___ facial features, mental retardation

Klinefelter’s___XXY 47 chromosome___Have male genitals, but testis are abnormal and men are sterile

Incomplete dominance: A form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele

Variations on Mendel’s Laws

Codominance:Inheritance in which two alleles of a gene pair in a heterozygote both have full phenotypic expression.

Variations on Mendel’s Laws

Pleiotropy: Pleiotropy occurs when one gene influences two or more seemingly unrelated phenotypic traits.

Variations on Mendel’s Laws

Polygenic Inheritance: Polygenic inheritance occurs when one characteristic is controlled by two or more genes.

Variations on Mendel’s Laws

The Chromosomal Basis of Inheritance

Linked Genes:Linked genes sit close together on a chromosome, making them likely to be inherited together (left).Genes on separate chromosomes are never linked (center).But not all genes on a chromosome are linked. Genes that are farther away from each other are more likely to be separated during a process called homologous recombination (right).

The Chromosomal Basis of Inheritance

Linked Genes:Linked genes sit close together on a chromosome, making them likely to be inherited together (left).Genes on separate chromosomes are never linked (center).But not all genes on a chromosome are linked. Genes that are farther away from each other are more likely to be separated during a process called homologous recombination (right).

The Chromosomal Basis of Inheritance

Morgan’s test on genetic linkage:

GgLl X ggll

-> 83% of the flies displayed the phenotypes of parents17% showed nonparental phenotypes

Sex Chromosomes and Sex-Linked Genes

Sex Chromosomes and Sex-Linked Genes

Sex Chromosomes and Sex-Linked Genes